# Changelog

## Python 3.9.5 final

Release date: 2021-05-03

### Security

- bpo-43434: Creating a `sqlite3.Connection` object now also produces a `sqlite3.connect` auditing event. Previously this event was only produced by `sqlite3.connect()` calls. Patch by Erlend E. Aasland.

- bpo-43882: The presence of newline or tab characters in parts of a URL could allow some forms of attacks.

  Following the controlling specification for URLs defined by WHATWG `urllib.parse()` now removes ASCII newlines and tabs from URLs, preventing such attacks.

- bpo-43472: Ensures interpreter-level audit hooks receive the `cpython.PyInterpreterState_New` event when called through the `_xxsubinterpreters` module.

- bpo-36384: `ipaddress` module no longer accepts any leading zeros in IPv4 address strings. Leading zeros are ambiguous and interpreted as octal notation by some libraries. For example the legacy function `socket.inet_aton()` treats leading zeros as octal notatation. glibc implementation of modern `inet_pton()` does not accept any leading zeros. For a while the `ipaddress` module used to accept ambiguous leading zeros.

- bpo-43075: Fix Regular Expression Denial of Service (ReDoS) vulnerability in `urllib.request.AbstractBasicAuthHandler`. The ReDoS-vulnerable regex has quadratic worst-case complexity and it allows cause a denial of service when identifying crafted invalid RFCs. This ReDoS issue is on the client side and needs remote attackers to control the HTTP server.

- bpo-42800: Audit hooks are now fired for frame.f_code, traceback.tb_frame, and generator code/frame attribute access.

### Core and Builtins

- bpo-43105: Importlib now resolves relative paths when creating module spec objects from file locations.

- bpo-42924: Fix `bytearray` repetition incorrectly copying data from the start of the buffer, even if the data is offset within the buffer (e.g. after reassigning a slice at the start of the `bytearray` to a shorter byte string).

### Library

- bpo-43993: Update bundled pip to 21.1.1.

- bpo-43937: Fixed the `turtle` module working with non-default root window.

- bpo-43930: Update bundled pip to 21.1 and setuptools to 56.0.0

- bpo-43920: OpenSSL 3.0.0: `load_verify_locations()` now returns a consistent error message when cadata contains no valid certificate.

- bpo-43607: `urllib` can now convert Windows paths with `\\?\` prefixes into URL paths.

- bpo-43284: platform.win32_ver derives the windows version from sys.getwindowsversion().platform_version which in turn derives the version from kernel32.dll (which can be of a different version than Windows itself). Therefore change the platform.win32_ver to determine the version using the platform module’s _syscmd_ver private function to return an accurate version.

- bpo-42248: [Enum] ensure exceptions raised in `_missing__` are released

- bpo-43799: OpenSSL 3.0.0: define `OPENSSL_API_COMPAT` 1.1.1 to suppress deprecation warnings. Python requires OpenSSL 1.1.1 APIs.

- bpo-43794: Add `ssl.OP_IGNORE_UNEXPECTED_EOF` constants (OpenSSL 3.0.0)

- bpo-43789: OpenSSL 3.0.0: Don’t call the password callback function a second time when first call has signaled an error condition.

- bpo-43788: The header files for `ssl` error codes are now OpenSSL version-specific. Exceptions will now show correct reason and library codes. The `make_ssl_data.py` script has been rewritten to use OpenSSL’s text file with error codes.

- bpo-43655: `tkinter` dialog windows are now recognized as dialogs by window managers on macOS and X Window.

- bpo-43534: `turtle.textinput()` and `turtle.numinput()` create now a transient window working on behalf of the canvas window.

- bpo-43522: Fix problem with `hostname_checks_common_name`. OpenSSL does not copy hostflags from struct SSL_CTX to struct SSL.

- bpo-42967: Allow `bytes` `separator` argument in `urllib.parse.parse_qs` and `urllib.parse.parse_qsl` when parsing `str` query strings. Previously, this raised a `TypeError`.

- bpo-43176: Fixed processing of a dataclass that inherits from a frozen dataclass with no fields. It is now correctly detected as an error.

- bpo-41735: Fix thread locks in zlib module may go wrong in rare case. Patch by Ma Lin.

- bpo-36470: Fix dataclasses with `InitVar`s and `replace()`. Patch by Claudiu Popa.

- bpo-32745: Fix a regression in the handling of ctypes’ `ctypes.c_wchar_p` type: embedded null characters would cause a `ValueError` to be raised. Patch by Zackery Spytz.

### Documentation

- bpo-43959: The documentation on the PyContextVar C-API was clarified.

- bpo-43938: Update dataclasses documentation to express that FrozenInstanceError is derived from AttributeError.

- bpo-43755: Update documentation to reflect that unparenthesized lambda expressions can no longer be the expression part in an `if` clause in comprehensions and generator expressions since Python 3.9.

- bpo-43739: Fixing the example code in Doc/extending/extending.rst to declare and initialize the pmodule variable to be of the right type.

### Tests

- bpo-43961: Fix test_logging.test_namer_rotator_inheritance() on Windows: use `os.replace()` rather than `os.rename()`. Patch by Victor Stinner.

- bpo-43842: Fix a race condition in the SMTP test of test_logging. Don’t close a file descriptor (socket) from a different thread while asyncore.loop() is polling the file descriptor. Patch by Victor Stinner.

- bpo-43811: Tests multiple OpenSSL versions on GitHub Actions. Use ccache to speed up testing.

- bpo-43791: OpenSSL 3.0.0: Disable testing of legacy protocols TLS 1.0 and 1.1. Tests are failing with TLSV1_ALERT_INTERNAL_ERROR.

### Windows

- bpo-35306: Avoid raising errors from `pathlib.Path.exists()` when passed an invalid filename.

- bpo-38822: Fixed `os.stat()` failing on inaccessible directories with a trailing slash, rather than falling back to the parent directory’s metadata. This implicitly affected `os.path.exists()` and `os.path.isdir()`.

- bpo-26227: Fixed decoding of host names in `socket.gethostbyaddr()` and `socket.gethostbyname_ex()`.

- bpo-40432: Updated pegen regeneration script on Windows to find and use Python 3.8 or higher. Prior to this, pegen regeneration already required 3.8 or higher, but the script may have used lower versions of Python.

- bpo-43745: Actually updates Windows release to OpenSSL 1.1.1k. Earlier releases were mislabelled and actually included 1.1.1i again.

- bpo-43492: Upgrade Windows installer to use SQLite 3.35.5.

### macOS

- bpo-42119: Fix check for macOS SDK paths when building Python. Narrow search to match contents of SDKs, namely only files in `/System/Library`, `/System/IOSSupport`, and `/usr` other than `/usr/local`. Previously, anything under `/System` was assumed to be in an SDK which causes problems with the new file system layout in 10.15+ where user file systems may appear to be mounted under `/System`. Paths in `/Library` were also incorrectly treated as SDK locations.

- bpo-44009: Provide “python3.x-intel64” executable to allow reliably forcing macOS universal2 framework builds to run under Rosetta 2 Intel-64 emulation on Apple Silicon Macs. This can be useful for testing or when universal2 wheels are not yet available.

- bpo-43492: Update macOS installer to use SQLite 3.35.4.

### IDLE

- bpo-43655: IDLE dialog windows are now recognized as dialogs by window managers on macOS and X Window.

## Python 3.9.4 final

Release date: 2021-04-04

### Core and Builtins

- bpo-43710: Reverted the fix for https://bugs.python.org/issue42500 as it changed the PyThreadState struct size and broke the 3.9.x ABI in the 3.9.3 release (visible on 32-bit platforms using binaries compiled using an earlier version of Python 3.9.x headers).

### Library

- bpo-26053: Fixed bug where the `pdb` interactive run command echoed the args from the shell command line, even if those have been overridden at the pdb prompt.

## Python 3.9.3 final

Release date: 2021-04-02

### Security

- bpo-42988: CVE-2021-3426: Remove the `getfile` feature of the `pydoc` module which could be abused to read arbitrary files on the disk (directory traversal vulnerability). Moreover, even source code of Python modules can contain sensitive data like passwords. Vulnerability reported by David Schwörer.

- bpo-43285: `ftplib` no longer trusts the IP address value returned from the server in response to the PASV command by default. This prevents a malicious FTP server from using the response to probe IPv4 address and port combinations on the client network.

  Code that requires the former vulnerable behavior may set a `trust_server_pasv_ipv4_address` attribute on their `ftplib.FTP` instances to `True` to re-enable it.

- bpo-43439: Add audit hooks for `gc.get_objects()`, `gc.get_referrers()` and `gc.get_referents()`. Patch by Pablo Galindo.

### Core and Builtins

- bpo-43660: Fix crash that happens when replacing `sys.stderr` with a callable that can remove the object while an exception is being printed. Patch by Pablo Galindo.

- bpo-43555: Report the column offset for `SyntaxError` for invalid line continuation characters. Patch by Pablo Galindo.

- bpo-43517: Fix misdetection of circular imports when using `from pkg.mod import attr`, which caused false positives in non-trivial multi-threaded code.

- bpo-35883: Python no longer fails at startup with a fatal error if a command line argument contains an invalid Unicode character. The `Py_DecodeLocale()` function now escapes byte sequences which would be decoded as Unicode characters outside the [U+0000; U+10ffff] range.

- bpo-43406: Fix a possible race condition where `PyErr_CheckSignals` tries to execute a non-Python signal handler.

- bpo-42500: Improve handling of exceptions near recursion limit. Converts a number of Fatal Errors in RecursionErrors.

### Library

- bpo-43433: `xmlrpc.client.ServerProxy` no longer ignores query and fragment in the URL of the server.

- bpo-35930: Raising an exception raised in a “future” instance will create reference cycles.

- bpo-43577: Fix deadlock when using `ssl.SSLContext` debug callback with `ssl.SSLContext.sni_callback()`.

- bpo-43521: `ast.unparse` can now render NaNs and empty sets.

- bpo-43423: `subprocess.communicate()` no longer raises an IndexError when there is an empty stdout or stderr IO buffer during a timeout on Windows.

- bpo-27820: Fixed long-standing bug of smtplib.SMTP where doing AUTH LOGIN with initial_response_ok=False will fail.

  The cause is that SMTP.auth_login _always_ returns a password if provided with a challenge string, thus non-compliant with the standard for AUTH LOGIN.

  Also fixes bug with the test for smtpd.

- bpo-43332: Improves the networking efficiency of `http.client` when using a proxy via `set_tunnel()`. Fewer small send calls are made during connection setup.

- bpo-43399: Fix `ElementTree.extend` not working on iterators when using the Python implementation

- bpo-43316: The `python -m gzip` command line application now properly fails when detecting an unsupported extension. It exits with a non-zero exit code and prints an error message to stderr.

- bpo-43260: Fix TextIOWrapper can not flush internal buffer forever after very large text is written.

- bpo-42782: Fail fast in `shutil.move()` to avoid creating destination directories on failure.

- bpo-37193: Fixed memory leak in `socketserver.ThreadingMixIn` introduced in Python 3.7.

### Documentation

- bpo-43199: Answer “Why is there no goto?” in the Design and History FAQ.

- bpo-43407: Clarified that a result from `time.monotonic()`, `time.perf_counter()`, `time.process_time()`, or `time.thread_time()` can be compared with the result from any following call to the same function - not just the next immediate call.

- bpo-27646: Clarify that ‘yield from <expr>’ works with any iterable, not just iterators.

- bpo-36346: Update some deprecated unicode APIs which are documented as “will be removed in 4.0” to “3.12”. See PEP 623 for detail.

### Tests

- bpo-37945: Fix test_getsetlocale_issue1813() of test_locale: skip the test if `setlocale()` fails. Patch by Victor Stinner.

- bpo-41561: Add workaround for Ubuntu’s custom OpenSSL security level policy.

- bpo-43288: Fix test_importlib to correctly skip Unicode file tests if the fileystem does not support them.

### Build

- bpo-43631: Update macOS, Windows, and CI to OpenSSL 1.1.1k.

- bpo-43617: Improve configure.ac: Check for presence of autoconf-archive package and remove our copies of M4 macros.

### macOS

- bpo-41837: Update macOS installer build to use OpenSSL 1.1.1j.

### IDLE

- bpo-42225: Document that IDLE can fail on Unix either from misconfigured IP masquerage rules or failure displaying complex colored (non-ascii) characters.

- bpo-43283: Document why printing to IDLE’s Shell is often slower than printing to a system terminal and that it can be made faster by pre-formatting a single string before printing.

## Python 3.9.2 final

Release date: 2021-02-19

### Windows

- bpo-43155: `PyCMethod_New()` is now present in `python3.lib`.

## Python 3.9.2 release candidate 1

Release date: 2021-02-16

### Security

- bpo-42967: Fix web cache poisoning vulnerability by defaulting the query args separator to `&`, and allowing the user to choose a custom separator.

- bpo-42938: Avoid static buffers when computing the repr of `ctypes.c_double` and `ctypes.c_longdouble` values.

### Core and Builtins

- bpo-42819: `readline`: Explicitly disable bracketed paste in the interactive interpreter, even if it’s set in the inputrc, is enabled by default (eg GNU Readline 8.1), or a user calls `readline.read_init_file()`. The Python REPL has not implemented bracketed paste support. Also, bracketed mode writes the `"\x1b[?2004h"` escape sequence into stdout which causes test failures in applications that don’t support it. It can still be explicitly enabled by calling `readline.parse_and_bind("set enable-bracketed-paste on")`. Patch by Dustin Rodrigues.

- bpo-42806: Fix the column offsets for f-strings `ast` nodes surrounded by parentheses and for nodes that spawn multiple lines. Patch by Pablo Galindo.

- bpo-40631: Fix regression where a single parenthesized starred expression was a valid assignment target.

- bpo-32381: Fix encoding name when running a `.pyc` file on Windows: `PyRun_SimpleFileExFlags()` now uses the correct encoding to decode the filename.

- bpo-42536: Several built-in and standard library types now ensure that their internal result tuples are always tracked by the garbage collector:

  - `collections.OrderedDict.items()`

  - `dict.items()`

  - `enumerate()`

  - `functools.reduce()`

  - `itertools.combinations()`

  - `itertools.combinations_with_replacement()`

  - `itertools.permutations()`

  - `itertools.product()`

  - `itertools.zip_longest()`

  - `zip()`

  Previously, they could have become untracked by a prior garbage collection. Patch by Brandt Bucher.

- bpo-42195: The `__args__` of the parameterized generics for `typing.Callable` and `collections.abc.Callable` are now consistent. The `__args__` for `collections.abc.Callable` are now flattened while `typing.Callable`’s have not changed. To allow this change, `types.GenericAlias` can now be subclassed and `collections.abc.Callable`’s `__class_getitem__` will now return a subclass of `types.GenericAlias`. Tests for typing were also updated to not subclass things like `Callable[..., T]` as that is not a valid base class. Finally, both types no longer validate their `argtypes`, in `Callable[[argtypes], resulttype]` to prepare for PEP 612. Patch by Ken Jin.

### Library

- bpo-43102: The namedtuple __new__ method had its __builtins__ set to None instead of an actual dictionary. This created problems for introspection tools.

- bpo-43108: Fixed a reference leak in the `curses` module. Patch by Pablo Galindo

- bpo-42944: Fix `random.Random.sample` when `counts` argument is not `None`.

- bpo-42931: Add `randbytes()` to `random.__all__`.

- bpo-42780: Fix os.set_inheritable() for O_PATH file descriptors on Linux.

- bpo-42851: remove __init_subclass__ support for Enum members

- bpo-41748: Fix HTMLParser parsing rules for element attributes containing commas with spaces. Patch by Karl Dubost.

- bpo-42759: Fixed equality comparison of `tkinter.Variable` and `tkinter.font.Font`. Objects which belong to different Tcl interpreters are now always different, even if they have the same name.

- bpo-42756: Configure LMTP Unix-domain socket to use socket global default timeout when a timeout is not explicitly provided.

- bpo-23328: Allow / character in username, password fields on _PROXY envars.

- bpo-42655: `subprocess` extra_groups is now correctly passed into setgroups() system call.

- bpo-42727: `EnumMeta.__prepare__` now accepts `**kwds` to properly support `__init_subclass__`

- bpo-42681: Fixed range checks for color and pair numbers in `curses`.

- bpo-37961: Fix crash in `tracemalloc.Traceback.__repr__()` (regressed in Python 3.9).

- bpo-42630: `tkinter` functions and constructors which need a default root window raise now `RuntimeError` with descriptive message instead of obscure `AttributeError` or `NameError` if it is not created yet or cannot be created automatically.

- bpo-42644: `logging.disable` will now validate the types and value of its parameter. It also now accepts strings representing the levels (as does `loging.setLevel`) instead of only the numerical values.

- bpo-36541: Fixed lib2to3.pgen2 to be able to parse PEP-570 positional only argument syntax.

- bpo-42517: Enum: private names will raise a DeprecationWarning; in 3.10 they will become normal attributes

- bpo-42678: `Enum`: call `__init_subclass__` after members have been added

- bpo-42532: Remove unexpected call of `__bool__` when passing a `spec_arg` argument to a Mock.

- bpo-42388: Fix subprocess.check_output(…, input=None) behavior when text=True to be consistent with that of the documentation and universal_newlines=True.

- bpo-34463: Fixed discrepancy between `traceback` and the interpreter in formatting of SyntaxError with lineno not set (`traceback` was changed to match interpreter).

- bpo-42375: subprocess module update for DragonFlyBSD support.

- bpo-42384: Make pdb populate sys.path[0] exactly the same as regular python execution.

- bpo-42383: Fix pdb: previously pdb would fail to restart the debugging target if it was specified using a relative path and the current directory changed.

- bpo-42318: Fixed support of non-BMP characters in `tkinter` on macOS.

- bpo-42163: Restore compatibility for `uname_result` around deepcopy and _replace.

- bpo-39825: Windows: Change `sysconfig.get_config_var('EXT_SUFFIX')` to the expected full `platform_tag.extension` format. Previously it was hard-coded to `.pyd`, now it is compatible with `distutils.sysconfig` and will result in something like `.cp38-win_amd64.pyd`. This brings windows into conformance with the other platforms.

- bpo-42059: `typing.TypedDict` types created using the alternative call-style syntax now correctly respect the `total` keyword argument when setting their `__required_keys__` and `__optional_keys__` class attributes.

- bpo-39101: Fixed tests using IsolatedAsyncioTestCase from hanging on BaseExceptions.

- bpo-42005: Fix CLI of `cProfile` and `profile` to catch `BrokenPipeError`.

- bpo-41907: fix `format()` behavior for `IntFlag`

- bpo-41889: Enum: fix regression involving inheriting a multiply-inherited enum

- bpo-41891: Ensure asyncio.wait_for waits for task completion

- bpo-41604: Don’t decrement the reference count of the previous user_ptr when set_panel_userptr fails.

- bpo-40219: Lowered `tkinter.ttk.LabeledScale` dummy widget to prevent hiding part of the content label.

- bpo-40084: Fix `Enum.__dir__`: dir(Enum.member) now includes attributes as well as methods.

- bpo-39068: Fix initialization race condition in `a85encode()` and `b85encode()` in `base64`. Patch by Brandon Stansbury.

- bpo-33289: Correct call to `tkinter.colorchooser` to return RGB triplet of ints instead of floats. Patch by Cheryl Sabella.

### Documentation

- bpo-40304: Fix doc for type(name, bases, dict). Patch by Boris Verkhovskiy and Éric Araujo.

- bpo-42811: Updated importlib.utils.resolve_name() doc to use __spec__.parent instead of __package__. (Thanks Yair Frid.)

- bpo-17140: Add documentation for the `multiprocessing.pool.ThreadPool` class.

### Tests

- bpo-42794: Update test_nntplib to use offical group name of news.aioe.org for testing. Patch by Dong-hee Na.

- bpo-40810: In `sqlite3`, fix `CheckTraceCallbackContent` for SQLite pre 3.7.15.

### Build

- bpo-43174: Windows build now uses `/utf-8` compiler option.

- bpo-42692: Fix __builtin_available check on older compilers. Patch by Joshua Root.

- bpo-42604: Now all platforms use a value for the “EXT_SUFFIX” build variable derived from SOABI (for instance in freeBSD, “EXT_SUFFIX” is now “.cpython-310d.so” instead of “.so”). Previosuly only Linux, Mac and VxWorks were using a value for “EXT_SUFFIX” that included “SOABI”.

- bpo-42598: Fix implicit function declarations in configure which could have resulted in incorrect configuration checks. Patch contributed by Joshua Root.

- bpo-29076: Add fish shell support to macOS installer.

### Windows

- bpo-41837: Updated Windows installer to include OpenSSL 1.1.1i

- bpo-42584: Upgrade Windows installer to use SQLite 3.34.0.

### macOS

- bpo-42504: Ensure that the value of sysconfig.get_config_var(‘MACOSX_DEPLOYMENT_TARGET’) is always a string, even in when the value is parsable as an integer.

- bpo-42361: Update macOS installer build to use Tcl/Tk 8.6.11 (rc2, expected to be final release).

- bpo-41837: Update macOS installer build to use OpenSSL 1.1.1i.

- bpo-42584: Update macOS installer to use SQLite 3.34.0.

### IDLE

- bpo-43008: Make IDLE invoke `sys.excepthook()` in normal, 2-process mode. Patch by Ken Hilton.

- bpo-33065: Fix problem debugging user classes with __repr__ method.

- bpo-23544: Disable Debug=>Stack Viewer when user code is running or Debugger is active, to prevent hang or crash. Patch by Zackery Spytz.

- bpo-32631: Finish zzdummy example extension module: make menu entries work; add docstrings and tests with 100% coverage.

### Tools/Demos

- bpo-42726: Fixed Python 3 compatibility issue with gdb/libpython.py handling of attribute dictionaries.

- bpo-42613: Fix `freeze.py` tool to use the prope config and library directories. Patch by Victor Stinner.

### C API

- bpo-43030: Fixed a compiler warning in `Py_UNICODE_ISSPACE()` on platforms with signed `wchar_t`.

- bpo-42591: Export the `Py_FrozenMain()` function: fix a Python 3.9.0 regression. Python 3.9 uses `-fvisibility=hidden` and the function was not exported explicitly and so not exported.

- bpo-40052: Fix an alignment build warning/error in function `PyVectorcall_Function()`. Patch by Andreas Schneider, Antoine Pitrou and Petr Viktorin.

## Python 3.9.1 final

Release date: 2020-12-07

### Core and Builtins

- bpo-42576: `types.GenericAlias` will now raise a `TypeError` when attempting to initialize with a keyword argument. Previously, this would cause the interpreter to crash if the interpreter was compiled with debug symbols. This does not affect interpreters compiled for release. Patch by Ken Jin.

### Library

- bpo-5054: CGIHTTPRequestHandler.run_cgi() HTTP_ACCEPT improperly parsed. Replace the special purpose getallmatchingheaders with generic get_all method and add relevant tests.

  Original Patch by Martin Panter. Modified by Senthil Kumaran.

- bpo-17735: `inspect.findsource()` now raises `OSError` instead of `IndexError` when `co_lineno` of a code object is greater than the file length. This can happen, for example, when a file is edited after it was imported. PR by Irit Katriel.

- bpo-42116: Fix handling of trailing comments by `inspect.getsource()`.

- bpo-42487: ChainMap.__iter__ no longer calls __getitem__ on underlying maps

- bpo-42482: `TracebackException` no longer holds a reference to the exception’s traceback object. Consequently, instances of TracebackException for equivalent but non-equal exceptions now compare as equal.

- bpo-42406: We fixed an issue in `pickle.whichmodule` in which importing `multiprocessing` could change the how pickle identifies which module an object belongs to, potentially breaking the unpickling of those objects.

- bpo-34215: Clarify the error message for `asyncio.IncompleteReadError` when `expected` is `None`.

- bpo-12800: Extracting a symlink from a tarball should succeed and overwrite the symlink if it already exists. The fix is to remove the existing file or symlink before extraction. Based on patch by Chris AtLee, Jeffrey Kintscher, and Senthil Kumaran.

### Tests

- bpo-41473: Reenable test_gdb on gdb 9.2 and newer: https://bugzilla.redhat.com/show_bug.cgi?id=1866884 bug is fixed in gdb 10.1.

- bpo-42553: Fix `test_asyncio.test_call_later()` race condition: don’t measure asyncio performance in the `call_later()` unit test. The test failed randomly on the CI.

### macOS

- bpo-41116: If no explicit macOS SDK was specified, setup.py should check for Tcl and TK frameworks in /Library/Frameworks; the previous commit inadvertently broke that test.

- bpo-42504: Fix build on macOS Big Sur when MACOSX_DEPLOYMENT_TARGET=11

### IDLE

- bpo-42508: Keep IDLE running on macOS. Remove obsolete workaround that prevented running files with shortcuts when using new universal2 installers built on macOS 11.

## Python 3.9.1 release candidate 1

Release date: 2020-11-24

### Security

- bpo-42103: Prevented potential DoS attack via CPU and RAM exhaustion when processing malformed Apple Property List files in binary format.

- bpo-42051: The `plistlib` module no longer accepts entity declarations in XML plist files to avoid XML vulnerabilities. This should not affect users as entity declarations are not used in regular plist files.

- bpo-40791: Add `volatile` to the accumulator variable in `hmac.compare_digest`, making constant-time-defeating optimizations less likely.

### Core and Builtins

- bpo-41686: On Windows, the `SIGINT` event, `_PyOS_SigintEvent()`, is now created even if Python is configured to not install signal handlers (if `PyConfig.install_signal_handlers` equals to 0, or `Py_InitializeEx(0)`).

- bpo-42381: Allow assignment expressions in set literals and set comprehensions as per PEP 572. Patch by Pablo Galindo.

- bpo-42374: Fix a regression introduced by the new parser, where an unparenthesized walrus operator was not allowed within generator expressions.

- bpo-42296: On Windows, fix a regression in signal handling which prevented to interrupt a program using CTRL+C. The signal handler can be run in a thread different than the Python thread, in which case the test deciding if the thread can handle signals is wrong.

- bpo-42332: `types.GenericAlias` objects can now be the targets of weakrefs.

- bpo-42218: Fixed a bug in the PEG parser that was causing crashes in debug mode. Now errors are checked in left-recursive rules to avoid cases where such errors do not get handled in time and appear as long-distance crashes in other places.

- bpo-42214: Fixed a possible crash in the PEG parser when checking for the ‘!=’ token in the `barry_as_flufl` rule. Patch by Pablo Galindo.

- bpo-42143: Fix handling of errors during creation of `PyFunctionObject`, which resulted in operations on uninitialized memory. Patch by Yonatan Goldschmidt.

- bpo-41659: Fix a bug in the parser, where a curly brace following a `primary` didn’t fail immediately. This led to invalid expressions like `a {b}` to throw a `SyntaxError` with a wrong offset, or invalid expressions ending with a curly brace like `a {` to not fail immediately in the REPL.

- bpo-42150: Fix possible buffer overflow in the new parser when checking for continuation lines. Patch by Pablo Galindo.

- bpo-42123: Run the parser two times. On the first run, disable all the rules that only generate better error messages to gain performance. If there’s a parse failure, run the parser a second time with those enabled.

- bpo-42057: Fix peephole optimizer misoptimize conditional jump + JUMP_IF_NOT_EXC_MATCH pair.

- bpo-41984: The garbage collector now tracks all user-defined classes. Patch by Brandt Bucher.

- bpo-41993: Fixed potential issues with removing not completely initialized module from `sys.modules` when import fails.

- bpo-41979: Star-unpacking is now allowed for with item’s targets in the PEG parser.

- bpo-41909: Fixed stack overflow in `issubclass()` and `isinstance()` when getting the `__bases__` attribute leads to infinite recursion.

- bpo-41894: When loading a native module and a load failure occurs, prevent a possible UnicodeDecodeError when not running in a UTF-8 locale by decoding the load error message using the current locale’s encoding.

- bpo-39934: Correctly count control blocks in ‘except’ in compiler. Ensures that a syntax error, rather a fatal error, occurs for deeply nested, named exception handlers.

### Library

- bpo-42328: Fixed `tkinter.ttk.Style.map()`. The function accepts now the representation of the default state as empty sequence (as returned by `Style.map()`). The structure of the result is now the same on all platform and does not depend on the value of `wantobjects`.

- bpo-42345: Fix various issues with `typing.Literal` parameter handling (flatten, deduplicate, use type to cache key). Patch provided by Yurii Karabas.

- bpo-42350: Fix the `threading.Thread` class at fork: do nothing if the thread is already stopped (ex: fork called at Python exit). Previously, an error was logged in the child process.

- bpo-42014: The `onerror` callback from `shutil.rmtree` now receives correct function when `os.open` fails.

- bpo-42237: Fix `os.sendfile()` on illumos.

- bpo-42249: Fixed writing binary Plist files larger than 4 GiB.

- bpo-35455: On Solaris, `thread_time()` is now implemented with `gethrvtime()` because `clock_gettime(CLOCK_THREAD_CPUTIME_ID)` is not always available. Patch by Jakub Kulik.

- bpo-42233: The `repr()` of `typing` types containing Generic Alias Types previously did not show the parameterized types in the `GenericAlias`. They have now been changed to do so.

- bpo-41754: webbrowser: Ignore NotADirectoryError when calling `xdg-settings`.

- bpo-29566: `binhex.binhex()` consisently writes macOS 9 line endings.

- bpo-42183: Fix a stack overflow error for asyncio Task or Future repr().

  The overflow occurs under some circumstances when a Task or Future recursively returns itself.

- bpo-42146: Fix memory leak in `subprocess.Popen()` in case an uid (gid) specified in `user` (`group`, `extra_groups`) overflows `uid_t` (`gid_t`).

- bpo-42140: Improve asyncio.wait function to create the futures set just one time.

- bpo-42103: `InvalidFileException` and `RecursionError` are now the only errors caused by loading malformed binary Plist file (previously ValueError and TypeError could be raised in some specific cases).

- bpo-41052: Pickling heap types implemented in C with protocols 0 and 1 raises now an error instead of producing incorrect data.

- bpo-41491: plistlib: fix parsing XML plists with hexadecimal integer values

- bpo-42065: Fix an incorrectly formatted error from `_codecs.charmap_decode()` when called with a mapped value outside the range of valid Unicode code points. PR by Max Bernstein.

- bpo-41966: Fix pickling pure Python `datetime.time` subclasses. Patch by Dean Inwood.

- bpo-41976: Fixed a bug that was causing `ctypes.util.find_library()` to return `None` when triying to locate a library in an environment when gcc>=9 is available and `ldconfig` is not. Patch by Pablo Galindo

- bpo-41900: C14N 2.0 serialisation in xml.etree.ElementTree failed for unprefixed attributes when a default namespace was defined.

- bpo-41840: Fix a bug in the `symtable` module that was causing module-scope global variables to not be reported as both local and global. Patch by Pablo Galindo.

- bpo-41831: `str()` for the `type` attribute of the `tkinter.Event` object always returns now the numeric code returned by Tk instead of the name of the event type.

- bpo-41817: fix `tkinter.EventType` Enum so all members are strings, and none are tuples

- bpo-41815: Fix SQLite3 segfault when backing up closed database. Patch contributed by Peter David McCormick.

- bpo-41316: Fix the `tarfile` module to write only basename of TAR file to GZIP compression header.

- bpo-16396: Allow `ctypes.wintypes` to be imported on non-Windows systems.

- bpo-40592: `shutil.which()` now ignores empty entries in `PATHEXT` instead of treating them as a match.

- bpo-40550: Fix time-of-check/time-of-action issue in subprocess.Popen.send_signal.

- bpo-40492: Fix `--outfile` for `cProfile` / `profile` not writing the output file in the original directory when the program being profiled changes the working directory. PR by Anthony Sottile.

- bpo-40105: ZipFile truncates files to avoid corruption when a shorter comment is provided in append (“a”) mode. Patch by Jan Mazur.

- bpo-27321: Fixed KeyError exception when flattening an email to a string attempts to replace a non-existent Content-Transfer-Encoding header.

### Documentation

- bpo-42153: Fix the URL for the IMAP protocol documents.

- bpo-42061: Document __format__ functionality for IP addresses.

- bpo-41910: Document the default implementation of `object.__eq__`.

- bpo-42010: Clarify that subscription expressions are also valid for certain classes and types in the standard library, and for user-defined classes and types if the classmethod `__class_getitem__()` is provided.

- bpo-41805: Documented generic alias type and `types.GenericAlias`. Also added an entry in glossary for generic types.

- bpo-41774: In Programming FAQ “Sequences (Tuples/Lists)” section, add “How do you remove multiple items from a list”.

- bpo-35293: Fix RemovedInSphinx40Warning when building the documentation. Patch by Dong-hee Na.

- bpo-41726: Update the refcounts info of `PyType_FromModuleAndSpec`.

- bpo-39693: Fix tarfile’s extractfile documentation

- bpo-39416: Document some restrictions on the default string representations of numeric classes.

### Tests

- bpo-40754: Include `_testinternalcapi` module in Windows installer for test suite

- bpo-41739: Fix test_logging.test_race_between_set_target_and_flush(): the test now waits until all threads complete to avoid leaking running threads.

- bpo-41970: Avoid a test failure in `test_lib2to3` if the module has already imported at the time the test executes. Patch by Pablo Galindo.

- bpo-41944: Tests for CJK codecs no longer call `eval()` on content received via HTTP.

- bpo-41939: Fix test_site.test_license_exists_at_url(): call `urllib.request.urlcleanup()` to reset the global `urllib.request._opener`. Patch by Victor Stinner.

- bpo-41561: test_ssl: skip test_min_max_version_mismatch when TLS 1.0 is not available

- bpo-41602: Add tests for SIGINT handling in the runpy module.

- bpo-41306: Fixed a failure in `test_tk.test_widgets.ScaleTest` happening when executing the test with Tk 8.6.10.

### Build

- bpo-42398: Fix a race condition in “make regen-all” when make -jN option is used to run jobs in parallel. The clinic.py script now only use atomic write to write files. Moveover, generated files are now left unchanged if the content does not change, to not change the file modification time.

- bpo-41617: Fix building `pycore_bitutils.h` internal header on old clang version without `__builtin_bswap16()` (ex: Xcode 4.6.3 on Mac OS X 10.7). Patch by Joshua Root and Victor Stinner.

- bpo-38249: Update `Py_UNREACHABLE` to use __builtin_unreachable() if only the compiler is able to use it. Patch by Dong-hee Na.

- bpo-40998: Addressed three compiler warnings found by undefined behavior sanitizer (ubsan).

### Windows

- bpo-42120: Remove macro definition of `copysign` (to `_copysign`) in headers.

- bpo-38439: Updates the icons for IDLE in the Windows Store package.

- bpo-41744: Fixes automatic import of props file when using the Nuget package.

- bpo-41557: Update Windows installer to use SQLite 3.33.0.

- bpo-38324: Avoid Unicode errors when accessing certain locale data on Windows.

### macOS

- bpo-41116: Ensure distutils.unixxcompiler.find_library_file can find system provided libraries on macOS 11.

- bpo-41100: Add support for macOS 11 and Apple Silicon systems.

  It is now possible to build “Universal 2” binaries using “–enable-universalsdk –with-universal-archs=universal2”.

  Binaries build on later macOS versions can be deployed back to older versions (tested up to macOS 10.9), when using the correct deployment target. This is tested using Xcode 11 and later.

- bpo-38443: The `--enable-universalsdk` and `--with-universal-archs` options for the configure script now check that the specified architectures can be used.

- bpo-41471: Ignore invalid prefix lengths in system proxy excludes.

- bpo-41557: Update macOS installer to use SQLite 3.33.0.

### IDLE

- bpo-42426: Fix reporting offset of the RE error in searchengine.

- bpo-42415: Get docstrings for IDLE calltips more often by using inspect.getdoc.

- bpo-33987: Mostly finish using ttk widgets, mainly for editor, settings, and searches. Some patches by Mark Roseman.

- bpo-41775: Use ‘IDLE Shell’ as shell title

- bpo-35764: Rewrite the Calltips doc section.

- bpo-40181: In calltips, stop reminding that ‘/’ marks the end of positional-only arguments.

- bpo-40511: Typing opening and closing parentheses inside the parentheses of a function call will no longer cause unnecessary “flashing” off and on of an existing open call-tip, e.g. when typed in a string literal.

- bpo-38439: Add a 256×256 pixel IDLE icon to the Windows .ico file. Created by Andrew Clover. Remove the low-color gif variations from the .ico file.

### C API

- bpo-42015: Fix potential crash in deallocating method objects when dynamically allocated `PyMethodDef`’s lifetime is managed through the `self` argument of a `PyCFunction`.

- bpo-41986: `Py_FileSystemDefaultEncodeErrors` and `Py_UTF8Mode` are available again in limited API.

## Python 3.9.0 final

Release date: 2020-10-04

### Library

- bpo-41815: Fix SQLite3 segfault when backing up closed database. Patch contributed by Peter David McCormick.

- bpo-41662: No longer override exceptions raised in `__len__()` of a sequence of parameters in `sqlite3` with `ProgrammingError`.

- bpo-41662: Fixed crash when mutate list of parameters during iteration in `sqlite3`.

- bpo-39728: fix default `_missing_` so a duplicate `ValueError` is not set as the `__context__` of the original `ValueError`

### Tests

- bpo-41602: Add tests for SIGINT handling in the runpy module.

### Build

- bpo-38249: Update `Py_UNREACHABLE` to use __builtin_unreachable() if only the compiler is able to use it. Patch by Dong-hee Na.

## Python 3.9.0 release candidate 2

Release date: 2020-09-16

### Core and Builtins

- bpo-41780: Fix `__dir__()` of `types.GenericAlias`. Patch by Batuhan Taskaya.

- bpo-41690: Fix a possible stack overflow in the parser when parsing functions and classes with a huge ammount of arguments. Patch by Pablo Galindo.

- bpo-41681: Fixes the wrong error description in the error raised by using 2 `,` in format string in f-string and `str.format()`.

- bpo-41654: Fix a crash that occurred when destroying subclasses of `MemoryError`. Patch by Pablo Galindo.

- bpo-41631: The `_ast` module uses again a global state. Using a module state per module instance is causing subtle practical problems. For example, the Mercurial project replaces the `__import__()` function to implement lazy import, whereas Python expected that `import _ast` always return a fully initialized `_ast` module.

- bpo-41533: Free the stack allocated in `va_build_stack` if `do_mkstack` fails and the stack is not a `small_stack`.

- bpo-41531: Fix a bug that was dropping keys when compiling dict literals with more than 0xFFFF elements. Patch by Pablo Galindo.

- bpo-41525: The output of `python --help` contains now only ASCII characters.

- bpo-29590: Make the stack trace correct after calling `generator.throw()` on a generator that has yielded from a `yield from`.

### Library

- bpo-41517: fix bug allowing Enums to be extended via multiple inheritance

- bpo-39587: use the correct mix-in data type when constructing Enums

- bpo-41789: Honor `object` overrides in `Enum` class creation (specifically, `__str__`, `__repr__`, `__format__`, and `__reduce_ex__`).

- bpo-39651: Fix a race condition in the `call_soon_threadsafe()` method of `asyncio.ProactorEventLoop`: do nothing if the self-pipe socket has been closed.

- bpo-41720: Fixed `turtle.Vec2D.__rmul__()` for arguments which are not int or float.

- bpo-41696: Fix handling of debug mode in `asyncio.run()`. This allows setting `PYTHONASYNCIODEBUG` or `-X dev` to enable asyncio debug mode when using `asyncio.run()`.

- bpo-41687: Fix implementation of sendfile to be compatible with Solaris.

- bpo-39010: Restarting a `ProactorEventLoop` on Windows no longer logs spurious `ConnectionResetErrors`.

- bpo-41609: The pdb whatis command correctly reports instance methods as ‘Method’ rather than ‘Function’.

- bpo-32751: When cancelling the task due to a timeout, `asyncio.wait_for()` will now wait until the cancellation is complete also in the case when timeout is <= 0, like it does with positive timeouts.

- bpo-37658: `asyncio.wait_for()` now properly handles races between cancellation of itself and the completion of the wrapped awaitable.

- bpo-40782: Change the method asyncio.AbstractEventLoop.run_in_executor to not be a coroutine.

- bpo-41520: Fix `codeop` regression that prevented turning compile warnings into errors.

- bpo-41503: Fixed a race between setTarget and flush in logging.handlers.MemoryHandler.

- bpo-41344: Prevent creating `shared_memory.SharedMemory` objects with `size=0`.

- bpo-41025: Fixed an issue preventing the C implementation of `zoneinfo.ZoneInfo` from being subclassed.

- bpo-31122: ssl.wrap_socket() now raises ssl.SSLEOFError rather than OSError when peer closes connection during TLS negotiation

- bpo-33660: Fix pathlib.PosixPath to resolve a relative path located on the root directory properly.

### Documentation

- bpo-37149: Change Shipman tkinter doc link from archive.org to TkDocs. (The doc has been removed from the NMT server.) The new link responds much faster and includes a short explanatory note.

- bpo-41624: Fix the signature of `typing.Coroutine`.

- bpo-40204: Enable Sphinx 3.2 `c_allow_pre_v3` option and disable `c_warn_on_allowed_pre_v3` option to make the documentation compatible with Sphinx 2 and Sphinx 3.

- bpo-40979: Refactored typing.rst, arranging more than 70 classes, functions, and decorators into new sub-sections.

- bpo-39883: Make code, examples, and recipes in the Python documentation be licensed under the more permissive BSD0 license in addition to the existing Python 2.0 license.

### Tests

- bpo-41731: Make test_cmd_line_script pass with option ‘-vv’.

### Build

- bpo-41617: Fix `pycore_byteswap.h` header file to support old clang versions: `__builtin_bswap16()` is not available in LLVM clang 3.0.

### Windows

- bpo-41526: Fixed layout of final page of the installer by removing the special thanks to Mark Hammond (with his permission).

### C API

- bpo-41524: Fix bug in PyOS_mystrnicmp and PyOS_mystricmp that incremented pointers beyond the end of a string.

## Python 3.9.0 release candidate 1

Release date: 2020-08-11

### Core and Builtins

- bpo-38156: Handle interrupts that come after EOF correctly in `PyOS_StdioReadline`.

### Library

- bpo-41497: Fix potential UnicodeDecodeError in dis module.

- bpo-41490: Update `ensurepip` to install pip 20.2.1 and setuptools 49.2.1.

- bpo-41467: On Windows, fix asyncio `recv_into()` return value when the socket/pipe is closed (`BrokenPipeError`): return `0` rather than an empty byte string (`b''`).

- bpo-41425: Make tkinter doc example runnable.

- bpo-41384: Raise TclError instead of TypeError when an unknown option is passed to tkinter.OptionMenu.

- bpo-38731: Fix `NameError` in command-line interface of `py_compile`.

- bpo-41317: Use add_done_callback() in asyncio.loop.sock_accept() to unsubscribe reader early on cancellation.

- bpo-41364: Reduce import overhead of `uuid`.

- bpo-41341: Recursive evaluation of `typing.ForwardRef` in `get_type_hints`.

- bpo-41182: selector: use DefaultSelector based upon implementation

- bpo-40726: Handle cases where the `end_lineno` is `None` on `ast.increment_lineno()`.

### Documentation

- bpo-41045: Add documentation for debug feature of f-strings.

- bpo-41314: Changed the release when `from __future__ import annotations` becomes the default from `4.0` to `3.10` (following a change in PEP 563).

### Windows

- bpo-41492: Fixes the description that appears in UAC prompts.

- bpo-40948: Improve post-install message to direct people to the “py” command.

- bpo-41412: The installer will now fail to install on Windows 7 and Windows 8. Further, the UCRT dependency is now always downloaded on demand.

- bpo-40741: Update Windows release to include SQLite 3.32.3.

### IDLE

- bpo-41468: Improve IDLE run crash error message (which users should never see).

- bpo-41373: Save files loaded with no line ending, as when blank, or different line endings, by setting its line ending to the system default. Fix regression in 3.8.4 and 3.9.0b4.

## Python 3.9.0 beta 5

Release date: 2020-07-20

### Security

- bpo-41304: Fixes `python3x._pth` being ignored on Windows, caused by the fix for bpo-29778 (CVE-2020-15801).

- bpo-41162: Audit hooks are now cleared later during finalization to avoid missing events.

- bpo-29778: Ensure `python3.dll` is loaded from correct locations when Python is embedded (CVE-2020-15523).

- bpo-39603: Prevent http header injection by rejecting control characters in http.client.putrequest(…).

### Core and Builtins

- bpo-41295: Resolve a regression in CPython 3.8.4 where defining “__setattr__” in a multi-inheritance setup and calling up the hierarchy chain could fail if builtins/extension types were involved in the base types.

- bpo-41247: Always cache the running loop holder when running `asyncio.set_running_loop`.

- bpo-41252: Fix incorrect refcounting in _ssl.c’s `_servername_callback()`.

- bpo-41215: Use non-NULL default values in the PEG parser keyword list to overcome a bug that was preventing Python from being properly compiled when using the XLC compiler. Patch by Pablo Galindo.

- bpo-41218: Python 3.8.3 had a regression where compiling with ast.PyCF_ALLOW_TOP_LEVEL_AWAIT would aggressively mark list comprehension with CO_COROUTINE. Now only list comprehension making use of async/await will tagged as so.

- bpo-41175: Guard against a NULL pointer dereference within bytearrayobject triggered by the `bytearray() + bytearray()` operation.

- bpo-39960: The “hackcheck” that prevents sneaking around a type’s __setattr__() by calling the superclass method was rewritten to allow C implemented heap types.

### Library

- bpo-41288: Unpickling invalid NEWOBJ_EX opcode with the C implementation raises now UnpicklingError instead of crashing.

- bpo-39017: Avoid infinite loop when reading specially crafted TAR files using the tarfile module (CVE-2019-20907).

- bpo-41235: Fix the error handling in `ssl.SSLContext.load_dh_params()`.

- bpo-41207: In distutils.spawn, restore expectation that DistutilsExecError is raised when the command is not found.

- bpo-39168: Remove the `__new__` method of `typing.Generic`.

- bpo-41194: Fix a crash in the `_ast` module: it can no longer be loaded more than once. It now uses a global state rather than a module state.

- bpo-39384: Fixed email.contentmanager to allow set_content() to set a null string.

### Documentation

- bpo-37703: Updated Documentation to comprehensively elaborate on the behaviour of gather.cancel()

### macOS

- bpo-40741: Update macOS installer to use SQLite 3.32.3.

### IDLE

- bpo-41300: Save files with non-ascii chars. Fix regression released in 3.9.0b4 and 3.8.4.

- bpo-37765: Add keywords to module name completion list. Rewrite Completions section of IDLE doc.

### C API

- bpo-40170: Revert `PyType_HasFeature()` change: it reads again directly the `PyTypeObject.tp_flags` member when the limited C API is not used, rather than always calling `PyType_GetFlags()` which hides implementation details.

## Python 3.9.0 beta 4

Release date: 2020-07-02

### Security

- bpo-41004: The __hash__() methods of ipaddress.IPv4Interface and ipaddress.IPv6Interface incorrectly generated constant hash values of 32 and 128 respectively. This resulted in always causing hash collisions. The fix uses hash() to generate hash values for the tuple of (address, mask length, network address).

### Core and Builtins

- bpo-41094: Fix decoding errors with audit when open files with non-ASCII names on non-UTF-8 locale.

- bpo-41084: Prefix the error message with ‘f-string: ‘, when parsing an f-string expression which throws a `SyntaxError`.

- bpo-41076: Pre-feed the parser with the location of the f-string expression, not the f-string itself, which allows us to skip the shifting of the AST node locations after the parsing is completed.

- bpo-40939: Deprecate `PyNode_Compile()`.

- bpo-41056: Fixes a reference to deallocated stack space during startup when constructing sys.path involving a relative symlink when code was supplied via -c. (discovered via Coverity)

- bpo-41061: Fix incorrect expressions and asserts in hashtable code and tests.

- bpo-41052: Opt out serialization/deserialization for _random.Random

- bpo-40939: Deprecate `PyParser_SimpleParseStringFlags()`, `PyParser_SimpleParseStringFlagsFilename()` and `PyParser_SimpleParseFileFlags()`.

- bpo-35975: Stefan Behnel reported that cf_feature_version is used even when PyCF_ONLY_AST is not set. This is against the intention and against the documented behavior, so it’s been fixed.

- bpo-40985: Fix a bug that caused the `SyntaxError` text to be empty when a file ends with a line ending in a line continuation character (i.e. backslash). The error text should contain the text of the last line.

- bpo-40958: Fix a possible buffer overflow in the PEG parser when gathering information for emitting syntax errors. Patch by Pablo Galindo.

- bpo-40957: Fix refleak in _Py_fopen_obj() when PySys_Audit() fails

- bpo-40947: The Python Path Configuration now takes `PyConfig.platlibdir` in account.

- bpo-40847: Fix a bug where a line with only a line continuation character is not considered a blank line at tokenizer level. In such cases, more than a single `NEWLINE` token was emitted. The old parser was working around the issue, but the new parser threw a `SyntaxError` for valid input due to this. For example, an empty line following a line continuation character was interpreted as a `SyntaxError`.

- bpo-40824: Unexpected errors in calling the `__iter__` method are no longer masked by `TypeError` in the `in` operator and functions `contains()`, `indexOf()` and `countOf()` of the `operator` module.

- bpo-19569: Add the private macros `_Py_COMP_DIAG_PUSH`, `_Py_COMP_DIAG_IGNORE_DEPR_DECLS`, and `_Py_COMP_DIAG_POP`.

### Library

- bpo-41193: The `write_history()` atexit function of the readline completer now ignores any `OSError` to ignore error if the filesystem is read-only, instead of only ignoring `FileNotFoundError` and `PermissionError`.

- bpo-41161: The decimal module now requires libmpdec-2.5.0. Users of –with-system-libmpdec should update their system library.

- bpo-40874: The decimal module now requires libmpdec-2.5.0.

- bpo-41138: Fixed the `trace` module CLI for Python source files with non-UTF-8 encoding.

- bpo-31938: Fix default-value signatures of several functions in the `select` module - by Anthony Sottile.

- bpo-41068: Fixed reading files with non-ASCII names from ZIP archive directly after writing them.

- bpo-41058: `pdb.find_function()` now correctly determines the source file encoding.

- bpo-41056: Fix a NULL pointer dereference within the ssl module during a MemoryError in the keylog callback. (discovered by Coverity)

- bpo-41056: Fixed an instance where a MemoryError within the zoneinfo module might not be reported or not reported at its source. (found by Coverity)

- bpo-41048: `mimetypes.read_mime_types()` function reads the rule file using UTF-8 encoding, not the locale encoding. Patch by Srinivas Reddy Thatiparthy.

- bpo-41043: Fixed the use of `glob()` in the stdlib: literal part of the path is now always correctly escaped.

- bpo-40448: `ensurepip` now disables the use of `pip` cache when installing the bundled versions of `pip` and `setuptools`. Patch by Krzysztof Konopko.

- bpo-40967: Removed `asyncio.Task.current_task()` and `asyncio.Task.all_tasks()`. Patch contributed by Rémi Lapeyre.

- bpo-40955: Fix a minor memory leak in `subprocess` module when extra_groups was specified.

- bpo-40855: The standard deviation and variance functions in the statistics module were ignoring their mu and xbar arguments.

- bpo-40924: Removed support for loaders implementing .files and supplying TraversableResources.

- bpo-40939: Use the new PEG parser when generating the stdlib `keyword` module.

- bpo-40834: Fix truncate when sending str object with_xxsubinterpreters.channel_send.

- bpo-26407: Unexpected errors in calling the `__iter__` method are no longer masked by `TypeError` in `csv.reader()`, `csv.writer.writerow()` and `csv.writer.writerows()`.

- bpo-38488: Update ensurepip to install pip 20.1.1 and setuptools 47.1.0.

- bpo-36543: Restored the deprecated `xml.etree.cElementTree` module.

- bpo-34226: Fix `cgi.parse_multipart` without content_length. Patch by Roger Duran

### Tests

- bpo-41085: Fix integer overflow in the `array.array.index()` method on 64-bit Windows for index larger than `2**31`.

- bpo-41069: `test.support.TESTFN` and the current directory for tests when run via `test.regrtest` contain now non-ascii characters if possible.

- bpo-38377: On Linux, skip tests using multiprocessing if the current user cannot create a file in `/dev/shm/` directory. Add the `skip_if_broken_multiprocessing_synchronize()` function to the `test.support` module.

- bpo-41009: Fix use of `support.require_{linux|mac|freebsd}_version()` decorators as class decorator.

- bpo-41003: Fix `test_copyreg` when `numpy` is installed: `test.pickletester` now saves/restores warnings filters when importing `numpy`, to ignore filters installed by `numpy`.

- bpo-40964: Disable remote `imaplib` tests, host cyrus.andrew.cmu.edu is blocking incoming connections.

- bpo-40927: Fix test_binhex when run twice: it now uses import_fresh_module() to ensure that it raises DeprecationWarning each time.

- bpo-34401: Make test_gdb properly run on HP-UX. Patch by Michael Osipov.

### Build

- bpo-40204: Pin Sphinx version to 2.3.1 in `Doc/Makefile`.

### Windows

- bpo-41074: Fixed support of non-ASCII names in functions `msilib.OpenDatabase()` and `msilib.init_database()` and non-ASCII SQL in method `msilib.Database.OpenView()`.

- bpo-40164: Updates Windows OpenSSL to 1.1.1g

- bpo-37556: Extend py.exe help to mention overrides via venv, shebang, environmental variables & ini files.

### macOS

- bpo-39580: Avoid opening Finder window if running installer from the command line. Patch contributed by Rick Heil.

- bpo-41100: Fix configure error when building on macOS 11. Note that the current Python release was released shortly after the first developer preview of macOS 11 (Big Sur); there are other known issues with building and running on the developer preview. Big Sur is expected to be fully supported in a future bugfix release of Python 3.8.x and with 3.9.0.

- bpo-41005: fixed an XDG settings issue not allowing macos to open browser in webbrowser.py

### IDLE

- bpo-41152: The encoding of `stdin`, `stdout` and `stderr` in IDLE is now always UTF-8.

- bpo-41144: Make Open Module open a special module such as os.path.

### C API

- bpo-36346: Mark `Py_UNICODE_COPY`, `Py_UNICODE_FILL`, `PyUnicode_WSTR_LENGTH`, `PyUnicode_FromUnicode`, `PyUnicode_AsUnicode`, `_PyUnicode_AsUnicode`, and `PyUnicode_AsUnicodeAndSize` as deprecated in C. Remove `Py_UNICODE_MATCH` which was deprecated and broken since Python 3.3.

- bpo-36020: On Windows, `#include "pyerrors.h"` no longer defines `snprintf` and `vsnprintf` macros.

- bpo-40703: The PyType_FromSpec*() functions no longer overwrite the type’s “__module__” attribute if it is set via “Py_tp_members” or “Py_tp_getset”.

## Python 3.9.0 beta 3

Release date: 2020-06-09

### Library

- bpo-40924: `importlib.resources`: Reverted `TraversableResources` implementations from the built-in loaders (SourceFileLoader and ZipImporter) as it was an incompatible change introduced in 3.9.0 beta 2 causing through a chain of events for root TLS certificates to be missing.

### Build

- bpo-40684: `make install` now uses the `PLATLIBDIR` variable for the destination `lib-dynload/` directory when `./configure --with-platlibdir` is used.

## Python 3.9.0 beta 2

Release date: 2020-06-08

### Core and Builtins

- bpo-40904: Fix possible segfault in the new PEG parser when parsing f-string containing yield statements with no value (`f"{yield}"`). Patch by Pablo Galindo

- bpo-40903: Fixed a possible segfault in the new PEG parser when producing error messages for invalid assignments of the form `p=p=`. Patch by Pablo Galindo

- bpo-40880: Fix invalid memory read in the new parser when checking newlines in string literals. Patch by Pablo Galindo.

- bpo-40883: Fix memory leak in when parsing f-strings in the new parser. Patch by Pablo Galindo

- bpo-40870: Raise `ValueError` when validating custom AST’s where the constants `True`, `False` and `None` are used within a `ast.Name` node.

- bpo-40854: Allow overriding `sys.platlibdir` via a new `PYTHONPLATLIBDIR` environment variable.

- bpo-40826: Fix GIL usage in `PyOS_Readline()`: lock the GIL to set an exception and pass the Python thread state when checking if there is a pending signal.

- bpo-40780: Fix a corner case where g-style string formatting of a float failed to remove trailing zeros.

- bpo-38964: When there’s a `SyntaxError` in the expression part of an fstring, the filename attribute of the `SyntaxError` gets correctly set to the name of the file the fstring resides in.

- bpo-40750: Support the “-d” debug flag in the new PEG parser. Patch by Pablo Galindo

- bpo-40217: Instances of types created with `PyType_FromSpecWithBases()` will no longer automatically visit their class object when traversing references in the garbage collector. The user is expected to manually visit the object’s class. Patch by Pablo Galindo.

- bpo-40696: Fix a hang that can arise after `generator.throw()` due to a cycle in the exception context chain.

### Library

- bpo-39791: Refresh importlib.metadata from importlib_metadata 1.6.1.

- bpo-40807: Stop codeop._maybe_compile, used by code.InteractiveInterpreter (and IDLE). from from emitting each warning three times.

- bpo-39791: Built-in loaders (SourceFileLoader and ZipImporter) now supply `TraversableResources` implementations for `ResourceReader`, and the fallback function has been removed.

- bpo-17005: The topological sort functionality that was introduced initially in the `functools` module has been moved to a new `graphlib` module to better accommodate the new tools and keep the original scope of the `functools` module. Patch by Pablo Galindo

- bpo-40777: Initialize PyDateTime_IsoCalendarDateType.tp_base at run-time to avoid errors on some compilers.

- bpo-40767: `webbrowser` now properly finds the default browser in pure Wayland systems by checking the WAYLAND_DISPLAY environment variable. Patch contributed by Jérémy Attali.

- bpo-40791: `hashlib.compare_digest()` uses OpenSSL’s `CRYPTO_memcmp()` function when OpenSSL is available.

- bpo-40795: `ctypes` module: If ctypes fails to convert the result of a callback or if a ctypes callback function raises an exception, sys.unraisablehook is now called with an exception set. Previously, the error was logged into stderr by `PyErr_Print()`.

- bpo-30008: Fix `ssl` code to be compatible with OpenSSL 1.1.x builds that use `no-deprecated` and `--api=1.1.0`.

- bpo-30064: Fix asyncio `loop.sock_*` race condition issue

- bpo-40759: Deprecate the `symbol` module.

- bpo-40737: Fix possible reference leak for `sqlite3` initialization.

- bpo-40698: `distutils` upload creates SHA2-256 and Blake2b-256 digests. MD5 digests is skipped if platform blocks MD5.

- bpo-40695: `hashlib` no longer falls back to builtin hash implementations when OpenSSL provides a hash digest and the algorithm is blocked by security policy.

- bpo-9216: func:`hashlib.new` passed `usedforsecurity` to OpenSSL EVP constructor `_hashlib.new()`. test_hashlib and test_smtplib handle strict security policy better.

- bpo-40614: `ast.parse()` will not parse self documenting expressions in f-strings when passed `feature_version` is less than `(3, 8)`.

- bpo-40671: Prepare `_hashlib` for PEP 489 and use `PyModule_AddType()`.

- bpo-32309: Added a new coroutine `asyncio.to_thread()`. It is mainly used for running IO-bound functions in a separate thread to avoid blocking the event loop, and essentially works as a high-level version of `run_in_executor()` that can directly take keyword arguments.

- bpo-40630: Added `tracemalloc.reset_peak()` to set the peak size of traced memory blocks to the current size, to measure the peak of specific pieces of code.

- bpo-13097: `ctypes` now raises an `ArgumentError` when a callback is invoked with more than 1024 arguments.

- bpo-23082: Updated the error message and docs of PurePath.relative_to() to better reflect the function behaviour.

- bpo-39244: Fixed `multiprocessing.context.get_all_start_methods` to properly return the default method first on macOS.

- bpo-39040: Fix parsing of invalid mime headers parameters by collapsing whitespace between encoded words in a bare-quote-string.

- bpo-35714: `struct.error` is now raised if there is a null character in a `struct` format string.

- bpo-36290: AST nodes are now raising `TypeError` on conflicting keyword arguments. Patch contributed by Rémi Lapeyre.

### Tests

- bpo-17258: Skip some `multiprocessing` tests when MD5 hash digest is blocked.

### Build

- bpo-40514: Remove `--with-experimental-isolated-subinterpreters` configure option in Python 3.9: the experiment continues in the master branch, but it’s no longer needed in 3.9.

- bpo-40683: Fixed an issue where the `zoneinfo` module and its tests were not included when Python is installed with `make`.

### Windows

- bpo-39631: Changes the registered MIME type for `.py` files on Windows to `text/x-python` instead of `text/plain`.

- bpo-40677: Manually define IO_REPARSE_TAG_APPEXECLINK in case some old Windows SDK doesn’t have it.

### macOS

- bpo-40741: Update macOS installer to use SQLite 3.32.2.

### IDLE

- bpo-39885: Make context menu Cut and Copy work again when right-clicking within a selection.

- bpo-40723: Make test_idle pass when run after import.

### C API

- bpo-40910: Export explicitly the `Py_GetArgcArgv()` function to the C API and document the function. Previously, it was exported implicitly which no longer works since Python is built with `-fvisibility=hidden`.

- bpo-40724: Allow defining buffer slots in type specs.

- bpo-40826: `PyOS_InterruptOccurred()` now fails with a fatal error if it is called with the GIL released.

## Python 3.9.0 beta 1

Release date: 2020-05-19

### Security

- bpo-40501: `uuid` no longer uses `ctypes` to load `libuuid` or `rpcrt4.dll` at runtime.

### Core and Builtins

- bpo-40663: Correctly generate annotations where parentheses are omitted but required (e.g: `Type[(str, int, *other))]`.

- bpo-40596: Fixed `str.isidentifier()` for non-canonicalized strings containing non-BMP characters on Windows.

- bpo-40593: Improved syntax errors for invalid characters in source code.

- bpo-40585: Fixed a bug when using `codeop.compile_command()` that was causing exceptions to be swallowed with the new parser. Patch by Pablo Galindo

- bpo-40566: Apply PEP 573 to `abc`.

- bpo-40502: Initialize `n->n_col_offset`. (Patch by Joannah Nanjekye)

- bpo-40527: Fix command line argument parsing: no longer write errors multiple times into stderr.

- bpo-1635741: Port `errno` to multiphase initialization (PEP 489).

- bpo-40523: Add pass-throughs for `hash()` and `reversed()` to `weakref.proxy` objects. Patch by Pablo Galindo.

- bpo-1635741: Port `syslog` to multiphase initialization (PEP 489).

- bpo-40246: Reporting a specialised error message for invalid string prefixes, which was introduced in bpo-40246, is being reverted due to backwards compatibility concerns for strings that immediately follow a reserved keyword without whitespace between them. Constructs like `bg="#d00" if clear else"#fca"` were failing to parse, which is not an acceptable breakage on such short notice.

- bpo-40417: Fix imp module deprecation warning when PyImport_ReloadModule is called. Patch by Robert Rouhani.

- bpo-40408: Fixed support of nested type variables in GenericAlias (e.g. `list[list[T]]`).

- bpo-1635741: Port _stat module to multiphase initialization (PEP 489).

- bpo-29587: Enable implicit exception chaining when calling `generator.throw()`.

- bpo-40328: Add tools for generating mappings headers for CJKCodecs.

- bpo-40228: Setting frame.f_lineno is now robust w.r.t. changes in the source-to-bytecode compiler

- bpo-38880: Added the ability to list interpreters associated with channel ends in the internal subinterpreters module.

- bpo-37986: Improve performance of `PyLong_FromDouble()` for values that fit into `long`.

### Library

- bpo-40662: Fixed `ast.get_source_segment()` for ast nodes that have incomplete location information. Patch by Irit Katriel.

- bpo-40665: Convert `bisect` to use Argument Clinic.

- bpo-40536: Added the `available_timezones()` function to the `zoneinfo` module. Patch by Paul Ganssle.

- bpo-40645: The `hmac.HMAC` exposes internal implementation details. The attributes `digest_cons`, `inner`, and `outer` are deprecated and will be removed in the future.

- bpo-40645: The internal module `_hashlib` wraps and exposes OpenSSL’s HMAC API. The new code will be used in Python 3.10 after the internal implementation details of the pure Python HMAC module are no longer part of the public API.

- bpo-40637: Builtin hash modules can now be disabled or selectively enabled with `configure --with-builtin-hashlib-hashes=sha3,blake1` or `--without-builtin-hashlib-hashes`.

- bpo-37630: The `hashlib` module can now use SHA3 hashes and SHAKE XOF from OpenSSL when available.

- bpo-40479: The `hashlib` now compiles with OpenSSL 3.0.0-alpha2.

- bpo-40257: Revert changes to `inspect.getdoc()`.

- bpo-40607: When cancelling a task due to timeout, `asyncio.wait_for()` will now propagate the exception if an error happens during cancellation. Patch by Roman Skurikhin.

- bpo-40612: Fix edge cases in SyntaxError formatting. If the offset is <= 0, no caret is printed. If the offset is > line length, the caret is printed pointing just after the last character.

- bpo-40597: If text content lines are longer than policy.max_line_length, always use a content-encoding to make sure they are wrapped.

- bpo-40571: Added functools.cache() as a simpler, more discoverable way to access the unbounded cache variant of lru_cache(maxsize=None).

- bpo-40503: PEP 615, the `zoneinfo` module. Adds support for the IANA time zone database.

- bpo-40397: Removed attributes `__args__` and `__parameters__` from special generic aliases like `typing.List` (not subscripted).

- bpo-40549: Convert posixmodule.c (“posix” or “nt” module) to the multiphase initialization (PEP 489).

- bpo-31033: Add a `msg` argument to `Future.cancel()` and `Task.cancel()`.

- bpo-40541: Added an optional counts parameter to random.sample().

- bpo-40515: The `ssl` and `hashlib` modules now actively check that OpenSSL is build with thread support. Python 3.7.0 made thread support mandatory and no longer works safely with a no-thread builds.

- bpo-31033: When a `asyncio.Task` is cancelled, the exception traceback now chains all the way back to where the task was first interrupted.

- bpo-40504: `functools.lru_cache()` objects can now be the targets of weakrefs.

- bpo-40559: Fix possible memory leak in the C implementation of `asyncio.Task`.

- bpo-40480: `fnmatch.fnmatch()` could take exponential time in the presence of multiple `*` pattern characters. This was repaired by generating more elaborate regular expressions to avoid futile backtracking.

- bpo-40495: `compileall` is now able to use hardlinks to prevent duplicates in a case when `.pyc` files for different optimization levels have the same content.

- bpo-40457: The ssl module now support OpenSSL builds without TLS 1.0 and 1.1 methods.

- bpo-40355: Improve error reporting in `ast.literal_eval()` in the presence of malformed `ast.Dict` nodes instead of silently ignoring any non-conforming elements. Patch by Curtis Bucher.

- bpo-40465: Deprecated the optional random argument to random.shuffle().

- bpo-40459: `platform.win32_ver()` now produces correct ptype strings instead of empty strings.

- bpo-39435: The first argument of `pickle.loads()` is now positional-only.

- bpo-39305: Update `nntplib` to merge `nntplib.NNTP` and `nntplib._NNTPBase`. Patch by Dong-hee Na.

- bpo-32494: Update `dbm.gnu` to use gdbm_count if possible when calling `len()`. Patch by Dong-hee Na.

- bpo-40453: Add `isolated=True` keyword-only parameter to `_xxsubinterpreters.create()`. An isolated subinterpreter cannot spawn threads, spawn a child process or call `os.fork()`.

- bpo-40286: Remove `_random.Random.randbytes()`: the C implementation of `randbytes()`. Implement the method in Python to ease subclassing: `randbytes()` now directly reuses `getrandbits()`.

- bpo-40394: Added default arguments to `difflib.SequenceMatcher.find_longest_match()`.

- bpo-39995: Fix a race condition in concurrent.futures._ThreadWakeup: access to _ThreadWakeup is now protected with the shutdown lock.

- bpo-30966: `Process.shutdown(wait=True)` of `concurrent.futures` now closes explicitly the result queue.

- bpo-30966: Add a new `close()` method to the `SimpleQueue` class to explicitly close the queue.

- bpo-39966: Revert bpo-25597. `unittest.mock.MagicMock` with wraps’ set uses default return values for magic methods.

- bpo-39791: Added `files()` function to importlib.resources with support for subdirectories in package data, matching backport in importlib_resources 1.5.

- bpo-40375: `imaplib.IMAP4.unselect()` is added. Patch by Dong-hee Na.

- bpo-40389: `repr()` now returns `typing.Optional[T]` when called for `typing.Union` of two types, one of which is `NoneType`.

- bpo-40291: Add support for CAN_J1939 sockets (available on Linux 5.4+)

- bpo-40273: `types.MappingProxyType` is now reversible.

- bpo-39075: The repr for `types.SimpleNamespace` is now insertion ordered rather than alphabetical.

- bpo-40192: On AIX, `thread_time()` is now implemented with `thread_cputime()` which has nanosecond resolution, rather than `clock_gettime(CLOCK_THREAD_CPUTIME_ID)` which has a resolution of 10 ms. Patch by Batuhan Taskaya.

- bpo-40025: Raise TypeError when _generate_next_value_ is defined after members. Patch by Ethan Onstott.

- bpo-39058: In the argparse module, the repr for Namespace() and other argument holders now displayed in the order attributes were added. Formerly, it displayed in alphabetical order even though argument order is preserved the user visible parts of the module.

- bpo-24416: The `isocalendar()` methods of `datetime.date` and `datetime.datetime` now return a named tuple instead of a `tuple`.

### Documentation

- bpo-34790: Add version of removal for explicit passing of coros to `asyncio.wait()`’s documentation

- bpo-40561: Provide docstrings for webbrowser open functions.

- bpo-40499: Mention that `asyncio.wait()` requires a non-empty set of awaitables.

- bpo-39705: Tutorial example for sorted() in the Loop Techniques section is given a better explanation. Also a new example is included to explain sorted()’s basic behavior.

- bpo-39435: Fix an incorrect signature for `pickle.loads()` in the docs

### Tests

- bpo-40055: distutils.tests now saves/restores warnings filters to leave them unchanged. Importing tests imports docutils which imports pkg_resources which adds a warnings filter.

- bpo-40436: test_gdb and test.pythoninfo now check gdb command exit code.

### Build

- bpo-40653: Move _dirnameW out of HAVE_SYMLINK to fix a potential compiling issue.

- bpo-40514: Add `--with-experimental-isolated-subinterpreters` build option to `configure`: better isolate subinterpreters, experimental build mode.

### Windows

- bpo-40650: Include winsock2.h in pytime.c for timeval.

- bpo-40458: Increase reserved stack space to prevent overflow crash on Windows.

- bpo-39148: Add IPv6 support to `asyncio` datagram endpoints in ProactorEventLoop. Change the raised exception for unknown address families to ValueError as it’s not coming from Windows API.

### macOS

- bpo-34956: When building Python on macOS from source, `_tkinter` now links with non-system Tcl and Tk frameworks if they are installed in `/Library/Frameworks`, as had been the case on older releases of macOS. If a macOS SDK is explicitly configured, by using `--enable-universalsdk=` or `-isysroot`, only the SDK itself is searched. The default behavior can still be overridden with `--with-tcltk-includes` and `--with-tcltk-libs`.

- bpo-35569: Expose RFC 3542 IPv6 socket options.

### Tools/Demos

- bpo-40479: Update multissltest helper to test with latest OpenSSL 1.0.2, 1.1.0, 1.1.1, and 3.0.0-alpha.

- bpo-40431: Fix a syntax typo in `turtledemo` that now raises a `SyntaxError`.

- bpo-40163: Fix multissltest tool. OpenSSL has changed download URL for old releases. The multissltest tool now tries to download from current and old download URLs.

### C API

- bpo-39465: Remove the `_PyUnicode_ClearStaticStrings()` function from the C API.

- bpo-38787: Add PyCFunction_CheckExact() macro for exact type checks now that we allow subtypes of PyCFunction, as well as PyCMethod_CheckExact() and PyCMethod_Check() for the new PyCMethod subtype.

- bpo-40545: Declare `_PyErr_GetTopmostException()` with `PyAPI_FUNC()` to properly export the function in the C API. The function remains private (`_Py`) prefix.

- bpo-40412: Nullify inittab_copy during finalization, preventing future interpreter initializations in an embedded situation from crashing. Patch by Gregory Szorc.

- bpo-40429: The `PyThreadState_GetFrame()` function now returns a strong reference to the frame.

- bpo-40428: Remove the following functions from the C API. Call `PyGC_Collect()` explicitly to free all free lists.

  - `PyAsyncGen_ClearFreeLists()`

  - `PyContext_ClearFreeList()`

  - `PyDict_ClearFreeList()`

  - `PyFloat_ClearFreeList()`

  - `PyFrame_ClearFreeList()`

  - `PyList_ClearFreeList()`

  - `PySet_ClearFreeList()`

  - `PyTuple_ClearFreeList()`

- bpo-40421: New `PyFrame_GetBack()` function: get the frame next outer frame.

- bpo-40421: New `PyFrame_GetCode()` function: return a borrowed reference to the frame code.

- bpo-40217: Ensure that instances of types created with `PyType_FromSpecWithBases()` will visit its class object when traversing references in the garbage collector (implemented as an extension of the provided `tp_traverse`). Patch by Pablo Galindo.

- bpo-38787: Module C state is now accessible from C-defined heap type methods (PEP 573). Patch by Marcel Plch and Petr Viktorin.

## Python 3.9.0 alpha 6

Release date: 2020-04-27

### Security

- bpo-40121: Fixes audit events raised on creating a new socket.

- bpo-39073: Disallow CR or LF in email.headerregistry.Address arguments to guard against header injection attacks.

- bpo-39503: CVE-2020-8492: The `AbstractBasicAuthHandler` class of the `urllib.request` module uses an inefficient regular expression which can be exploited by an attacker to cause a denial of service. Fix the regex to prevent the catastrophic backtracking. Vulnerability reported by Ben Caller and Matt Schwager.

### Core and Builtins

- bpo-40313: Improve the performance of bytes.hex().

- bpo-40334: Switch to a new parser, based on PEG. For more details see PEP 617. To temporarily switch back to the old parser, use `-X oldparser` or `PYTHONOLDPARSER=1`. In Python 3.10 we will remove the old parser completely, including the `parser` module (already deprecated) and anything that depends on it.

- bpo-40267: Fix the tokenizer to display the correct error message, when there is a SyntaxError on the last input character and no newline follows. It used to be `unexpected EOF while parsing`, while it should be `invalid syntax`.

- bpo-39522: Correctly unparse explicit `u` prefix for strings when postponed evaluation for annotations activated. Patch by Batuhan Taskaya.

- bpo-40246: Report a specialized error message, `invalid string prefix`, when the tokenizer encounters a string with an invalid prefix.

- bpo-40082: Fix the signal handler: it now always uses the main interpreter, rather than trying to get the current Python thread state.

- bpo-37388: str.encode() and str.decode() no longer check the encoding and errors in development mode or in debug mode during Python finalization. The codecs machinery can no longer work on very late calls to str.encode() and str.decode().

- bpo-40077: Fix possible refleaks in `_json`, memo of PyScannerObject should be traversed.

- bpo-37207: Speed up calls to `dict()` by using the PEP 590 `vectorcall` calling convention.

- bpo-40141: Add column and line information to `ast.keyword` nodes. Patch by Pablo Galindo.

- bpo-1635741: Port `resource` to multiphase initialization (PEP 489).

- bpo-1635741: Port `math` to multiphase initialization (PEP 489).

- bpo-1635741: Port _uuid module to multiphase initialization (PEP 489).

- bpo-40077: Convert json module to use `PyType_FromSpec()`.

- bpo-40067: Improve the error message for multiple star expressions in an assignment. Patch by Furkan Onder

- bpo-1635741: Port _functools module to multiphase initialization (PEP 489). Patch by Paulo Henrique Silva.

- bpo-1635741: Port operator module to multiphase initialization (PEP 489). Patch by Paulo Henrique Silva.

- bpo-20526: Fix `PyThreadState_Clear()`. `PyThreadState.frame` is a borrowed reference, not a strong reference: `PyThreadState_Clear()` must not call `Py_CLEAR(tstate->frame)`.

- bpo-1635741: Port time module to multiphase initialization (PEP 489). Patch by Paulo Henrique Silva.

- bpo-1635741: Port _weakref extension module to multiphase initialization (PEP 489).

- bpo-40020: Fix a leak and subsequent crash in parsetok.c caused by realloc misuse on a rare codepath.

- bpo-39939: Added str.removeprefix and str.removesuffix methods and corresponding bytes, bytearray, and collections.UserString methods to remove affixes from a string if present. See PEP 616 for a full description. Patch by Dennis Sweeney.

- bpo-39481: Implement PEP 585. This supports list[int], tuple[str, …] etc.

- bpo-32894: Support unparsing of infinity numbers in postponed annotations. Patch by Batuhan Taşkaya.

- bpo-37207: Speed up calls to `list()` by using the PEP 590 `vectorcall` calling convention. Patch by Mark Shannon.

### Library

- bpo-40398: `typing.get_args()` now always returns an empty tuple for special generic aliases.

- bpo-40396: Functions `typing.get_origin()`, `typing.get_args()` and `typing.get_type_hints()` support now generic aliases like `list[int]`.

- bpo-38061: Optimize the `subprocess` module on FreeBSD using `closefrom()`. A single `close(fd)` syscall is cheap, but when `sysconf(_SC_OPEN_MAX)` is high, the loop calling `close(fd)` on each file descriptor can take several milliseconds.

  The workaround on FreeBSD to improve performance was to load and mount the fdescfs kernel module, but this is not enabled by default.

  Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans (kevans) and Kubilay Kocak (koobs): https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274

- bpo-38061: On FreeBSD, `os.closerange(fd_low, fd_high)` now calls `closefrom(fd_low)` if fd_high is greater than or equal to `sysconf(_SC_OPEN_MAX)`.

  Initial patch by Ed Maste (emaste), Conrad Meyer (cem), Kyle Evans (kevans) and Kubilay Kocak (koobs): https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=242274

- bpo-40360: The `lib2to3` module is pending deprecation due to PEP 617.

- bpo-40138: Fix the Windows implementation of `os.waitpid()` for exit code larger than `INT_MAX >> 8`. The exit status is now interpreted as an unsigned number.

- bpo-39942: Set “__main__” as the default module name when “__name__” is missing in `typing.TypeVar`. Patch by Weipeng Hong.

- bpo-40275: The `logging` package is now imported lazily in `unittest` only when the `assertLogs()` assertion is used.

- bpo-40275: The `asyncio` package is now imported lazily in `unittest` only when the `IsolatedAsyncioTestCase` class is used.

- bpo-40330: In `ShareableList.__setitem__()`, check the size of a new string item after encoding it to utf-8, not before.

- bpo-40148: Added `pathlib.Path.with_stem()` to create a new Path with the stem replaced.

- bpo-40325: Deprecated support for set objects in random.sample().

- bpo-40257: Improved help for the `typing` module. Docstrings are now shown for all special forms and special generic aliases (like `Union` and `List`). Using `help()` with generic alias like `List[int]` will show the help for the correspondent concrete type (`list` in this case).

- bpo-40257: func:`inspect.getdoc` no longer returns docstring inherited from the type of the object or from parent class if it is a class if it is not defined in the object itself. In `pydoc` the documentation string is now shown not only for class, function, method etc, but for any object that has its own `__doc__` attribute.

- bpo-40287: Fixed `SpooledTemporaryFile.seek()` to return the position.

- bpo-40290: Added zscore() to statistics.NormalDist().

- bpo-40282: Allow `random.getrandbits(0)` to succeed and to return 0.

- bpo-40286: Add `random.randbytes()` function and `random.Random.randbytes()` method to generate random bytes.

- bpo-40277: `collections.namedtuple()` now provides a human-readable repr for its field accessors.

- bpo-40270: The included copy of sqlite3 on Windows is now compiled with the json extension. This allows the use of functions such as `json_object`.

- bpo-29255: Wait in `KqueueSelector.select` when no fds are registered

- bpo-40260: Ensure `modulefinder` uses `io.open_code()` and respects coding comments.

- bpo-40234: Allow again to spawn daemon threads in subinterpreters (revert change which denied them).

- bpo-39207: Workers in `ProcessPoolExecutor` are now spawned on demand, only when there are no available idle workers to reuse. This optimizes startup overhead and reduces the amount of lost CPU time to idle workers. Patch by Kyle Stanley.

- bpo-40091: Fix a hang at fork in the logging module: the new private _at_fork_reinit() method is now used to reinitialize locks at fork in the child process.

- bpo-40149: Implement traverse and clear slots in _abc._abc_data type.

- bpo-40208: Remove deprecated `symtable.SymbolTable.has_exec()`.

- bpo-40196: Fix a bug in the `symtable` module that was causing incorrectly report global variables as local. Patch by Pablo Galindo.

- bpo-40190: Add support for `_SC_AIX_REALMEM` to `posix.sysconf()`.

- bpo-40182: Removed the `_field_types` attribute of the `typing.NamedTuple` class.

- bpo-36517: Multiple inheritance with `typing.NamedTuple` now raises an error instead of silently ignoring other types.

- bpo-40126: Fixed reverting multiple patches in unittest.mock. Patcher’s `__exit__()` is now never called if its `__enter__()` is failed. Returning true from `__exit__()` silences now the exception.

- bpo-40094: CGIHTTPRequestHandler of http.server now logs the CGI script exit code, rather than the CGI script exit status of os.waitpid(). For example, if the script is killed by signal 11, it now logs: “CGI script exit code -11.”

- bpo-40108: Improve the error message when triying to import a module using `runpy` and incorrently use the “.py” extension at the end of the module name. Patch by Pablo Galindo.

- bpo-40094: Add `os.waitstatus_to_exitcode()` function: convert a wait status to an exit code.

- bpo-40089: Fix threading._after_fork(): if fork was not called by a thread spawned by threading.Thread, threading._after_fork() now creates a _MainThread instance for _main_thread, instead of a _DummyThread instance.

- bpo-40089: Add a private `_at_fork_reinit()` method to `_thread.Lock`, `_thread.RLock`, `threading.RLock` and `threading.Condition` classes: reinitialize the lock at fork in the child process, reset the lock to the unlocked state. Rename also the private `_reset_internal_locks()` method of `threading.Event` to `_at_fork_reinit()`.

- bpo-25780: Expose `CAN_RAW_JOIN_FILTERS` in the `socket` module.

- bpo-39503: `AbstractBasicAuthHandler` of `urllib.request` now parses all WWW-Authenticate HTTP headers and accepts multiple challenges per header: use the realm of the first Basic challenge.

- bpo-39812: Removed daemon threads from `concurrent.futures` by adding an internal `threading._register_atexit()`, which calls registered functions prior to joining all non-daemon threads. This allows for compatibility with subinterpreters, which don’t support daemon threads.

- bpo-40050: Fix `importlib._bootstrap_external`: avoid creating a new `winreg` builtin module if it’s already available in `sys.modules`, and remove redundant imports.

- bpo-40014: Fix `os.getgrouplist()`: if `getgrouplist()` function fails because the group list is too small, retry with a larger group list. On failure, the glibc implementation of `getgrouplist()` sets `ngroups` to the total number of groups. For other implementations, double the group list size.

- bpo-40017: Add `time.CLOCK_TAI` constant if the operating system support it.

- bpo-40016: In re docstring, clarify the relationship between inline and argument compile flags.

- bpo-39953: Update internal table of OpenSSL error codes in the `ssl` module.

- bpo-36144: Added PEP 584 operators to `weakref.WeakValueDictionary`.

- bpo-36144: Added PEP 584 operators to `weakref.WeakKeyDictionary`.

- bpo-38891: Fix linear runtime behaviour of the `__getitem__` and `__setitem__` methods in `multiprocessing.shared_memory.ShareableList`. This avoids quadratic performance when iterating a `ShareableList`. Patch by Thomas Krennwallner.

- bpo-39682: Remove undocumented support for closing a `pathlib.Path` object via its context manager. The context manager magic methods remain, but they are now a no-op, making `Path` objects immutable.

- bpo-36144: Added PEP 584 operators (`|` and `|=`) to `collections.ChainMap`.

- bpo-39011: Normalization of line endings in ElementTree attributes was removed, as line endings which were replaced by entity numbers should be preserved in original form.

- bpo-38410: Properly handle `sys.audit()` failures in `sys.set_asyncgen_hooks()`.

- bpo-36541: lib2to3 now recognizes named assignment expressions (the walrus operator, `:=`)

- bpo-35967: In platform, delay the invocation of ‘uname -p’ until the processor attribute is requested.

- bpo-35113: `inspect.getsource()` now returns correct source code for inner class with same name as module level class. Decorators are also returned as part of source of the class. Patch by Karthikeyan Singaravelan.

- bpo-33262: Deprecate passing None as an argument for `shlex.split()`’s `s` parameter. Patch by Zackery Spytz.

- bpo-31758: Prevent crashes when using an uninitialized `_elementtree.XMLParser` object. Patch by Oren Milman.

### Documentation

- bpo-27635: The pickle documentation incorrectly claimed that `__new__` isn’t called by default when unpickling.

- bpo-39879: Updated Data model docs to include `dict()` insertion order preservation. Patch by Furkan Onder and Samy Lahfa.

- bpo-38387: Document `PyDoc_STRVAR` macro in the C-API reference.

- bpo-13743: Some methods within xml.dom.minidom.Element class are now better documented.

### Tests

- bpo-31904: Set expected default encoding in test_c_locale_coercion.py for VxWorks RTOS.

- bpo-40162: Update Travis CI configuration to OpenSSL 1.1.1f.

- bpo-40146: Update OpenSSL to 1.1.1f in Azure Pipelines.

- bpo-40094: Add `test.support.wait_process()` function.

- bpo-40003: `test.bisect_cmd` now copies Python command line options like `-O` or `-W`. Moreover, emit a warning if `test.bisect_cmd` is used with `-w`/`--verbose2` option.

- bpo-39380: Add the encoding in `ftplib.FTP` and `ftplib.FTP_TLS` to the constructor as keyword-only and change the default from `latin-1` to `utf-8` to follow RFC 2640.

- bpo-39793: Use the same domain when testing `make_msgid`. Patch by Batuhan Taskaya.

- bpo-1812: Fix newline handling in doctest.testfile when loading from a package whose loader has a get_data method. Patch by Peter Donis.

### Build

- bpo-38360: Support single-argument form of macOS -isysroot flag.

- bpo-40158: Fix CPython MSBuild Properties in NuGet Package (build/native/python.props)

- bpo-38527: Fix configure check on Solaris for “float word ordering”: sometimes, the correct “grep” command was not being used. Patch by Arnon Yaari.

### Windows

- bpo-40164: Updates Windows to OpenSSL 1.1.1f

- bpo-8901: Ignore the Windows registry when the `-E` option is used.

### macOS

- bpo-38329: python.org macOS installers now update the Current version symlink of /Library/Frameworks/Python.framework/Versions for 3.9 installs. Previously, Current was only updated for Python 2.x installs. This should make it easier to embed Python 3 into other macOS applications.

- bpo-40164: Update macOS installer builds to use OpenSSL 1.1.1g.

### IDLE

- bpo-38439: Add a 256×256 pixel IDLE icon to support more modern environments. Created by Andrew Clover. Delete the unused macOS idle.icns icon file.

- bpo-38689: IDLE will no longer freeze when inspect.signature fails when fetching a calltip.

### Tools/Demos

- bpo-40385: Removed the checkpyc.py tool. Please see compileall without force mode as a potential alternative.

- bpo-40179: Fixed translation of `#elif` in Argument Clinic.

- bpo-40094: Fix `which.py` script exit code: it now uses `os.waitstatus_to_exitcode()` to convert `os.system()` exit status into an exit code.

### C API

- bpo-40241: Move the `PyGC_Head` structure to the internal C API.

- bpo-40170: Convert `PyObject_IS_GC()` macro to a function to hide implementation details.

- bpo-40241: Add the functions `PyObject_GC_IsTracked()` and `PyObject_GC_IsFinalized()` to the public API to allow to query if Python objects are being currently tracked or have been already finalized by the garbage collector respectively. Patch by Pablo Galindo.

- bpo-40170: The `PyObject_NEW()` macro becomes an alias to the `PyObject_New()` macro, and the `PyObject_NEW_VAR()` macro becomes an alias to the `PyObject_NewVar()` macro, to hide implementation details. They no longer access directly the `PyTypeObject.tp_basicsize` member.

- bpo-40170: `PyType_HasFeature()` now always calls `PyType_GetFlags()` to hide implementation details. Previously, it accessed directly the `PyTypeObject.tp_flags` member when the limited C API was not used.

- bpo-40170: Convert the `PyObject_GET_WEAKREFS_LISTPTR()` macro to a function to hide implementation details: the macro accessed directly to the `PyTypeObject.tp_weaklistoffset` member.

- bpo-40170: Convert `PyObject_CheckBuffer()` macro to a function to hide implementation details: the macro accessed directly the `PyTypeObject.tp_as_buffer` member.

- bpo-40170: Always declare `PyIndex_Check()` as an opaque function to hide implementation details: remove `PyIndex_Check()` macro. The macro accessed directly the `PyTypeObject.tp_as_number` member.

- bpo-39947: Add `PyThreadState_GetID()` function: get the unique identifier of a Python thread state.

## Python 3.9.0 alpha 5

Release date: 2020-03-23

### Security

- bpo-38576: Disallow control characters in hostnames in http.client, addressing CVE-2019-18348. Such potentially malicious header injection URLs now cause a InvalidURL to be raised.

### Core and Builtins

- bpo-40010: Optimize pending calls in multithreaded applications. If a thread different than the main thread schedules a pending call (`Py_AddPendingCall()`), the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending calls which cannot be executed. Only the main thread can execute pending calls.

  Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread executes pending calls.

- bpo-1635741: Port _weakref extension module to multiphase initialization (PEP 489).

- bpo-1635741: Port _collections module to multiphase initialization (PEP 489).

- bpo-40010: Optimize signal handling in multithreaded applications. If a thread different than the main thread gets a signal, the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending signals which cannot be handled. Only the main thread of the main interpreter can handle signals.

  Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread handles signals.

- bpo-39984: If `Py_AddPendingCall()` is called in a subinterpreter, the function is now scheduled to be called from the subinterpreter, rather than being called from the main interpreter. Each subinterpreter now has its own list of scheduled calls.

- bpo-1635741: Port _heapq module to multiphase initialization.

- bpo-1635741: Port itertools module to multiphase initialization (PEP 489).

- bpo-37207: Speed up calls to `frozenset()` by using the PEP 590 `vectorcall` calling convention. Patch by Dong-hee Na.

- bpo-39984: subinterpreters: Move `_PyRuntimeState.ceval.tracing_possible` to `PyInterpreterState.ceval.tracing_possible`: each interpreter now has its own variable.

- bpo-37207: Speed up calls to `set()` by using the PEP 590 `vectorcall` calling convention. Patch by Dong-hee Na.

- bpo-1635741: Port _statistics module to multiphase initialization (PEP 489).

- bpo-39968: Use inline function to replace extension modules’ get_module_state macros.

- bpo-39965: Correctly raise `SyntaxError` if await is used inside non-async functions and `PyCF_ALLOW_TOP_LEVEL_AWAIT` is set (like in the asyncio REPL). Patch by Pablo Galindo.

- bpo-39562: Allow executing asynchronous comprehensions on the top level when the `PyCF_ALLOW_TOP_LEVEL_AWAIT` flag is given. Patch by Batuhan Taskaya.

- bpo-37207: Speed up calls to `tuple()` by using the PEP 590 `vectorcall` calling convention. Patch by Dong-hee Na.

- bpo-38373: Chaged list overallocation strategy. It no longer overallocates if the new size is closer to overalocated size than to the old size and adds padding.

- bpo-39926: Update Unicode database to Unicode version 13.0.0.

- bpo-19466: Clear the frames of daemon threads earlier during the Python shutdown to call objects destructors. So “unclosed file” resource warnings are now emitted for daemon threads in a more reliable way.

- bpo-38894: Fix a bug that was causing incomplete results when calling `pathlib.Path.glob` in the presence of symlinks that point to files where the user does not have read access. Patch by Pablo Galindo and Matt Wozniski.

- bpo-39877: Fix `PyEval_RestoreThread()` random crash at exit with daemon threads. It now accesses the `_PyRuntime` variable directly instead of using `tstate->interp->runtime`, since `tstate` can be a dangling pointer after `Py_Finalize()` has been called. Moreover, the daemon thread now exits before trying to take the GIL.

- bpo-39871: Fix a possible `SystemError` in `math.{atan2,copysign,remainder}()` when the first argument cannot be converted to a `float`. Patch by Zackery Spytz.

- bpo-39776: Fix race condition where threads created by PyGILState_Ensure() could get a duplicate id.

  This affects consumers of tstate->id like the contextvar caching machinery, which could return invalid cached objects under heavy thread load (observed in embedded scenarios).

- bpo-39778: Fixed a crash due to incorrect handling of weak references in `collections.OrderedDict` classes. Patch by Pablo Galindo.

- bpo-1635741: Port audioop extension module to multiphase initialization (PEP 489).

- bpo-39702: Relax decorator grammar restrictions to allow any valid expression (PEP 614).

- bpo-38091: Tweak import deadlock detection code to not deadlock itself.

- bpo-1635741: Port _locale extension module to multiphase initialization (PEP 489).

- bpo-39087: Optimize `PyUnicode_AsUTF8()` and `PyUnicode_AsUTF8AndSize()` slightly when they need to create internal UTF-8 cache.

- bpo-39520: Fix unparsing of ext slices with no items (`foo[:,]`). Patch by Batuhan Taskaya.

- bpo-39220: Do not optimize annotations if ‘from __future__ import annotations’ is used. Patch by Pablo Galindo.

- bpo-35712: Using `NotImplemented` in a boolean context has been deprecated. Patch contributed by Josh Rosenberg.

- bpo-22490: Don’t leak environment variable `__PYVENV_LAUNCHER__` into the interpreter session on macOS.

### Library

- bpo-39830: Add `zipfile.Path` to `__all__` in the `zipfile` module.

- bpo-40000: Improved error messages for validation of `ast.Constant` nodes. Patch by Batuhan Taskaya.

- bpo-39999: `__module__` of the AST node classes is now set to “ast” instead of “_ast”. Added docstrings for dummy AST node classes and deprecated attributes.

- bpo-39991: `uuid.getnode()` now skips IPv6 addresses with the same string length than a MAC address (17 characters): only use MAC addresses.

- bpo-39988: Deprecated `ast.AugLoad` and `ast.AugStore` node classes because they are no longer used.

- bpo-39656: Ensure `bin/python3.#` is always present in virtual environments on POSIX platforms - by Anthony Sottile.

- bpo-39969: Deprecated `ast.Param` node class because it’s no longer used. Patch by Batuhan Taskaya.

- bpo-39360: Ensure all workers exit when finalizing a `multiprocessing.Pool` implicitly via the module finalization handlers of multiprocessing. This fixes a deadlock situation that can be experienced when the Pool is not properly finalized via the context manager or a call to `multiprocessing.Pool.terminate`. Patch by Batuhan Taskaya and Pablo Galindo.

- bpo-35370: sys.settrace(), sys.setprofile() and _lsprof.Profiler.enable() now properly report `PySys_Audit()` error if “sys.setprofile” or “sys.settrace” audit event is denied.

- bpo-39936: AIX: Fix _aix_support module when the subprocess is not available, when building Python from scratch. It now uses new private _bootsubprocess module, rather than having two implementations depending if subprocess is available or not. So _aix_support.aix_platform() result is now the same if subprocess is available or not.

- bpo-36144: `collections.OrderedDict` now implements `|` and `|=` (PEP 584).

- bpo-39652: The column name found in `sqlite3.Cursor.description` is now truncated on the first ‘[’ only if the PARSE_COLNAMES option is set.

- bpo-39915: Ensure `unittest.mock.AsyncMock.await_args_list` has call objects in the order of awaited arguments instead of using `unittest.mock.Mock.call_args` which has the last value of the call. Patch by Karthikeyan Singaravelan.

- bpo-36144: Updated `os.environ` and `os.environb` to support PEP 584’s merge (`|`) and update (`|=`) operators.

- bpo-38662: The `ensurepip` module now invokes `pip` via the `runpy` module. Hence it is no longer tightly coupled with the internal API of the bundled `pip` version, allowing easier updates to a newer `pip` version both internally and for distributors.

- bpo-38075: Fix the `random.Random.seed()` method when a `bool` is passed as the seed.

- bpo-39916: More reliable use of `os.scandir()` in `Path.glob()`. It no longer emits a ResourceWarning when interrupted.

- bpo-39850: `multiprocessing` now supports abstract socket addresses (if abstract sockets are supported in the running platform). When creating arbitrary addresses (like when default-constructing `multiprocessing.connection.Listener` objects) abstract sockets are preferred to avoid the case when the temporary-file-generated address is too large for an AF_UNIX socket address. Patch by Pablo Galindo.

- bpo-36287: `ast.dump()` no longer outputs optional fields and attributes with default values. The default values for optional fields and attributes of AST nodes are now set as class attributes (e.g. `Constant.kind` is set to `None`).

- bpo-39889: Fixed `ast.unparse()` for extended slices containing a single element (e.g. `a[i:j,]`). Remove redundant tuples when index with a tuple (e.g. `a[i, j]`).

- bpo-39828: Fix `json.tool` to catch `BrokenPipeError`. Patch by Dong-hee Na.

- bpo-13487: Avoid a possible “RuntimeError: dictionary changed size during iteration” from `inspect.getmodule()` when it tried to loop through `sys.modules`.

- bpo-39674: Revert “bpo-37330: open() no longer accept ‘U’ in file mode”. The “U” mode of open() is kept in Python 3.9 to ease transition from Python 2.7, but will be removed in Python 3.10.

- bpo-28577: The hosts method on 32-bit prefix length IPv4Networks and 128-bit prefix IPv6Networks now returns a list containing the single Address instead of an empty list.

- bpo-39826: Add getConnection method to logging HTTPHandler to enable custom connections.

- bpo-39763: Reimplement `distutils.spawn.spawn()` function with the `subprocess` module.

- bpo-39794: Add –without-decimal-contextvar build option. This enables a thread-local rather than a coroutine local context.

- bpo-36144: `collections.defaultdict` now implements `|` (PEP 584).

- bpo-39517: Fix runpy.run_path() when using pathlike objects

- bpo-39775: Change `inspect.Signature.parameters` back to `collections.OrderedDict`. This was changed to `dict` in Python 3.9.0a4.

- bpo-39678: Refactor queue_manager in `concurrent.futures.ProcessPoolExecutor` to make it easier to maintain.

- bpo-39764: Fix AttributeError when calling get_stack on a PyAsyncGenObject Task

- bpo-39769: The `compileall.compile_dir()` function’s ddir parameter and the compileall command line flag `-d` no longer write the wrong pathname to the generated pyc file for submodules beneath the root of the directory tree being compiled. This fixes a regression introduced with Python 3.5.

- bpo-36144: `types.MappingProxyType` objects now support the merge (`|`) operator from PEP 584.

- bpo-38691: The `importlib` module now ignores the `PYTHONCASEOK` environment variable when the `-E` or `-I` command line options are being used.

- bpo-39719: Remove `tempfile.SpooledTemporaryFile.softspace()` as files no longer have the `softspace` attribute in Python 3. Patch by Shantanu.

- bpo-39667: Improve pathlib.Path compatibility on zipfile.Path and correct performance degradation as found in zipp 3.0.

- bpo-39638: Keep ASDL signatures in the docstrings for `AST` nodes. Patch by Batuhan Taskaya

- bpo-39639: Deprecated `ast.Suite` node class because it’s no longer used. Patch by Batuhan Taskaya.

- bpo-39609: Add thread_name_prefix to default asyncio executor

- bpo-39548: Fix handling of header in `urllib.request.AbstractDigestAuthHandler` when the optional `qop` parameter is not present.

- bpo-39509: HTTP status codes `103 EARLY_HINTS` and `425 TOO_EARLY` are added to `http.HTTPStatus`. Patch by Dong-hee Na.

- bpo-39507: Adding HTTP status 418 “I’m a Teapot” to HTTPStatus in http library. Patch by Ross Rhodes.

- bpo-39495: Remove default value from attrs parameter of `xml.etree.ElementTree.TreeBuilder.start()` for consistency between Python and C implementations.

- bpo-38971: Open issue in the BPO indicated a desire to make the implementation of codecs.open() at parity with io.open(), which implements a try/except to assure file stream gets closed before an exception is raised.

- bpo-38641: Added starred expressions support to `return` and `yield` statements for `lib2to3`. Patch by Vlad Emelianov.

- bpo-37534: When using minidom module to generate XML documents the ability to add Standalone Document Declaration is added. All the changes are made to generate a document in compliance with Extensible Markup Language (XML) 1.0 (Fifth Edition) W3C Recommendation (available here: https://www.w3.org/TR/xml/#sec-prolog-dtd).

- bpo-34788: Add support for scoped IPv6 addresses to `ipaddress`. Patch by Oleksandr Pavliuk.

- bpo-34822: Simplified AST for subscription. Simple indices are now represented by their value, extended slices are represented as tuples. `ast` classes `Index` and `ExtSlice` are considered deprecated and will be removed in future Python versions. In the meantime, `Index(value)` now returns a `value` itself, `ExtSlice(slices)` returns `Tuple(slices, Load())`.

### Documentation

- bpo-39868: Updated the Language Reference for PEP 572.

- bpo-13790: Change ‘string’ to ‘specification’ in format doc.

- bpo-17422: The language reference no longer restricts default class namespaces to dicts only.

- bpo-39530: Fix misleading documentation about mixed-type numeric comparisons.

- bpo-39718: Update `token` documentation to reflect additions in Python 3.8

- bpo-39677: Changed operand name of MAKE_FUNCTION from argc to flags for module `dis`

### Tests

- bpo-40019: test_gdb now skips tests if it detects that gdb failed to read debug information because the Python binary is optimized.

- bpo-27807: `test_site.test_startup_imports()` is now skipped if a path of `sys.path` contains a `.pth` file.

- bpo-26067: Do not fail test_shutil test_chown test when uid or gid of user cannot be resolved to a name.

- bpo-39855: test_subprocess.test_user() now skips the test on an user name if the user name doesn’t exist. For example, skip the test if the user “nobody” doesn’t exist on Linux.

### Build

- bpo-39761: Fix build with DTrace but without additional DFLAGS.

- bpo-39763: setup.py now uses a basic implementation of the `subprocess` module if the `subprocess` module is not available: before required C extension modules are built.

- bpo-1294959: Add `--with-platlibdir` option to the configure script: name of the platform-specific library directory, stored in the new `sys.platlibdir` attribute. It is used to build the path of platform-specific extension modules and the path of the standard library. It is equal to `"lib"` on most platforms. On Fedora and SuSE, it is equal to `"lib64"` on 64-bit platforms. Patch by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner.

### Windows

- bpo-39930: Ensures the required `vcruntime140.dll` is included in install packages.

- bpo-39847: Avoid hang when computer is hibernated whilst waiting for a mutex (for lock-related objects from `threading`) around 49-day uptime.

- bpo-38597: `distutils` will no longer statically link `vcruntime140.dll` when a redistributable version is unavailable. All future releases of CPython will include a copy of this DLL to ensure distributed extensions can continue to load.

- bpo-38380: Update Windows builds to use SQLite 3.31.1

- bpo-39789: Update Windows release build machines to Visual Studio 2019 (MSVC 14.2).

- bpo-34803: Package for nuget.org now includes repository reference and bundled icon image.

### macOS

- bpo-38380: Update macOS builds to use SQLite 3.31.1

### IDLE

- bpo-27115: For ‘Go to Line’, use a Query box subclass with IDLE standard behavior and improved error checking.

- bpo-39885: Since clicking to get an IDLE context menu moves the cursor, any text selection should be and now is cleared.

- bpo-39852: Edit “Go to line” now clears any selection, preventing accidental deletion. It also updates Ln and Col on the status bar.

- bpo-39781: Selecting code context lines no longer causes a jump.

### Tools/Demos

- bpo-36184: Port python-gdb.py to FreeBSD. python-gdb.py now checks for “take_gil” function name to check if a frame tries to acquire the GIL, instead of checking for “pthread_cond_timedwait” which is specific to Linux and can be a different condition than the GIL.

- bpo-38080: Added support to fix `getproxies` in the `lib2to3.fixes.fix_urllib` module. Patch by José Roberto Meza Cabrera.

### C API

- bpo-40024: Add `PyModule_AddType()` helper function: add a type to a module. Patch by Dong-hee Na.

- bpo-39946: Remove `_PyRuntime.getframe` hook and remove `_PyThreadState_GetFrame` macro which was an alias to `_PyRuntime.getframe`. They were only exposed by the internal C API. Remove also `PyThreadFrameGetter` type.

- bpo-39947: Add `PyThreadState_GetFrame()` function: get the current frame of a Python thread state.

- bpo-37207: Add _PyArg_NoKwnames helper function. Patch by Dong-hee Na.

- bpo-39947: Add `PyThreadState_GetInterpreter()`: get the interpreter of a Python thread state.

- bpo-39947: Add `PyInterpreterState_Get()` function to the limited C API.

- bpo-35370: If `PySys_Audit()` fails in `PyEval_SetProfile()` or `PyEval_SetTrace()`, log the error as an unraisable exception.

- bpo-39947: Move the static inline function flavor of Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() to the internal C API: they access PyThreadState attributes. The limited C API provides regular functions which hide implementation details.

- bpo-39947: Py_TRASHCAN_BEGIN_CONDITION and Py_TRASHCAN_END macro no longer access PyThreadState attributes, but call new private _PyTrash_begin() and _PyTrash_end() functions which hide implementation details.

- bpo-39884: `PyDescr_NewMethod()` and `PyCFunction_NewEx()` now include the method name in the SystemError “bad call flags” error message to ease debug.

- bpo-39877: Deprecated `PyEval_InitThreads()` and `PyEval_ThreadsInitialized()`. Calling `PyEval_InitThreads()` now does nothing.

- bpo-38249: `Py_UNREACHABLE` is now implemented with `__builtin_unreachable()` and analogs in release mode.

- bpo-38643: `PyNumber_ToBase()` now raises a `SystemError` instead of crashing when called with invalid base.

- bpo-39882: The `Py_FatalError()` function is replaced with a macro which logs automatically the name of the current function, unless the `Py_LIMITED_API` macro is defined.

- bpo-39824: Extension modules: `m_traverse`, `m_clear` and `m_free` functions of `PyModuleDef` are no longer called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed (`Py_mod_exec` function). More precisely, these functions are not called if `m_size` is greater than 0 and the module state (as returned by `PyModule_GetState()`) is `NULL`.

  Extension modules without module state (`m_size <= 0`) are not affected.

- bpo-38913: Fixed segfault in `Py_BuildValue()` called with a format containing “#” and undefined PY_SSIZE_T_CLEAN whwn an exception is set.

- bpo-38500: Add a private API to get and set the frame evaluation function: add `_PyInterpreterState_GetEvalFrameFunc()` and `_PyInterpreterState_SetEvalFrameFunc()` C functions. The `_PyFrameEvalFunction` function type now takes a tstate parameter.

## Python 3.9.0 alpha 4

Release date: 2020-02-25

### Security

- bpo-39184: Add audit events to functions in `fcntl`, `msvcrt`, `os`, `resource`, `shutil`, `signal` and `syslog`.

- bpo-39401: Avoid unsafe DLL load at startup on Windows 7 and earlier.

- bpo-39184: Add audit events to command execution functions in os and pty modules.

### Core and Builtins

- bpo-39382: Fix a use-after-free in the single inheritance path of `issubclass()`, when the `__bases__` of an object has a single reference, and so does its first item. Patch by Yonatan Goldschmidt.

- bpo-39573: Update clinic tool to use `Py_IS_TYPE()`. Patch by Dong-hee Na.

- bpo-39619: Enable use of `os.chroot()` on HP-UX systems.

- bpo-39573: Add `Py_IS_TYPE()` static inline function to check whether the object o type is type.

- bpo-39606: Fix regression caused by fix for bpo-39386, that prevented calling `aclose` on an async generator that had already been closed or exhausted.

- bpo-39579: Change the ending column offset of `Attribute` nodes constructed in `ast_for_dotted_name` to point at the end of the current node and not at the end of the last `NAME` node.

- bpo-1635741: Port _crypt extension module to multiphase initialization (PEP 489).

- bpo-1635741: Port _contextvars extension module to multiphase initialization (PEP 489).

- bpo-39510: Fix segfault in `readinto()` method on closed BufferedReader.

- bpo-39502: Fix `time.localtime()` on 64-bit AIX to support years before 1902 and after 2038. Patch by M Felt.

- bpo-39492: Fix a reference cycle in the C Pickler that was preventing the garbage collection of deleted, pickled objects.

- bpo-39453: Fixed a possible crash in `list.__contains__()` when a list is changed during comparing items. Patch by Dong-hee Na.

- bpo-39434: floor division of float operation now has a better performance. Also the message of `ZeroDivisionError` for this operation is updated. Patch by Dong-hee Na.

- bpo-1635741: Port _codecs extension module to multiphase initialization (PEP 489).

- bpo-1635741: Port _bz2 extension module to multiphase initialization (PEP 489).

- bpo-1635741: Port _abc extension module to multiphase initialization (PEP 489).

- bpo-39320: Replace two complex bytecodes for building dicts with two simpler ones. The new bytecodes `DICT_MERGE` and `DICT_UPDATE` have been added The old bytecodes `BUILD_MAP_UNPACK` and `BUILD_MAP_UNPACK_WITH_CALL` have been removed.

- bpo-39219: Syntax errors raised in the tokenizer now always set correct “text” and “offset” attributes.

- bpo-36051: Drop the GIL during large `bytes.join` operations. Patch by Bruce Merry.

- bpo-38960: Fix DTrace build issues on FreeBSD. Patch by David Carlier.

- bpo-37207: Speed up calls to `range()` by about 30%, by using the PEP 590 `vectorcall` calling convention. Patch by Mark Shannon.

- bpo-36144: `dict` (and `collections.UserDict`) objects now support PEP 584’s merge (`|`) and update (`|=`) operators. Patch by Brandt Bucher.

- bpo-32856: Optimized the idiom for assignment a temporary variable in comprehensions. Now `for y in [expr]` in comprehensions is as fast as a simple assignment `y = expr`.

### Library

- bpo-30566: Fix `IndexError` when trying to decode an invalid string with punycode codec.

- bpo-39649: Remove obsolete check for `__args__` in bdb.Bdb.format_stack_entry.

- bpo-39648: Expanded `math.gcd()` and `math.lcm()` to handle multiple arguments.

- bpo-39681: Fix a regression where the C pickle module wouldn’t allow unpickling from a file-like object that doesn’t expose a readinto() method.

- bpo-35950: Raise `io.UnsupportedOperation` in `io.BufferedReader.truncate()` when it is called on a read-only `io.BufferedReader` instance.

- bpo-39479: Add `math.lcm()` function: least common multiple.

- bpo-39674: Revert “Do not expose abstract collection classes in the collections module” change (bpo-25988). Aliases to ABC like collections.Mapping are kept in Python 3.9 to ease transition from Python 2.7, but will be removed in Python 3.10.

- bpo-39104: Fix hanging ProcessPoolExcutor on `shutdown(wait=False)` when a task has failed pickling.

- bpo-39627: Fixed TypedDict totality check for inherited keys.

- bpo-39474: Fixed starting position of AST for expressions like `(a)(b)`, `(a)[b]` and `(a).b`.

- bpo-21016: The `pydoc` and `trace` modules now use the `sysconfig` module to get the path to the Python standard library, to support uncommon installation path like `/usr/lib64/python3.9/` on Fedora. Patch by Jan Matějek.

- bpo-39590: Collections.deque now holds strong references during deque.__contains__ and deque.count, fixing crashes.

- bpo-39586: The distutils `bdist_msi` command is deprecated in Python 3.9, use `bdist_wheel` (wheel packages) instead.

- bpo-39595: Improved performance of zipfile.Path for files with a large number of entries. Also improved performance and fixed minor issue as published with importlib_metadata 1.5.

- bpo-39350: Fix regression in `fractions.Fraction` if the numerator and/or the denominator is an `int` subclass. The `math.gcd()` function is now used to normalize the numerator and denominator. `math.gcd()` always return a `int` type. Previously, the GCD type depended on numerator and denominator.

- bpo-39567: Added audit for `os.walk()`, `os.fwalk()`, `pathlib.Path.glob()` and `pathlib.Path.rglob()`.

- bpo-39559: Remove unused, undocumented argument `getters` from `uuid.getnode()`

- bpo-38149: `sys.audit()` is now called only once per call of `glob.glob()` and `glob.iglob()`.

- bpo-39546: Fix a regression in `ArgumentParser` where `allow_abbrev=False` was ignored for long options that used a prefix character other than “-“.

- bpo-39450: Striped whitespace from docstring before returning it from `unittest.case.shortDescription()`.

- bpo-12915: A new function `resolve_name` has been added to the `pkgutil` module. This resolves a string of the form `'a.b.c.d'` or `'a.b:c.d'` to an object. In the example, `a.b` is a package/module and `c.d` is an object within that package/module reached via recursive attribute access.

- bpo-39353: The `binascii.crc_hqx()` function is no longer deprecated.

- bpo-39493: Mark `typing.IO.closed` as a property

- bpo-39491: Add `typing.Annotated` and `include_extras` parameter to `typing.get_type_hints()` as part of PEP 593. Patch by Till Varoquaux, documentation by Till Varoquaux and Konstantin Kashin.

- bpo-39485: Fix a bug in `unittest.mock.create_autospec()` that would complain about the wrong number of arguments for custom descriptors defined in an extension module returning functions.

- bpo-38932: Mock fully resets child objects on reset_mock(). Patch by Vegard Stikbakke

- bpo-39082: Allow AsyncMock to correctly patch static/class methods

- bpo-39432: Implement PEP-489 algorithm for non-ascii “PyInit_…” symbol names in distutils to make it export the correct init symbol also on Windows.

- bpo-18819: Omit `devmajor` and `devminor` fields for non-device files in `tarfile` archives, enabling bit-for-bit compatibility with GNU `tar(1)`.

- bpo-39349: Added a new cancel_futures parameter to `concurrent.futures.Executor.shutdown()` that cancels all pending futures which have not started running, instead of waiting for them to complete before shutting down the executor.

- bpo-39274: `bool(fraction.Fraction)` now returns a boolean even if (numerator != 0) does not return a boolean (ex: numpy number).

- bpo-34793: Remove support for `with (await asyncio.lock):` and `with (yield from asyncio.lock):`. The same is correct for `asyncio.Condition` and `asyncio.Semaphore`.

- bpo-25597: Ensure, if `wraps` is supplied to `unittest.mock.MagicMock`, it is used to calculate return values for the magic methods instead of using the default return values. Patch by Karthikeyan Singaravelan.

- bpo-36350: `inspect.Signature.parameters` and `inspect.BoundArguments.arguments` are now dicts instead of OrderedDicts. Patch contributed by Rémi Lapeyre.

- bpo-35727: Fix sys.exit() and sys.exit(None) exit code propagation when used in multiprocessing.Process.

- bpo-32173: * Add `lazycache` function to `__all__`. * Use `dict.clear` to clear the cache. * Refactoring `getline` function and `checkcache` function.

### Documentation

- bpo-17422: The language reference now specifies restrictions on class namespaces. Adapted from a patch by Ethan Furman.

- bpo-39572: Updated documentation of `total` flag of `TypedDict`.

- bpo-39654: In pyclbr doc, update ‘class’ to ‘module’ where appropriate and add readmodule comment. Patch by Hakan Çelik.

- bpo-39153: Clarify refcounting semantics for the following functions: - PyObject_SetItem - PyMapping_SetItemString - PyDict_SetItem - PyDict_SetItemString

- bpo-39392: Explain that when filling with turtle, overlap regions may be left unfilled.

- bpo-39369: Update mmap readline method description. The fact that the readline method does update the file position should not be ignored since this might give the impression for the programmer that it doesn’t update it.

- bpo-9056: Include subsection in TOC for PDF version of docs.

### Tests

- bpo-38325: Skip tests on non-BMP characters of test_winconsoleio.

- bpo-39502: Skip test_zipfile.test_add_file_after_2107() if `time.localtime()` fails with `OverflowError`. It is the case on AIX 6.1 for example.

### Build

- bpo-39489: Remove `COUNT_ALLOCS` special build.

### Windows

- bpo-39553: Delete unused code related to SxS manifests.

- bpo-39439: Honor the Python path when a virtualenv is active on Windows.

- bpo-39393: Improve the error message when attempting to load a DLL with unresolved dependencies.

- bpo-38883: `home()` and `expanduser()` on Windows now prefer `USERPROFILE` and no longer use `HOME`, which is not normally set for regular user accounts. This makes them again behave like `os.path.expanduser()`, which was changed to ignore `HOME` in 3.8, see bpo-36264.

- bpo-39185: The build.bat script has additional options for very-quiet output (-q) and very-verbose output (-vv)

### IDLE

- bpo-39663: Add tests for pyparse find_good_parse_start().

- bpo-39600: In the font configuration window, remove duplicated font names.

- bpo-30780: Add remaining configdialog tests for buttons and highlights and keys tabs.

- bpo-39388: IDLE Settings Cancel button now cancels pending changes

- bpo-38792: Close an IDLE shell calltip if a `KeyboardInterrupt` or shell restart occurs. Patch by Zackery Spytz.

### C API

- bpo-35081: Move the `bytes_methods.h` header file to the internal C API as `pycore_bytes_methods.h`: it only contains private symbols (prefixed by `_Py`), except of the `PyDoc_STRVAR_shared()` macro.

- bpo-35081: Move the `dtoa.h` header file to the internal C API as `pycore_dtoa.h`: it only contains private functions (prefixed by `_Py`). The `math` and `cmath` modules must now be compiled with the `Py_BUILD_CORE` macro defined.

- bpo-39573: Add `Py_SET_SIZE()` function to set the size of an object.

- bpo-39500: `PyUnicode_IsIdentifier()` does not call `Py_FatalError()` anymore if the string is not ready.

- bpo-39573: Add `Py_SET_TYPE()` function to set the type of an object.

- bpo-39573: Add a `Py_SET_REFCNT()` function to set the reference counter of an object.

- bpo-39542: Convert `PyType_HasFeature()`, `PyType_Check()` and `PyType_CheckExact()` macros to static inline functions.

- bpo-39542: In the limited C API, `PyObject_INIT()` and `PyObject_INIT_VAR()` are now defined as aliases to `PyObject_Init()` and `PyObject_InitVar()` to make their implementation opaque. It avoids to leak implementation details in the limited C API. Exclude the following functions from the limited C API: `_Py_NewReference()`, `_Py_ForgetReference()`, `_PyTraceMalloc_NewReference()` and `_Py_GetRefTotal()`.

- bpo-39542: Exclude trashcan mechanism from the limited C API: it requires access to PyTypeObject and PyThreadState structure fields, whereas these structures are opaque in the limited C API.

- bpo-39511: The `PyThreadState_Clear()` function now calls the `PyThreadState.on_delete` callback. Previously, that happened in `PyThreadState_Delete()`.

- bpo-38076: Fix to clear the interpreter state only after clearing module globals to guarantee module state access from C Extensions during runtime destruction

- bpo-39245: The Vectorcall API (PEP 590) was made public, adding the functions `PyObject_Vectorcall`, `PyObject_VectorcallMethod`, `PyVectorcall_Function`, `PyObject_CallOneArg`, `PyObject_CallMethodNoArgs`, `PyObject_CallMethodOneArg`, `PyObject_FastCallDict`, and the flag `Py_TPFLAGS_HAVE_VECTORCALL`.

## Python 3.9.0 alpha 3

Release date: 2020-01-24

### Core and Builtins

- bpo-39427: Document all possibilities for the `-X` options in the command line help section. Patch by Pablo Galindo.

- bpo-39421: Fix possible crashes when operating with the functions in the `heapq` module and custom comparison operators.

- bpo-39386: Prevent double awaiting of async iterator.

- bpo-17005: Add `functools.TopologicalSorter` to the `functools` module to offers functionality to perform topological sorting of graphs. Patch by Pablo Galindo, Tim Peters and Larry Hastings.

- bpo-39320: Replace four complex bytecodes for building sequences with three simpler ones.

  The following four bytecodes have been removed:

  - BUILD_LIST_UNPACK

  - BUILD_TUPLE_UNPACK

  - BUILD_SET_UNPACK

  - BUILD_TUPLE_UNPACK_WITH_CALL

  The following three bytecodes have been added:

  - LIST_TO_TUPLE

  - LIST_EXTEND

  - SET_UPDATE

- bpo-39336: Import loaders which publish immutable module objects can now publish immutable packages in addition to individual modules.

- bpo-39322: Added a new function `gc.is_finalized()` to check if an object has been finalized by the garbage collector. Patch by Pablo Galindo.

- bpo-39048: Improve the displayed error message when incorrect types are passed to `async with` statements by looking up the `__aenter__()` special method before the `__aexit__()` special method when entering an asynchronous context manager. Patch by Géry Ogam.

- bpo-39235: Fix AST end location for lone generator expression in function call, e.g. f(i for i in a).

- bpo-39209: Correctly handle multi-line tokens in interactive mode. Patch by Pablo Galindo.

- bpo-1635741: Port _json extension module to multiphase initialization (PEP 489).

- bpo-39216: Fix constant folding optimization for positional only arguments - by Anthony Sottile.

- bpo-39215: Fix `SystemError` when nested function has annotation on positional-only argument - by Anthony Sottile.

- bpo-39200: Correct the error message when calling the `min()` or `max()` with no arguments. Patch by Dong-hee Na.

- bpo-39200: Correct the error message when trying to construct `range` objects with no arguments. Patch by Pablo Galindo.

- bpo-39166: Fix incorrect line execution reporting in trace functions when tracing the last iteration of asynchronous for loops. Patch by Pablo Galindo.

- bpo-39114: Fix incorrent line execution reporting in trace functions when tracing exception handlers with name binding. Patch by Pablo Galindo.

- bpo-39156: Split the COMPARE_OP bytecode instruction into four distinct instructions.

  - COMPARE_OP for rich comparisons

  - IS_OP for ‘is’ and ‘is not’ tests

  - CONTAINS_OP for ‘in’ and ‘is not’ tests

  - JUMP_IF_NOT_EXC_MATCH for checking exceptions in ‘try-except’ statements.

  This improves the clarity of the interpreter and should provide a modest speedup.

- bpo-38588: Fix possible crashes in dict and list when calling `PyObject_RichCompareBool()`.

- bpo-13601: By default, `sys.stderr` is line-buffered now, even if `stderr` is redirected to a file. You can still make `sys.stderr` unbuffered by passing the `-u` command-line option or setting the `PYTHONUNBUFFERED` environment variable.

  (Contributed by Jendrik Seipp in bpo-13601.)

- bpo-38610: Fix possible crashes in several list methods by holding strong references to list elements when calling `PyObject_RichCompareBool()`.

- bpo-32021: Include brotli .br encoding in mimetypes encodings_map

### Library

- bpo-39430: Fixed race condition in lazy imports in `tarfile`.

- bpo-39413: The `os.unsetenv()` function is now also available on Windows.

- bpo-39390: Fixed a regression with the `ignore` callback of `shutil.copytree()`. The argument types are now str and List[str] again.

- bpo-39395: The `os.putenv()` and `os.unsetenv()` functions are now always available.

- bpo-39406: If `setenv()` C function is available, `os.putenv()` is now implemented with `setenv()` instead of `putenv()`, so Python doesn’t have to handle the environment variable memory.

- bpo-39396: Fix `math.nextafter(-0.0, +0.0)` on AIX 7.1.

- bpo-29435: Allow `tarfile.is_tarfile()` to be used with file and file-like objects, like `zipfile.is_zipfile()`. Patch by William Woodruff.

- bpo-39377: Removed `encoding` option from `json.loads()`. It has been deprecated since Python 3.1.

- bpo-39389: Write accurate compression level metadata in `gzip` archives, rather than always signaling maximum compression.

- bpo-39366: The previously deprecated `xpath()` and `xgtitle()` methods of `nntplib.NNTP` have been removed.

- bpo-39357: Remove the buffering parameter of `bz2.BZ2File`. Since Python 3.0, it was ignored and using it was emitting `DeprecationWarning`. Pass an open file object, to control how the file is opened. The compresslevel parameter becomes keyword-only.

- bpo-39353: Deprecate binhex4 and hexbin4 standards. Deprecate the `binhex` module and the following `binascii` functions: `b2a_hqx()`, `a2b_hqx()`, `rlecode_hqx()`, `rledecode_hqx()`, `crc_hqx()`.

- bpo-39351: Remove `base64.encodestring()` and `base64.decodestring()`, aliases deprecated since Python 3.1: use `base64.encodebytes()` and `base64.decodebytes()` instead.

- bpo-39350: Remove `fractions.gcd()` function, deprecated since Python 3.5 (bpo-22486): use `math.gcd()` instead.

- bpo-39329: `LMTP` constructor now has an optional timeout parameter. Patch by Dong-hee Na.

- bpo-39313: Add a new `exec_function` option (–exec-function in the CLI) to `RefactoringTool` for making `exec` a function. Patch by Batuhan Taskaya.

- bpo-39259: `FTP_TLS` and `FTP_TLS` now raise a `ValueError` if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-39259: `SMTP` and `SMTP_SSL` now raise a `ValueError` if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-39310: Add `math.ulp()`: return the value of the least significant bit of a float.

- bpo-39297: Improved performance of importlib.metadata distribution discovery and resilients to inaccessible sys.path entries (importlib_metadata v1.4.0).

- bpo-39259: `NNTP` and `NNTP_SSL` now raise a `ValueError` if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-38901: When you specify prompt=’.’ or equivalently python -m venv –prompt . … the basename of the current directory is used to set the created venv’s prompt when it’s activated.

- bpo-39288: Add `math.nextafter()`: return the next floating-point value after x towards y.

- bpo-39259: `POP3` and `POP3_SSL` now raise a `ValueError` if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. Patch by Dong-hee Na.

- bpo-39242: Updated the Gmane domain from news.gmane.org to news.gmane.io which is used for examples of `NNTP` news reader server and nntplib tests.

- bpo-35292: Proxy the `SimpleHTTPRequestHandler.guess_type` to `mimetypes.guess_type` so the `mimetypes.init` is called lazily to avoid unnecessary costs when `http.server` module is imported.

- bpo-39239: The `select.epoll.unregister()` method no longer ignores the `EBADF` error.

- bpo-38907: In http.server script, restore binding to IPv4 on Windows.

- bpo-39152: Fix ttk.Scale.configure([name]) to return configuration tuple for name or all options. Giovanni Lombardo contributed part of the patch.

- bpo-39198: If an exception were to be thrown in `Logger.isEnabledFor` (say, by asyncio timeouts or stopit) , the `logging` global lock may not be released appropriately, resulting in deadlock. This change wraps that block of code with `try...finally` to ensure the lock is released.

- bpo-39191: Perform a check for running loop before starting a new task in `loop.run_until_complete()` to fail fast; it prevents the side effect of new task spawning before exception raising.

- bpo-38871: Correctly parenthesize filter-based statements that contain lambda expressions in mod:`lib2to3`. Patch by Dong-hee Na.

- bpo-39142: A change was made to logging.config.dictConfig to avoid converting instances of named tuples to ConvertingTuple. It’s assumed that named tuples are too specialised to be treated like ordinary tuples; if a user of named tuples requires ConvertingTuple functionality, they will have to implement that themselves in their named tuple class.

- bpo-39158: ast.literal_eval() now supports empty sets.

- bpo-39129: Fix import path for `asyncio.TimeoutError`

- bpo-39057: `urllib.request.proxy_bypass_environment()` now ignores leading dots and no longer ignores a trailing newline.

- bpo-39056: Fixed handling invalid warning category in the -W option. No longer import the re module if it is not needed.

- bpo-39055: `base64.b64decode()` with `validate=True` raises now a binascii.Error if the input ends with a single `\n`.

- bpo-21600: Fix `mock.patch.stopall()` to stop active patches that were created with `mock.patch.dict()`.

- bpo-39019: Implement dummy `__class_getitem__` for `tempfile.SpooledTemporaryFile`.

- bpo-39019: Implement dummy `__class_getitem__` for `subprocess.Popen`, `subprocess.CompletedProcess`

- bpo-38914: Adjusted the wording of the warning issued by distutils’ `check` command when the `author` and `maintainer` fields are supplied but no corresponding e-mail field (`author_email` or `maintainer_email`) is found. The wording now reflects the fact that these fields are suggested, but not required. Patch by Juergen Gmach.

- bpo-38878: Fixed __subclasshook__ of `os.PathLike` to return a correct result upon inheritence. Patch by Bar Harel.

- bpo-38615: `IMAP4` and `IMAP4_SSL` now have an optional timeout parameter for their constructors. Also, the `open()` method now has an optional timeout parameter with this change. The overridden methods of `IMAP4_SSL` and `IMAP4_stream` were applied to this change. Patch by Dong-hee Na.

- bpo-35182: Fixed `Popen.communicate()` subsequent call crash when the child process has already closed any piped standard stream, but still continues to be running. Patch by Andriy Maletsky.

- bpo-38630: On Unix, `subprocess.Popen.send_signal()` now polls the process status. Polling reduces the risk of sending a signal to the wrong process if the process completed, the `subprocess.Popen.returncode` attribute is still `None`, and the pid has been reassigned (recycled) to a new different process.

- bpo-38536: Removes trailing space in formatted currency with `international=True` and a locale with symbol following value. E.g. `locale.currency(12.34, international=True)` returned `'12,34 EUR '` instead of `'12,34 EUR'`.

- bpo-38473: Use signature from inner mock for autospecced methods attached with `unittest.mock.attach_mock()`. Patch by Karthikeyan Singaravelan.

- bpo-38361: Fixed an issue where `ident` could include a leading path separator when `syslog.openlog()` was called without arguments.

- bpo-38293: Add `copy.copy()` and `copy.deepcopy()` support to `property()` objects.

- bpo-37958: Added the pstats.Stats.get_profile_dict() method to return the profile data as a StatsProfile instance.

- bpo-28367: Termios magic constants for the following baud rates: - B500000 - B576000 - B921600 - B1000000 - B1152000 - B1500000 - B2000000 - B2500000 - B3000000 - B3500000 - B4000000 Patch by Andrey Smirnov

### Documentation

- bpo-39381: Mention in docs that `asyncio.get_event_loop()` implicitly creates new event loop only if called from the main thread.

- bpo-38918: Add an entry for `__module__` in the “function” & “method” sections of the inspect docs types and members table

- bpo-3530: In the `ast` module documentation, fix a misleading `NodeTransformer` example and add advice on when to use the `fix_missing_locations` function.

### Build

- bpo-39395: On non-Windows platforms, the `setenv()` and `unsetenv()` functions are now required to build Python.

- bpo-39160: Updated the documentation in `/configure --help` to show default values, reference documentation where required and add additional explanation where needed.

- bpo-39144: The ctags and etags build targets both include Modules/_ctypes and Python standard library source files.

### IDLE

- bpo-39050: Make IDLE Settings dialog Help button work again.

- bpo-34118: Tag memoryview, range, and tuple as classes, the same as list, etcetera, in the library manual built-in functions list.

- bpo-32989: Add tests for editor newline_and_indent_event method. Remove dead code from pyparse find_good_parse_start method.

### C API

- bpo-39372: Clean header files of interfaces defined but with no implementation. The public API symbols being removed are: `_PyBytes_InsertThousandsGroupingLocale`, `_PyBytes_InsertThousandsGrouping`, `_Py_InitializeFromArgs`, `_Py_InitializeFromWideArgs`, `_PyFloat_Repr`, `_PyFloat_Digits`, `_PyFloat_DigitsInit`, `PyFrame_ExtendStack`, `_PyAIterWrapper_Type`, `PyNullImporter_Type`, `PyCmpWrapper_Type`, `PySortWrapper_Type`, `PyNoArgsFunction`.

- bpo-39164: Add a private `_PyErr_GetExcInfo()` function to retrieve exception information of the specified Python thread state.

## Python 3.9.0 alpha 2

Release date: 2019-12-18

### Security

- bpo-38945: Newline characters have been escaped when performing uu encoding to prevent them from overflowing into to content section of the encoded file. This prevents malicious or accidental modification of data during the decoding process.

- bpo-37228: Due to significant security concerns, the reuse_address parameter of `asyncio.loop.create_datagram_endpoint()` is no longer supported. This is because of the behavior of `SO_REUSEADDR` in UDP. For more details, see the documentation for `loop.create_datagram_endpoint()`. (Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in bpo-37228.)

- bpo-38804: Fixes a ReDoS vulnerability in `http.cookiejar`. Patch by Ben Caller.

### Core and Builtins

- bpo-39028: Slightly improve the speed of keyword argument parsing with many kwargs by strengthening the assumption that kwargs are interned strings.

- bpo-39080: Fix the value of end_col_offset for Starred Expression AST nodes when they are among the elements in the args attribute of Call AST nodes.

- bpo-39031: When parsing an “elif” node, lineno and col_offset of the node now point to the “elif” keyword and not to its condition, making it consistent with the “if” node. Patch by Lysandros Nikolaou.

- bpo-20443: In Python 3.9.0a1, sys.argv[0] was made an absolute path if a filename was specified on the command line. Revert this change, since most users expect sys.argv to be unmodified.

- bpo-39008: `PySys_Audit()` now requires `Py_ssize_t` to be used for size arguments in the format string, regardless of whether `PY_SSIZE_T_CLEAN` was defined at include time.

- bpo-38673: In REPL mode, don’t switch to PS2 if the line starts with comment or whitespace. Based on work by Batuhan Taşkaya.

- bpo-38922: Calling `replace` on a code object now raises the `code.__new__` audit event.

- bpo-38920: Add audit hooks for when `sys.excepthook()` and `sys.unraisablehook()` are invoked.

- bpo-38892: Improve documentation for audit events table and functions.

- bpo-38852: Set the thread stack size to 8 Mb for debug builds on android platforms.

- bpo-38858: Each Python subinterpreter now has its own “small integer singletons”: numbers in [-5; 257] range. It is no longer possible to change the number of small integers at build time by overriding `NSMALLNEGINTS` and `NSMALLPOSINTS` macros: macros should now be modified manually in `pycore_pystate.h` header file.

- bpo-36854: The garbage collector state becomes per interpreter (`PyInterpreterState.gc`), rather than being global (`_PyRuntimeState.gc`).

- bpo-38835: The `PyFPE_START_PROTECT()` and `PyFPE_END_PROTECT()` macros are empty: they have been doing nothing for the last year, so stop using them.

- bpo-38328: Sped up the creation time of constant `list` and `set` displays. Patch by Brandt Bucher.

- bpo-38707: `MainThread.native_id` is now correctly reset in child processes spawned using `multiprocessing.Process`, instead of retaining the parent’s value.

- bpo-38629: Added `__floor__` and `__ceil__` methods to float object. Patch by Batuhan Taşkaya.

- bpo-27145: int + int and int - int operators can now return small integer singletons. Patch by hongweipeng.

- bpo-38021: Provide a platform tag for AIX that is sufficient for PEP425 binary distribution identification. Patch by Michael Felt.

- bpo-35409: Ignore GeneratorExit exceptions when throwing an exception into the aclose coroutine of an asynchronous generator.

- bpo-33387: Removed WITH_CLEANUP_START, WITH_CLEANUP_FINISH, BEGIN_FINALLY, END_FINALLY, CALL_FINALLY and POP_FINALLY bytecodes. Replaced with RERAISE and WITH_EXCEPT_START bytecodes. The compiler now generates different code for exceptional and non-exceptional branches for ‘with’ and ‘try-except’ statements. For ‘try-finally’ statements the ‘finally’ block is replicated for each exit from the ‘try’ body.

### Library

- bpo-39033: Fix `NameError` in `zipimport`. Patch by Karthikeyan Singaravelan.

- bpo-39022: Update importlib.metadata to include improvements from importlib_metadata 1.3 including better serialization of EntryPoints and improved documentation for custom finders.

- bpo-39006: Fix asyncio when the ssl module is missing: only check for ssl.SSLSocket instance if the ssl module is available.

- bpo-38708: Fix a potential IndexError in email parser when parsing an empty msg-id.

- bpo-38698: Add a new `InvalidMessageID` token to email parser to represent invalid Message-ID headers. Also, add defects when there is remaining value after parsing the header.

- bpo-38994: Implement `__class_getitem__` for `os.PathLike`, `pathlib.Path`.

- bpo-38979: Return class from `ContextVar.__class_getitem__` to simplify subclassing.

- bpo-38978: Implement `__class_getitem__` on asyncio objects (Future, Task, Queue). Patch by Batuhan Taskaya.

- bpo-38916: `array.array`: Remove `tostring()` and `fromstring()` methods. They were aliases to `tobytes()` and `frombytes()`, deprecated since Python 3.2.

- bpo-38986: Make repr of C accelerated TaskWakeupMethWrapper the same as of pure Python version.

- bpo-38982: Fix asyncio `PidfdChildWatcher`: handle `waitpid()` error. If `waitpid()` is called elsewhere, `waitpid()` call fails with `ChildProcessError`: use return code 255 in this case, and log a warning. It ensures that the pidfd file descriptor is closed if this error occurs.

- bpo-38529: Drop too noisy asyncio warning about deletion of a stream without explicit `.close()` call.

- bpo-27413: Added ability to pass through `ensure_ascii` options to json.dumps in the `json.tool` command-line interface.

- bpo-38634: The `readline` module now detects if Python is linked to libedit at runtime on all platforms. Previously, the check was only done on macOS.

- bpo-33684: Fix `json.tool` failed to read a JSON file with non-ASCII characters when locale encoding is not UTF-8.

- bpo-38698: Prevent UnboundLocalError to pop up in parse_message_id.

  parse_message_id() was improperly using a token defined inside an exception handler, which was raising `UnboundLocalError` on parsing an invalid value. Patch by Claudiu Popa.

- bpo-38927: Use `python -m pip` instead of `pip` to upgrade dependencies in venv.

- bpo-26730: Fix `SpooledTemporaryFile.rollover()` might corrupt the file when it is in text mode. Patch by Serhiy Storchaka.

- bpo-38881: random.choices() now raises a ValueError when all the weights are zero.

- bpo-38876: Raise pickle.UnpicklingError when loading an item from memo for invalid input.

  The previous code was raising a `KeyError` for both the Python and C implementation. This was caused by the specified index of an invalid input which did not exist in the memo structure, where the pickle stores what objects it has seen. The malformed input would have caused either a `BINGET` or `LONG_BINGET` load from the memo, leading to a `KeyError` as the determined index was bogus. Patch by Claudiu Popa

- bpo-38688: Calling func:`shutil.copytree` to copy a directory tree from one directory to another subdirectory resulted in an endless loop and a RecursionError. A fix was added to consume an iterator and create the list of the entries to be copied, avoiding the recursion for newly created directories. Patch by Bruno P. Kinoshita.

- bpo-38863: Improve `is_cgi()` function in `http.server`, which enables processing the case that cgi directory is a child of another directory other than root.

- bpo-37838: `typing.get_type_hints()` properly handles functions decorated with `functools.wraps()`.

- bpo-38870: Expose `ast.unparse()` as a function of the `ast` module that can be used to unparse an `ast.AST` object and produce a string with code that would produce an equivalent `ast.AST` object when parsed. Patch by Pablo Galindo and Batuhan Taskaya.

- bpo-38859: AsyncMock now returns StopAsyncIteration on the exhaustion of a side_effects iterable. Since PEP-479 its Impossible to raise a StopIteration exception from a coroutine.

- bpo-38857: AsyncMock fix for return values that are awaitable types. This also covers side_effect iterable values that happened to be awaitable, and wraps callables that return an awaitable type. Before these awaitables were being awaited instead of being returned as is.

- bpo-38834: `typing.TypedDict` subclasses now track which keys are optional using the `__required_keys__` and `__optional_keys__` attributes, to enable runtime validation by downstream projects. Patch by Zac Hatfield-Dodds.

- bpo-38821: Fix unhandled exceptions in `argparse` when internationalizing error messages for arguments with `nargs` set to special (non-integer) values. Patch by Federico Bond.

- bpo-38820: Make Python compatible with OpenSSL 3.0.0. `ssl.SSLSocket.getpeercert()` no longer returns IPv6 addresses with a trailing new line.

- bpo-38811: Fix an unhandled exception in `pathlib` when `os.link()` is missing. Patch by Toke Høiland-Jørgensen.

- bpo-38686: Added support for multiple `qop` values in `urllib.request.AbstractDigestAuthHandler`.

- bpo-38712: Add the Linux-specific `signal.pidfd_send_signal()` function, which allows sending a signal to a process identified by a file descriptor rather than a pid.

- bpo-38348: Add `-i` and `--indent` (indentation level), and `--no-type-comments` (type comments) command line options to ast parsing tool.

- bpo-37523: Change `zipfile.ZipExtFile` to raise `ValueError` when trying to access the underlying file object after it has been closed. This new behavior is consistent with how accessing closed files is handled in other parts of Python.

- bpo-38045: Improve the performance of `enum._decompose()` in `enum`. Patch by hongweipeng.

- bpo-36820: Break cycle generated when saving an exception in socket.py, codeop.py and dyld.py as they keep alive not only the exception but user objects through the `__traceback__` attribute. Patch by Mario Corchero.

- bpo-36406: Handle namespace packages in `doctest`. Patch by Karthikeyan Singaravelan.

- bpo-34776: Fix dataclasses to support forward references in type annotations

- bpo-20928: ElementTree supports recursive XInclude processing. Patch by Stefan Behnel.

- bpo-29636: Add whitespace options for formatting JSON with the `json.tool` CLI. The following mutually exclusive options are now supported: `--indent` for setting the indent level in spaces; `--tab` for indenting with tabs; `--no-indent` for suppressing newlines; and `--compact` for suppressing all whitespace. The default behavior remains the same as `--indent=4`.

### Documentation

- bpo-38928: Correct when venv’s `upgrade_dependencies()` and `--upgrade-deps` are added.

- bpo-38899: Update documentation to state that to activate virtual environments under fish one should use `source`, not `` as documented at https://fishshell.com/docs/current/commands.html#source.

- bpo-22377: Improves documentation of the values that `datetime.datetime.strptime()` accepts for `%Z`. Patch by Karl Dubost.

### Tests

- bpo-38546: Fix test_ressources_gced_in_workers() of test_concurrent_futures: explicitly stop the manager to prevent leaking a child process running in the background after the test completes.

- bpo-38546: Multiprocessing and concurrent.futures tests now stop the resource tracker process when tests complete.

- bpo-38614: Replace hardcoded timeout constants in tests with new `test.support` constants: `LOOPBACK_TIMEOUT`, `INTERNET_TIMEOUT`, `SHORT_TIMEOUT` and `LONG_TIMEOUT`. It becomes easier to adjust these four timeout constants for all tests at once, rather than having to adjust every single test file.

- bpo-38547: Fix test_pty: if the process is the session leader, closing the master file descriptor raises a SIGHUP signal: simply ignore SIGHUP when running the tests.

- bpo-38992: Fix a test for `math.fsum()` that was failing due to constant folding.

- bpo-38991: `test.support`: `run_python_until_end()`, `assert_python_ok()` and `assert_python_failure()` functions no longer strip whitespaces from stderr. Remove `test.support.strip_python_stderr()` function.

- bpo-38965: Fix test_faulthandler on GCC 10. Use the “volatile” keyword in `faulthandler._stack_overflow()` to prevent tail call optimization on any compiler, rather than relying on compiler specific pragma.

- bpo-38875: test_capi: trashcan tests now require the test “cpu” resource.

- bpo-38841: Skip asyncio test_create_datagram_endpoint_existing_sock_unix on platforms lacking a functional bind() for named unix domain sockets.

- bpo-38692: Skip the test_posix.test_pidfd_open() test if `os.pidfd_open()` fails with a `PermissionError`. This situation can happen in a Linux sandbox using a syscall whitelist which doesn’t allow the `pidfd_open()` syscall yet.

- bpo-38839: Fix some unused functions in tests. Patch by Adam Johnson.

- bpo-38669: Raise `TypeError` when passing target as a string with `unittest.mock.patch.object()`.

- bpo-37957: test.regrtest now can receive a list of test patterns to ignore (using the -i/–ignore argument) or a file with a list of patterns to ignore (using the –ignore-file argument). Patch by Pablo Galindo.

### Build

- bpo-37404: `asyncio` now raises `TyperError` when calling incompatible methods with an `ssl.SSLSocket` socket. Patch by Ido Michael.

- bpo-36500: Added an optional “regen” project to the Visual Studio solution that will regenerate all grammar, tokens, and opcodes.

### Windows

- bpo-39007: Add auditing events to functions in `winreg`.

- bpo-33125: Add support for building and releasing Windows ARM64 packages.

### macOS

- bpo-37931: Fixed a crash on OSX dynamic builds that occurred when re-initializing the posix module after a Py_Finalize if the environment had changed since the previous `import posix`. Patch by Benoît Hudson.

### IDLE

- bpo-38944: Escape key now closes IDLE completion windows. Patch by Johnny Najera.

- bpo-38943: Fix IDLE autocomplete windows not always appearing on some systems. Patch by Johnny Najera.

- bpo-38862: ‘Strip Trailing Whitespace’ on the Format menu removes extra newlines at the end of non-shell files.

- bpo-38636: Fix IDLE Format menu tab toggle and file indent width. These functions (default shortcuts Alt-T and Alt-U) were mistakenly disabled in 3.7.5 and 3.8.0.

### C API

- bpo-38896: Remove `PyUnicode_ClearFreeList()` function: the Unicode free list has been removed in Python 3.3.

- bpo-37340: Remove `PyMethod_ClearFreeList()` and `PyCFunction_ClearFreeList()` functions: the free lists of bound method objects have been removed.

- bpo-38835: Exclude `PyFPE_START_PROTECT()` and `PyFPE_END_PROTECT()` macros of `pyfpe.h` from `Py_LIMITED_API` (stable API).

## Python 3.9.0 alpha 1

Release date: 2019-11-19

### Security

- bpo-38722: `runpy` now uses `io.open_code()` to open code files. Patch by Jason Killen.

- bpo-38622: Add additional audit events for the `ctypes` module.

- bpo-38418: Fixes audit event for `os.system()` to be named `os.system`.

- bpo-38243: Escape the server title of `xmlrpc.server.DocXMLRPCServer` when rendering the document page as HTML. (Contributed by Dong-hee Na in bpo-38243.)

- bpo-38174: Update vendorized expat library version to 2.2.8, which resolves CVE-2019-15903.

- bpo-37764: Fixes email._header_value_parser.get_unstructured going into an infinite loop for a specific case in which the email header does not have trailing whitespace, and the case in which it contains an invalid encoded word. Patch by Ashwin Ramaswami.

- bpo-37461: Fix an infinite loop when parsing specially crafted email headers. Patch by Abhilash Raj.

- bpo-37363: Adds audit events for the range of supported run commands (see Command line and environment).

- bpo-37463: ssl.match_hostname() no longer accepts IPv4 addresses with additional text after the address and only quad-dotted notation without trailing whitespaces. Some inet_aton() implementations ignore whitespace and all data after whitespace, e.g. ‘127.0.0.1 whatever’.

- bpo-37363: Adds audit events for `ensurepip`, `ftplib`, `glob`, `imaplib`, `nntplib`, `pdb`, `poplib`, `shutil`, `smtplib`, `sqlite3`, `subprocess`, `telnetlib`, `tempfile` and `webbrowser`, as well as `os.listdir()`, `os.scandir()` and `breakpoint()`.

- bpo-37364: `io.open_code()` is now used when reading `.pth` files.

- bpo-34631: Updated OpenSSL to 1.1.1c in Windows installer

- bpo-34155: Fix parsing of invalid email addresses with more than one `@` (e.g. a@b@c.com.) to not return the part before 2nd `@` as valid email address. Patch by maxking & jpic.

### Core and Builtins

- bpo-38631: Replace `Py_FatalError()` call with a regular `RuntimeError` exception in `float.__getformat__()`.

- bpo-38639: Optimized `math.floor()`, `math.ceil()` and `math.trunc()` for floats.

- bpo-38640: Fixed a bug in the compiler that was causing to raise in the presence of break statements and continue statements inside always false while loops. Patch by Pablo Galindo.

- bpo-38613: Optimized some set operations (e.g. `|`, `^`, and `-`) of `dict_keys`. `d.keys() | other` was slower than `set(d) | other` but they are almost same performance for now.

- bpo-28029: `"".replace("", s, n)` now returns `s` instead of an empty string for all non-zero `n`. There are similar changes for `bytes` and `bytearray` objects.

- bpo-38535: Fixed line numbers and column offsets for AST nodes for calls without arguments in decorators.

- bpo-38525: Fix a segmentation fault when using reverse iterators of empty `dict` objects. Patch by Dong-hee Na and Inada Naoki.

- bpo-38465: `bytearray`, `array` and `mmap` objects allow now to export more than 2**31 buffers at a time.

- bpo-38469: Fixed a bug where the scope of named expressions was not being resolved correctly in the presence of the global keyword. Patch by Pablo Galindo.

- bpo-38437: Activate the `GC_DEBUG` macro for debug builds of the interpreter (when `Py_DEBUG` is set). Patch by Pablo Galindo.

- bpo-38379: When the garbage collector makes a collection in which some objects resurrect (they are reachable from outside the isolated cycles after the finalizers have been executed), do not block the collection of all objects that are still unreachable. Patch by Pablo Galindo and Tim Peters.

- bpo-38379: When cyclic garbage collection (gc) runs finalizers that resurrect unreachable objects, the current gc run ends, without collecting any cyclic trash. However, the statistics reported by `collect()` and `get_stats()` claimed that all cyclic trash found was collected, and that the resurrected objects were collected. Changed the stats to report that none were collected.

- bpo-38392: In debug mode, `PyObject_GC_Track()` now calls `tp_traverse()` of the object type to ensure that the object is valid: test that objects visited by `tp_traverse()` are valid.

- bpo-38210: Remove unecessary intersection and update set operation in dictview with empty set. (Contributed by Dong-hee Na in bpo-38210.)

- bpo-38402: Check the error from the system’s underlying `crypt` or `crypt_r`.

- bpo-37474: On FreeBSD, Python no longer calls `fedisableexcept()` at startup to control the floating point control mode. The call became useless since FreeBSD 6: it became the default mode.

- bpo-38006: Fix a bug due to the interaction of weakrefs and the cyclic garbage collector. We must clear any weakrefs in garbage in order to prevent their callbacks from executing and causing a crash.

- bpo-38317: Fix warnings options priority: `PyConfig.warnoptions` has the highest priority, as stated in the PEP 587.

- bpo-38310: Predict `BUILD_MAP_UNPACK_WITH_CALL` -> `CALL_FUNCTION_EX` opcode pairs in the main interpreter loop. Patch by Brandt Bucher.

- bpo-36871: Improve error handling for the assert_has_calls and assert_has_awaits methods of mocks. Fixed a bug where any errors encountered while binding the expected calls to the mock’s spec were silently swallowed, leading to misleading error output.

- bpo-11410: Better control over symbol visibility is provided through use of the visibility attributes available in gcc >= 4.0, provided in a uniform way across POSIX and Windows. The POSIX build files have been updated to compile with -fvisibility=hidden, minimising exported symbols.

- bpo-38219: Optimized the `dict` constructor and the `update()` method for the case when the argument is a dict.

- bpo-38236: Python now dumps path configuration if it fails to import the Python codecs of the filesystem and stdio encodings.

- bpo-38013: Allow to call `async_generator_athrow().throw(...)` even for non-started async generator helper. It fixes annoying warning at the end of `asyncio.run()` call.

- bpo-38124: Fix an off-by-one error in PyState_AddModule that could cause out-of-bounds memory access.

- bpo-38116: The select module is now PEP-384 compliant and no longer has static state

- bpo-38113: ast module updated to PEP-384 and all statics removed

- bpo-38076: The struct module is now PEP-384 compatible

- bpo-38075: The random module is now PEP-384 compatible

- bpo-38074: zlib module made PEP-384 compatible

- bpo-38073: Make pwd extension module PEP-384 compatible

- bpo-38072: grp module made PEP-384 compatible

- bpo-38069: Make _posixsubprocess PEP-384 compatible

- bpo-38071: Make termios extension module PEP-384 compatible

- bpo-38005: Fixed comparing and creating of InterpreterID and ChannelID.

- bpo-36946: Fix possible signed integer overflow when handling slices. Patch by hongweipeng.

- bpo-37994: Fixed silencing arbitrary errors if an attribute lookup fails in several sites. Only AttributeError should be silenced.

- bpo-8425: Optimize set difference_update for the case when the other set is much larger than the base set. (Suggested by Evgeny Kapun with code contributed by Michele Orrù).

- bpo-37966: The implementation of `is_normalized()` has been greatly sped up on strings that aren’t normalized, by implementing the full normalization-quick-check algorithm from the Unicode standard.

- bpo-37947: Adjust correctly the recursion level in the symtable generation for named expressions. Patch by Pablo Galindo.

- bpo-37812: The `CHECK_SMALL_INT` macro used inside `Object/longobject.c` has been replaced with an explicit `return` at each call site.

- bpo-37751: Fix `codecs.lookup()` to normalize the encoding name the same way than `encodings.normalize_encoding()`, except that `codecs.lookup()` also converts the name to lower case.

- bpo-37830: Fixed compilation of `break` and `continue` in the `finally` block when the corresponding `try` block contains `return` with a non-constant value.

- bpo-20490: Improve import error message for partially initialized module on circular `from` imports - by Anthony Sottile.

- bpo-37840: Fix handling of negative indices in `sq_item` of `bytearray`. Patch by Sergey Fedoseev.

- bpo-37802: Slightly improve performance of `PyLong_FromUnsignedLong()`, `PyLong_FromUnsignedLongLong()` and `PyLong_FromSize_t()`. Patch by Sergey Fedoseev.

- bpo-37409: Ensure explicit relative imports from interactive sessions and scripts (having no parent package) always raise ImportError, rather than treating the current module as the package. Patch by Ben Lewis.

- bpo-32912: Reverted bpo-32912: emitting `SyntaxWarning` instead of `DeprecationWarning` for invalid escape sequences in string and bytes literals.

- bpo-37757: PEP 572: As described in the PEP, assignment expressions now raise `SyntaxError` when their interaction with comprehension scoping results in an ambiguous target scope.

  The `TargetScopeError` subclass originally proposed by the PEP has been removed in favour of just raising regular syntax errors for the disallowed cases.

- bpo-36279: Fix potential use of uninitialized memory in `os.wait3()`.

- bpo-36311: Decoding bytes objects larger than 2GiB is faster and no longer fails when a multibyte characters spans a chunk boundary.

- bpo-34880: The `assert` statement now works properly if the `AssertionError` exception is being shadowed. Patch by Zackery Spytz.

- bpo-37340: Removed object cache (`free_list`) for bound method objects. Temporary bound method objects are less used than before thanks to the `LOAD_METHOD` opcode and the `_PyObject_VectorcallMethod` C API.

- bpo-37648: Fixed minor inconsistency in `list.__contains__()`, `tuple.__contains__()` and a few other places. The collection’s item is now always at the left and the needle is on the right of `==`.

- bpo-37444: Update differing exception between `builtins.__import__()` and `importlib.__import__()`.

- bpo-37619: When adding a wrapper descriptor from one class to a different class (for example, setting `__add__ = str.__add__` on an `int` subclass), an exception is correctly raised when the operator is called.

- bpo-37593: Swap the positions of the posonlyargs and args parameters in the constructor of `ast.parameters` nodes.

- bpo-37543: Optimized pymalloc for non PGO build.

- bpo-37537: Compute allocated pymalloc blocks inside _Py_GetAllocatedBlocks(). This slows down _Py_GetAllocatedBlocks() but gives a small speedup to _PyObject_Malloc() and _PyObject_Free().

- bpo-37467: Fix `sys.excepthook()` and `PyErr_Display()` if a filename is a bytes string. For example, for a SyntaxError exception where the filename attribute is a bytes string.

- bpo-37433: Fix `SyntaxError` indicator printing too many spaces for multi-line strings - by Anthony Sottile.

- bpo-37417: `bytearray.extend()` now correctly handles errors that arise during iteration. Patch by Brandt Bucher.

- bpo-37414: The undocumented `sys.callstats()` function has been removed. Since Python 3.7, it was deprecated and always returned `None`. It required a special build option `CALL_PROFILE` which was already removed in Python 3.7.

- bpo-37392: Remove `sys.getcheckinterval()` and `sys.setcheckinterval()` functions. They were deprecated since Python 3.2. Use `sys.getswitchinterval()` and `sys.setswitchinterval()` instead. Remove also `check_interval` field of the `PyInterpreterState` structure.

- bpo-37388: In development mode and in debug build, encoding and errors arguments are now checked on string encoding and decoding operations. Examples: `open()`, `str.encode()` and `bytes.decode()`.

  By default, for best performances, the errors argument is only checked at the first encoding/decoding error, and the encoding argument is sometimes ignored for empty strings.

- bpo-37348: Optimized decoding short ASCII string with UTF-8 and ascii codecs. `b"foo".decode()` is about 15% faster. Patch by Inada Naoki.

- bpo-24214: Improved support of the surrogatepass error handler in the UTF-8 and UTF-16 incremental decoders.

- bpo-37330: `open()`, `io.open()`, `codecs.open()` and `fileinput.FileInput` no longer accept `'U'` (“universal newline”) in the file mode. This flag was deprecated since Python 3.3.

- bpo-35224: Reverse evaluation order of key: value in dict comprehensions as proposed in PEP 572. I.e. in `{k: v for ...}`, `k` will be evaluated before `v`.

- bpo-37316: Fix the `PySys_Audit()` call in `mmap.mmap`.

- bpo-37300: Remove an unnecssary Py_XINCREF in classobject.c.

- bpo-37269: Fix a bug in the peephole optimizer that was not treating correctly constant conditions with binary operators. Patch by Pablo Galindo.

- bpo-20443: Python now gets the absolute path of the script filename specified on the command line (ex: “python3 script.py”): the __file__ attribute of the __main__ module and sys.path[0] become an absolute path, rather than a relative path.

- bpo-37257: Python’s small object allocator (`obmalloc.c`) now allows (no more than) one empty arena to remain available for immediate reuse, without returning it to the OS. This prevents thrashing in simple loops where an arena could be created and destroyed anew on each iteration.

- bpo-37231: The dispatching of type slots to special methods (for example calling `__mul__` when doing `x * y`) has been made faster.

- bpo-36974: Implemented separate vectorcall functions for every calling convention of builtin functions and methods. This improves performance for calls.

- bpo-37213: Handle correctly negative line offsets in the peephole optimizer. Patch by Pablo Galindo.

- bpo-37219: Remove erroneous optimization for empty set differences.

- bpo-15913: Implement `PyBuffer_SizeFromFormat()` function (previously documented but not implemented): call `struct.calcsize()`. Patch by Joannah Nanjekye.

- bpo-36922: Slot functions optimize any callable with `Py_TPFLAGS_METHOD_DESCRIPTOR` instead of only instances of `function`.

- bpo-36974: The slot `tp_vectorcall_offset` is inherited unconditionally to support `super().__call__()` when the base class uses vectorcall.

- bpo-37160: `threading.get_native_id()` now also supports NetBSD.

- bpo-37077: Add `threading.get_native_id()` support for AIX. Patch by M. Felt

- bpo-36781: `sum()` has been optimized for boolean values.

- bpo-34556: Add `--upgrade-deps` to venv module. Patch by Cooper Ry Lees

- bpo-20523: `pdb.Pdb` supports ~/.pdbrc in Windows 7. Patch by Tim Hopper and Dan Lidral-Porter.

- bpo-35551: Updated encodings: - Removed the “tis260” encoding, which was an alias for the nonexistent “tactis” codec. - Added “mac_centeuro” as an alias for the mac_latin2 encoding.

- bpo-19072: The `classmethod` decorator can now wrap other descriptors such as property objects. Adapted from a patch written by Graham Dumpleton.

- bpo-27575: Improve speed of dictview intersection by directly using set intersection logic. Patch by David Su.

- bpo-30773: Prohibit parallel running of aclose() / asend() / athrow(). Fix ag_running to reflect the actual running status of the AG.

### Library

- bpo-36589: The `curses.update_lines_cols()` function now returns `None` instead of `1` on success.

- bpo-38807: Update `TypeError` messages for `os.path.join()` to include `os.PathLike` objects as acceptable input types.

- bpo-38724: Add a repr for `subprocess.Popen` objects. Patch by Andrey Doroschenko.

- bpo-38786: pydoc now recognizes and parses HTTPS URLs. Patch by python273.

- bpo-38785: Prevent asyncio from crashing if parent `__init__` is not called from a constructor of object derived from `asyncio.Future`.

- bpo-38723: `pdb` now uses `io.open_code()` to trigger auditing events.

- bpo-27805: Allow opening pipes and other non-seekable files in append mode with `open()`.

- bpo-38438: Simplify the `argparse` usage message for `nargs="*"`.

- bpo-38761: WeakSet is now registered as a collections.abc.MutableSet.

- bpo-38716: logging: change RotatingHandler namer and rotator to class-level attributes. This stops __init__ from setting them to None in the case where a subclass defines them with eponymous methods.

- bpo-38713: Add `os.P_PIDFD` constant, which may be passed to `os.waitid()` to wait on a Linux process file descriptor.

- bpo-38692: Add `asyncio.PidfdChildWatcher`, a Linux-specific child watcher implementation that polls process file descriptors.

- bpo-38692: Expose the Linux `pidfd_open` syscall as `os.pidfd_open()`.

- bpo-38602: Added constants `F_OFD_GETLK`, `F_OFD_SETLK` and `F_OFD_SETLKW` to the `fcntl` module. Patch by Dong-hee Na.

- bpo-38334: Fixed seeking backward on an encrypted `zipfile.ZipExtFile`.

- bpo-38312: Add `curses.get_escdelay()`, `curses.set_escdelay()`, `curses.get_tabsize()`, and `curses.set_tabsize()` functions - by Anthony Sottile.

- bpo-38586: Now `fileConfig()` correcty sets the .name of handlers loaded.

- bpo-38565: Add new cache_parameters() method for functools.lru_cache() to better support pickling.

- bpo-34679: asynci.ProactorEventLoop.close() now only calls signal.set_wakeup_fd() in the main thread.

- bpo-31202: The case the result of `pathlib.WindowsPath.glob()` matches now the case of the pattern for literal parts.

- bpo-36321: Remove misspelled attribute. The 3.8 changelog noted that this would be removed in 3.9.

- bpo-38521: Fixed erroneous equality comparison in statistics.NormalDist().

- bpo-38493: Added `CLD_KILLED` and `CLD_STOPPED` for `si_code`. Patch by Dong-hee Na.

- bpo-38478: Fixed a bug in `inspect.signature.bind()` that was causing it to fail when handling a keyword argument with same name as positional-only parameter. Patch by Pablo Galindo.

- bpo-33604: Fixed `hmac.new` and `hmac.HMAC` to raise TypeError instead of ValueError when the digestmod parameter, now required in 3.8, is omitted. Also clarified the hmac module documentation and docstrings.

- bpo-38378: Parameters out and in of `os.sendfile()` was renamed to out_fd and in_fd.

- bpo-38417: Added support for setting the umask in the child process to the subprocess module on POSIX systems.

- bpo-38449: Revert GH-15522, which introduces a regression in `mimetypes.guess_type()` due to improper handling of filenames as urls.

- bpo-38431: Fix `__repr__` method for `dataclasses.InitVar` to support typing objects, patch by Samuel Colvin.

- bpo-38109: Add missing `stat.S_IFDOOR`, `stat.S_IFPORT`, `stat.S_IFWHT`, `stat.S_ISDOOR()`, `stat.S_ISPORT()`, and `stat.S_ISWHT()` values to the Python implementation of `stat`.

- bpo-38422: Clarify docstrings of pathlib suffix(es)

- bpo-38405: Nested subclasses of `typing.NamedTuple` are now pickleable.

- bpo-38332: Prevent `KeyError` thrown by `_encoded_words.decode()` when given an encoded-word with invalid content-type encoding from propagating all the way to `email.message.get()`.

- bpo-38371: Deprecated the `split()` method in `_tkinter.TkappType` in favour of the `splitlist()` method which has more consistent and predicable behavior.

- bpo-38341: Add `smtplib.SMTPNotSupportedError` to the `smtplib` exported names.

- bpo-38319: sendfile() used in socket and shutil modules was raising OverflowError for files >= 2GiB on 32-bit architectures. (patch by Giampaolo Rodola)

- bpo-38242: Revert the new asyncio Streams API

- bpo-13153: OS native encoding is now used for converting between Python strings and Tcl objects. This allows to display, copy and paste to clipboard emoji and other non-BMP characters. Converting strings from Tcl to Python and back now never fails (except MemoryError).

- bpo-38019: Correctly handle pause/resume reading of closed asyncio unix pipe.

- bpo-38163: Child mocks will now detect their type as either synchronous or asynchronous, asynchronous child mocks will be AsyncMocks and synchronous child mocks will be either MagicMock or Mock (depending on their parent type).

- bpo-38161: Removes _AwaitEvent from AsyncMock.

- bpo-38216: Allow the rare code that wants to send invalid http requests from the `http.client` library a way to do so. The fixes for bpo-30458 led to breakage for some projects that were relying on this ability to test their own behavior in the face of bad requests.

- bpo-28286: Deprecate opening `GzipFile` for writing implicitly. Always specify the mode argument for writing.

- bpo-38108: Any synchronous magic methods on an AsyncMock now return a MagicMock. Any asynchronous magic methods on a MagicMock now return an AsyncMock.

- bpo-38265: Update the length parameter of `os.pread()` to accept `Py_ssize_t` instead of `int`.

- bpo-38112: `compileall` has a higher default recursion limit and new command-line arguments for path manipulation, symlinks handling, and multiple optimization levels.

- bpo-38248: asyncio: Fix inconsistent immediate Task cancellation

- bpo-38237: The arguments for the builtin pow function are more descriptive. They can now also be passed in as keywords.

- bpo-34002: Improve efficiency in parts of email package by changing while-pop to a for loop, using isdisjoint instead of set intersections.

- bpo-38191: Constructors of `NamedTuple` and `TypedDict` types now accept arbitrary keyword argument names, including “cls”, “self”, “typename”, “_typename”, “fields” and “_fields”.

- bpo-38155: Add `__all__` to `datetime`. Patch by Tahia Khan.

- bpo-38185: Fixed case-insensitive string comparison in `sqlite3.Row` indexing.

- bpo-38136: Changes AsyncMock call count and await count to be two different counters. Now await count only counts when a coroutine has been awaited, not when it has been called, and vice-versa. Update the documentation around this.

- bpo-37828: Fix default mock name in `unittest.mock.Mock.assert_called()` exceptions. Patch by Abraham Toriz Cruz.

- bpo-38175: Fix a memory leak in comparison of `sqlite3.Row` objects.

- bpo-33936: _hashlib no longer calls obsolete OpenSSL initialization function with OpenSSL 1.1.0+.

- bpo-34706: Preserve subclassing in inspect.Signature.from_callable.

- bpo-38153: Names of hashing algorithms frome OpenSSL are now normalized to follow Python’s naming conventions. For example OpenSSL uses sha3-512 instead of sha3_512 or blake2b512 instead of blake2b.

- bpo-38115: Fix a bug in dis.findlinestarts() where it would return invalid bytecode offsets. Document that a code object’s co_lnotab can contain invalid bytecode offsets.

- bpo-38148: Add slots to `asyncio` transport classes, which can reduce memory usage.

- bpo-38142: The _hashlib OpenSSL wrapper extension module is now PEP-384 compliant.

- bpo-9216: hashlib constructors now support usedforsecurity flag to signal that a hashing algorithm is not used in a security context.

- bpo-36991: Fixes a potential incorrect AttributeError exception escaping ZipFile.extract() in some unsupported input error situations.

- bpo-38134: Remove obsolete copy of PBKDF2_HMAC_fast. All supported OpenSSL versions contain a fast implementation.

- bpo-38132: The OpenSSL hashlib wrapper uses a simpler implementation. Several Macros and pointless caches are gone. The hash name now comes from OpenSSL’s EVP. The algorithm name stays the same, except it is now always lower case.

- bpo-38008: Fix parent class check in protocols to correctly identify the module that provides a builtin protocol, instead of assuming they all come from the `collections.abc` module

- bpo-34037: For `asyncio`, add a new coroutine `loop.shutdown_default_executor()`. The new coroutine provides an API to schedule an executor shutdown that waits on the threadpool to finish closing. Also, `asyncio.run()` has been updated to utilize the new coroutine. Patch by Kyle Stanley.

- bpo-37405: Fixed regression bug for socket.getsockname() for non-CAN_ISOTP AF_CAN address family sockets by returning a 1-tuple instead of string.

- bpo-38121: Update parameter names on functions in importlib.metadata matching the changes in the 0.22 release of importlib_metadata.

- bpo-38110: The os.closewalk() implementation now uses the libc fdwalk() API on platforms where it is available.

- bpo-38093: Fixes AsyncMock so it doesn’t crash when used with AsyncContextManagers or AsyncIterators.

- bpo-37488: Add warning to `datetime.utctimetuple()`, `datetime.utcnow()` and `datetime.utcfromtimestamp()` .

- bpo-35640: Allow passing a path-like object as `directory` argument to the `http.server.SimpleHTTPRequestHandler` class. Patch by Géry Ogam.

- bpo-38086: Update importlib.metadata with changes from importlib_metadata 0.21.

- bpo-37251: Remove `__code__` check in AsyncMock that incorrectly evaluated function specs as async objects but failed to evaluate classes with `__await__` but no `__code__` attribute defined as async objects.

- bpo-38037: Fix reference counters in the `signal` module.

- bpo-38066: Hide internal asyncio.Stream methods: feed_eof(), feed_data(), set_exception() and set_transport().

- bpo-38059: inspect.py now uses sys.exit() instead of exit()

- bpo-38049: Added command-line interface for the `ast` module.

- bpo-37953: In `typing`, improved the `__hash__` and `__eq__` methods for `ForwardReferences`.

- bpo-38026: Fixed `inspect.getattr_static()` used `isinstance` while it should avoid dynamic lookup.

- bpo-35923: Update `importlib.machinery.BuiltinImporter` to use `loader._ORIGIN` instead of a hardcoded value. Patch by Dong-hee Na.

- bpo-38010: In `importlib.metadata` sync with `importlib_metadata` 0.20, clarifying behavior of `files()` and fixing issue where only one requirement was returned for `requires()` on `dist-info` packages.

- bpo-38006: weakref.WeakValueDictionary defines a local remove() function used as callback for weak references. This function was created with a closure. Modify the implementation to avoid the closure.

- bpo-37995: Added the indent option to `ast.dump()` which allows it to produce a multiline indented output.

- bpo-34410: Fixed a crash in the `tee()` iterator when re-enter it. RuntimeError is now raised in this case.

- bpo-37140: Fix a ctypes regression of Python 3.8. When a ctypes.Structure is passed by copy to a function, ctypes internals created a temporary object which had the side effect of calling the structure finalizer (__del__) twice. The Python semantics requires a finalizer to be called exactly once. Fix ctypes internals to no longer call the finalizer twice.

- bpo-37587: `_json.scanstring` is now up to 3x faster when there are many backslash escaped characters in the JSON string.

- bpo-37834: Prevent shutil.rmtree exception when built on non-Windows system without fd system call support, like older versions of macOS.

- bpo-10978: Semaphores and BoundedSemaphores can now release more than one waiting thread at a time.

- bpo-37972: Subscripts to the `unittest.mock.call` objects now receive the same chaining mechanism as any other custom attributes, so that the following usage no longer raises a `TypeError`:

  call().foo().__getitem__(‘bar’)

  Patch by blhsing

- bpo-37965: Fix C compiler warning caused by distutils.ccompiler.CCompiler.has_function.

- bpo-37964: Add `F_GETPATH` command to `fcntl`.

- bpo-37960: `repr()` of buffered and text streams now silences only expected exceptions when get the value of “name” and “mode” attributes.

- bpo-37961: Add a `total_nframe` field to the traces collected by the tracemalloc module. This field indicates the original number of frames before it was truncated.

- bpo-37951: Most features of the subprocess module now work again in subinterpreters. Only preexec_fn is restricted in subinterpreters.

- bpo-36205: Fix the rusage implementation of time.process_time() to correctly report the sum of the system and user CPU time.

- bpo-37950: Fix `ast.dump()` when call with incompletely initialized node.

- bpo-34679: Restores instantiation of Windows IOCP event loops from the non-main thread.

- bpo-36917: Add default implementation of the `ast.NodeVisitor.visit_Constant()` method which emits a deprecation warning and calls corresponding methody `visit_Num()`, `visit_Str()`, etc.

- bpo-37798: Update test_statistics.py to verify that the statistics module works well for both C and Python implementations. Patch by Dong-hee Na

- bpo-26589: Added a new status code to the http module: 451 UNAVAILABLE_FOR_LEGAL_REASONS

- bpo-37915: Fix a segmentation fault that appeared when comparing instances of `datetime.timezone` and `datetime.tzinfo` objects. Patch by Pablo Galindo.

- bpo-32554: Deprecate having random.seed() call hash on arbitrary types.

- bpo-9938: Add optional keyword argument `exit_on_error` for `ArgumentParser`.

- bpo-37851: The `faulthandler` module no longer allocates its alternative stack at Python startup. Now the stack is only allocated at the first faulthandler usage.

- bpo-32793: Fix a duplicated debug message when `smtplib.SMTP.connect()` is called.

- bpo-37885: venv: Don’t generate unset variable warning on deactivate.

- bpo-37868: Fix dataclasses.is_dataclass when given an instance that never raises AttributeError in __getattr__. That is, an object that returns something for __dataclass_fields__ even if it’s not a dataclass.

- bpo-37811: Fix `socket` module’s `socket.connect(address)` function being unable to establish connection in case of interrupted system call. The problem was observed on all OSes which `poll(2)` system call can take only non-negative integers and -1 as a timeout value.

- bpo-37863: Optimizations for Fraction.__hash__ suggested by Tim Peters.

- bpo-21131: Fix `faulthandler.register(chain=True)` stack. faulthandler now allocates a dedicated stack of `SIGSTKSZ*2` bytes, instead of just `SIGSTKSZ` bytes. Calling the previous signal handler in faulthandler signal handler uses more than `SIGSTKSZ` bytes of stack memory on some platforms.

- bpo-37798: Add C fastpath for statistics.NormalDist.inv_cdf() Patch by Dong-hee Na

- bpo-37804: Remove the deprecated method `threading.Thread.isAlive()`. Patch by Dong-hee Na.

- bpo-37819: Add Fraction.as_integer_ratio() to match the corresponding methods in bool, int, float, and decimal.

- bpo-14465: Add an xml.etree.ElementTree.indent() function for pretty-printing XML trees. Contributed by Stefan Behnel.

- bpo-37810: Fix `difflib` `?` hint in diff output when dealing with tabs. Patch by Anthony Sottile.

- bpo-37772: In `zipfile.Path`, when adding implicit dirs, ensure that ancestral directories are added and that duplicates are excluded.

- bpo-18578: Renamed and documented `test.bytecode_helper` as `test.support.bytecode_helper`. Patch by Joannah Nanjekye.

- bpo-37785: Fix xgettext warnings in `argparse`.

- bpo-34488: `writelines()` method of `io.BytesIO` is now slightly faster when many small lines are passed. Patch by Sergey Fedoseev.

- bpo-37449: `ensurepip` now uses `importlib.resources.read_binary()` to read data instead of `pkgutil.get_data()`. Patch by Joannah Nanjekye.

- bpo-28292: Mark calendar.py helper functions as being private. The follows PEP 8 guidance to maintain the style conventions in the module and it addresses a known case of user confusion.

- bpo-18049: Add definition of THREAD_STACK_SIZE for AIX in Python/thread_pthread.h The default thread stacksize caused crashes with the default recursion limit Patch by M Felt

- bpo-37742: The logging.getLogger() API now returns the root logger when passed the name ‘root’, whereas previously it returned a non-root logger named ‘root’. This could affect cases where user code explicitly wants a non-root logger named ‘root’, or instantiates a logger using logging.getLogger(__name__) in some top-level module called ‘root.py’.

- bpo-37738: Fix the implementation of curses `addch(str, color_pair)`: pass the color pair to `setcchar()`, instead of always passing 0 as the color pair.

- bpo-37723: Fix performance regression on regular expression parsing with huge character sets. Patch by Yann Vaginay.

- bpo-35943: The function `PyImport_GetModule()` now ensures any module it returns is fully initialized. Patch by Joannah Nanjekye.

- bpo-32178: Fix IndexError in `email` package when trying to parse invalid address fields starting with `:`.

- bpo-37268: The `parser` module is deprecated and will be removed in future versions of Python.

- bpo-11953: Completing WSA* error codes in `socket`.

- bpo-37685: Fixed comparisons of `datetime.timedelta` and `datetime.timezone`.

- bpo-37697: Syncronize `importlib.metadata` with importlib_metadata 0.19, improving handling of EGG-INFO files and fixing a crash when entry point names contained colons.

- bpo-37695: Correct `curses.unget_wch()` error message. Patch by Anthony Sottile.

- bpo-37689: Add `is_relative_to()` in `PurePath` to determine whether or not one path is relative to another.

- bpo-29553: Fixed `argparse.ArgumentParser.format_usage()` for mutually exclusive groups. Patch by Andrew Nester.

- bpo-37691: Let math.dist() accept coordinates as sequences (or iterables) rather than just tuples.

- bpo-37685: Fixed `__eq__`, `__lt__` etc implementations in some classes. They now return `NotImplemented` for unsupported type of the other operand. This allows the other operand to play role (for example the equality comparison with `ANY` will return `True`).

- bpo-37354: Make Activate.ps1 Powershell script static to allow for signing it.

- bpo-37664: Update wheels bundled with ensurepip (pip 19.2.3 and setuptools 41.2.0)

- bpo-37663: Bring consistency to venv shell activation scripts by always using __VENV_PROMPT__.

- bpo-37642: Allowed the pure Python implementation of `datetime.timezone` to represent sub-minute offsets close to minimum and maximum boundaries, specifically in the ranges (23:59, 24:00) and (-23:59, 24:00). Patch by Ngalim Siregar

- bpo-36161: In `posix`, use `ttyname_r` instead of `ttyname` for thread safety.

- bpo-36324: Make internal attributes for statistics.NormalDist() private.

- bpo-37555: Fix `NonCallableMock._call_matcher` returning tuple instead of `_Call` object when `self._spec_signature` exists. Patch by Elizabeth Uselton

- bpo-29446: Make `from tkinter import *` import only the expected objects.

- bpo-16970: Adding a value error when an invalid value in passed to nargs Patch by Robert Leenders

- bpo-34443: Exceptions from `enum` now use the `__qualname` of the enum class in the exception message instead of the `__name__`.

- bpo-37491: Fix `IndexError` when parsing email headers with unexpectedly ending bare-quoted string value. Patch by Abhilash Raj.

- bpo-37587: Make json.loads faster for long strings. (Patch by Marco Paolini)

- bpo-18378: Recognize “UTF-8” as a valid value for LC_CTYPE in locale._parse_localename.

- bpo-37579: Return `NotImplemented` in Python implementation of `__eq__` for `timedelta` and `time` when the other object being compared is not of the same type to match C implementation. Patch by Karthikeyan Singaravelan.

- bpo-21478: Record calls to parent when autospecced object is attached to a mock using `unittest.mock.attach_mock()`. Patch by Karthikeyan Singaravelan.

- bpo-37531: “python3 -m test -jN –timeout=TIMEOUT” now kills a worker process if it runs longer than TIMEOUT seconds.

- bpo-37482: Fix serialization of display name in originator or destination address fields with both encoded words and special chars.

- bpo-36993: Improve error reporting for corrupt zip files with bad zip64 extra data. Patch by Daniel Hillier.

- bpo-37502: pickle.loads() no longer raises TypeError when the buffers argument is set to None

- bpo-37520: Correct behavior for zipfile.Path.parent when the path object identifies a subdirectory.

- bpo-18374: Fix the `.col_offset` attribute of nested `ast.BinOp` instances which had a too large value in some situations.

- bpo-37424: Fixes a possible hang when using a timeout on `subprocess.run()` while capturing output. If the child process spawned its own children or otherwise connected its stdout or stderr handles with another process, we could hang after the timeout was reached and our child was killed when attempting to read final output from the pipes.

- bpo-37421: Fix `multiprocessing.util.get_temp_dir()` finalizer: clear also the ‘tempdir’ configuration of the current process, so next call to `get_temp_dir()` will create a new temporary directory, rather than reusing the removed temporary directory.

- bpo-37481: The distutils `bdist_wininst` command is deprecated in Python 3.8, use `bdist_wheel` (wheel packages) instead.

- bpo-37479: When `Enum.__str__` is overridden in a derived class, the override will be used by `Enum.__format__` regardless of whether mixin classes are present.

- bpo-37440: http.client now enables TLS 1.3 post-handshake authentication for default context or if a cert_file is passed to HTTPSConnection.

- bpo-37437: Update vendorized expat version to 2.2.7.

- bpo-37428: SSLContext.post_handshake_auth = True no longer sets SSL_VERIFY_POST_HANDSHAKE verify flag for client connections. Although the option is documented as ignored for clients, OpenSSL implicitly enables cert chain validation when the flag is set.

- bpo-37420: `os.sched_setaffinity()` now correctly handles errors that arise during iteration over its `mask` argument. Patch by Brandt Bucher.

- bpo-37412: The `os.getcwdb()` function now uses the UTF-8 encoding on Windows, rather than the ANSI code page: see PEP 529 for the rationale. The function is no longer deprecated on Windows.

- bpo-37406: The sqlite3 module now raises TypeError, rather than ValueError, if operation argument type is not str: execute(), executemany() and calling a connection.

- bpo-29412: Fix IndexError in parsing a header value ending unexpectedly. Patch by Abhilash Raj.

- bpo-36546: The dist argument for statistics.quantiles() is now positional only. The current name doesn’t reflect that the argument can be either a dataset or a distribution. Marking the parameter as positional avoids confusion and makes it possible to change the name later.

- bpo-37394: Fix a bug that was causing the `queue` module to fail if the accelerator module was not available. Patch by Pablo Galindo.

- bpo-37376: `pprint` now has support for `types.SimpleNamespace`. Patch by Carl Bordum Hansen.

- bpo-26967: An `ArgumentParser` with `allow_abbrev=False` no longer disables grouping of short flags, such as `-vv`, but only disables abbreviation of long flags as documented. Patch by Zac Hatfield-Dodds.

- bpo-37212: `unittest.mock.call()` now preserves the order of keyword arguments in repr output. Patch by Karthikeyan Singaravelan.

- bpo-37372: Fix error unpickling datetime.time objects from Python 2 with seconds>=24. Patch by Justin Blanchard.

- bpo-37345: Add formal support for UDPLITE sockets. Support was present before, but it is now easier to detect support with `hasattr(socket, 'IPPROTO_UDPLITE')` and there are constants defined for each of the values needed: `socket.IPPROTO_UDPLITE`, `UDPLITE_SEND_CSCOV`, and `UDPLITE_RECV_CSCOV`. Patch by Gabe Appleton.

- bpo-37358: Optimized `functools.partial` by using vectorcall.

- bpo-37347: `sqlite3.Connection.create_aggregate()`, `sqlite3.Connection.create_function()`, `sqlite3.Connection.set_authorizer()`, `sqlite3.Connection.set_progress_handler()` `sqlite3.Connection.set_trace_callback()` methods lead to segfaults if some of these methods are called twice with an equal object but not the same. Now callbacks are stored more carefully. Patch by Aleksandr Balezin.

- bpo-37163: The obj argument of `dataclasses.replace()` is positional-only now.

- bpo-37085: Add the optional Linux SocketCAN Broadcast Manager constants, used as flags to configure the BCM behaviour, in the socket module. Patch by Karl Ding.

- bpo-37328: `HTMLParser.unescape` is removed. It was undocumented and deprecated since Python 3.4.

- bpo-37305: Add .webmanifest -> application/manifest+json to list of recognized file types and content type headers

- bpo-37320: `aifc.openfp()` alias to `aifc.open()`, `sunau.openfp()` alias to `sunau.open()`, and `wave.openfp()` alias to `wave.open()` have been removed. They were deprecated since Python 3.7.

- bpo-37315: Deprecated accepting floats with integral value (like `5.0`) in `math.factorial()`.

- bpo-37312: `_dummy_thread` and `dummy_threading` modules have been removed. These modules were deprecated since Python 3.7 which requires threading support.

- bpo-33972: Email with single part but content-type set to `multipart/*` doesn’t raise AttributeError anymore.

- bpo-37280: Use threadpool for reading from file for sendfile fallback mode.

- bpo-37279: Fix asyncio sendfile support when sendfile sends extra data in fallback mode.

- bpo-19865: `ctypes.create_unicode_buffer()` now also supports non-BMP characters on platforms with 16-bit `wchar_t` (for example, Windows and AIX).

- bpo-37266: In a subinterpreter, spawning a daemon thread now raises an exception. Daemon threads were never supported in subinterpreters. Previously, the subinterpreter finalization crashed with a Pyton fatal error if a daemon thread was still running.

- bpo-37210: Allow pure Python implementation of `pickle` to work even when the C `_pickle` module is unavailable.

- bpo-21872: Fix `lzma`: module decompresses data incompletely. When decompressing a FORMAT_ALONE format file, and it doesn’t have the end marker, sometimes the last one to dozens bytes can’t be output. Patch by Ma Lin.

- bpo-35922: Fix `RobotFileParser.crawl_delay()` and `RobotFileParser.request_rate()` to return `None` rather than raise `AttributeError` when no relevant rule is defined in the robots.txt file. Patch by Rémi Lapeyre.

- bpo-35766: Change the format of feature_version to be a (major, minor) tuple.

- bpo-36607: Eliminate `RuntimeError` raised by `asyncio.all_tasks()` if internal tasks weak set is changed by another thread during iteration.

- bpo-18748: `_pyio.IOBase` destructor now does nothing if getting the `closed` attribute fails to better mimick `_io.IOBase` finalizer.

- bpo-36402: Fix a race condition at Python shutdown when waiting for threads. Wait until the Python thread state of all non-daemon threads get deleted (join all non-daemon threads), rather than just wait until non-daemon Python threads complete.

- bpo-37206: Default values which cannot be represented as Python objects no longer improperly represented as `None` in function signatures.

- bpo-37111: Added `encoding` and `errors` keyword parameters to `logging.basicConfig`.

- bpo-12144: Ensure cookies with `expires` attribute are handled in `CookieJar.make_cookies()`.

- bpo-34886: Fix an unintended ValueError from `subprocess.run()` when checking for conflicting `input` and `stdin` or `capture_output` and `stdout` or `stderr` args when they were explicitly provided but with `None` values within a passed in `**kwargs` dict rather than as passed directly by name. Patch contributed by Rémi Lapeyre.

- bpo-37173: The exception message for `inspect.getfile()` now correctly reports the passed class rather than the builtins module.

- bpo-37178: Give math.perm() a one argument form that means the same as math.factorial().

- bpo-37178: For math.perm(n, k), let k default to n, giving the same result as factorial.

- bpo-37165: Converted _collections._count_elements to use the Argument Clinic.

- bpo-34767: Do not always create a `collections.deque` in `asyncio.Lock`.

- bpo-37158: Speed-up statistics.fmean() by switching from a function to a generator.

- bpo-34282: Remove `Enum._convert` method, deprecated in 3.8.

- bpo-37150: `argparse._ActionsContainer.add_argument` now throws error, if someone accidentally pass FileType class object instead of instance of FileType as `type` argument

- bpo-28724: The socket module now has the `socket.send_fds()` and `socket.recv.fds()` methods. Contributed by Joannah Nanjekye, Shinya Okano and Victor Stinner.

- bpo-35621: Support running asyncio subprocesses when execution event loop in a thread on UNIX.

- bpo-36520: Lengthy email headers with UTF-8 characters are now properly encoded when they are folded. Patch by Jeffrey Kintscher.

- bpo-30835: Fixed a bug in email parsing where a message with invalid bytes in content-transfer-encoding of a multipart message can cause an AttributeError. Patch by Andrew Donnellan.

- bpo-31163: pathlib.Path instance’s rename and replace methods now return the new Path instance.

- bpo-25068: `urllib.request.ProxyHandler` now lowercases the keys of the passed dictionary.

- bpo-26185: Fix `repr()` on empty `ZipInfo` object. Patch by Mickaël Schoentgen.

- bpo-21315: Email headers containing RFC2047 encoded words are parsed despite the missing whitespace, and a defect registered. Also missing trailing whitespace after encoded words is now registered as a defect.

- bpo-31904: Port test_datetime to VxWorks: skip zoneinfo tests on VxWorks

- bpo-35805: Add parser for Message-ID header and add it to default HeaderRegistry. This should prevent folding of Message-ID using RFC 2048 encoded words.

- bpo-36871: Ensure method signature is used instead of constructor signature of a class while asserting mock object against method calls. Patch by Karthikeyan Singaravelan.

- bpo-35070: posix.getgrouplist() now works correctly when the user belongs to NGROUPS_MAX supplemental groups. Patch by Jeffrey Kintscher.

- bpo-31783: Fix race condition in ThreadPoolExecutor when worker threads are created during interpreter shutdown.

- bpo-36582: Fix `UserString.encode()` to correctly return `bytes` rather than a `UserString` instance.

- bpo-32424: Deprecate xml.etree.ElementTree.Element.copy() in favor of copy.copy().

  Patch by Gordon P. Hemsley

- bpo-36564: Fix infinite loop in email header folding logic that would be triggered when an email policy’s max_line_length is not long enough to include the required markup and any values in the message. Patch by Paul Ganssle

- bpo-36543: Removed methods Element.getchildren(), Element.getiterator() and ElementTree.getiterator() and the xml.etree.cElementTree module.

- bpo-36409: Remove the old plistlib API deprecated in Python 3.4

- bpo-36302: distutils sorts source file lists so that Extension .so files build more reproducibly by default

- bpo-36250: Ignore `ValueError` from `signal` with `interaction` in non-main thread.

- bpo-36046: Added `user`, `group` and `extra_groups` parameters to the subprocess.Popen constructor. Patch by Patrick McLean.

- bpo-32627: Fix compile error when `_uuid` headers conflicting included.

- bpo-35800: Deprecate `smtpd.MailmanProxy` ready for future removal.

- bpo-35168: `shlex.shlex.punctuation_chars` is now a read-only property.

- bpo-8538: Add support for boolean actions like `--foo` and `--no-foo` to argparse. Patch contributed by Rémi Lapeyre.

- bpo-20504: Fixes a bug in `cgi` module when a multipart/form-data request has no `Content-Length` header.

- bpo-25988: The abstract base classes in `collections.abc` no longer are exposed in the regular `collections` module.

- bpo-11122: Distutils won’t check for rpmbuild in specified paths only.

- bpo-34775: Division handling of PurePath now returns NotImplemented instead of raising a TypeError when passed something other than an instance of str or PurePath. Patch by Roger Aiudi.

- bpo-34749: `binascii.a2b_base64()` is now up to 2 times faster. Patch by Sergey Fedoseev.

- bpo-34519: Add additional aliases for HP Roman 8. Patch by Michael Osipov.

- bpo-28009: Fix uuid.getnode() on platforms with ‘.’ as MAC Addr delimiter as well fix for MAC Addr format that omits a leading 0 in MAC Addr values. Currently, AIX is the only know platform with these settings. Patch by Michael Felt.

- bpo-30618: Add `readlink()`. Patch by Girts Folkmanis.

- bpo-32498: Made `urllib.parse.unquote()` accept bytes in addition to strings. Patch by Stein Karlsen.

- bpo-33348: lib2to3 now recognizes expressions after `*` and `**` like in `f(*[] or [])`.

- bpo-32689: Update `shutil.move()` function to allow for Path objects to be used as source argument. Patch by Emily Morehouse and Maxwell “5.13b” McKinnon.

- bpo-32820: Added __format__ to IPv4 and IPv6 classes. Always outputs a fully zero- padded string. Supports b/x/n modifiers (bin/hex/native format). Native format for IPv4 is bin, native format for IPv6 is hex. Also supports ‘#’ and ‘_’ modifiers.

- bpo-27657: Fix urllib.parse.urlparse() with numeric paths. A string like “path:80” is no longer parsed as a path but as a scheme (“path”) and a path (“80”).

- bpo-4963: Fixed non-deterministic behavior related to mimetypes extension mapping and module reinitialization.

### Documentation

- bpo-21767: Explicitly mention abc support in functools.singledispatch

- bpo-38816: Provides more details about the interaction between `fork()` and CPython’s runtime, focusing just on the C-API. This includes cautions about where `fork()` should and shouldn’t be called.

- bpo-38351: Modernize `email` examples from %-formatting to f-strings.

- bpo-38778: Document the fact that `RuntimeError` is raised if `os.fork()` is called in a subinterpreter.

- bpo-38592: Add Brazilian Portuguese to the language switcher at Python Documentation website.

- bpo-38294: Add list of no-longer-escaped chars to re.escape documentation

- bpo-38053: Modernized the plistlib documentation

- bpo-26868: Fix example usage of `PyModule_AddObject()` to properly handle errors.

- bpo-36797: Fix a dead link in the distutils API Reference.

- bpo-37977: Warn more strongly and clearly about pickle insecurity

- bpo-37979: Added a link to dateutil.parser.isoparse in the datetime.fromisoformat documentation. Patch by Paul Ganssle

- bpo-12707: Deprecate info(), geturl(), getcode() methods in favor of the headers, url, and status properties, respectively, for HTTPResponse and addinfourl. Also deprecate the code attribute of addinfourl in favor of the status attribute. Patch by Ashwin Ramaswami

- bpo-37937: Mention `frame.f_trace` in `sys.settrace()` docs.

- bpo-37878: Make `PyThreadState_DeleteCurrent()` Internal.

- bpo-37759: Beginning edits to Whatsnew 3.8

- bpo-37726: Stop recommending getopt in the tutorial for command line argument parsing and promote argparse.

- bpo-32910: Remove implementation-specific behaviour of how venv’s Deactivate works.

- bpo-37256: Fix wording of arguments for `Request` in `urllib.request`

- bpo-37284: Add a brief note to indicate that any new `sys.implementation` required attributes must go through the PEP process.

- bpo-30088: Documented that `mailbox.Maildir` constructor doesn’t attempt to verify the maildir folder layout correctness. Patch by Sviatoslav Sydorenko.

- bpo-37521: Fix `importlib` examples to insert any newly created modules via importlib.util.module_from_spec() immediately into sys.modules instead of after calling loader.exec_module().

  Thanks to Benjamin Mintz for finding the bug.

- bpo-37456: Slash (‘/’) is now part of syntax.

- bpo-37487: Fix PyList_GetItem index description to include 0.

- bpo-37149: Replace the dead link to the Tkinter 8.5 reference by John Shipman, New Mexico Tech, with a link to the archive.org copy.

- bpo-37478: Added possible exceptions to the description of os.chdir().

- bpo-34903: Documented that in `datetime.datetime.strptime()`, the leading zero in some two-digit formats is optional. Patch by Mike Gleen.

- bpo-36260: Add decompression pitfalls to zipfile module documentation.

- bpo-37004: In the documentation for difflib, a note was added explicitly warning that the results of SequenceMatcher’s ratio method may depend on the order of the input strings.

- bpo-36960: Restructured the `datetime` docs in the interest of making them more user-friendly and improving readability. Patch by Brad Solomon.

- bpo-36487: Make C-API docs clear about what the “main” interpreter is.

- bpo-23460: The documentation for decimal string formatting using the `:g` specifier has been updated to reflect the correct exponential notation cutoff point. Original patch contributed by Tuomas Suutari.

- bpo-35803: Document and test that `tempfile` functions may accept a path-like object for the `dir` argument. Patch by Anthony Sottile.

- bpo-33944: Added a note about the intended use of code in .pth files.

- bpo-34293: Fix the Doc/Makefile regarding PAPER environment variable and PDF builds

- bpo-25237: Add documentation for tkinter modules

### Tests

- bpo-38614: Fix test_communicate() of test_asyncio.test_subprocess: use `support.LONG_TIMEOUT` (5 minutes), instead of just 1 minute.

- bpo-38614: Add timeout constants to `test.support`: `LOOPBACK_TIMEOUT`, `INTERNET_TIMEOUT`, `SHORT_TIMEOUT` and `LONG_TIMEOUT`.

- bpo-38502: test.regrtest now uses process groups in the multiprocessing mode (-jN command line option) if process groups are available: if `os.setsid()` and `os.killpg()` functions are available.

- bpo-35998: Fix a race condition in test_asyncio.test_start_tls_server_1(). Previously, there was a race condition between the test main() function which replaces the protocol and the test ServerProto protocol which sends ANSWER once it gets HELLO. Now, only the test main() function is responsible to send data, ServerProto no longer sends data.

- bpo-38470: Fix `test_compileall.test_compile_dir_maxlevels()` on Windows without long path support: only create 3 subdirectories instead of between 20 and 100 subdirectories.

- bpo-37531: On timeout, regrtest no longer attempts to call `popen.communicate()` again: it can hang until all child processes using stdout and stderr pipes completes. Kill the worker process and ignores its output. Change also the faulthandler timeout of the main process from 1 minute to 5 minutes, for Python slowest buildbots.

- bpo-38239: Fix test_gdb for Link Time Optimization (LTO) builds.

- bpo-38275: test_ssl now handles disabled TLS/SSL versions better. OpenSSL’s crypto policy and run-time settings are recognized and tests for disabled versions are skipped. Tests also accept more TLS minimum_versions for platforms that override OpenSSL’s default with strict settings.

- bpo-38271: The private keys for test_ssl were encrypted with 3DES in traditional PKCS#5 format. 3DES and the digest algorithm of PKCS#5 are blocked by some strict crypto policies. Use PKCS#8 format with AES256 encryption instead.

- bpo-38270: test.support now has a helper function to check for availibility of a hash digest function. Several tests are refactored avoid MD5 and use SHA256 instead. Other tests are marked to use MD5 and skipped when MD5 is disabled.

- bpo-37123: Multiprocessing test test_mymanager() now also expects -SIGTERM, not only exitcode 0. BaseManager._finalize_manager() sends SIGTERM to the manager process if it takes longer than 1 second to stop, which happens on slow buildbots.

- bpo-38212: Multiprocessing tests: increase test_queue_feeder_donot_stop_onexc() timeout from 1 to 60 seconds.

- bpo-38117: Test with OpenSSL 1.1.1d

- bpo-38018: Increase code coverage for multiprocessing.shared_memory.

- bpo-37805: Add tests for json.dump(…, skipkeys=True). Patch by Dong-hee Na.

- bpo-37531: Enhance regrtest multiprocess timeout: write a message when killing a worker process, catch popen.kill() and popen.wait() exceptions, put a timeout on the second call to popen.communicate().

- bpo-37876: Add tests for ROT-13 codec.

- bpo-36833: Added tests for PyDateTime_xxx_GET_xxx() macros of the C API of the `datetime` module. Patch by Joannah Nanjekye.

- bpo-37558: Fix test_shared_memory_cleaned_after_process_termination name handling

- bpo-37526: Add `test.support.catch_threading_exception()`: context manager catching `threading.Thread` exception using `threading.excepthook()`.

- bpo-37421: test_concurrent_futures now explicitly stops the ForkServer instance if it’s running.

- bpo-37421: multiprocessing tests now stop the ForkServer instance if it’s running: close the “alive” file descriptor to ask the server to stop and then remove its UNIX address.

- bpo-37421: test_distutils.test_build_ext() is now able to remove the temporary directory on Windows: don’t import the newly built C extension (“xx”) in the current process, but test it in a separated process.

- bpo-37421: test_concurrent_futures now cleans up multiprocessing to remove immediately temporary directories created by multiprocessing.util.get_temp_dir().

- bpo-37421: test_winconsoleio doesn’t leak a temporary file anymore: use tempfile.TemporaryFile() to remove it when the test completes.

- bpo-37421: multiprocessing tests now explicitly call `_run_finalizers()` to immediately remove temporary directories created by tests.

- bpo-37421: urllib.request tests now call `urlcleanup()` to remove temporary files created by `urlretrieve()` tests and to clear the `_opener` global variable set by `urlopen()` and functions calling indirectly `urlopen()`.

- bpo-37472: Remove `Lib/test/outstanding_bugs.py`.

- bpo-37199: Fix test failures when IPv6 is unavailable or disabled.

- bpo-19696: Replace deprecated method “random.choose” with “random.choice” in “test_pkg_import.py”.

- bpo-37335: Remove no longer necessary code from c locale coercion tests

- bpo-37421: Fix test_shutil to no longer leak temporary files.

- bpo-37411: Fix test_wsgiref.testEnviron() to no longer depend on the environment variables (don’t fail if “X” variable is set).

- bpo-37400: Fix test_os.test_chown(): use os.getgroups() rather than grp.getgrall() to get groups. Rename also the test to test_chown_gid().

- bpo-37359: Add –cleanup option to python3 -m test to remove `test_python_*` directories of previous failed jobs. Add “make cleantest” to run `python3 -m test --cleanup`.

- bpo-37362: test_gdb no longer fails if it gets an “unexpected” message on stderr: it now ignores stderr. The purpose of test_gdb is to test that python-gdb.py commands work as expected, not to test gdb.

- bpo-35998: Avoid TimeoutError in test_asyncio: test_start_tls_server_1()

- bpo-37278: Fix test_asyncio ProactorLoopCtrlC: join the thread to prevent leaking a running thread and leaking a reference.

- bpo-37261: Fix `test.support.catch_unraisable_exception()`: its __exit__() method now ignores unraisable exception raised when clearing its `unraisable` attribute.

- bpo-37069: regrtest now uses `sys.unraisablehook()` to mark a test as “environment altered” (ENV_CHANGED) if it emits an “unraisable exception”. Moreover, regrtest logs a warning in this case.

  Use `python3 -m test --fail-env-changed` to catch unraisable exceptions in tests.

- bpo-37252: Fix assertions in `test_close` and `test_events_mask_overflow` devpoll tests.

- bpo-37169: Rewrite `_PyObject_IsFreed()` unit tests.

- bpo-37153: `test_venv.test_multiprocessing()` now explicitly calls `pool.terminate()` to wait until the pool completes.

- bpo-34001: Make test_ssl pass with LibreSSL. LibreSSL handles minimum and maximum TLS version differently than OpenSSL.

- bpo-36919: Make `test_source_encoding.test_issue2301` implementation independent. The test will work now for both CPython and IronPython.

- bpo-30202: Update `test.test_importlib.test_abc` to test `find_spec()`.

- bpo-28009: Modify the test_uuid logic to test when a program is available AND can be used to obtain a MACADDR as basis for an UUID. Patch by M. Felt

- bpo-34596: Fallback to a default reason when `unittest.skip()` is uncalled. Patch by Naitree Zhu.

### Build

- bpo-38809: On Windows, build scripts will now recognize and use python.exe from an active virtual env.

- bpo-38684: Fix _hashlib build when Blake2 is disabled, but OpenSSL supports it.

- bpo-38468: Misc/python-config.in now uses `getvar()` for all still existing `sysconfig.get_config_var()` calls. Patch by Joannah Nanjekye.

- bpo-37415: Fix stdatomic.h header check for ICC compiler: the ICC implementation lacks atomic_uintptr_t type which is needed by Python.

- bpo-38301: In Solaris family, we must be sure to use `-D_REENTRANT`. Patch by Jesús Cea Avión.

- bpo-36002: Locate `llvm-profdata` and `llvm-ar` binaries using `AC_PATH_TOOL` rather than `AC_PATH_TARGET_TOOL`.

- bpo-37936: The `.gitignore` file systematically keeps “rooted”, with a non-trailing slash, all the rules that are meant to apply to files in a specific place in the repo. Previously, when the intended file to ignore happened to be at the root of the repo, we’d most often accidentally also ignore files and directories with the same name anywhere in the tree.

- bpo-37760: The `Tools/unicode/makeunicodedata.py` script, which is used for converting information from the Unicode Character Database into generated code and data used by the methods of `str` and by the `unicodedata` module, now handles each character’s data as a `dataclass` with named attributes, rather than a length-18 list of different fields.

- bpo-37936: The `.gitignore` file no longer applies to any files that are in fact tracked in the Git repository. Patch by Greg Price.

- bpo-37725: Change “clean” makefile target to also clean the program guided optimization (PGO) data. Previously you would have to use “make clean” and “make profile-removal”, or “make clobber”.

- bpo-37707: Mark some individual tests to skip when –pgo is used. The tests marked increase the PGO task time significantly and likely don’t help improve optimization of the final executable.

- bpo-36044: Reduce the number of unit tests run for the PGO generation task. This speeds up the task by a factor of about 15x. Running the full unit test suite is slow. This change may result in a slightly less optimized build since not as many code branches will be executed. If you are willing to wait for the much slower build, the old behavior can be restored using ‘./configure [..] PROFILE_TASK=”-m test –pgo-extended”’. We make no guarantees as to which PGO task set produces a faster build. Users who care should run their own relevant benchmarks as results can depend on the environment, workload, and compiler tool chain.

- bpo-37468: `make install` no longer installs `wininst-*.exe` files used by distutils bdist_wininst: bdist_wininst only works on Windows.

- bpo-37189: Many `PyRun_XXX()` functions like `PyRun_String()` were no longer exported in `libpython38.dll` by mistake. Export them again to fix the ABI compatibility.

- bpo-25361: Enables use of SSE2 instructions in Windows 32-bit build.

- bpo-36210: Update optional extension module detection for AIX. ossaudiodev and spwd are not applicable for AIX, and are no longer reported as missing. 3rd-party packaging of ncurses (with ASIS support) conflicts with officially supported AIX curses library, so configure AIX to use libcurses.a. However, skip trying to build _curses_panel.

  patch by M Felt

### Windows

- bpo-38589: Fixes HTML Help shortcut when Windows is not installed to C drive

- bpo-38453: Ensure ntpath.realpath() correctly resolves relative paths.

- bpo-38519: Restores the internal C headers that were missing from the nuget.org and Microsoft Store packages.

- bpo-38492: Remove `pythonw.exe` dependency on the Microsoft C++ runtime.

- bpo-38344: Fix error message in activate.bat

- bpo-38359: Ensures `pyw.exe` launcher reads correct registry key.

- bpo-38355: Fixes `ntpath.realpath` failing on `sys.executable`.

- bpo-38117: Update bundled OpenSSL to 1.1.1d

- bpo-38092: Reduce overhead when using multiprocessing in a Windows virtual environment.

- bpo-38133: Allow py.exe launcher to locate installations from the Microsoft Store and improve display of active virtual environments.

- bpo-38114: The `pip.ini` is no longer included in the Nuget package.

- bpo-32592: Set Windows 8 as the minimum required version for API support

- bpo-36634: `os.cpu_count()` now returns active processors rather than maximum processors.

- bpo-36634: venv activate.bat now works when the existing variables contain double quote characters.

- bpo-38081: Prevent error calling `os.path.realpath()` on `'NUL'`.

- bpo-38087: Fix case sensitivity in test_pathlib and test_ntpath.

- bpo-38088: Fixes distutils not finding vcruntime140.dll with only the v142 toolset installed.

- bpo-37283: Ensure command-line and unattend.xml setting override previously detected states in Windows installer.

- bpo-38030: Fixes `os.stat()` failing for block devices on Windows

- bpo-38020: Fixes potential crash when calling `os.readlink()` (or indirectly through `realpath()`) on a file that is not a supported link.

- bpo-37705: Improve the implementation of `winerror_to_errno()`.

- bpo-37549: `os.dup()` no longer fails for standard streams on Windows 7.

- bpo-1311: The `nul` file on Windows now returns True from `exists()` and a valid result from `os.stat()` with `S_IFCHR` set.

- bpo-9949: Enable support for following symlinks in `os.realpath()`.

- bpo-37834: Treat all name surrogate reparse points on Windows in `os.lstat()` and other reparse points as regular files in `os.stat()`.

- bpo-36266: Add the module name in the formatted error message when DLL load fail happens during module import in `_PyImport_FindSharedFuncptrWindows()`. Patch by Srinivas Nyayapati.

- bpo-25172: Trying to import the `crypt` module on Windows will result in an `ImportError` with a message explaining that the module isn’t supported on Windows. On other platforms, if the underlying `_crypt` module is not available, the ImportError will include a message explaining the problem.

- bpo-37778: Fixes the icons used for file associations to the Microsoft Store package.

- bpo-37734: Fix use of registry values to launch Python from Microsoft Store app.

- bpo-37702: Fix memory leak on Windows in creating an SSLContext object or running urllib.request.urlopen(’https://…’).

- bpo-37672: Switch Windows Store package’s pip to use bundled `pip.ini` instead of `PIP_USER` variable.

- bpo-10945: Officially drop support for creating bdist_wininst installers on non-Windows systems.

- bpo-37445: Include the `FORMAT_MESSAGE_IGNORE_INSERTS` flag in `FormatMessageW()` calls.

- bpo-37369: Fixes path for `sys.executable` when running from the Microsoft Store.

- bpo-37380: Don’t collect unfinished processes with `subprocess._active` on Windows to cleanup later. Patch by Ruslan Kuprieiev.

- bpo-37351: Removes libpython38.a from standard Windows distribution.

- bpo-35360: Update Windows builds to use SQLite 3.28.0.

- bpo-37267: On Windows, `os.dup()` no longer creates an inheritable fd when handling a character file.

- bpo-36779: Ensure `time.tzname` is correct on Windows when the active code page is set to CP_UTF7 or CP_UTF8.

- bpo-32587: Make `winreg.REG_MULTI_SZ` support zero-length strings.

- bpo-28269: Replace use of `strcasecmp()` for the system function `_stricmp()`. Patch by Minmin Gong.

- bpo-36590: Add native Bluetooth RFCOMM support to socket module.

### macOS

- bpo-38117: Updated OpenSSL to 1.1.1d in macOS installer.

- bpo-38089: Move Azure Pipelines to latest VM versions and make macOS tests optional

- bpo-18049: Increase the default stack size of threads from 5MB to 16MB on macOS, to match the stack size of the main thread. This avoids crashes on deep recursion in threads.

- bpo-34602: Avoid test suite failures on macOS by no longer calling resource.setrlimit to increase the process stack size limit at runtime. The runtime change is no longer needed since the interpreter is being built with a larger default stack size.

- bpo-35360: Update macOS installer to use SQLite 3.28.0.

- bpo-34631: Updated OpenSSL to 1.1.1c in macOS installer.

### IDLE

- bpo-26353: Stop adding newline when saving an IDLE shell window.

- bpo-4630: Add an option to toggle IDLE’s cursor blink for shell, editor, and output windows. See Settings, General, Window Preferences, Cursor Blink. Patch by Zackery Spytz.

- bpo-38598: Do not try to compile IDLE shell or output windows

- bpo-36698: IDLE no longer fails when write non-encodable characters to stderr. It now escapes them with a backslash, as the regular Python interpreter. Added the `errors` field to the standard streams.

- bpo-35379: When exiting IDLE, catch any AttributeError. One happens when EditorWindow.close is called twice. Printing a traceback, when IDLE is run from a terminal, is useless and annoying.

- bpo-38183: To avoid problems, test_idle ignores the user config directory. It no longer tries to create or access .idlerc or any files within. Users must run IDLE to discover problems with saving settings.

- bpo-38077: IDLE no longer adds ‘argv’ to the user namespace when initializing it. This bug only affected 3.7.4 and 3.8.0b2 to 3.8.0b4.

- bpo-38041: Shell restart lines now fill the window width, always start with ‘=’, and avoid wrapping unnecessarily. The line will still wrap if the included file name is long relative to the width.

- bpo-35771: To avoid occasional spurious test_idle failures on slower machines, increase the `hover_delay` in test_tooltip.

- bpo-37824: Properly handle user input warnings in IDLE shell. Cease turning SyntaxWarnings into SyntaxErrors.

- bpo-37929: IDLE Settings dialog now closes properly when there is no shell window.

- bpo-37902: Add mousewheel scrolling for IDLE module, path, and stack browsers. Patch by George Zhang.

- bpo-37849: Fixed completions list appearing too high or low when shown above the current line.

- bpo-36419: Refactor IDLE autocomplete and improve testing.

- bpo-37748: Reorder the Run menu. Put the most common choice, Run Module, at the top.

- bpo-37692: Improve highlight config sample with example shell interaction and better labels for shell elements.

- bpo-37628: Settings dialog no longer expands with font size.

- bpo-37627: Initialize the Customize Run dialog with the command line arguments most recently entered before. The user can optionally edit before submitting them.

- bpo-33610: Fix code context not showing the correct context when first toggled on.

- bpo-37530: Optimize code context to reduce unneeded background activity. Font and highlight changes now occur along with text changes instead of after a random delay.

- bpo-27452: Cleanup `config.py` by inlining `RemoveFile` and simplifying the handling of `file` in `CreateConfigHandlers`.

- bpo-37325: Fix tab focus traversal order for help source and custom run dialogs.

- bpo-37321: Both subprocess connection error messages now refer to the ‘Startup failure’ section of the IDLE doc.

- bpo-17535: Add optional line numbers for IDLE editor windows. Windows open without line numbers unless set otherwise in the General tab of the configuration dialog.

- bpo-26806: To compensate for stack frames added by IDLE and avoid possible problems with low recursion limits, add 30 to limits in the user code execution process. Subtract 30 when reporting recursion limits to make this addition mostly transparent.

- bpo-37177: Properly ‘attach’ search dialogs to their main window so that they behave like other dialogs and do not get hidden behind their main window.

- bpo-37039: Adjust “Zoom Height” to individual screens by momentarily maximizing the window on first use with a particular screen. Changing screen settings may invalidate the saved height. While a window is maximized, “Zoom Height” has no effect.

- bpo-35763: Make calltip reminder about ‘/’ meaning positional-only less obtrusive by only adding it when there is room on the first line.

- bpo-5680: Add ‘Run… Customized’ to the Run menu to run a module with customized settings. Any ‘command line arguments’ entered are added to sys.argv. One can suppress the normal Shell main module restart.

- bpo-36390: Gather Format menu functions into format.py. Combine paragraph.py, rstrip.py, and format methods from editor.py.

### Tools/Demos

- bpo-38118: Update Valgrind suppression file to ignore a false alarm in `PyUnicode_Decode()` when using GCC builtin strcmp().

- bpo-38347: pathfix.py: Assume all files that end on ‘.py’ are Python scripts when working recursively.

- bpo-37803: pdb’s `--help` and `--version` long options now work.

- bpo-37942: Improve ArgumentClinic converter for floats.

- bpo-37704: Remove `Tools/scripts/h2py.py`: use cffi to access a C API in Python.

- bpo-37675: 2to3 now works when run from a zipped standard library.

- bpo-37034: Argument Clinic now uses the argument name on errors with keyword-only argument instead of their position. Patch contributed by Rémi Lapeyre.

- bpo-37064: Add option -k to pathscript.py script: preserve shebang flags. Add option -a to pathscript.py script: add flags.

### C API

- bpo-37633: Re-export some function compatibility wrappers for macros in `pythonrun.h`.

- bpo-38644: Provide `Py_EnterRecursiveCall()` and `Py_LeaveRecursiveCall()` as regular functions for the limited API. Previously, there were defined as macros, but these macros didn’t work with the limited API which cannot access `PyThreadState.recursion_depth` field. Remove `_Py_CheckRecursionLimit` from the stable ABI.

- bpo-38650: The global variable `PyStructSequence_UnnamedField` is now a constant and refers to a constant string.

- bpo-38540: Fixed possible leak in `PyArg_Parse()` and similar functions for format units `"es#"` and `"et#"` when the macro `PY_SSIZE_T_CLEAN` is not defined.

- bpo-38395: Fix a crash in `weakref.proxy` objects due to incorrect lifetime management when calling some associated methods that may delete the last reference to object being referenced by the proxy. Patch by Pablo Galindo.

- bpo-36389: The `_PyObject_CheckConsistency()` function is now also available in release mode. For example, it can be used to debug a crash in the `visit_decref()` function of the GC.

- bpo-38266: Revert the removal of PyThreadState_DeleteCurrent() with documentation.

- bpo-38303: Update audioop extension module to use the stable ABI (PEP-384). Patch by Tyler Kieft.

- bpo-38234: `Py_SetPath()` now sets `sys.executable` to the program full path (`Py_GetProgramFullPath()`) rather than to the program name (`Py_GetProgramName()`).

- bpo-38234: Python ignored arguments passed to `Py_SetPath()`, `Py_SetPythonHome()` and `Py_SetProgramName()`: fix Python initialization to use specified arguments.

- bpo-38205: The `Py_UNREACHABLE()` macro now calls `Py_FatalError()`.

- bpo-38140: Make dict and weakref offsets opaque for C heap types by passing the offsets through PyMemberDef

- bpo-15088: The C function `PyGen_NeedsFinalizing` has been removed. It was not documented, tested or used anywhere within CPython after the implementation of PEP 442. Patch by Joannah Nanjekye. (Patch by Joannah Nanjekye)

- bpo-36763: Options added by `PySys_AddXOption()` are now handled the same way than `PyConfig.xoptions` and command line `-X` options.

- bpo-37926: Fix a crash in `PySys_SetArgvEx(0, NULL, 0)`.

- bpo-37879: Fix subtype_dealloc to suppress the type decref when the base type is a C heap type

- bpo-37645: Add `_PyObject_FunctionStr()` to get a user-friendly string representation of a function-like object. Patch by Jeroen Demeyer.

- bpo-29548: The functions `PyEval_CallObject`, `PyEval_CallFunction`, `PyEval_CallMethod` and `PyEval_CallObjectWithKeywords` are deprecated. Use `PyObject_Call()` and its variants instead.

- bpo-37151: `PyCFunction_Call` is now a deprecated alias of `PyObject_Call()`.

- bpo-37540: The vectorcall protocol now requires that the caller passes only strings as keyword names.

- bpo-37207: The vectorcall protocol is now enabled for `type` objects: set `tp_vectorcall` to a vectorcall function to be used instead of `tp_new` and `tp_init` when calling the class itself.

- bpo-21120: Exclude Python-ast.h, ast.h and asdl.h from the limited API.

- bpo-37483: Add new function `_PyObject_CallOneArg` for calling an object with one positional argument.

- bpo-36763: Add `PyConfig_SetWideStringList()` function.

- bpo-37337: Add fast functions for calling methods: `_PyObject_VectorcallMethod()`, `_PyObject_CallMethodNoArgs()` and `_PyObject_CallMethodOneArg()`.

- bpo-28805: The `METH_FASTCALL` calling convention has been documented.

- bpo-37221: The new function `PyCode_NewWithPosOnlyArgs()` allows to create code objects like `PyCode_New()`, but with an extra posonlyargcount parameter for indicating the number of positonal-only arguments.

- bpo-37215: Fix dtrace issue introduce by bpo-36842

- bpo-37194: Add a new public `PyObject_CallNoArgs()` function to the C API: call a callable Python object without any arguments. It is the most efficient way to call a callback without any argument. On x86-64, for example, `PyObject_CallFunctionObjArgs(func, NULL)` allocates 960 bytes on the stack per call, whereas `PyObject_CallNoArgs(func)` only allocates 624 bytes per call.

- bpo-37170: Fix the cast on error in `PyLong_AsUnsignedLongLongMask()`.

- bpo-35381: Convert posixmodule.c statically allocated types `DirEntryType` and `ScandirIteratorType` to heap-allocated types.

- bpo-34331: Use singular/plural noun in error message when instantiating an abstract class with non-overriden abstract method(s).

## Python 3.8.0 beta 1

Release date: 2019-06-04

### Security

- bpo-35907: CVE-2019-9948: Avoid file reading by disallowing `local-file://` and `local_file://` URL schemes in `URLopener().open()` and `URLopener().retrieve()` of `urllib.request`.

- bpo-33529: Prevent fold function used in email header encoding from entering infinite loop when there are too many non-ASCII characters in a header.

- bpo-33164: Updated blake2 implementation which uses secure memset implementation provided by platform.

### Core and Builtins

- bpo-35814: Allow unpacking in the right hand side of annotated assignments. In particular, `t: Tuple[int, ...] = x, y, *z` is now allowed.

- bpo-37126: All structseq objects are now tracked by the garbage collector. Patch by Pablo Galindo.

- bpo-37122: Make the co_argcount attribute of code objects represent the total number of positional arguments (including positional-only arguments). The value of co_posonlyargcount can be used to distinguish which arguments are positional only, and the difference (co_argcount - co_posonlyargcount) is the number of positional-or-keyword arguments. Patch by Pablo Galindo.

- bpo-20092: Constructors of `int`, `float` and `complex` will now use the `__index__()` special method, if available and the corresponding method `__int__()`, `__float__()` or `__complex__()` is not available.

- bpo-37087: Add native thread ID (TID) support to OpenBSD.

- bpo-26219: Implemented per opcode cache mechanism and `LOAD_GLOBAL` instruction use it. `LOAD_GLOBAL` is now about 40% faster. Contributed by Yury Selivanov, and Inada Naoki.

- bpo-37072: Fix crash in PyAST_FromNodeObject() when flags is NULL.

- bpo-37029: Freeing a great many small objects could take time quadratic in the number of arenas, due to using linear search to keep `obmalloc.c`’s list of usable arenas sorted by order of number of free memory pools. This is accomplished without search now, leaving the worst-case time linear in the number of arenas. For programs where this quite visibly matters (typically with more than 100 thousand small objects alive simultaneously), this can greatly reduce the time needed to release their memory.

- bpo-26423: Fix possible overflow in `wrap_lenfunc()` when `sizeof(long) < sizeof(Py_ssize_t)` (e.g., 64-bit Windows).

- bpo-37050: Improve the AST for “debug” f-strings, which use ‘=’ to print out the source of the expression being evaluated. Delete expr_text from the FormattedValue node, and instead use a Constant string node (possibly merged with adjacent constant expressions inside the f-string).

- bpo-22385: The `bytes.hex`, `bytearray.hex`, and `memoryview.hex` methods as well as the `binascii.hexlify` and `b2a_hex` functions now have the ability to include an optional separator between hex bytes. This functionality was inspired by MicroPython’s hexlify implementation.

- bpo-26836: Add `os.memfd_create()`.

- bpo-37032: Added new `replace()` method to the code type (`types.CodeType`).

- bpo-37007: Implement `socket.if_nameindex()`, `socket.if_nametoindex()`, and `socket.if_indextoname()` on Windows.

- bpo-36829: `PyErr_WriteUnraisable()` now creates a traceback object if there is no current traceback. Moreover, call `PyErr_NormalizeException()` and `PyException_SetTraceback()` to normalize the exception value. Ignore any error.

- bpo-36878: Only accept text after `# type: ignore` if the first character is ASCII. This is to disallow things like `# type: ignoreé`.

- bpo-36878: Store text appearing after a `# type: ignore` comment in the AST. For example a type ignore like `# type: ignore[E1000]` will have the string `"[E1000]"` stored in its AST node.

- bpo-2180: Treat line continuation at EOF as a `SyntaxError` by Anthony Sottile.

- bpo-36907: Fix a crash when calling a C function with a keyword dict (`f(**kwargs)`) and changing the dict `kwargs` while that function is running.

- bpo-36946: Fix possible signed integer overflow when handling slices.

- bpo-36826: Add NamedExpression kind support to ast_unparse.c

- bpo-1875: A `SyntaxError` is now raised if a code blocks that will be optimized away (e.g. if conditions that are always false) contains syntax errors. Patch by Pablo Galindo.

- bpo-36027: Allow computation of modular inverses via three-argument `pow`: the second argument is now permitted to be negative in the case where the first and third arguments are relatively prime.

- bpo-36861: Update the Unicode database to version 12.1.0.

- bpo-28866: Avoid caching attributes of classes which type defines mro() to avoid a hard cache invalidation problem.

- bpo-36851: The `FrameType` stack is now correctly cleaned up if the execution ends with a return and the stack is not empty.

- bpo-34616: The `compile()` builtin functions now support the `ast.PyCF_ALLOW_TOP_LEVEL_AWAIT` flag, which allow to compile sources that contains top-level `await`, `async with` or `async for`. This is useful to evaluate async-code from with an already async functions; for example in a custom REPL.

- bpo-36842: Implement PEP 578, adding sys.audit, io.open_code and related APIs.

- bpo-27639: Correct return type for UserList slicing operations. Patch by Michael Blahay, Erick Cervantes, and vaultah

- bpo-36737: Move PyRuntimeState.warnings into per-interpreter state (via “module state”).

- bpo-36793: Removed `__str__` implementations from builtin types `bool`, `int`, `float`, `complex` and few classes from the standard library. They now inherit `__str__()` from `object`.

- bpo-36817: Add a `=` feature f-strings for debugging. This can precede `!s`, `!r`, or `!a`. It produces the text of the expression, followed by an equal sign, followed by the repr of the value of the expression. So `f'{3*9+15=}'` would be equal to the string `'3*9+15=42'`. If `=` is specified, the default conversion is set to `!r`, unless a format spec is given, in which case the formatting behavior is unchanged, and __format__ will be used.

- bpo-24048: Save the live exception during import.c’s `remove_module()`.

- bpo-27987: pymalloc returns memory blocks aligned by 16 bytes, instead of 8 bytes, on 64-bit platforms to conform x86-64 ABI. Recent compilers assume this alignment more often. Patch by Inada Naoki.

- bpo-36601: A long-since-meaningless check for `getpid() == main_pid` was removed from Python’s internal C signal handler.

- bpo-36594: Fix incorrect use of `%p` in format strings. Patch by Zackery Spytz.

- bpo-36045: builtins.help() now prefixes `async` for async functions

- bpo-36084: Add native thread ID (TID) to threading.Thread objects (supported platforms: Windows, FreeBSD, Linux, macOS)

- bpo-36035: Added fix for broken symlinks in combination with pathlib

- bpo-35983: Added new trashcan macros to deal with a double deallocation that could occur when the `tp_dealloc` of a subclass calls the `tp_dealloc` of a base class and that base class uses the trashcan mechanism. Patch by Jeroen Demeyer.

- bpo-20602: Do not clear `sys.flags` and `sys.float_info` during shutdown. Patch by Zackery Spytz.

- bpo-26826: Expose `copy_file_range()` as a low level API in the `os` module.

- bpo-32388: Remove cross-version binary compatibility requirement in tp_flags.

- bpo-31862: Port binascii to PEP 489 multiphase initialization. Patch by Marcel Plch.

### Library

- bpo-37128: Added `math.perm()`.

- bpo-37120: Add SSLContext.num_tickets to control the number of TLSv1.3 session tickets.

- bpo-12202: Fix the error handling in `msilib.SummaryInformation.GetProperty()`. Patch by Zackery Spytz.

- bpo-26835: The fcntl module now contains file sealing constants for sealing of memfds.

- bpo-29262: Add `get_origin()` and `get_args()` introspection helpers to `typing` module.

- bpo-12639: `msilib.Directory.start_component()` no longer fails if keyfile is not `None`.

- bpo-36999: Add the `asyncio.Task.get_coro()` method to publicly expose the tasks’s coroutine object.

- bpo-35246: Make `asyncio.create_subprocess_exec()` accept path-like arguments.

- bpo-35279: Change default max_workers of `ThreadPoolExecutor` from `cpu_count() * 5` to `min(32, cpu_count() + 4))`. Previous value was unreasonably large on many cores machines.

- bpo-37076: `_thread.start_new_thread()` now logs uncaught exception raised by the function using `sys.unraisablehook()`, rather than `sys.excepthook()`, so the hook gets access to the function which raised the exception.

- bpo-33725: On macOS, the `multiprocessing` module now uses spawn start method by default.

- bpo-37054: Fix destructor `_pyio.BytesIO` and `_pyio.TextIOWrapper`: initialize their `_buffer` attribute as soon as possible (in the class body), because it’s used by `__del__()` which calls `close()`.

- bpo-37058: PEP 544: Add `Protocol` and `@runtime_checkable` to the `typing` module.

- bpo-36933: The functions `sys.set_coroutine_wrapper` and `sys.get_coroutine_wrapper` that were deprecated and marked for removal in 3.8 have been removed.

- bpo-37047: Handle late binding and attribute access in `unittest.mock.AsyncMock` setup for autospeccing. Document newly implemented async methods in `unittest.mock.MagicMock`.

- bpo-37049: PEP 589: Add `TypedDict` to the `typing` module.

- bpo-37046: PEP 586: Add `Literal` to the `typing` module.

- bpo-37045: PEP 591: Add `Final` qualifier and `@final` decorator to the `typing` module.

- bpo-37035: Don’t log OSError based exceptions if a fatal error has occurred in asyncio transport. Peer can generate almost any OSError, user cannot avoid these exceptions by fixing own code. Errors are still propagated to user code, it’s just logging them is pointless and pollute asyncio logs.

- bpo-37001: `symtable.symtable()` now accepts the same input types for source code as the built-in `compile()` function. Patch by Dino Viehland.

- bpo-37028: Implement asyncio REPL

- bpo-37027: Return safe to use proxy socket object from transport.get_extra_info(‘socket’)

- bpo-32528: Make asyncio.CancelledError a BaseException.

  This will address the common mistake many asyncio users make: an “except Exception” clause breaking Tasks cancellation.

  In addition to this change, we stop inheriting asyncio.TimeoutError and asyncio.InvalidStateError from their concurrent.futures.* counterparts. There’s no point for these exceptions to share the inheritance chain.

- bpo-1230540: Add a new `threading.excepthook()` function which handles uncaught `threading.Thread.run()` exception. It can be overridden to control how uncaught `threading.Thread.run()` exceptions are handled.

- bpo-36996: Handle `unittest.mock.patch()` used as a decorator on async functions.

- bpo-37008: Add support for calling `next()` with the mock resulting from `unittest.mock.mock_open()`

- bpo-27737: Allow whitespace only header encoding in `email.header` - by Batuhan Taskaya

- bpo-36969: PDB command `args` now display positional only arguments. Patch contributed by Rémi Lapeyre.

- bpo-36969: PDB command `args` now display keyword only arguments. Patch contributed by Rémi Lapeyre.

- bpo-36983: Add missing names to `typing.__all__`: `ChainMap`, `ForwardRef`, `OrderedDict` - by Anthony Sottile.

- bpo-36972: Add SupportsIndex protocol to the typing module to allow type checking to detect classes that can be passed to `hex()`, `oct()` and `bin()`.

- bpo-32972: Implement `unittest.IsolatedAsyncioTestCase` to help testing asyncio-based code.

- bpo-36952: `fileinput.input()` and `fileinput.FileInput` bufsize argument has been removed (was deprecated and ignored since Python 3.6), and as a result the mode and openhook arguments have been made keyword-only.

- bpo-36952: Starting with Python 3.3, importing ABCs from `collections` is deprecated, and import should be done from `collections.abc`. Still being able to import from `collections` was marked for removal in 3.8, but has been delayed to 3.9; documentation and `DeprecationWarning` clarified.

- bpo-36949: Implement __repr__ for WeakSet objects.

- bpo-36948: Fix `NameError` in `urllib.request.URLopener.retrieve()`. Patch by Karthikeyan Singaravelan.

- bpo-33524: Fix the folding of email header when the max_line_length is 0 or None and the header contains non-ascii characters. Contributed by Licht Takeuchi (@Licht-T).

- bpo-24564: `shutil.copystat()` now ignores `errno.EINVAL` on `os.setxattr()` which may occur when copying files on filesystems without extended attributes support.

  Original patch by Giampaolo Rodola, updated by Ying Wang.

- bpo-36888: Python child processes can now access the status of their parent process using multiprocessing.process.parent_process

- bpo-36921: Deprecate `@coroutine` for sake of `async def`.

- bpo-25652: Fix bug in `__rmod__` of `UserString` - by Batuhan Taskaya.

- bpo-36916: Remove a message about an unhandled exception in a task when writer.write() is used without await and writer.drain() fails with an exception.

- bpo-36889: Introduce `asyncio.Stream` class that merges `asyncio.StreamReader` and `asyncio.StreamWriter` functionality. `asyncio.Stream` can work in readonly, writeonly and readwrite modes. Provide `asyncio.connect()`, `asyncio.connect_unix()`, `asyncio.connect_read_pipe()` and `asyncio.connect_write_pipe()` factories to open `asyncio.Stream` connections. Provide `asyncio.StreamServer` and `UnixStreamServer` to serve servers with asyncio.Stream API. Modify `asyncio.create_subprocess_shell()` and `asyncio.create_subprocess_exec()` to use `asyncio.Stream` instead of deprecated `StreamReader` and `StreamWriter`. Deprecate `asyncio.StreamReader` and `asyncio.StreamWriter`. Deprecate usage of private classes, e.g. `asyncio.FlowControlMixing` and `asyncio.StreamReaderProtocol` outside of asyncio package.

- bpo-36845: Added validation of integer prefixes to the construction of IP networks and interfaces in the ipaddress module.

- bpo-23378: Add an extend action to argparser.

- bpo-36867: Fix a bug making a SharedMemoryManager instance and its parent process use two separate resource_tracker processes.

- bpo-23896: Adds a grammar to lib2to3.pygram that contains exec as a function not as statement.

- bpo-36895: The function `time.clock()` was deprecated in 3.3 in favor of `time.perf_counter()` and marked for removal in 3.8, it has removed.

- bpo-35545: Fix asyncio discarding IPv6 scopes when ensuring hostname resolutions internally

- bpo-36887: Add new function `math.isqrt()` to compute integer square roots.

- bpo-34632: Introduce the `importlib.metadata` module with (provisional) support for reading metadata from third-party packages.

- bpo-36878: When using `type_comments=True` in `ast.parse`, treat `# type: ignore` followed by a non-alphanumeric character and then arbitrary text as a type ignore, instead of requiring nothing but whitespace or another comment. This is to permit formations such as `# type: ignore[E1000]`.

- bpo-36778: `cp65001` encoding (Windows code page 65001) becomes an alias to `utf_8` encoding.

- bpo-36867: The multiprocessing.resource_tracker replaces the multiprocessing.semaphore_tracker module. Other than semaphores, resource_tracker also tracks shared_memory segments.

- bpo-30262: The `Cache` and `Statement` objects of the `sqlite3` module are not exposed to the user. Patch by Aviv Palivoda.

- bpo-24538: In `shutil.copystat()`, first copy extended file attributes and then file permissions, since extended attributes can only be set on the destination while it is still writeable.

- bpo-36829: Add new `sys.unraisablehook()` function which can be overridden to control how “unraisable exceptions” are handled. It is called when an exception has occurred but there is no way for Python to handle it. For example, when a destructor raises an exception or during garbage collection (`gc.collect()`).

- bpo-36832: Introducing `zipfile.Path`, a pathlib-compatible wrapper for traversing zip files.

- bpo-36814: Fix an issue where os.posix_spawnp() would incorrectly raise a TypeError when file_actions is None.

- bpo-33110: Handle exceptions raised by functions added by concurrent.futures add_done_callback correctly when the Future has already completed.

- bpo-26903: Limit `max_workers` in `ProcessPoolExecutor` to 61 to work around a WaitForMultipleObjects limitation.

- bpo-36813: Fix `QueueListener` to call `queue.task_done()` upon stopping. Patch by Bar Harel.

- bpo-36806: Forbid creation of asyncio stream objects like StreamReader, StreamWriter, Process, and their protocols outside of asyncio package.

- bpo-36802: Provide both sync and async calls for StreamWriter.write() and StreamWriter.close()

- bpo-36801: Properly handle SSL connection closing in asyncio StreamWriter.drain() call.

- bpo-36785: Implement PEP 574 (pickle protocol 5 with out-of-band buffers).

- bpo-36772: functools.lru_cache() can now be used as a straight decorator in addition to its existing usage as a function that returns a decorator.

- bpo-6584: Add a `BadGzipFile` exception to the `gzip` module.

- bpo-36748: Optimized write buffering in C implementation of `TextIOWrapper`. Writing ASCII string to `TextIOWrapper` with ascii, latin1, or utf-8 encoding is about 20% faster. Patch by Inada Naoki.

- bpo-8138: Don’t mark `wsgiref.simple_server.SimpleServer` as multi-threaded since `wsgiref.simple_server.WSGIServer` is single-threaded.

- bpo-22640: `py_compile.compile()` now supports silent mode. Patch by Joannah Nanjekye

- bpo-29183: Fix double exceptions in `wsgiref.handlers.BaseHandler` by calling its `close()` method only when no exception is raised.

- bpo-36548: Improved the repr of regular expression flags.

- bpo-36542: The signature of Python functions can now be overridden by specifying the `__text_signature__` attribute.

- bpo-36533: Reinitialize logging.Handler locks in forked child processes instead of attempting to acquire them all in the parent before forking only to be released in the child process. The acquire/release pattern was leading to deadlocks in code that has implemented any form of chained logging handlers that depend upon one another as the lock acquisition order cannot be guaranteed.

- bpo-35252: Throw a TypeError instead of an AssertionError when using an invalid type annotation with singledispatch.

- bpo-35900: Allow reduction methods to return a 6-item tuple where the 6th item specifies a custom state-setting method that’s called instead of the regular `__setstate__` method.

- bpo-35900: enable custom reduction callback registration for functions and classes in _pickle.c, using the new Pickler’s attribute `reducer_override`

- bpo-36368: Fix a bug crashing SharedMemoryManager instances in interactive sessions after a ctrl-c (KeyboardInterrupt) was sent

- bpo-31904: Fix mmap fail for VxWorks

- bpo-27497: `csv.DictWriter.writeheader()` now returns the return value of the underlying `csv.Writer.writerow()` method. Patch contributed by Ashish Nitin Patil.

- bpo-36239: Parsing .mo files now ignores comments starting and ending with #-#-#-#-#.

- bpo-26707: Enable plistlib to read and write binary plist files that were created as a KeyedArchive file. Specifically, this allows the plistlib to process 0x80 tokens as UID objects.

- bpo-31904: Add posix module support for VxWorks.

- bpo-35125: Asyncio: Remove inner callback on outer cancellation in shield

- bpo-35721: Fix `asyncio.SelectorEventLoop.subprocess_exec()` leaks file descriptors if `Popen` fails and called with `stdin=subprocess.PIPE`. Patch by Niklas Fiekas.

- bpo-31855: `unittest.mock.mock_open()` results now respects the argument of read([size]). Patch contributed by Rémi Lapeyre.

- bpo-35431: Implement `math.comb()` that returns binomial coefficient, that computes the number of ways to choose k items from n items without repetition and without order. Patch by Yash Aggarwal and Keller Fuchs.

- bpo-26660: Fixed permission errors in `TemporaryDirectory` clean up. Previously `TemporaryDirectory.cleanup()` failed when non-writeable or non-searchable files or directories were created inside a temporary directory.

- bpo-34271: Add debugging helpers to ssl module. It’s now possible to dump key material and to trace TLS protocol. The default and stdlib contexts also support SSLKEYLOGFILE env var.

- bpo-26467: Added AsyncMock to support using unittest to mock asyncio coroutines. Patch by Lisa Roach.

- bpo-33569: dataclasses.InitVar: Exposes the type used to create the init var.

- bpo-34424: Fix serialization of messages containing encoded strings when the policy.linesep is set to a multi-character string. Patch by Jens Troeger.

- bpo-34303: Performance of `functools.reduce()` is slightly improved. Patch by Sergey Fedoseev.

- bpo-33361: Fix a bug in `codecs.StreamRecoder` where seeking might leave old data in a buffer and break subsequent read calls. Patch by Ammar Askar.

- bpo-22454: The `shlex` module now exposes `shlex.join()`, the inverse of `shlex.split()`. Patch by Bo Bayles.

- bpo-31922: `asyncio.AbstractEventLoop.create_datagram_endpoint()`: Do not connect UDP socket when broadcast is allowed. This allows to receive replies after a UDP broadcast.

- bpo-24882: Change ThreadPoolExecutor to use existing idle threads before spinning up new ones.

- bpo-31961: Added support for bytes and path-like objects in `subprocess.Popen()` on Windows. The args parameter now accepts a path-like object if shell is `False` and a sequence containing bytes and path-like objects. The executable parameter now accepts a bytes and path-like object. The cwd parameter now accepts a bytes object. Based on patch by Anders Lorentsen.

- bpo-33123: `pathlib.Path.unlink` now accepts a missing_ok parameter to avoid a `FileNotFoundError` from being raised. Patch by Robert Buchholz.

- bpo-32941: Allow `mmap.mmap` objects to access the madvise() system call (through `mmap.mmap.madvise()`).

- bpo-22102: Added support for ZIP files with disks set to 0. Such files are commonly created by builtin tools on Windows when use ZIP64 extension. Patch by Francisco Facioni.

- bpo-32515: trace.py can now run modules via python3 -m trace -t –module module_name

- bpo-32299: Changed `unittest.mock.patch.dict()` to return the patched dictionary when used as context manager. Patch by Vadim Tsander.

- bpo-27141: Added a `__copy__()` to `collections.UserList` and `collections.UserDict` in order to correctly implement shallow copying of the objects. Patch by Bar Harel.

- bpo-31829: `\r`, `\0` and `\x1a` (end-of-file on Windows) are now escaped in protocol 0 pickles of Unicode strings. This allows to load them without loss from files open in text mode in Python 2.

- bpo-23395: `_thread.interrupt_main()` now avoids setting the Python error status if the `SIGINT` signal is ignored or not handled by Python.

### Documentation

- bpo-36896: Clarify that some types have unstable constructor signature between Python versions.

- bpo-36686: Improve documentation of the stdin, stdout, and stderr arguments of the `asyncio.subprocess_exec` function to specify which values are supported. Also mention that decoding as text is not supported.

  Add a few tests to verify that the various values passed to the std* arguments actually work.

- bpo-36984: Improve version added references in `typing` module - by Anthony Sottile.

- bpo-36868: What’s new now mentions SSLContext.hostname_checks_common_name instead of SSLContext.host_flags.

- bpo-35924: Add a note to the `curses.addstr()` documentation to warn that multiline strings can cause segfaults because of an ncurses bug.

- bpo-36783: Added C API Documentation for Time_FromTimeAndFold and PyDateTime_FromDateAndTimeAndFold as per PEP 495. Patch by Edison Abahurire.

- bpo-36797: More of the legacy distutils documentation has been either pruned, or else more clearly marked as being retained solely until the setuptools documentation covers it independently.

- bpo-22865: Add detail to the documentation on the `pty.spawn` function.

- bpo-35397: Remove deprecation and document urllib.parse.unwrap(). Patch contributed by Rémi Lapeyre.

- bpo-32995: Added the context variable in glossary.

- bpo-33519: Clarify that `copy()` is not part of the `MutableSequence` ABC.

- bpo-33482: Make `codecs.StreamRecoder.writelines` take a list of bytes.

- bpo-25735: Added documentation for func factorial to indicate that returns integer values

- bpo-20285: Expand object.__doc__ (docstring) to make it clearer. Modify pydoc.py so that help(object) lists object methods (for other classes, help omits methods of the object base class.)

### Tests

- bpo-37069: Modify test_coroutines, test_cprofile, test_generators, test_raise, test_ssl and test_yield_from to use `test.support.catch_unraisable_exception()` rather than `test.support.captured_stderr()`.

- bpo-37098: Fix test_memfd_create on older Linux Kernels.

- bpo-37081: Test with OpenSSL 1.1.1c

- bpo-36829: Add `test.support.catch_unraisable_exception()`: context manager catching unraisable exception using `sys.unraisablehook()`.

- bpo-36915: The main regrtest process now always removes all temporary directories of worker processes even if they crash or if they are killed on KeyboardInterrupt (CTRL+c).

- bpo-36719: “python3 -m test -jN …” now continues the execution of next tests when a worker process crash (CHILD_ERROR state). Previously, the test suite stopped immediately. Use –failfast to stop at the first error.

- bpo-36816: Update Lib/test/selfsigned_pythontestdotnet.pem to match self-signed.pythontest.net’s new TLS certificate.

- bpo-35925: Skip httplib and nntplib networking tests when they would otherwise fail due to a modern OS or distro with a default OpenSSL policy of rejecting connections to servers with weak certificates.

- bpo-36782: Add tests for several C API functions in the `datetime` module. Patch by Edison Abahurire.

- bpo-36342: Fix test_multiprocessing in test_venv if platform lacks functioning sem_open.

### Build

- bpo-36721: To embed Python into an application, a new `--embed` option must be passed to `python3-config --libs --embed` to get `-lpython3.8` (link the application to libpython). To support both 3.8 and older, try `python3-config --libs --embed` first and fallback to `python3-config --libs` (without `--embed`) if the previous command fails.

  Add a pkg-config `python-3.8-embed` module to embed Python into an application: `pkg-config python-3.8-embed --libs` includes `-lpython3.8`. To support both 3.8 and older, try `pkg-config python-X.Y-embed --libs` first and fallback to `pkg-config python-X.Y --libs` (without `--embed`) if the previous command fails (replace `X.Y` with the Python version).

  On the other hand, `pkg-config python3.8 --libs` no longer contains `-lpython3.8`. C extensions must not be linked to libpython (except on Android, case handled by the script); this change is backward incompatible on purpose.

- bpo-36786: “make install” now runs compileall in parallel.

### Windows

- bpo-36965: include of STATUS_CONTROL_C_EXIT without depending on MSC compiler

- bpo-35926: Update to OpenSSL 1.1.1b for Windows.

- bpo-29883: Add Windows support for UDP transports for the Proactor Event Loop. Patch by Adam Meily.

- bpo-33407: The `Py_DEPRECATED()` macro has been implemented for MSVC.

### macOS

- bpo-36231: Support building Python on macOS without /usr/include installed. As of macOS 10.14, system header files are only available within an SDK provided by either the Command Line Tools or the Xcode app.

### IDLE

- bpo-35610: Replace now redundant .context_use_ps1 with .prompt_last_line. This finishes change started in bpo-31858.

- bpo-37038: Make idlelib.run runnable; add test clause.

- bpo-36958: Print any argument other than None or int passed to SystemExit or sys.exit().

- bpo-36807: When saving a file, call os.fsync() so bits are flushed to e.g. USB drive.

- bpo-32411: In browser.py, remove extraneous sorting by line number since dictionary was created in line number order.

### Tools/Demos

- bpo-37053: Handle strings like u”bar” correctly in Tools/parser/unparse.py. Patch by Chih-Hsuan Yen.

### C API

- bpo-36763: Implement the PEP 587 “Python Initialization Configuration”.

- bpo-36379: Fix crashes when attempting to use the modulo parameter when `__ipow__` is implemented in C.

- bpo-37107: Update `PyObject_CallMethodObjArgs()` and `_PyObject_CallMethodIdObjArgs` to use `_PyObject_GetMethod` to avoid creating a bound method object in many cases. Patch by Michael J. Sullivan.

- bpo-36974: Implement PEP 590: Vectorcall: a fast calling protocol for CPython. This is a new protocol to optimize calls of custom callable objects.

- bpo-36763: `Py_Main()` now returns the exitcode rather than calling `Py_Exit(exitcode)` when calling `PyErr_Print()` if the current exception type is `SystemExit`.

- bpo-36922: Add new type flag `Py_TPFLAGS_METHOD_DESCRIPTOR` for objects behaving like unbound methods. These are objects supporting the optimization given by the `LOAD_METHOD`/`CALL_METHOD` opcodes. See PEP 590.

- bpo-36728: The `PyEval_ReInitThreads()` function has been removed from the C API. It should not be called explicitly: use `PyOS_AfterFork_Child()` instead.

## Python 3.8.0 alpha 4

Release date: 2019-05-06

### Security

- bpo-36742: Fixes mishandling of pre-normalization characters in urlsplit().

- bpo-30458: Address CVE-2019-9740 by disallowing URL paths with embedded whitespace or control characters through into the underlying http client request. Such potentially malicious header injection URLs now cause an http.client.InvalidURL exception to be raised.

- bpo-35755: `shutil.which()` now uses `os.confstr("CS_PATH")` if available and if the `PATH` environment variable is not set. Remove also the current directory from `posixpath.defpath`. On Unix, `shutil.which()` and the `subprocess` module no longer search the executable in the current directory if the `PATH` environment variable is not set.

### Core and Builtins

- bpo-36722: In debug build, import now also looks for C extensions compiled in release mode and for C extensions compiled in the stable ABI.

- bpo-32849: Fix Python Initialization code on FreeBSD to detect properly when stdin file descriptor (fd 0) is invalid.

- bpo-36623: Remove parser headers and related function declarations that lack implementations after the removal of pgen.

- bpo-20180: `dict.pop()` is now up to 33% faster thanks to Argument Clinic. Patch by Inada Naoki.

- bpo-36611: Debug memory allocators: disable serialno field by default from debug hooks on Python memory allocators to reduce the memory footprint by 5%. Enable `tracemalloc` to get the traceback where a memory block has been allocated when a fatal memory error is logged to decide where to put a breakpoint. Compile Python with `PYMEM_DEBUG_SERIALNO` defined to get back the field.

- bpo-36588: On AIX, `sys.platform` doesn’t contain the major version anymore. Always return `'aix'`, instead of `'aix3'` .. `'aix7'`. Since older Python versions include the version number, it is recommended to always use `sys.platform.startswith('aix')`. Contributed by M. Felt.

- bpo-36549: Change str.capitalize to use titlecase for the first character instead of uppercase.

- bpo-36540: Implement PEP 570 (Python positional-only parameters). Patch by Pablo Galindo.

- bpo-36475: `PyEval_AcquireLock()` and `PyEval_AcquireThread()` now terminate the current thread if called while the interpreter is finalizing, making them consistent with `PyEval_RestoreThread()`, `Py_END_ALLOW_THREADS()`, and `PyGILState_Ensure()`.

- bpo-36504: Fix signed integer overflow in _ctypes.c’s `PyCArrayType_new()`.

- bpo-20844: Fix running script with encoding cookie and LF line ending may fail on Windows.

- bpo-24214: Fixed support of the surrogatepass error handler in the UTF-8 incremental decoder.

- bpo-36452: Changing `dict` keys during iteration of the dict itself, `keys()`, `values()`, or `items()` will now be detected in certain corner cases where keys are deleted/added so that the number of keys isn’t changed. A `RuntimeError` will be raised after `len(dict)` iterations. Contributed by Thomas Perl.

- bpo-36459: Fix a possible double `PyMem_FREE()` due to tokenizer.c’s `tok_nextc()`.

- bpo-36433: Fixed TypeError message in classmethoddescr_call.

- bpo-36430: Fix a possible reference leak in `itertools.count()`.

- bpo-36440: Include node names in `ParserError` messages, instead of numeric IDs. Patch by A. Skrobov.

- bpo-36143: Regenerate `keyword` from the Grammar and Tokens file using pgen. Patch by Pablo Galindo.

- bpo-18372: Add missing `PyObject_GC_Track()` calls in the `pickle` module. Patch by Zackery Spytz.

### Library

- bpo-35952: Fix pythoninfo when the compiler is missing.

- bpo-28238: The `.find*()` methods of xml.etree.ElementTree can now search for wildcards like `{*}tag` and `{ns}*` that match a tag in any namespace or all tags in a namespace. Patch by Stefan Behnel.

- bpo-26978: `pathlib.path.link_to()` is now implemented. It creates a hard link pointing to a path.

- bpo-1613500: `fileinput.FileInput` now uses the input file mode to correctly set the output file mode (previously it was hardcoded to `'w'`) when `inplace=True` is passed to its constructor.

- bpo-36734: Fix compilation of `faulthandler.c` on HP-UX. Initialize `stack_t current_stack` to zero using `memset()`.

- bpo-13611: The xml.etree.ElementTree packages gained support for C14N 2.0 serialisation. Patch by Stefan Behnel.

- bpo-36669: Add missing matrix multiplication operator support to weakref.proxy.

- bpo-36676: The XMLParser() in xml.etree.ElementTree provides namespace prefix context to the parser target if it defines the callback methods “start_ns()” and/or “end_ns()”. Patch by Stefan Behnel.

- bpo-36673: The TreeBuilder and XMLPullParser in xml.etree.ElementTree gained support for parsing comments and processing instructions. Patch by Stefan Behnel.

- bpo-36650: The C version of functools.lru_cache() was treating calls with an empty `**kwargs` dictionary as being distinct from calls with no keywords at all. This did not result in an incorrect answer, but it did trigger an unexpected cache miss.

- bpo-28552: Fix `distutils.sysconfig` if `sys.executable` is `None` or an empty string: use `os.getcwd()` to initialize `project_base`. Fix also the distutils build command: don’t use `sys.executable` if it is `None` or an empty string.

- bpo-35755: `shutil.which()` and `distutils.spawn.find_executable()` now use `os.confstr("CS_PATH")` if available instead of `os.defpath`, if the `PATH` environment variable is not set. Moreover, don’t use `os.confstr("CS_PATH")` nor `os.defpath` if the `PATH` environment variable is set to an empty string.

- bpo-25430: improve performance of `IPNetwork.__contains__()`

- bpo-30485: Path expressions in xml.etree.ElementTree can now avoid explicit namespace prefixes for tags (or the “{namespace}tag” notation) by passing a default namespace with an empty string prefix.

- bpo-36613: Fix `asyncio` wait() not removing callback if exception

- bpo-36598: Fix `isinstance` check for Mock objects with spec when the code is executed under tracing. Patch by Karthikeyan Singaravelan.

- bpo-18748: In development mode (`-X` `dev`) and in debug build, the `io.IOBase` destructor now logs `close()` exceptions. These exceptions are silent by default in release mode.

- bpo-36575: The `_lsprof` module now uses internal timer same to `time.perf_counter()` by default. `gettimeofday(2)` was used on Unix. New timer has better resolution on most Unix platforms and timings are no longer impacted by system clock updates since `perf_counter()` is monotonic. Patch by Inada Naoki.

- bpo-33461: `json.loads` now emits `DeprecationWarning` when `encoding` option is specified. Patch by Matthias Bussonnier.

- bpo-36559: The random module now prefers the lean internal _sha512 module over hashlib for seed(version=2) to optimize import time.

- bpo-17561: Set backlog=None as the default for socket.create_server.

- bpo-34373: Fix `time.mktime()` error handling on AIX for year before 1970.

- bpo-36232: Improve error message when trying to open existing DBM database that actually doesn’t exist. Patch by Marco Rougeth.

- bpo-36546: Add statistics.quantiles()

- bpo-36050: Optimized `http.client.HTTPResponse.read()` for large response. Patch by Inada Naoki.

- bpo-36522: If debuglevel is set to >0 in `http.client`, print all values for headers with multiple values for the same header name. Patch by Matt Houglum.

- bpo-36492: Deprecated passing required arguments like func as keyword arguments in functions which should accept arbitrary keyword arguments and pass them to other function. Arbitrary keyword arguments (even with names “self” and “func”) can now be passed to these functions if the required arguments are passed as positional arguments.

- bpo-27181: Add statistics.geometric_mean().

- bpo-30427: `os.path.normcase()` relies on `os.fspath()` to check the type of its argument. Redundant checks have been removed from its `posixpath.normcase()` and `ntpath.normcase()` implementations. Patch by Wolfgang Maier.

- bpo-36385: Stop rejecting IPv4 octets for being ambiguously octal. Leading zeros are ignored, and no longer are assumed to specify octal octets. Octets are always decimal numbers. Octets must still be no more than three digits, including leading zeroes.

- bpo-36434: Errors during writing to a ZIP file no longer prevent to properly close it.

- bpo-36407: Fixed wrong indentation writing for CDATA section in xml.dom.minidom. Patch by Vladimir Surjaninov.

- bpo-36326: inspect.getdoc() can now find docstrings for member objects when __slots__ is a dictionary.

- bpo-36366: Calling `stop()` on an unstarted or stopped `unittest.mock.patch()` object will now return `None` instead of raising `RuntimeError`, making the method idempotent. Patch by Karthikeyan Singaravelan.

- bpo-36348: The `imap.IMAP4.logout()` method no longer ignores silently arbitrary exceptions.

- bpo-31904: Add time module support and fix test_time faiures for VxWorks.

- bpo-36227: Added support for keyword arguments `default_namespace` and `xml_declaration` in functions ElementTree.tostring() and ElementTree.tostringlist().

- bpo-36004: Added new alternate constructors `datetime.date.fromisocalendar()` and `datetime.datetime.fromisocalendar()`, which construct date objects from ISO year, week number and weekday; these are the inverse of each class’s `isocalendar` method. Patch by Paul Ganssle.

- bpo-35936: `modulefinder` no longer depends on the deprecated `imp` module, and the initializer for `modulefinder.ModuleFinder` now has immutable default arguments. Patch by Brandt Bucher.

- bpo-35376: `modulefinder` correctly handles modules that have the same name as a bad package. Patch by Brandt Bucher.

- bpo-17396: `modulefinder` no longer crashes when encountering syntax errors in followed imports. Patch by Brandt Bucher.

- bpo-35934: Added `create_server()` and `has_dualstack_ipv6()` convenience functions to automate the necessary tasks usually involved when creating a server socket, including accepting both IPv4 and IPv6 connections on the same socket. (Contributed by Giampaolo Rodola in bpo-17561.)

- bpo-23078: Add support for `classmethod()` and `staticmethod()` to `unittest.mock.create_autospec()`. Initial patch by Felipe Ochoa.

- bpo-35416: Fix potential resource warnings in distutils. Patch by Mickaël Schoentgen.

- bpo-25451: Add transparency methods to `tkinter.PhotoImage`. Patch by Zackery Spytz.

- bpo-35082: Don’t return deleted attributes when calling dir on a `unittest.mock.Mock`.

- bpo-34547: `wsgiref.handlers.BaseHandler` now handles abrupt client connection terminations gracefully. Patch by Petter Strandmark.

- bpo-31658: `xml.sax.parse()` now supports path-like. Patch by Mickaël Schoentgen.

- bpo-34139: Remove stale unix datagram socket before binding

- bpo-33530: Implemented Happy Eyeballs in `asyncio.create_connection()`. Added two new arguments, happy_eyeballs_delay and interleave, to specify Happy Eyeballs behavior.

- bpo-33291: Do not raise AttributeError when calling the inspect functions isgeneratorfunction, iscoroutinefunction, isasyncgenfunction on a method created from an arbitrary callable. Instead, return False.

- bpo-31310: Fix the multiprocessing.semaphore_tracker so it is reused by child processes

- bpo-31292: Fix `setup.py check --restructuredtext` for files containing `include` directives.

### Documentation

- bpo-36625: Remove obsolete comments from docstrings in fractions.Fraction

- bpo-30840: Document relative imports

- bpo-36523: Add docstring for io.IOBase.writelines().

- bpo-36425: New documentation translation: Simplified Chinese.

- bpo-36345: Avoid the duplication of code from `Tools/scripts/serve.py` in using the `literalinclude` directive for the basic wsgiref-based web server in the documentation of `wsgiref`. Contributed by Stéphane Wirtel.

- bpo-36345: Using the code of the `Tools/scripts/serve.py` script as an example in the `wsgiref` documentation. Contributed by Stéphane Wirtel.

- bpo-36157: Added Documention for PyInterpreterState_Main().

- bpo-33043: Updates the docs.python.org page with the addition of a ‘Contributing to Docs’ link at the end of the page (between ‘Reporting Bugs’ and ‘About Documentation’). Updates the ‘Found a Bug’ page with additional links and information in the Documentation Bugs section.

- bpo-35581: @typing.type_check_only now allows type stubs to mark functions and classes not available during runtime.

- bpo-33832: Add glossary entry for ‘magic method’.

- bpo-32913: Added re.Match.groupdict example to regex HOWTO.

### Tests

- bpo-36719: regrtest now always detects uncollectable objects. Previously, the check was only enabled by `--findleaks`. The check now also works with `-jN/--multiprocess N`. `--findleaks` becomes a deprecated alias to `--fail-env-changed`.

- bpo-36725: When using multiprocessing mode (-jN), regrtest now better reports errors if a worker process fails, and it exits immediately on a worker thread failure or when interrupted.

- bpo-36454: Change test_time.test_monotonic() to test only the lower bound of elapsed time after a sleep command rather than the upper bound. This prevents unnecessary test failures on slow buildbots. Patch by Victor Stinner.

- bpo-32424: Improve test coverage for xml.etree.ElementTree. Patch by Gordon P. Hemsley.

- bpo-32424: Fix typo in test_cyclic_gc() test for xml.etree.ElementTree. Patch by Gordon P. Hemsley.

- bpo-36635: Add a new `_testinternalcapi` module to test the internal C API.

- bpo-36629: Fix `test_imap4_host_default_value()` of `test_imaplib`: catch also `errno.ENETUNREACH` error.

- bpo-36611: Fix `test_sys.test_getallocatedblocks()` when `tracemalloc` is enabled.

- bpo-36560: Fix reference leak hunting in regrtest: compute also deltas (of reference count, allocated memory blocks, file descriptor count) during warmup, to ensure that everything is initialized before starting to hunt reference leaks.

- bpo-36565: Fix reference hunting (`python3 -m test -R 3:3`) when Python has no built-in abc module.

- bpo-31904: Port test_resource to VxWorks: skip tests cases setting RLIMIT_FSIZE and RLIMIT_CPU.

- bpo-31904: Fix test_tabnanny on VxWorks: adjust ENOENT error message.

- bpo-36436: Fix `_testcapi.pymem_buffer_overflow()`: handle memory allocation failure.

- bpo-31904: Fix test_utf8_mode on VxWorks: Python always use UTF-8 on VxWorks.

- bpo-36341: Fix tests that may fail with PermissionError upon calling bind() on AF_UNIX sockets.

### Build

- bpo-36747: Remove the stale scriptsinstall Makefile target.

- bpo-21536: On Unix, C extensions are no longer linked to libpython except on Android and Cygwin.

  It is now possible for a statically linked Python to load a C extension built using a shared library Python.

  When Python is embedded, `libpython` must not be loaded with `RTLD_LOCAL`, but `RTLD_GLOBAL` instead. Previously, using `RTLD_LOCAL`, it was already not possible to load C extensions which were not linked to `libpython`, such as C extensions of the standard library built by the `*shared*` section of `Modules/Setup`.

  distutils, python-config and python-config.py have been modified.

- bpo-36707: `./configure --with-pymalloc` no longer adds the `m` flag to SOABI (sys.implementation.cache_tag). Enabling or disabling pymalloc has no impact on the ABI.

- bpo-36635: Change `PyAPI_FUNC(type)`, `PyAPI_DATA(type)` and `PyMODINIT_FUNC` macros of `pyport.h` when `Py_BUILD_CORE_MODULE` is defined. The `Py_BUILD_CORE_MODULE` define must be now be used to build a C extension as a dynamic library accessing Python internals: export the PyInit_xxx() function in DLL exports on Windows.

- bpo-31904: Don’t build the `_crypt` extension on VxWorks.

- bpo-36618: Add `-fmax-type-align=8` to CFLAGS when clang compiler is detected. The pymalloc memory allocator aligns memory on 8 bytes. On x86-64, clang expects alignment on 16 bytes by default and so uses MOVAPS instruction which can lead to segmentation fault. Instruct clang that Python is limited to alignment on 8 bytes to use MOVUPS instruction instead: slower but don’t trigger a SIGSEGV if the memory is not aligned on 16 bytes. Sadly, the flag must be added to `CFLAGS` and not just `CFLAGS_NODIST`, since third party C extensions can have the same issue.

- bpo-36605: `make tags` and `make TAGS` now also parse `Modules/_io/*.c` and `Modules/_io/*.h`.

- bpo-36465: Release builds and debug builds are now ABI compatible: defining the `Py_DEBUG` macro no longer implies the `Py_TRACE_REFS` macro, which introduces the only ABI incompatibility. The `Py_TRACE_REFS` macro, which adds the `sys.getobjects()` function and the `PYTHONDUMPREFS` environment variable, can be set using the new `./configure --with-trace-refs` build option.

- bpo-36577: setup.py now correctly reports missing OpenSSL headers and libraries again.

- bpo-36544: Fix regression introduced in bpo-36146 refactoring setup.py

- bpo-36508: `python-config --ldflags` no longer includes flags of the `LINKFORSHARED` variable. The `LINKFORSHARED` variable must only be used to build executables.

- bpo-36503: Remove references to “aix3” and “aix4”. Patch by M. Felt.

### Windows

- bpo-35920: Added platform.win32_edition() and platform.win32_is_iot(). Added support for cross-compiling packages for Windows ARM32. Skip tests that are not expected to work on Windows IoT Core ARM32.

- bpo-36649: Remove trailing spaces for registry keys when installed via the Store.

- bpo-34144: Fixed activate.bat to correctly update codepage when chcp.com returns dots in output. Patch by Lorenz Mende.

- bpo-36509: Added preset-iot layout for Windows IoT ARM containers. This layout doesn’t contain UI components like tkinter or IDLE. It also doesn’t contain files to support on-target builds since Windows ARM32 builds must be cross-compiled when using MSVC.

- bpo-35941: enum_certificates function of the ssl module now returns certificates from all available certificate stores inside windows in a query instead of returning only certificates from the system wide certificate store. This includes certificates from these certificate stores: local machine, local machine enterprise, local machine group policy, current user, current user group policy, services, users. ssl.enum_crls() function is changed in the same way to return all certificate revocation lists inside the windows certificate revocation list stores.

- bpo-36441: Fixes creating a venv when debug binaries are installed.

- bpo-36085: Enable better DLL resolution on Windows by using safe DLL search paths and adding `os.add_dll_directory()`.

- bpo-36010: Add the venv standard library module to the nuget distribution for Windows.

- bpo-29515: Add the following socket module constants on Windows: IPPROTO_AH IPPROTO_CBT IPPROTO_DSTOPTS IPPROTO_EGP IPPROTO_ESP IPPROTO_FRAGMENT IPPROTO_GGP IPPROTO_HOPOPTS IPPROTO_ICLFXBM IPPROTO_ICMPV6 IPPROTO_IDP IPPROTO_IGMP IPPROTO_IGP IPPROTO_IPV4 IPPROTO_IPV6 IPPROTO_L2TP IPPROTO_MAX IPPROTO_ND IPPROTO_NONE IPPROTO_PGM IPPROTO_PIM IPPROTO_PUP IPPROTO_RDP IPPROTO_ROUTING IPPROTO_SCTP IPPROTO_ST

- bpo-35947: Added current version of libffi to cpython-source-deps. Change _ctypes to use current version of libffi on Windows.

- bpo-34060: Report system load when running test suite on Windows. Patch by Ammar Askar. Based on prior work by Jeremy Kloth.

- bpo-31512: With the Windows 10 Creators Update, non-elevated users can now create symlinks as long as the computer has Developer Mode enabled.

### macOS

- bpo-34602: Avoid failures setting macOS stack resource limit with resource.setrlimit. This reverts an earlier fix for bpo-18075 which forced a non-default stack size when building the interpreter executable on macOS.

### IDLE

- bpo-36429: Fix starting IDLE with pyshell. Add idlelib.pyshell alias at top; remove pyshell alias at bottom. Remove obsolete __name__==’__main__’ command.

### Tools/Demos

- bpo-14546: Fix the argument handling in Tools/scripts/lll.py.

### C API

- bpo-36763: Fix memory leak in `Py_SetStandardStreamEncoding()`: release memory if the function is called twice.

- bpo-36641: `PyDoc_VAR(name)` and `PyDoc_STRVAR(name,str)` now create `static const char name[]` instead of `static char name[]`. Patch by Inada Naoki.

- bpo-36389: Change the value of `CLEANBYTE`, `DEADDYTE` and `FORBIDDENBYTE` internal constants used by debug hooks on Python memory allocators (`PyMem_SetupDebugHooks()` function). Byte patterns `0xCB`, `0xDB` and `0xFB` have been replaced with `0xCD`, `0xDD` and `0xFD` to use the same values than Windows CRT debug `malloc()` and `free()`.

- bpo-36443: Since Python 3.7.0, calling `Py_DecodeLocale()` before `Py_Initialize()` produces mojibake if the `LC_CTYPE` locale is coerced and/or if the UTF-8 Mode is enabled by the user configuration. The LC_CTYPE coercion and UTF-8 Mode are now disabled by default to fix the mojibake issue. They must now be enabled explicitly (opt-in) using the new `_Py_PreInitialize()` API with `_PyPreConfig`.

- bpo-36025: Fixed an accidental change to the datetime C API where the arguments to the `PyDate_FromTimestamp()` function were incorrectly interpreted as a single timestamp rather than an arguments tuple, which causes existing code to start raising `TypeError`. The backwards-incompatible change was only present in alpha releases of Python 3.8. Patch by Paul Ganssle.

- bpo-35810: Modify `PyObject_Init` to correctly increase the refcount of heap- allocated Type objects. Also fix the refcounts of the heap-allocated types that were either doing this manually or not decreasing the type’s refcount in tp_dealloc

## Python 3.8.0 alpha 3

Release date: 2019-03-25

### Security

- bpo-36216: Changes urlsplit() to raise ValueError when the URL contains characters that decompose under IDNA encoding (NFKC-normalization) into characters that affect how the URL is parsed.

- bpo-35121: Don’t send cookies of domain A without Domain attribute to domain B when domain A is a suffix match of domain B while using a cookiejar with `http.cookiejar.DefaultCookiePolicy` policy. Patch by Karthikeyan Singaravelan.

### Core and Builtins

- bpo-36421: Fix a possible double decref in _ctypes.c’s `PyCArrayType_new()`.

- bpo-36412: Fix a possible crash when creating a new dictionary.

- bpo-36398: Fix a possible crash in `structseq_repr()`.

- bpo-36256: Fix bug in parsermodule when parsing a state in a DFA that has two or more arcs with labels of the same type. Patch by Pablo Galindo.

- bpo-36365: repr(structseq) is no longer limited to 512 bytes.

- bpo-36374: Fix a possible null pointer dereference in `merge_consts_recursive()`. Patch by Zackery Spytz.

- bpo-36236: At Python initialization, the current directory is no longer prepended to `sys.path` if it has been removed.

- bpo-36352: Python initialization now fails with an error, rather than silently truncating paths, if a path is too long.

- bpo-36301: Python initialization now fails if decoding `pybuilddir.txt` configuration file fails at startup.

- bpo-36333: Fix leak in _PyRuntimeState_Fini. Contributed by Stéphane Wirtel.

- bpo-36332: The builtin `compile()` can now handle AST objects that contain assignment expressions. Patch by Pablo Galindo.

- bpo-36282: Improved error message for too much positional arguments in some builtin functions.

- bpo-30040: New empty dict uses fewer memory for now. It used more memory than empty dict created by `dict.clear()`. And empty dict creation and deletion is about 2x faster. Patch by Inada Naoki.

- bpo-36262: Fix an unlikely memory leak on conversion from string to float in the function `_Py_dg_strtod()` used by `float(str)`, `complex(str)`, `pickle.load()`, `marshal.load()`, etc.

- bpo-36252: Update Unicode databases to version 12.0.0.

- bpo-36218: Fix a segfault occurring when sorting a list of heterogeneous values. Patch contributed by Rémi Lapeyre and Elliot Gorokhovsky.

- bpo-36188: Cleaned up left-over vestiges of Python 2 unbound method handling in method objects and documentation. Patch by Martijn Pieters

- bpo-36124: Add a new interpreter-specific dict and expose it in the C-API via PyInterpreterState_GetDict(). This parallels PyThreadState_GetDict(). However, extension modules should continue using PyModule_GetState() for their own internal per-interpreter state.

- bpo-35975: Add a `feature_version` flag to `ast.parse()` (documented) and `compile()` (hidden) that allows tweaking the parser to support older versions of the grammar. In particular, if `feature_version` is 5 or 6, the hacks for the `async` and `await` keyword from PEP 492 are reinstated. (For 7 or higher, these are unconditionally treated as keywords, but they are still special tokens rather than `NAME` tokens that the parser driver recognizes.)

- bpo-31904: Use UTF-8 as the system encoding on VxWorks.

- bpo-36048: The `__index__()` special method will be used instead of `__int__()` for implicit conversion of Python numbers to C integers. Using the `__int__()` method in implicit conversions has been deprecated.

- bpo-35808: Retire pgen and use a modified version of pgen2 to generate the parser. Patch by Pablo Galindo.

### Library

- bpo-36401: The class documentation created by pydoc now has a separate section for readonly properties.

- bpo-36320: The typing.NamedTuple() class has deprecated the _field_types attribute in favor of the __annotations__ attribute which carried the same information. Also, both attributes were converted from OrderedDict to a regular dict.

- bpo-34745: Fix `asyncio` ssl memory issues caused by circular references

- bpo-36324: Add method to statistics.NormalDist for computing the inverse cumulative normal distribution.

- bpo-36321: collections.namedtuple() misspelled the name of an attribute. To be consistent with typing.NamedTuple, the attribute name should have been “_field_defaults” instead of “_fields_defaults”. For backwards compatibility, both spellings are now created. The misspelled version may be removed in the future.

- bpo-36297: “unicode_internal” codec is removed. It was deprecated since Python 3.3. Patch by Inada Naoki.

- bpo-36298: Raise ModuleNotFoundError in pyclbr when a module can’t be found. Thanks to ‘mental’ for the bug report.

- bpo-36268: Switch the default format used for writing tars with mod:`tarfile` to the modern POSIX.1-2001 pax standard, from the vendor-specific GNU. Contributed by C.A.M. Gerlach.

- bpo-36285: Fix integer overflows in the array module. Patch by Stephan Hohe.

- bpo-31904: Add _signal module support for VxWorks.

- bpo-36272: `logging` does not silently ignore RecursionError anymore. Patch contributed by Rémi Lapeyre.

- bpo-36280: Add a kind field to ast.Constant. It is ‘u’ if the literal has a ‘u’ prefix (i.e. a Python 2 style unicode literal), else None.

- bpo-35931: The `pdb` `debug` command now gracefully handles all exceptions.

- bpo-36251: Fix format strings used for stderrprinter and re.Match reprs. Patch by Stephan Hohe.

- bpo-36235: Fix `CFLAGS` in `customize_compiler()` of `distutils.sysconfig`: when the `CFLAGS` environment variable is defined, don’t override `CFLAGS` variable with the `OPT` variable anymore. Initial patch written by David Malcolm.

- bpo-35807: Update ensurepip to install pip 19.0.3 and setuptools 40.8.0.

- bpo-36139: Release GIL when closing `mmap` objects.

- bpo-36179: Fix two unlikely reference leaks in _hashopenssl. The leaks only occur in out-of-memory cases.

- bpo-36169: Add overlap() method to statistics.NormalDist. Computes the overlapping coefficient for two normal distributions.

- bpo-36103: Default buffer size used by `shutil.copyfileobj()` is changed from 16 KiB to 64 KiB on non-Windows platform to reduce system call overhead. Contributed by Inada Naoki.

- bpo-36130: Fix `pdb` with `skip=...` when stepping into a frame without a `__name__` global. Patch by Anthony Sottile.

- bpo-35652: shutil.copytree(copy_function=…) erroneously pass DirEntry instead of a path string.

- bpo-35178: Ensure custom `warnings.formatwarning()` function can receive `line` as positional argument. Based on patch by Tashrif Billah.

- bpo-36106: Resolve potential name clash with libm’s sinpi(). Patch by Dmitrii Pasechnik.

- bpo-36091: Clean up reference to async generator in Lib/types. Patch by Henry Chen.

- bpo-36043: `FileCookieJar` supports path-like object. Contributed by Stéphane Wirtel

- bpo-35899: Enum has been fixed to correctly handle empty strings and strings with non-Latin characters (ie. ‘α’, ‘א’) without crashing. Original patch contributed by Maxwell. Assisted by Stéphane Wirtel.

- bpo-21269: Add `args` and `kwargs` properties to mock call objects. Contributed by Kumar Akshay.

- bpo-30670: `pprint.pp` has been added to pretty-print objects with dictionary keys being sorted with their insertion order by default. Parameter sort_dicts has been added to `pprint.pprint`, `pprint.pformat` and `pprint.PrettyPrinter`. Contributed by Rémi Lapeyre.

- bpo-35843: Implement `__getitem__` for `_NamespacePath`. Patch by Anthony Sottile.

- bpo-35802: Clean up code which checked presence of `os.stat` / `os.lstat` / `os.chmod` which are always present. Patch by Anthony Sottile.

- bpo-35715: Librates the return value of a ProcessPoolExecutor _process_worker after it’s no longer needed to free memory

- bpo-35493: Use `multiprocessing.connection.wait()` instead of polling each 0.2 seconds for worker updates in `multiprocessing.Pool`. Patch by Pablo Galindo.

- bpo-35661: Store the venv prompt in pyvenv.cfg.

- bpo-35121: Don’t set cookie for a request when the request path is a prefix match of the cookie’s path attribute but doesn’t end with “/”. Patch by Karthikeyan Singaravelan.

- bpo-21478: Calls to a child function created with `unittest.mock.create_autospec()` should propagate to the parent. Patch by Karthikeyan Singaravelan.

- bpo-35198: Fix C++ extension compilation on AIX

### Documentation

- bpo-36329: Declare the path of the Python binary for the usage of `Tools/scripts/serve.py` when executing `make -C Doc/ serve`. Contributed by Stéphane Wirtel

- bpo-36138: Improve documentation about converting datetime.timedelta to scalars.

- bpo-21314: A new entry was added to the Core Language Section of the Programming FAQ, which explaines the usage of slash(/) in the signature of a function. Patch by Lysandros Nikolaou

### Tests

- bpo-36234: test_posix.PosixUidGidTests: add tests for invalid uid/gid type (str). Initial patch written by David Malcolm.

- bpo-29571: Fix `test_re.test_locale_flag()`: use `locale.getpreferredencoding()` rather than `locale.getlocale()` to get the locale encoding. With some locales, `locale.getlocale()` returns the wrong encoding.

- bpo-36123: Fix race condition in test_socket.

### Build

- bpo-36356: Fix leaks that led to build failure when configured with address sanitizer.

- bpo-36146: Add `TEST_EXTENSIONS` constant to `setup.py` to allow to not build test extensions like `_testcapi`.

- bpo-36146: Fix setup.py on macOS: only add `/usr/include/ffi` to include directories of _ctypes, not for all extensions.

- bpo-31904: Enable build system to cross-build for VxWorks RTOS.

### Windows

- bpo-36312: Fixed decoders for the following code pages: 50220, 50221, 50222, 50225, 50227, 50229, 57002 through 57011, 65000 and 42.

- bpo-36264: Don’t honor POSIX `HOME` in `os.path.expanduser` on windows. Patch by Anthony Sottile.

- bpo-24643: Fix name collisions due to `#define timezone _timezone` in PC/pyconfig.h.

### IDLE

- bpo-36405: Use dict unpacking in idlelib.

- bpo-36396: Remove fgBg param of idlelib.config.GetHighlight(). This param was only used twice and changed the return type.

- bpo-36176: Fix IDLE autocomplete & calltip popup colors. Prevent conflicts with Linux dark themes (and slightly darken calltip background).

- bpo-23205: For the grep module, add tests for findfiles, refactor findfiles to be a module-level function, and refactor findfiles to use os.walk.

- bpo-23216: Add docstrings to IDLE search modules.

- bpo-36152: Remove colorizer.ColorDelegator.close_when_done and the corresponding argument of .close(). In IDLE, both have always been None or False since 2007.

- bpo-32129: Avoid blurry IDLE application icon on macOS with Tk 8.6. Patch by Kevin Walzer.

- bpo-36096: Refactor class variables to instance variables in colorizer.

- bpo-30348: Increase test coverage of idlelib.autocomplete by 30%. Patch by Louie Lu

### Tools/Demos

- bpo-35132: Fix py-list and py-bt commands of python-gdb.py on gdb7.

- bpo-32217: Fix freeze script on Windows.

### C API

- bpo-36381: Raise `DeprecationWarning` when ‘#’ formats are used for building or parsing values without `PY_SSIZE_T_CLEAN`.

- bpo-36142: The whole coreconfig.h header is now excluded from Py_LIMITED_API. Move functions definitions into a new internal pycore_coreconfig.h header.

## Python 3.8.0 alpha 2

Release date: 2019-02-25

### Core and Builtins

- bpo-36052: Raise a `SyntaxError` when assigning a value to `__debug__` with the Assignment Operator. Contributed by Stéphane Wirtel and Pablo Galindo.

- bpo-36012: Doubled the speed of class variable writes. When a non-dunder attribute was updated, there was an unnecessary call to update slots.

- bpo-35942: The error message emitted when returning invalid types from `__fspath__` in interfaces that allow passing `PathLike` objects has been improved and now it does explain the origin of the error.

- bpo-36016: `gc.get_objects` can now receive an optional parameter indicating a generation to get objects from. Patch by Pablo Galindo.

- bpo-1054041: When the main interpreter exits due to an uncaught KeyboardInterrupt, the process now exits in the appropriate manner for its parent process to detect that a SIGINT or ^C terminated the process. This allows shells and batch scripts to understand that the user has asked them to stop.

- bpo-35992: Fix `__class_getitem__()` not being called on a class with a custom non-subscriptable metaclass.

- bpo-35993: Fix a crash on fork when using subinterpreters. Contributed by Stéphane Wirtel

- bpo-35991: Fix a potential double free in Modules/_randommodule.c.

- bpo-35961: Fix a crash in slice_richcompare(): use strong references rather than stolen references for the two temporary internal tuples.

- bpo-35911: Enable the creation of cell objects by adding a `cell.__new__` method, and expose the type `cell` in `Lib/types.py` under the name CellType. Patch by Pierre Glaser.

- bpo-12822: Use monotonic clock for `pthread_cond_timedwait` when `pthread_condattr_setclock` and `CLOCK_MONOTONIC` are available.

- bpo-15248: The compiler emits now syntax warnings in the case when a comma is likely missed before tuple or list.

- bpo-35886: The implementation of PyInterpreterState has been moved into the internal header files (guarded by Py_BUILD_CORE).

- bpo-31506: Clarify the errors reported when `object.__new__` and `object.__init__` receive more than one argument. Contributed by Sanyam Khurana.

- bpo-35724: Signal-handling is now guaranteed to happen relative to the main interpreter.

- bpo-33608: We added a new internal _Py_AddPendingCall() that operates relative to the provided interpreter. This allows us to use the existing implementation to ask another interpreter to do work that cannot be done in the current interpreter, like decref an object the other interpreter owns. The existing Py_AddPendingCall() only operates relative to the main interpreter.

- bpo-33989: Fix a possible crash in `list.sort()` when sorting objects with `ob_type->tp_richcompare == NULL`. Patch by Zackery Spytz.

### Library

- bpo-35512: `unittest.mock.patch.dict()` used as a decorator with string target resolves the target during function call instead of during decorator construction. Patch by Karthikeyan Singaravelan.

- bpo-36018: Add statistics.NormalDist, a tool for creating and manipulating normal distributions of random variable. Features a composite class that treats the mean and standard deviation of measurement data as single entity.

- bpo-35904: Added statistics.fmean() as a faster, floating point variant of the existing mean() function.

- bpo-35918: Removed broken `has_key` method from multiprocessing.managers.SyncManager.dict. Contributed by Rémi Lapeyre.

- bpo-18283: Add support for bytes to `shutil.which()`.

- bpo-35960: Fix `dataclasses.field()` throwing away empty mapping objects passed as metadata.

- bpo-35500: Write expected and actual call parameters on separate lines in `unittest.mock.Mock.assert_called_with()` assertion errors. Contributed by Susan Su.

- bpo-35931: The `pdb` `debug` command now gracefully handles syntax errors.

- bpo-24209: In http.server script, rely on getaddrinfo to bind to preferred address based on the bind parameter. Now default bind or binding to a name may bind to IPv6 or dual-stack, depending on the environment.

- bpo-35321: Set `__spec__.origin` of `_frozen_importlib` to frozen so that it matches the behavior of `_frozen_importlib_external`. Patch by Nina Zakharenko.

- bpo-35378: Fix a reference issue inside `multiprocessing.Pool` that caused the pool to remain alive if it was deleted without being closed or terminated explicitly. A new strong reference is added to the pool iterators to link the lifetime of the pool to the lifetime of its iterators so the pool does not get destroyed if a pool iterator is still alive.

- bpo-34294: re module, fix wrong capturing groups in rare cases. `re.search()`, `re.findall()`, `re.sub()` and other functions that scan through string looking for a match, should reset capturing groups between two match attempts. Patch by Ma Lin.

- bpo-35615: `weakref`: Fix a RuntimeError when copying a WeakKeyDictionary or a WeakValueDictionary, due to some keys or values disappearing while iterating.

- bpo-35606: Implement `math.prod()` as analogous function to `sum()` that returns the product of a ‘start’ value (default: 1) times an iterable of numbers. Patch by Pablo Galindo.

- bpo-32417: Performing arithmetic between `datetime.datetime` subclasses and `datetime.timedelta` now returns an object of the same type as the `datetime.datetime` subclass. As a result, `datetime.datetime.astimezone()` and alternate constructors like `datetime.datetime.now()` and `datetime.fromtimestamp()` called with a `tz` argument now also retain their subclass.

- bpo-35153: Add headers optional keyword-only parameter to `xmlrpc.client.ServerProxy`, `xmlrpc.client.Transport` and `xmlrpc.client.SafeTransport`. Patch by Cédric Krier.

- bpo-34572: Fix C implementation of pickle.loads to use importlib’s locking mechanisms, and thereby avoid using partially-loaded modules. Patch by Tim Burgess.

### Documentation

- bpo-36083: Fix formatting of –check-hash-based-pycs options in the manpage Synopsis.

- bpo-36007: Bump minimum sphinx version to 1.8. Patch by Anthony Sottile.

- bpo-22062: Update documentation and docstrings for pathlib. Original patch by Mike Short.

### Tests

- bpo-27313: Avoid test_ttk_guionly ComboboxTest failure with macOS Cocoa Tk.

- bpo-36019: Add test.support.TEST_HTTP_URL and replace references of http://www.example.com by this new constant. Contributed by Stéphane Wirtel.

- bpo-36037: Fix test_ssl for strict OpenSSL configuration like RHEL8 strict crypto policy. Use older TLS version for minimum TLS version of the server SSL context if needed, to test TLS version older than default minimum TLS version.

- bpo-35798: Added `test.support.check_syntax_warning()`.

- bpo-35505: Make test_imap4_host_default_value independent on whether the local IMAP server is running.

- bpo-35917: multiprocessing: provide unit tests for SyncManager and SharedMemoryManager classes + all the shareable types which are supposed to be supported by them. (patch by Giampaolo Rodola)

- bpo-35704: Skip `test_shutil.test_unpack_archive_xztar` to prevent a MemoryError on 32-bit AIX when MAXDATA setting is less than 0x20000000.

  Patch by Michael Felt (aixtools)

- bpo-34720: Assert m_state != NULL to mimic GC traversal functions that do not correctly handle module creation when the module state has not been created.

### Windows

- bpo-35976: Added ARM build support to Windows build files in PCBuild.

- bpo-35692: `pathlib` no longer raises when checking file and directory existence on drives that are not ready

- bpo-35872: Uses the base Python executable when invoking venv in a virtual environment

- bpo-35873: Prevents venv paths being inherited by child processes

- bpo-35299: Fix sysconfig detection of the source directory and distutils handling of pyconfig.h during PGO profiling

### IDLE

- bpo-24310: IDLE – Document settings dialog font tab sample.

- bpo-35833: Revise IDLE doc for control codes sent to Shell. Add a code example block.

- bpo-35689: Add docstrings and unittests for colorizer.py.

## Python 3.8.0 alpha 1

Release date: 2019-02-03

### Security

- bpo-35746: [CVE-2019-5010] Fix a NULL pointer deref in ssl module. The cert parser did not handle CRL distribution points with empty DP or URI correctly. A malicious or buggy certificate can result into segfault. Vulnerability (TALOS-2018-0758) reported by Colin Read and Nicolas Edet of Cisco.

- bpo-34812: The `-I` command line option (run Python in isolated mode) is now also copied by the `multiprocessing` and `distutils` modules when spawning child processes. Previously, only `-E` and `-s` options (enabled by `-I`) were copied.

- bpo-34791: The xml.sax and xml.dom.domreg no longer use environment variables to override parser implementations when sys.flags.ignore_environment is set by -E or -I arguments.

- bpo-17239: The xml.sax and xml.dom.minidom parsers no longer processes external entities by default. External DTD and ENTITY declarations no longer load files or create network connections.

- bpo-34623: CVE-2018-14647: The C accelerated _elementtree module now initializes hash randomization salt from _Py_HashSecret instead of libexpat’s default CSPRNG.

- bpo-34405: Updated to OpenSSL 1.1.0i for Windows builds.

- bpo-33871: Fixed sending the part of the file in `os.sendfile()` on macOS. Using the trailers argument could cause sending more bytes from the input file than was specified.

- bpo-32533: Fixed thread-safety of error handling in _ssl.

- bpo-33136: Harden ssl module against LibreSSL CVE-2018-8970. X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test ensures that NULL bytes are not allowed.

- bpo-33001: Minimal fix to prevent buffer overrun in os.symlink on Windows

- bpo-32981: Regexes in difflib and poplib were vulnerable to catastrophic backtracking. These regexes formed potential DOS vectors (REDOS). They have been refactored. This resolves CVE-2018-1060 and CVE-2018-1061. Patch by Jamie Davis.

- bpo-28414: The ssl module now allows users to perform their own IDN en/decoding when using SNI.

### Core and Builtins

- bpo-35877: Make parenthesis optional for named expressions in while statement. Patch by Karthikeyan Singaravelan.

- bpo-35814: Allow same right hand side expressions in annotated assignments as in normal ones. In particular, `x: Tuple[int, int] = 1, 2` (without parentheses on the right) is now allowed.

- bpo-35766: Add the option to parse PEP 484 type comments in the ast module. (Off by default.) This is merging the key functionality of the third party fork thereof, [typed_ast](https://github.com/python/typed_ast).

- bpo-35713: Reorganize Python initialization to get working exceptions and sys.stderr earlier.

- bpo-33416: Add end line and end column position information to the Python AST nodes. This is a C-level backwards incompatible change.

- bpo-35720: Fixed a minor memory leak in pymain_parse_cmdline_impl function in Modules/main.c

- bpo-35634: `func(**kwargs)` will now raise an error when `kwargs` is a mapping containing multiple entries with the same key. An error was already raised when other keyword arguments are passed before `**kwargs` since Python 3.6.

- bpo-35623: Fix a crash when sorting very long lists. Patch by Stephan Hohe.

- bpo-35214: clang Memory Sanitizer build instrumentation was added to work around false positives from posix, socket, time, test_io, and test_faulthandler.

- bpo-35560: Fix an assertion error in `format()` in debug build for floating point formatting with “n” format, zero padding and small width. Release build is not impacted. Patch by Karthikeyan Singaravelan.

- bpo-35552: Format characters `%s` and `%V` in `PyUnicode_FromFormat()` and `%s` in `PyBytes_FromFormat()` no longer read memory past the limit if precision is specified.

- bpo-35504: Fix segfaults and `SystemError`s when deleting certain attributes. Patch by Zackery Spytz.

- bpo-35504: Fixed a SystemError when delete the characters_written attribute of an OSError.

- bpo-35494: Improved syntax error messages for unbalanced parentheses in f-string.

- bpo-35444: Fixed error handling in pickling methods when fail to look up builtin “getattr”. Sped up pickling iterators.

- bpo-35436: Fix various issues with memory allocation error handling. Patch by Zackery Spytz.

- bpo-35423: Separate the signal handling trigger in the eval loop from the “pending calls” machinery. There is no semantic change and the difference in performance is insignificant.

- bpo-35357: Internal attributes’ names of unittest.mock._Call and unittest.mock.MagicProxy (name, parent & from_kall) are now prefixed with _mock_ in order to prevent clashes with widely used object attributes. Fixed minor typo in test function name.

- bpo-35372: Fixed the code page decoder for input longer than 2 GiB containing undecodable bytes.

- bpo-35336: Fix PYTHONCOERCECLOCALE=1 environment variable: only coerce the C locale if the LC_CTYPE locale is “C”.

- bpo-31241: The lineno and col_offset attributes of AST nodes for list comprehensions, generator expressions and tuples are now point to the opening parenthesis or square brace. For tuples without parenthesis they point to the position of the first item.

- bpo-33954: For `str.format()`, `float.__format__()` and `complex.__format__()` methods for non-ASCII decimal point when using the “n” formatter.

- bpo-35269: Fix a possible segfault involving a newly-created coroutine. Patch by Zackery Spytz.

- bpo-35224: Implement PEP 572 (assignment expressions). Patch by Emily Morehouse.

- bpo-32492: Speed up `namedtuple` attribute access by 1.6x using a C fast-path for the name descriptors. Patch by Pablo Galindo.

- bpo-35214: Fixed an out of bounds memory access when parsing a truncated unicode escape sequence at the end of a string such as `'\N'`. It would read one byte beyond the end of the memory allocation.

- bpo-35214: The interpreter and extension modules have had annotations added so that they work properly under clang’s Memory Sanitizer. A new configure flag –with-memory-sanitizer has been added to make test builds of this nature easier to perform.

- bpo-35193: Fix an off by one error in the bytecode peephole optimizer where it could read bytes beyond the end of bounds of an array when removing unreachable code. This bug was present in every release of Python 3.6 and 3.7 until now.

- bpo-35169: Improved error messages for forbidden assignments.

- bpo-34022: Fix handling of hash-based bytecode files in `zipimport`. Patch by Elvis Pranskevichus.

- bpo-28401: Debug builds will no longer to attempt to import extension modules built for the ABI as they were never compatible to begin with. Patch by Stefano Rivera.

- bpo-29341: Clarify in the docstrings of `os` methods that path-like objects are also accepted as input parameters.

- bpo-35050: `socket`: Fix off-by-one bug in length check for `AF_ALG` name and type.

- bpo-29743: Raise `ValueError` instead of `OverflowError` in case of a negative `_length_` in a `ctypes.Array` subclass. Also raise `TypeError` instead of `AttributeError` for non-integer `_length_`. Original patch by Oren Milman.

- bpo-16806: Fix `lineno` and `col_offset` for multi-line string tokens.

- bpo-35029: `SyntaxWarning` raised as an exception at code generation time will be now replaced with a `SyntaxError` for better error reporting.

- bpo-34983: Expose `symtable.Symbol.is_nonlocal()` in the symtable module. Patch by Pablo Galindo.

- bpo-34974: `bytes` and `bytearray` constructors no longer convert unexpected exceptions (e.g. `MemoryError` and `KeyboardInterrupt`) to `TypeError`.

- bpo-34939: Allow annotated names in module namespace that are declared global before the annotation happens. Patch by Pablo Galindo.

- bpo-34973: Fixed crash in `bytes()` when the `list` argument is mutated while it is iterated.

- bpo-34876: The lineno and col_offset attributes of the AST for decorated function and class refer now to the position of the corresponding `def`, `async def` and `class` instead of the position of the first decorator. This leads to more correct line reporting in tracing. This is the only case when the position of child AST nodes can precede the position of the parent AST node.

- bpo-34879: Fix a possible null pointer dereference in bytesobject.c. Patch by Zackery Spytz.

- bpo-34784: Fix the implementation of PyStructSequence_NewType in order to create heap allocated StructSequences.

- bpo-32912: A `SyntaxWarning` is now emitted instead of a `DeprecationWarning` for invalid escape sequences in string and bytes literals.

- bpo-34854: Fixed a crash in compiling string annotations containing a lambda with a keyword-only argument that doesn’t have a default value.

- bpo-34850: The compiler now produces a `SyntaxWarning` when identity checks (`is` and `is not`) are used with certain types of literals (e.g. strings, ints). These can often work by accident in CPython, but are not guaranteed by the language spec. The warning advises users to use equality tests (`==` and `!=`) instead.

- bpo-34824: Fix a possible null pointer dereference in Modules/_ssl.c. Patch by Zackery Spytz.

- bpo-30156: The C function `property_descr_get()` uses a “cached” tuple to optimize function calls. But this tuple can be discovered in debug mode with `sys.getobjects()`. Remove the optimization, it’s not really worth it and it causes 3 different crashes last years.

- bpo-34762: Fix contextvars C API to use PyObject* pointer types.

- bpo-34751: The hash function for tuples is now based on xxHash which gives better collision results on (formerly) pathological cases. Additionally, on 64-bit systems it improves tuple hashes in general. Patch by Jeroen Demeyer with substantial contributions by Tim Peters.

- bpo-34735: Fix a memory leak in Modules/timemodule.c. Patch by Zackery Spytz.

- bpo-34683: Fixed a bug where some SyntaxError error pointed to locations that were off-by-one.

- bpo-34651: Only allow the main interpreter to fork. The avoids the possibility of affecting the main interpreter, which is critical to operation of the runtime.

- bpo-34653: Remove unused function PyParser_SimpleParseStringFilename.

- bpo-32236: Warn that line buffering is not supported if `open()` is called with binary mode and `buffering=1`.

- bpo-34641: Further restrict the syntax of the left-hand side of keyword arguments in function calls. In particular, `f((keyword)=arg)` is now disallowed.

- bpo-34637: Make the start argument to sum() visible as a keyword argument.

- bpo-1621: Do not assume signed integer overflow behavior (C undefined behavior) when performing set hash table resizing.

- bpo-34588: Fix an off-by-one in the recursive call pruning feature of traceback formatting.

- bpo-34485: On Windows, the LC_CTYPE is now set to the user preferred locale at startup. Previously, the LC_CTYPE locale was “C” at startup, but changed when calling setlocale(LC_CTYPE, “”) or setlocale(LC_ALL, “”).

- bpo-34485: Standard streams like sys.stdout now use the “surrogateescape” error handler, instead of “strict”, on the POSIX locale (when the C locale is not coerced and the UTF-8 Mode is disabled).

- bpo-34485: Fix the error handler of standard streams like sys.stdout: PYTHONIOENCODING=”:” is now ignored instead of setting the error handler to “strict”.

- bpo-34485: Python now gets the locale encoding with C code to initialize the encoding of standard streams like sys.stdout. Moreover, the encoding is now initialized to the Python codec name to get a normalized encoding name and to ensure that the codec is loaded. The change avoids importing _bootlocale and _locale modules at startup by default.

- bpo-34527: On FreeBSD, Py_DecodeLocale() and Py_EncodeLocale() now also forces the ASCII encoding if the LC_CTYPE locale is “POSIX”, not only if the LC_CTYPE locale is “C”.

- bpo-34527: The UTF-8 Mode is now also enabled by the “POSIX” locale, not only by the “C” locale.

- bpo-34403: On HP-UX with C or POSIX locale, sys.getfilesystemencoding() now returns “ascii” instead of “roman8” (when the UTF-8 Mode is disabled and the C locale is not coerced).

- bpo-34523: The Python filesystem encoding is now read earlier during the Python initialization.

- bpo-12458: Tracebacks show now correct line number for subexpressions in multiline expressions. Tracebacks show now the line number of the first line for multiline expressions instead of the line number of the last subexpression.

- bpo-34408: Prevent a null pointer dereference and resource leakage in `PyInterpreterState_New()`.

- bpo-34400: Fix undefined behavior in parsetok.c. Patch by Zackery Spytz.

- bpo-33073: Added as_integer_ratio to ints to make them more interoperable with floats.

- bpo-34377: Update valgrind suppression list to use `_PyObject_Free`/`_PyObject_Realloc` instead of `PyObject_Free`/`PyObject_Realloc`.

- bpo-34353: Added the “socket” option in the `stat.filemode()` Python implementation to match the C implementation.

- bpo-34320: Fix `dict(od)` didn’t copy iteration order of OrderedDict.

- bpo-34113: Fixed crash on debug builds when opcode stack was adjusted with negative numbers. Patch by Constantin Petrisor.

- bpo-34100: Compiler now merges constants in tuples and frozensets recursively. Code attributes like `co_names` are merged too.

- bpo-34151: Performance of list concatenation, repetition and slicing operations is slightly improved. Patch by Sergey Fedoseev.

- bpo-34170: -X dev: it is now possible to override the memory allocator using PYTHONMALLOC even if the developer mode is enabled.

- bpo-33237: Improved `AttributeError` message for partially initialized module.

- bpo-34149: Fix min and max functions to get default behavior when key is None.

- bpo-34125: Profiling of unbound built-in methods now works when `**kwargs` is given.

- bpo-34141: Optimized pickling atomic types (None, bool, int, float, bytes, str).

- bpo-34126: Fix crashes when profiling certain invalid calls of unbound methods. Patch by Jeroen Demeyer.

- bpo-24618: Fixed reading invalid memory when create the code object with too small varnames tuple or too large argument counts.

- bpo-34068: In `io.IOBase.close()`, ensure that the `closed` attribute is not set with a live exception. Patch by Zackery Spytz and Serhiy Storchaka.

- bpo-34087: Fix buffer overflow while converting unicode to numeric values.

- bpo-34080: Fixed a memory leak in the compiler when it raised some uncommon errors during tokenizing.

- bpo-34066: Disabled interruption by Ctrl-C between calling `open()` and entering a with block in `with open()`.

- bpo-34042: Fix dict.copy() to maintain correct total refcount (as reported by sys.gettotalrefcount()).

- bpo-33418: Fix potential memory leak in function object when it creates reference cycle.

- bpo-33985: Implement contextvars.ContextVar.name attribute.

- bpo-33956: Update vendored Expat library copy to version 2.2.5.

- bpo-24596: Decref the module object in `PyRun_SimpleFileExFlags()` before calling `PyErr_Print()`. Patch by Zackery Spytz.

- bpo-33451: Close directly executed pyc files before calling `PyEval_EvalCode()`.

- bpo-1617161: The hash of `BuiltinMethodType` instances (methods of built-in classes) now depends on the hash of the identity of __self__ instead of its value. The hash and equality of `ModuleType` and `MethodWrapperType` instances (methods of user-defined classes and some methods of built-in classes like `str.__add__`) now depend on the hash and equality of the identity of __self__ instead of its value. `MethodWrapperType` instances no longer support ordering.

- bpo-33824: Fix “LC_ALL=C python3.7 -V”: reset properly the command line parser when the encoding changes after reading the Python configuration.

- bpo-33803: Fix a crash in hamt.c caused by enabling GC tracking for an object that hadn’t all of its fields set to NULL.

- bpo-33738: Seven macro incompatibilities with the Limited API were fixed, and the macros `PyIter_Check()`, `PyIndex_Check()` and `PyExceptionClass_Name()` were added as functions. A script for automatic macro checks was added.

- bpo-33786: Fix asynchronous generators to handle GeneratorExit in athrow() correctly

- bpo-30167: `PyRun_SimpleFileExFlags` removes `__cached__` from module in addition to `__file__`.

- bpo-33706: Fix a crash in Python initialization when parsing the command line options. Thanks Christoph Gohlke for the bug report and the fix!

- bpo-33597: Reduce `PyGC_Head` size from 3 words to 2 words.

- bpo-30654: Fixed reset of the SIGINT handler to SIG_DFL on interpreter shutdown even when there was a custom handler set previously. Patch by Philipp Kerling.

- bpo-33622: Fixed a leak when the garbage collector fails to add an object with the `__del__` method or referenced by it into the `gc.garbage` list. `PyGC_Collect()` can now be called when an exception is set and preserves it.

- bpo-33462: Make dict and dict views reversible. Patch by Rémi Lapeyre.

- bpo-23722: A `RuntimeError` is now raised when the custom metaclass doesn’t provide the `__classcell__` entry in the namespace passed to `type.__new__`. A `DeprecationWarning` was emitted in Python 3.6–3.7.

- bpo-33499: Add `PYTHONPYCACHEPREFIX` environment variable and `-X` `pycache_prefix` command-line option to set an alternate root directory for writing module bytecode cache files.

- bpo-25711: The `zipimport` module has been rewritten in pure Python.

- bpo-33509: Fix module_globals parameter of warnings.warn_explicit(): don’t crash if module_globals is not a dict.

- bpo-31849: Fix signed/unsigned comparison warning in pyhash.c.

- bpo-33475: Fixed miscellaneous bugs in converting annotations to strings and optimized parentheses in the string representation.

- bpo-20104: Added support for the `setpgroup`, `resetids`, `setsigmask`, `setsigdef` and `scheduler` parameters of `posix_spawn`. Patch by Pablo Galindo.

- bpo-33391: Fix a leak in set_symmetric_difference().

- bpo-33363: Raise a SyntaxError for `async with` and `async for` statements outside of async functions.

- bpo-28055: Fix unaligned accesses in siphash24(). Patch by Rolf Eike Beer.

- bpo-33128: Fix a bug that causes PathFinder to appear twice on sys.meta_path. Patch by Pablo Galindo Salgado.

- bpo-33331: Modules imported last are now cleared first at interpreter shutdown.

- bpo-33312: Fixed clang ubsan (undefined behavior sanitizer) warnings in dictobject.c by adjusting how the internal struct _dictkeysobject shared keys structure is declared.

- bpo-33305: Improved syntax error messages for invalid numerical literals.

- bpo-33306: Improved syntax error messages for unbalanced parentheses.

- bpo-33234: The list constructor will pre-size and not over-allocate when the input length is known.

- bpo-33270: Intern the names for all anonymous code objects. Patch by Zackery Spytz.

- bpo-30455: The C and Python code and the documentation related to tokens are now generated from a single source file `Grammar/Tokens`.

- bpo-33176: Add a `toreadonly()` method to memoryviews.

- bpo-33231: Fix potential memory leak in `normalizestring()`.

- bpo-33205: Change dict growth function from `round_up_to_power_2(used*2+hashtable_size/2)` to `round_up_to_power_2(used*3)`. Previously, dict is shrinked only when `used == 0`. Now dict has more chance to be shrinked.

- bpo-29922: Improved error messages in ‘async with’ when `__aenter__()` or `__aexit__()` return non-awaitable object.

- bpo-33199: Fix `ma_version_tag` in dict implementation is uninitialized when copying from key-sharing dict.

- bpo-33053: When using the -m switch, sys.path[0] is now explicitly expanded as the starting working directory, rather than being left as the empty path (which allows imports from the current working directory at the time of the import)

- bpo-33138: Changed standard error message for non-pickleable and non-copyable types. It now says “cannot pickle” instead of “can’t pickle” or “cannot serialize”.

- bpo-33018: Improve consistency of errors raised by `issubclass()` when called with a non-class and an abstract base class as the first and second arguments, respectively. Patch by Josh Bronson.

- bpo-33083: `math.factorial` no longer accepts arguments that are not int-like. Patch by Pablo Galindo.

- bpo-33041: Added new opcode `END_ASYNC_FOR` and fixes the following issues:

  - Setting global `StopAsyncIteration` no longer breaks `async for` loops.

  - Jumping into an `async for` loop is now disabled.

  - Jumping out of an `async for` loop no longer corrupts the stack.

- bpo-25750: Fix rare Python crash due to bad refcounting in `type_getattro()` if a descriptor deletes itself from the class. Patch by Jeroen Demeyer.

- bpo-33041: Fixed bytecode generation for “async for” with a complex target. A StopAsyncIteration raised on assigning or unpacking will be now propagated instead of stopping the iteration.

- bpo-33026: Fixed jumping out of “with” block by setting f_lineno.

- bpo-33005: Fix a crash on fork when using a custom memory allocator (ex: using PYTHONMALLOC env var). _PyGILState_Reinit() and _PyInterpreterState_Enable() now use the default RAW memory allocator to allocate a new interpreters mutex on fork.

- bpo-32911: Due to unexpected compatibility issues discovered during downstream beta testing, reverted bpo-29463. `docstring` field is removed from Module, ClassDef, FunctionDef, and AsyncFunctionDef ast nodes which was added in 3.7a1. Docstring expression is restored as a first statement in their body. Based on patch by Inada Naoki.

- bpo-17288: Prevent jumps from ‘return’ and ‘exception’ trace events.

- bpo-32946: Importing names from already imported module with “from … import …” is now 30% faster if the module is not a package.

- bpo-32932: Make error message more revealing when there are non-str objects in `__all__`.

- bpo-32925: Optimized iterating and containing test for literal lists consisting of non-constants: `x in [a, b]` and `for x in [a, b]`. The case of all constant elements already was optimized.

- bpo-32889: Update Valgrind suppression list to account for the rename of `Py_ADDRESS_IN_RANG` to `address_in_range`.

- bpo-32836: Don’t use temporary variables in cases of list/dict/set comprehensions

- bpo-31356: Remove the new API added in bpo-31356 (gc.ensure_disabled() context manager).

- bpo-32305: For namespace packages, ensure that both `__file__` and `__spec__.origin` are set to None.

- bpo-32303: Make sure `__spec__.loader` matches `__loader__` for namespace packages.

- bpo-32711: Fix the warning messages for Python/ast_unparse.c. Patch by Stéphane Wirtel

- bpo-32583: Fix possible crashing in builtin Unicode decoders caused by write out-of-bound errors when using customized decode error handlers.

- bpo-32489: A `continue` statement is now allowed in the `finally` clause.

- bpo-17611: Simplified the interpreter loop by moving the logic of unrolling the stack of blocks into the compiler. The compiler emits now explicit instructions for adjusting the stack of values and calling the cleaning up code for `break`, `continue` and `return`.

  Removed opcodes `BREAK_LOOP`, `CONTINUE_LOOP`, `SETUP_LOOP` and `SETUP_EXCEPT`. Added new opcodes `ROT_FOUR`, `BEGIN_FINALLY` and `CALL_FINALLY` and `POP_FINALLY`. Changed the behavior of `END_FINALLY` and `WITH_CLEANUP_START`.

- bpo-32285: New function unicodedata.is_normalized, which can check whether a string is in a specific normal form.

- bpo-10544: Yield expressions are now disallowed in comprehensions and generator expressions except the expression for the outermost iterable.

- bpo-32117: Iterable unpacking is now allowed without parentheses in yield and return statements, e.g. `yield 1, 2, 3, *rest`. Thanks to David Cuthbert for the change and Jordan Chapman for added tests.

- bpo-31902: Fix the `col_offset` attribute for ast nodes `ast.AsyncFor`, `ast.AsyncFunctionDef`, and `ast.AsyncWith`. Previously, `col_offset` pointed to the keyword after `async`.

- bpo-25862: Fix assertion failures in the `tell()` method of `io.TextIOWrapper`. Patch by Zackery Spytz.

- bpo-21983: Fix a crash in `ctypes.cast()` in case the type argument is a ctypes structured data type. Patch by Eryk Sun and Oren Milman.

- bpo-31577: Fix a crash in `os.utime()` in case of a bad ns argument. Patch by Oren Milman.

- bpo-29832: Remove references to ‘getsockaddrarg’ from various socket error messages. Patch by Oren Milman.

### Library

- bpo-35845: Add ‘order’ parameter to memoryview.tobytes().

- bpo-35864: The _asdict() method for collections.namedtuple now returns a regular dict instead of an OrderedDict.

- bpo-35537: An ExitStack is now used internally within subprocess.POpen to clean up pipe file handles. No behavior change in normal operation. But if closing one handle were ever to cause an exception, the others will now be closed instead of leaked. (patch by Giampaolo Rodola)

- bpo-35847: RISC-V needed the CTYPES_PASS_BY_REF_HACK. Fixes ctypes Structure test_pass_by_value.

- bpo-35813: Shared memory submodule added to multiprocessing to avoid need for serialization between processes

- bpo-35780: Fix lru_cache() errors arising in recursive, reentrant, or multi-threaded code. These errors could result in orphan links and in the cache being trapped in a state with fewer than the specified maximum number of links. Fix handling of negative maxsize which should have been treated as zero. Fix errors in toggling the “full” status flag. Fix misordering of links when errors are encountered. Sync-up the C code and pure Python code for the space saving path in functions with a single positional argument. In this common case, the space overhead of an lru cache entry is reduced by almost half. Fix counting of cache misses. In error cases, the miss count was out of sync with the actual number of times the underlying user function was called.

- bpo-35537: `os.posix_spawn()` and `os.posix_spawnp()` now have a setsid parameter.

- bpo-23846: `asyncio.ProactorEventLoop` now catches and logs send errors when the self-pipe is full.

- bpo-34323: `asyncio`: Enhance `IocpProactor.close()` log: wait 1 second before the first log, then log every second. Log also the number of seconds since `close()` was called.

- bpo-35674: Add a new `os.posix_spawnp()` function. Patch by Joannah Nanjekye.

- bpo-35733: `ast.Constant(boolean)` no longer an instance of `ast.Num`. Patch by Anthony Sottile.

- bpo-35726: QueueHandler.prepare() now makes a copy of the record before modifying and enqueueing it, to avoid affecting other handlers in the chain.

- bpo-35719: Sped up multi-argument `math` functions atan2(), copysign(), remainder() and hypot() by 1.3–2.5 times.

- bpo-35717: Fix KeyError exception raised when using enums and compile. Patch contributed by Rémi Lapeyre.

- bpo-35699: Fixed detection of Visual Studio Build Tools 2017 in distutils

- bpo-32710: Fix memory leaks in asyncio ProactorEventLoop on overlapped operation failure.

- bpo-35702: The `time.CLOCK_UPTIME_RAW` constant is now available for macOS 10.12.

- bpo-32710: Fix a memory leak in asyncio in the ProactorEventLoop when `ReadFile()` or `WSASend()` overlapped operation fail immediately: release the internal buffer.

- bpo-35682: Fix `asyncio.ProactorEventLoop.sendfile()`: don’t attempt to set the result of an internal future if it’s already done.

- bpo-35283: Add a deprecated warning for the `threading.Thread.isAlive()` method. Patch by Dong-hee Na.

- bpo-35664: Improve operator.itemgetter() performance by 33% with optimized argument handling and with adding a fast path for the common case of a single non-negative integer index into a tuple (which is the typical use case in the standard library).

- bpo-35643: Fixed a SyntaxWarning: invalid escape sequence in Modules/_sha3/cleanup.py. Patch by Mickaël Schoentgen.

- bpo-35619: Improved support of custom data descriptors in `help()` and `pydoc`.

- bpo-28503: The `crypt` module now internally uses the `crypt_r()` library function instead of `crypt()` when available.

- bpo-35614: Fixed help() on metaclasses. Patch by Sanyam Khurana.

- bpo-35568: Expose `raise(signum)` as `raise_signal`

- bpo-35588: The floor division and modulo operations and the `divmod()` function on `fractions.Fraction` types are 2–4x faster. Patch by Stefan Behnel.

- bpo-35585: Speed-up building enums by value, e.g. http.HTTPStatus(200).

- bpo-30561: random.gammavariate(1.0, beta) now computes the same result as random.expovariate(1.0 / beta). This synchronizes the two algorithms and eliminates some idiosyncrasies in the old implementation. It does however produce a difference stream of random variables than it used to.

- bpo-35537: The `subprocess` module can now use the `os.posix_spawn()` function in some cases for better performance.

- bpo-35526: Delaying the ‘joke’ of barry_as_FLUFL.mandatory to Python version 4.0

- bpo-35523: Remove `ctypes` callback workaround: no longer create a callback at startup. Avoid SELinux alert on `import ctypes` and `import uuid`.

- bpo-31784: `uuid.uuid1()` now calls `time.time_ns()` rather than `int(time.time() * 1e9)`.

- bpo-35513: `TextTestRunner` of `unittest.runner` now uses `time.perf_counter()` rather than `time.time()` to measure the execution time of a test: `time.time()` can go backwards, whereas `time.perf_counter()` is monotonic.

- bpo-35502: Fixed reference leaks in `xml.etree.ElementTree.TreeBuilder` in case of unfinished building of the tree (in particular when an error was raised during parsing XML).

- bpo-35348: Make `platform.architecture()` parsing of `file` command output more reliable: add the `-b` option to the `file` command to omit the filename, force the usage of the C locale, and search also the “shared object” pattern.

- bpo-35491: `multiprocessing`: Add `Pool.__repr__()` and enhance `BaseProcess.__repr__()` (add pid and parent pid) to ease debugging. Pool state constant values are now strings instead of integers, for example `RUN` value becomes `'RUN'` instead of `0`.

- bpo-35477: `multiprocessing.Pool.__enter__()` now fails if the pool is not running: `with pool:` fails if used more than once.

- bpo-31446: Copy command line that was passed to CreateProcessW since this function can change the content of the input buffer.

- bpo-35471: Python 2.4 dropped MacOS 9 support. The macpath module was deprecated in Python 3.7. The module is now removed.

- bpo-23057: Unblock Proactor event loop when keyboard interrupt is received on Windows

- bpo-35052: Fix xml.dom.minidom cloneNode() on a document with an entity: pass the correct arguments to the user data handler of an entity.

- bpo-20239: Allow repeated assignment deletion of `unittest.mock.Mock` attributes. Patch by Pablo Galindo.

- bpo-17185: Set `__signature__` on mock for `inspect` to get signature. Patch by Karthikeyan Singaravelan.

- bpo-35445: Memory errors during creating posix.environ no longer ignored.

- bpo-35415: Validate fileno= argument to socket.socket().

- bpo-35424: `multiprocessing.Pool` destructor now emits `ResourceWarning` if the pool is still running.

- bpo-35330: When a `Mock` instance was used to wrap an object, if `side_effect` is used in one of the mocks of it methods, don’t call the original implementation and return the result of using the side effect the same way that it is done with return_value.

- bpo-35346: Drop Mac OS 9 and Rhapsody support from the `platform` module. Rhapsody last release was in 2000. Mac OS 9 last release was in 2001.

- bpo-10496: `check_environ()` of `distutils.utils` now catches `KeyError` on calling `pwd.getpwuid()`: don’t create the `HOME` environment variable in this case.

- bpo-10496: `posixpath.expanduser()` now returns the input path unchanged if the `HOME` environment variable is not set and the current user has no home directory (if the current user identifier doesn’t exist in the password database). This change fix the `site` module if the current user doesn’t exist in the password database (if the user has no home directory).

- bpo-35389: `platform.libc_ver()` now uses `os.confstr('CS_GNU_LIBC_VERSION')` if available and the executable parameter is not set.

- bpo-35394: Add empty slots to asyncio abstract protocols.

- bpo-35310: Fix a bug in `select.select()` where, in some cases, the file descriptor sequences were returned unmodified after a signal interruption, even though the file descriptors might not be ready yet. `select.select()` will now always return empty lists if a timeout has occurred. Patch by Oran Avraham.

- bpo-35380: Enable TCP_NODELAY on Windows for proactor asyncio event loop.

- bpo-35341: Add generic version of `collections.OrderedDict` to the `typing` module. Patch by Ismo Toijala.

- bpo-35371: Fixed possible crash in `os.utime()` on Windows when pass incorrect arguments.

- bpo-35346: `platform.uname()` now redirects `stderr` to `os.devnull` when running external programs like `cmd /c ver`.

- bpo-35066: Previously, calling the strftime() method on a datetime object with a trailing ‘%’ in the format string would result in an exception. However, this only occurred when the datetime C module was being used; the python implementation did not match this behavior. Datetime is now PEP-399 compliant, and will not throw an exception on a trailing ‘%’.

- bpo-35345: The function `platform.popen` has been removed, it was deprecated since Python 3.3: use `os.popen()` instead.

- bpo-35344: On macOS, `platform.platform()` now uses `platform.mac_ver()`, if it returns a non-empty release string, to get the macOS version rather than the darwin version.

- bpo-35312: Make `lib2to3.pgen2.parse.ParseError` round-trip pickle-able. Patch by Anthony Sottile.

- bpo-35308: Fix regression in `webbrowser` where default browsers may be preferred over browsers in the `BROWSER` environment variable.

- bpo-24746: Avoid stripping trailing whitespace in doctest fancy diff. Original patch by R. David Murray & Jairo Trad. Enhanced by Sanyam Khurana.

- bpo-28604: `locale.localeconv()` now sets temporarily the `LC_CTYPE` locale to the `LC_MONETARY` locale if the two locales are different and monetary strings are non-ASCII. This temporary change affects other threads.

- bpo-35277: Update ensurepip to install pip 18.1 and setuptools 40.6.2.

- bpo-24209: Adds IPv6 support when invoking http.server directly.

- bpo-35226: Recursively check arguments when testing for equality of `unittest.mock.call` objects and add note that tracking of parameters used to create ancestors of mocks in `mock_calls` is not possible.

- bpo-29564: The warnings module now suggests to enable tracemalloc if the source is specified, the tracemalloc module is available, but tracemalloc is not tracing memory allocations.

- bpo-35189: Modify the following fnctl function to retry if interrupted by a signal (EINTR): flock, lockf, fnctl

- bpo-30064: Use add_done_callback() in sock_* asyncio API to unsubscribe reader/writer early on calcellation.

- bpo-35186: Removed the “built with” comment added when `setup.py upload` is used with either `bdist_rpm` or `bdist_dumb`.

- bpo-35152: Allow sending more than 2 GB at once on a multiprocessing connection on non-Windows systems.

- bpo-35062: Fix incorrect parsing of `_io.IncrementalNewlineDecoder`’s translate argument.

- bpo-35065: Remove `StreamReaderProtocol._untrack_reader`. The call to `_untrack_reader` is currently performed too soon, causing the protocol to forget about the reader before `connection_lost` can run and feed the EOF to the reader.

- bpo-34160: ElementTree and minidom now preserve the attribute order specified by the user.

- bpo-35079: Improve difflib.SequenceManager.get_matching_blocks doc by adding ‘non-overlapping’ and changing ‘!=’ to ‘<’.

- bpo-33710: Deprecated `l*gettext()` functions and methods in the `gettext` module. They return encoded bytes instead of Unicode strings and are artifacts from Python 2 times. Also deprecated functions and methods related to setting the charset for `l*gettext()` functions and methods.

- bpo-35017: `socketserver.BaseServer.serve_forever()` now exits immediately if it’s `shutdown()` method is called while it is polling for new events.

- bpo-35024: `importlib` no longer logs `wrote` redundantly after `(created|could not create)` is already logged. Patch by Quentin Agren.

- bpo-35047: `unittest.mock` now includes mock calls in exception messages if `assert_not_called`, `assert_called_once`, or `assert_called_once_with` fails. Patch by Petter Strandmark.

- bpo-31047: Fix `ntpath.abspath` regression where it didn’t remove a trailing separator on Windows. Patch by Tim Graham.

- bpo-35053: tracemalloc now tries to update the traceback when an object is reused from a “free list” (optimization for faster object creation, used by the builtin list type for example).

- bpo-31553: Add the –json-lines option to json.tool. Patch by hongweipeng.

- bpo-34794: Fixed a leak in Tkinter when pass the Python wrapper around Tcl_Obj back to Tcl/Tk.

- bpo-34909: Enum: fix grandchildren subclassing when parent mixed with concrete data types.

- bpo-35022: `unittest.mock.MagicMock` now supports the `__fspath__` method (from `os.PathLike`).

- bpo-35008: Fixed references leaks when call the `__setstate__()` method of `xml.etree.ElementTree.Element` in the C implementation for already initialized element.

- bpo-23420: Verify the value for the parameter ‘-s’ of the cProfile CLI. Patch by Robert Kuska

- bpo-33947: dataclasses now handle recursive reprs without raising RecursionError.

- bpo-34890: Make `inspect.iscoroutinefunction()`, `inspect.isgeneratorfunction()` and `inspect.isasyncgenfunction()` work with `functools.partial()`. Patch by Pablo Galindo.

- bpo-34521: Use `socket.CMSG_SPACE()` to calculate ancillary data size instead of `socket.CMSG_LEN()` in `multiprocessing.reduction.recvfds()` as RFC 3542 requires the use of the former for portable applications.

- bpo-31522: The `mailbox.mbox.get_string` function from_ parameter can now successfully be set to a non-default value.

- bpo-34970: Protect tasks weak set manipulation in `asyncio.all_tasks()`

- bpo-34969: gzip: Add –fast, –best on the gzip CLI, these parameters will be used for the fast compression method (quick) or the best method compress (slower, but smaller file). Also, change the default compression level to 6 (tradeoff).

- bpo-16965: The 2to3 `execfile` fixer now opens the file with mode `'rb'`. Patch by Zackery Spytz.

- bpo-34966: `pydoc` now supports aliases not only to methods defined in the end class, but also to inherited methods. The docstring is not duplicated for aliases.

- bpo-34926: `mimetypes.MimeTypes.guess_type()` now accepts path-like object in addition to url strings. Patch by Mayank Asthana.

- bpo-23831: Add `moveto()` method to the `tkinter.Canvas` widget. Patch by Juliette Monsel.

- bpo-34941: Methods `find()`, `findtext()` and `findall()` of the `Element` class in the `xml.etree.ElementTree` module are now able to find children which are instances of `Element` subclasses.

- bpo-32680: `smtplib.SMTP` objects now always have a `sock` attribute present

- bpo-34769: Fix for async generators not finalizing when event loop is in debug mode and garbage collector runs in another thread.

- bpo-34936: Fix `TclError` in `tkinter.Spinbox.selection_element()`. Patch by Juliette Monsel.

- bpo-34829: Add methods `selection_from`, `selection_range`, `selection_present` and `selection_to` to the `tkinter.Spinbox` for consistency with the `tkinter.Entry` widget. Patch by Juliette Monsel.

- bpo-34911: Added secure_protocols argument to http.cookiejar.DefaultCookiePolicy to allow for tweaking of protocols and also to add support by default for wss, the secure websocket protocol.

- bpo-34922: Fixed integer overflow in the `digest()` and `hexdigest()` methods for the SHAKE algorithm in the `hashlib` module.

- bpo-34925: 25% speedup in argument parsing for the functions in the bisect module.

- bpo-34900: Fixed `unittest.TestCase.debug()` when used to call test methods with subtests. Patch by Bruno Oliveira.

- bpo-34844: logging.Formatter enhancement - Ensure styles and fmt matches in logging.Formatter - Added validate method in each format style class: StrFormatStyle, PercentStyle, StringTemplateStyle. - This method is called in the constructor of logging.Formatter class - Also re-raise the KeyError in the format method of each style class, so it would a bit clear that it’s an error with the invalid format fields.

- bpo-34897: Adjust test.support.missing_compiler_executable check so that a nominal command name of “” is ignored. Patch by Michael Felt.

- bpo-34871: Fix inspect module polluted `sys.modules` when parsing `__text_signature__` of callable.

- bpo-34898: Add `mtime` argument to `gzip.compress` for reproducible output. Patch by Guo Ci Teo.

- bpo-28441: On Cygwin and MinGW, ensure that `sys.executable` always includes the full filename in the path, including the `.exe` suffix (unless it is a symbolic link).

- bpo-34866: Adding `max_num_fields` to `cgi.FieldStorage` to make DOS attacks harder by limiting the number of `MiniFieldStorage` objects created by `FieldStorage`.

- bpo-34711: http.server ensures it reports HTTPStatus.NOT_FOUND when the local path ends with “/” and is not a directory, even if the underlying OS (e.g. AIX) accepts such paths as a valid file reference. Patch by Michael Felt.

- bpo-34872: Fix self-cancellation in C implementation of asyncio.Task

- bpo-34849: Don’t log waiting for `selector.select` in asyncio loop iteration. The waiting is pretty normal for any asyncio program, logging its time just adds a noise to logs without any useful information provided.

- bpo-34022: The `SOURCE_DATE_EPOCH` environment variable no longer overrides the value of the invalidation_mode argument to `py_compile.compile()`, and determines its default value instead.

- bpo-34819: Use a monotonic clock to compute timeouts in `Executor.map()` and `as_completed()`, in order to prevent timeouts from deviating when the system clock is adjusted.

- bpo-34758: Add .wasm -> application/wasm to list of recognized file types and content type headers

- bpo-34789: `xml.sax.make_parser()` now accepts any iterable as its parser_list argument. Patch by Andrés Delfino.

- bpo-34334: In `QueueHandler`, clear `exc_text` from `LogRecord` to prevent traceback from being written twice.

- bpo-34687: On Windows, asyncio now uses ProactorEventLoop, instead of SelectorEventLoop, by default.

- bpo-5950: Support reading zip files with archive comments in `zipimport`.

- bpo-32892: The parser now represents all constants as `ast.Constant` instead of using specific constant AST types (`Num`, `Str`, `Bytes`, `NameConstant` and `Ellipsis`). These classes are considered deprecated and will be removed in future Python versions.

- bpo-34728: Add deprecation warning when `loop` is used in methods: `asyncio.sleep`, `asyncio.wait` and `asyncio.wait_for`.

- bpo-34738: ZIP files created by `distutils` will now include entries for directories.

- bpo-34659: Add an optional initial argument to itertools.accumulate().

- bpo-29577: Support multiple mixin classes when creating Enums.

- bpo-34670: Add SSLContext.post_handshake_auth and SSLSocket.verify_client_post_handshake for TLS 1.3’s post handshake authentication feature.

- bpo-32718: The Activate.ps1 script from venv works with PowerShell Core 6.1 and is now available under all operating systems.

- bpo-31177: Fix bug that prevented using `reset_mock` on mock instances with deleted attributes

- bpo-34672: Add a workaround, so the `'Z'` `time.strftime()` specifier on the musl C library can work in some cases.

- bpo-34666: Implement `asyncio.StreamWriter.awrite` and `asyncio.StreamWriter.aclose()` coroutines. Methods are needed for providing a consistent stream API with control flow switched on by default.

- bpo-6721: Acquire the logging module’s commonly used internal locks while fork()ing to avoid deadlocks in the child process.

- bpo-34658: Fix a rare interpreter unhandled exception state SystemError only seen when using subprocess with a preexec_fn while an after_parent handler has been registered with os.register_at_fork and the fork system call fails.

- bpo-34652: Ensure `os.lchmod()` is never defined on Linux.

- bpo-34638: Store a weak reference to stream reader to break strong references loop between reader and protocol. It allows to detect and close the socket if the stream is deleted (garbage collected) without `close()` call.

- bpo-34536: `Enum._missing_`: raise `ValueError` if None returned and `TypeError` if non-member is returned.

- bpo-34636: Speed up re scanning of many non-matching characters for s w and d within bytes objects. (microoptimization)

- bpo-24412: Add `addModuleCleanup()` and `addClassCleanup()` to unittest to support cleanups for `setUpModule()` and `setUpClass()`. Patch by Lisa Roach.

- bpo-34630: Don’t log SSL certificate errors in asyncio code (connection error logging is skipped already).

- bpo-32490: Prevent filename duplication in `subprocess` exception messages. Patch by Zackery Spytz.

- bpo-34363: dataclasses.asdict() and .astuple() now handle namedtuples correctly.

- bpo-34625: Update vendorized expat library version to 2.2.6.

- bpo-32270: The subprocess module no longer mistakenly closes redirected fds even when they were in pass_fds when outside of the default {0, 1, 2} set.

- bpo-34622: Create a dedicated `asyncio.CancelledError`, `asyncio.InvalidStateError` and `asyncio.TimeoutError` exception classes. Inherit them from corresponding exceptions from `concurrent.futures` package. Extract `asyncio` exceptions into a separate file.

- bpo-34610: Fixed iterator of `multiprocessing.managers.DictProxy`.

- bpo-34421: Fix distutils logging for non-ASCII strings. This caused installation issues on Windows.

- bpo-34604: Fix possible mojibake in the error message of `pwd.getpwnam` and `grp.getgrnam` using string representation because of invisible characters or trailing whitespaces. Patch by William Grzybowski.

- bpo-30977: Make uuid.UUID use `__slots__` to reduce its memory footprint. Based on original patch by Wouter Bolsterlee.

- bpo-34574: OrderedDict iterators are not exhausted during pickling anymore. Patch by Sergey Fedoseev.

- bpo-8110: Refactored `subprocess` to check for Windows-specific modules rather than `sys.platform == 'win32'`.

- bpo-34530: `distutils.spawn.find_executable()` now falls back on `os.defpath` if the `PATH` environment variable is not set.

- bpo-34563: On Windows, fix multiprocessing.Connection for very large read: fix _winapi.PeekNamedPipe() and _winapi.ReadFile() for read larger than INT_MAX (usually 2^31-1).

- bpo-34558: Correct typo in Lib/ctypes/_aix.py

- bpo-34282: Move `Enum._convert` to `EnumMeta._convert_` and fix enum members getting shadowed by parent attributes.

- bpo-22872: When the queue is closed, `ValueError` is now raised by `multiprocessing.Queue.put()` and `multiprocessing.Queue.get()` instead of `AssertionError` and `OSError`, respectively. Patch by Zackery Spytz.

- bpo-34515: Fix parsing non-ASCII identifiers in `lib2to3.pgen2.tokenize` (PEP 3131).

- bpo-13312: Avoids a possible integer underflow (undefined behavior) in the time module’s year handling code when passed a very low negative year value.

- bpo-34472: Improved compatibility for streamed files in `zipfile`. Previously an optional signature was not being written and certain ZIP applications were not supported. Patch by Silas Sewell.

- bpo-34454: Fix the .fromisoformat() methods of datetime types crashing when given unicode with non-UTF-8-encodable code points. Specifically, datetime.fromisoformat() now accepts surrogate unicode code points used as the separator. Report and tests by Alexey Izbyshev, patch by Paul Ganssle.

- bpo-6700: Fix inspect.getsourcelines for module level frames/tracebacks. Patch by Vladimir Matveev.

- bpo-34171: Running the `trace` module no longer creates the `trace.cover` file.

- bpo-34441: Fix crash when an `ABC`-derived class with invalid `__subclasses__` is passed as the second argument to `issubclass()`. Patch by Alexey Izbyshev.

- bpo-34427: Fix infinite loop in `a.extend(a)` for `MutableSequence` subclasses.

- bpo-34412: Make `signal.strsignal()` work on HP-UX. Patch by Michael Osipov.

- bpo-20849: shutil.copytree now accepts a new `dirs_exist_ok` keyword argument. Patch by Josh Bronson.

- bpo-31715: Associate `.mjs` file extension with `application/javascript` MIME Type.

- bpo-34384: `os.readlink()` now accepts path-like and `bytes` objects on Windows.

- bpo-22602: The UTF-7 decoder now raises `UnicodeDecodeError` for ill-formed sequences starting with “+” (as specified in RFC 2152). Patch by Zackery Spytz.

- bpo-2122: The `mmap.flush()` method now returns `None` on success, raises an exception on error under all platforms.

- bpo-34341: Appending to the ZIP archive with the ZIP64 extension no longer grows the size of extra fields of existing entries.

- bpo-34333: Fix %-formatting in `pathlib.PurePath.with_suffix()` when formatting an error message.

- bpo-18540: The `imaplib.IMAP4` and `imaplib.IMAP4_SSL` classes now resolve to the local host IP correctly when the default value of host parameter (`''`) is used.

- bpo-26502: Implement `traceback.FrameSummary.__len__()` method to preserve compatibility with the old tuple API.

- bpo-34318: `assertRaises()`, `assertRaisesRegex()`, `assertWarns()` and `assertWarnsRegex()` no longer success if the passed callable is None. They no longer ignore unknown keyword arguments in the context manager mode. A DeprecationWarning was raised in these cases since Python 3.5.

- bpo-9372: Deprecate `__getitem__()` methods of `xml.dom.pulldom.DOMEventStream`, `wsgiref.util.FileWrapper` and `fileinput.FileInput`.

- bpo-33613: Fix a race condition in `multiprocessing.semaphore_tracker` when the tracker receives SIGINT before it can register signal handlers for ignoring it.

- bpo-34248: Report filename in the exception raised when the database file cannot be opened by `dbm.gnu.open()` and `dbm.ndbm.open()` due to OS-related error. Patch by Zsolt Cserna.

- bpo-33089: Add math.dist() to compute the Euclidean distance between two points.

- bpo-34246: `smtplib.SMTP.send_message()` no longer modifies the content of the mail_options argument. Patch by Pablo S. Blum de Aguiar.

- bpo-31047: Fix `ntpath.abspath` for invalid paths on windows. Patch by Franz Woellert.

- bpo-32321: Add pure Python fallback for functools.reduce. Patch by Robert Wright.

- bpo-34270: The default asyncio task class now always has a name which can be get or set using two new methods (`get_name()` and `set_name()`) and is visible in the `repr()` output. An initial name can also be set using the new `name` keyword argument to `asyncio.create_task()` or the `create_task()` method of the event loop. If no initial name is set, the default Task implementation generates a name like `Task-1` using a monotonic counter.

- bpo-34263: asyncio’s event loop will not pass timeouts longer than one day to epoll/select etc.

- bpo-34035: Fix several AttributeError in zipfile seek() methods. Patch by Mickaël Schoentgen.

- bpo-32215: Fix performance regression in `sqlite3` when a DML statement appeared in a different line than the rest of the SQL query.

- bpo-34075: Deprecate passing non-ThreadPoolExecutor instances to `AbstractEventLoop.set_default_executor()`.

- bpo-34251: Restore `msilib.Win64` to preserve backwards compatibility since it’s already used by `distutils`’ `bdist_msi` command.

- bpo-19891: Ignore errors caused by missing / non-writable homedir while writing history during exit of an interactive session. Patch by Anthony Sottile.

- bpo-33089: Enhanced math.hypot() to support more than two dimensions.

- bpo-34228: tracemalloc: PYTHONTRACEMALLOC=0 environment variable and -X tracemalloc=0 command line option are now allowed to disable explicitly tracemalloc at startup.

- bpo-13041: Use `shutil.get_terminal_size()` to calculate the terminal width correctly in the `argparse.HelpFormatter` class. Initial patch by Zbyszek Jędrzejewski-Szmek.

- bpo-34213: Allow frozen dataclasses to have a field named “object”. Previously this conflicted with an internal use of “object”.

- bpo-34052: `sqlite3.Connection.create_aggregate()`, `sqlite3.Connection.create_function()`, `sqlite3.Connection.set_authorizer()`, `sqlite3.Connection.set_progress_handler()` methods raises TypeError when unhashable objects are passed as callable. These methods now don’t pass such objects to SQLite API. Previous behavior could lead to segfaults. Patch by Sergey Fedoseev.

- bpo-34197: Attributes skipinitialspace, doublequote and strict of the dialect attribute of the `csv` reader are now `bool` instances instead of integers 0 or 1.

- bpo-32788: Errors other than `TypeError` raised in methods `__adapt__()` and `__conform__()` in the `sqlite3` module are now propagated to the user.

- bpo-21446: The `reload` fixer now uses `importlib.reload()` instead of deprecated `imp.reload()`.

- bpo-940286: pydoc’s `Helper.showtopic()` method now prints the cross references of a topic correctly.

- bpo-34164: `base64.b32decode()` could raise UnboundLocalError or OverflowError for incorrect padding. Now it always raises `base64.Error` in these cases.

- bpo-33729: Fixed issues with arguments parsing in `hashlib`.

- bpo-34097: ZipFile can zip files older than 1980-01-01 and newer than 2107-12-31 using a new `strict_timestamps` parameter at the cost of setting the timestamp to the limit.

- bpo-34108: Remove extraneous CR in 2to3 refactor.

- bpo-34070: Make sure to only check if the handle is a tty, when opening a file with `buffering=-1`.

- bpo-27494: Reverted bpo-27494. 2to3 rejects now a trailing comma in generator expressions.

- bpo-33967: functools.singledispatch now raises TypeError instead of IndexError when no positional arguments are passed.

- bpo-34041: Add the parameter deterministic to the `sqlite3.Connection.create_function()` method. Patch by Sergey Fedoseev.

- bpo-34056: Ensure the loader shim created by `imp.load_module` always returns bytes from its `get_data()` function. This fixes using `imp.load_module` with PEP 552 hash-based pycs.

- bpo-34054: The multiprocessing module now uses the monotonic clock `time.monotonic()` instead of the system clock `time.time()` to implement timeout.

- bpo-34043: Optimize tarfile uncompress performance about 15% when gzip is used.

- bpo-34044: `subprocess.Popen` now copies the startupinfo argument to leave it unchanged: it will modify the copy, so that the same `STARTUPINFO` object can be used multiple times.

- bpo-34010: Fixed a performance regression for reading streams with tarfile. The buffered read should use a list, instead of appending to a bytes object.

- bpo-34019: webbrowser: Correct the arguments passed to Opera Browser when opening a new URL using the `webbrowser` module. Patch by Bumsik Kim.

- bpo-34003: csv.DictReader now creates dicts instead of OrderedDicts. Patch by Michael Selik.

- bpo-33978: Closed existing logging handlers before reconfiguration via fileConfig and dictConfig. Patch by Karthikeyan Singaravelan.

- bpo-14117: Make minor tweaks to turtledemo. The ‘wikipedia’ example is now ‘rosette’, describing what it draws. The ‘penrose’ print output is reduced. The’1024’ output of ‘tree’ is eliminated.

- bpo-33974: Fixed passing lists and tuples of strings containing special characters `"`, `\`, `{`, `}` and `\n` as options to `ttk` widgets.

- bpo-27500: Fix getaddrinfo to resolve IPv6 addresses correctly.

- bpo-24567: Improve random.choices() to handle subnormal input weights that could occasionally trigger an IndexError.

- bpo-33871: Fixed integer overflow in `os.readv()`, `os.writev()`, `os.preadv()` and `os.pwritev()` and in `os.sendfile()` with headers or trailers arguments (on BSD-based OSes and macOS).

- bpo-25007: Add `copy.copy()` and `copy.deepcopy()` support to zlib compressors and decompressors. Patch by Zackery Spytz.

- bpo-33929: multiprocessing: Fix a race condition in Popen of multiprocessing.popen_spawn_win32. The child process now duplicates the read end of pipe instead of “stealing” it. Previously, the read end of pipe was “stolen” by the child process, but it leaked a handle if the child process had been terminated before it could steal the handle from the parent process.

- bpo-33899: Tokenize module now implicitly emits a NEWLINE when provided with input that does not have a trailing new line. This behavior now matches what the C tokenizer does internally. Contributed by Ammar Askar.

- bpo-33897: Added a ‘force’ keyword argument to logging.basicConfig().

- bpo-33695: `shutil.copytree()` uses `os.scandir()` function and all copy functions depending from it use cached `os.stat()` values. The speedup for copying a directory with 8000 files is around +9% on Linux, +20% on Windows and + 30% on a Windows SMB share. Also the number of `os.stat()` syscalls is reduced by 38% making `shutil.copytree()` especially faster on network filesystems. (Contributed by Giampaolo Rodola’ in bpo-33695.)

- bpo-33916: bz2 and lzma: When Decompressor.__init__() is called twice, free the old lock to not leak memory.

- bpo-32568: Make select.epoll() and its documentation consistent regarding sizehint and flags.

- bpo-33833: Fixed bug in asyncio where ProactorSocketTransport logs AssertionError if force closed during write.

- bpo-33663: Convert content length to string before putting to header.

- bpo-33721: `os.path` functions that return a boolean result like `exists()`, `lexists()`, `isdir()`, `isfile()`, `islink()`, and `ismount()`, and `pathlib.Path` methods that return a boolean result like `exists()`, `is_dir()`, `is_file()`, `is_mount()`, `is_symlink()`, `is_block_device()`, `is_char_device()`, `is_fifo()`, `is_socket()` now return `False` instead of raising `ValueError` or its subclasses `UnicodeEncodeError` and `UnicodeDecodeError` for paths that contain characters or bytes unrepresentable at the OS level.

- bpo-26544: Fixed implementation of `platform.libc_ver()`. It almost always returned version ‘2.9’ for glibc.

- bpo-33843: Remove deprecated `cgi.escape`, `cgi.parse_qs` and `cgi.parse_qsl`.

- bpo-33842: Remove `tarfile.filemode` which is deprecated since Python 3.3.

- bpo-30167: Prevent site.main() exception if PYTHONSTARTUP is set. Patch by Steve Weber.

- bpo-33805: Improve error message of dataclasses.replace() when an InitVar is not specified

- bpo-33687: Fix the call to `os.chmod()` for `uu.decode()` if a mode is given or decoded. Patch by Timo Furrer.

- bpo-33812: Datetime instance d with non-None tzinfo, but with d.tzinfo.utcoffset(d) returning None is now treated as naive by the astimezone() method.

- bpo-32108: In configparser, don’t clear section when it is assigned to itself.

- bpo-27397: Make email module properly handle invalid-length base64 strings.

- bpo-33578: Implement multibyte encoder/decoder state methods

- bpo-30805: Avoid race condition with debug logging

- bpo-33476: Fix _header_value_parser.py when address group is missing final ‘;’. Contributed by Enrique Perez-Terron

- bpo-33694: asyncio: Fix a race condition causing data loss on pause_reading()/resume_reading() when using the ProactorEventLoop.

- bpo-32493: Correct test for `uuid_enc_be` availability in `configure.ac`. Patch by Michael Felt.

- bpo-33792: Add asyncio.WindowsSelectorEventLoopPolicy and asyncio.WindowsProactorEventLoopPolicy.

- bpo-33274: W3C DOM Level 1 specifies return value of Element.removeAttributeNode() as “The Attr node that was removed.” xml.dom.minidom now complies with this requirement.

- bpo-33778: Update `unicodedata`’s database to Unicode version 11.0.0.

- bpo-33165: Added a stacklevel parameter to logging calls to allow use of wrapper/helper functions for logging APIs.

- bpo-33770: improve base64 exception message for encoded inputs of invalid length

- bpo-33769: asyncio/start_tls: Fix error message; cancel callbacks in case of an unhandled error; mark SSLTransport as closed if it is aborted.

- bpo-33767: The concatenation (`+`) and repetition (`*`) sequence operations now raise `TypeError` instead of `SystemError` when performed on `mmap.mmap` objects. Patch by Zackery Spytz.

- bpo-33734: asyncio/ssl: Fix AttributeError, increase default handshake timeout

- bpo-31014: Fixed creating a controller for `webbrowser` when a user specifies a path to an entry in the BROWSER environment variable. Based on patch by John Still.

- bpo-2504: Add gettext.pgettext() and variants.

- bpo-33197: Add description property for _ParameterKind

- bpo-32751: When cancelling the task due to a timeout, `asyncio.wait_for()` will now wait until the cancellation is complete.

- bpo-32684: Fix gather to propagate cancellation of itself even with return_exceptions.

- bpo-33654: Support protocol type switching in SSLTransport.set_protocol().

- bpo-33674: Pause the transport as early as possible to further reduce the risk of data_received() being called before connection_made().

- bpo-33671: `shutil.copyfile()`, `shutil.copy()`, `shutil.copy2()`, `shutil.copytree()` and `shutil.move()` use platform-specific fast-copy syscalls on Linux and macOS in order to copy the file more efficiently. On Windows `shutil.copyfile()` uses a bigger default buffer size (1 MiB instead of 16 KiB) and a `memoryview()`-based variant of `shutil.copyfileobj()` is used. The speedup for copying a 512MiB file is about +26% on Linux, +50% on macOS and +40% on Windows. Also, much less CPU cycles are consumed. (Contributed by Giampaolo Rodola’ in bpo-25427.)

- bpo-33674: Fix a race condition in SSLProtocol.connection_made() of asyncio.sslproto: start immediately the handshake instead of using call_soon(). Previously, data_received() could be called before the handshake started, causing the handshake to hang or fail.

- bpo-31647: Fixed bug where calling write_eof() on a _SelectorSocketTransport after it’s already closed raises AttributeError.

- bpo-32610: Make asyncio.all_tasks() return only pending tasks.

- bpo-32410: Avoid blocking on file IO in sendfile fallback code

- bpo-33469: Fix RuntimeError after closing loop that used run_in_executor

- bpo-33672: Fix Task.__repr__ crash with Cython’s bogus coroutines

- bpo-33654: Fix transport.set_protocol() to support switching between asyncio.Protocol and asyncio.BufferedProtocol. Fix loop.start_tls() to work with asyncio.BufferedProtocols.

- bpo-33652: Pickles of type variables and subscripted generics are now future-proof and compatible with older Python versions.

- bpo-32493: Fixed `uuid.uuid1()` on FreeBSD.

- bpo-33238: Add `InvalidStateError` to `concurrent.futures`. `Future.set_result` and `Future.set_exception` now raise `InvalidStateError` if the futures are not pending or running. Patch by Jason Haydaman.

- bpo-33618: Finalize and document preliminary and experimental TLS 1.3 support with OpenSSL 1.1.1

- bpo-33625: Release GIL on `grp.getgrnam`, `grp.getgrgid`, `pwd.getpwnam` and `pwd.getpwuid` if reentrant variants of these functions are available. Patch by William Grzybowski.

- bpo-33623: Fix possible SIGSGV when asyncio.Future is created in __del__

- bpo-11874: Use a better regex when breaking usage into wrappable parts. Avoids bogus assertion errors from custom metavar strings.

- bpo-30877: Fixed a bug in the Python implementation of the JSON decoder that prevented the cache of parsed strings from clearing after finishing the decoding. Based on patch by c-fos.

- bpo-33604: Remove HMAC default to md5 marked for removal in 3.8 (removal originally planned in 3.6, bump to 3.8 in gh-7062).

- bpo-33582: Emit a deprecation warning for inspect.formatargspec

- bpo-21145: Add `functools.cached_property` decorator, for computed properties cached for the life of the instance.

- bpo-33570: Change TLS 1.3 cipher suite settings for compatibility with OpenSSL 1.1.1-pre6 and newer. OpenSSL 1.1.1 will have TLS 1.3 ciphers enabled by default.

- bpo-28556: Do not simplify arguments to `typing.Union`. Now `Union[Manager, Employee]` is not simplified to `Employee` at runtime. Such simplification previously caused several bugs and limited possibilities for introspection.

- bpo-12486: `tokenize.generate_tokens()` is now documented as a public API to tokenize unicode strings. It was previously present but undocumented.

- bpo-33540: Add a new `block_on_close` class attribute to `ForkingMixIn` and `ThreadingMixIn` classes of `socketserver`.

- bpo-33548: tempfile._candidate_tempdir_list should consider common TEMP locations

- bpo-33109: argparse subparsers are once again not required by default, reverting the change in behavior introduced by bpo-26510 in 3.7.0a2.

- bpo-33541: Remove unused private method `_strptime.LocaleTime.__pad` (a.k.a. `_LocaleTime__pad`).

- bpo-33536: dataclasses.make_dataclass now checks for invalid field names and duplicate fields. Also, added a check for invalid field specifications.

- bpo-33542: Prevent `uuid.get_node` from using a DUID instead of a MAC on Windows. Patch by Zvi Effron

- bpo-26819: Fix race condition with `ReadTransport.resume_reading` in Windows proactor event loop.

- Fix failure in `typing.get_type_hints()` when ClassVar was provided as a string forward reference.

- bpo-33516: `unittest.mock.MagicMock` now supports the `__round__` magic method.

- bpo-28612: Added support for Site Maps to urllib’s `RobotFileParser` as `RobotFileParser.site_maps()`. Patch by Lady Red, based on patch by Peter Wirtz.

- bpo-28167: Remove platform.linux_distribution, which was deprecated since 3.5.

- bpo-33504: Switch the default dictionary implementation for `configparser` from `collections.OrderedDict` to the standard `dict` type.

- bpo-33505: Optimize asyncio.ensure_future() by reordering if checks: 1.17x faster.

- bpo-33497: Add errors param to cgi.parse_multipart and make an encoding in FieldStorage use the given errors (needed for Twisted). Patch by Amber Brown.

- bpo-29235: The `cProfile.Profile` class can now be used as a context manager. Patch by Scott Sanderson.

- bpo-33495: Change dataclasses.Fields repr to use the repr of each of its members, instead of str. This makes it more clear what each field actually represents. This is especially true for the ‘type’ member.

- bpo-26103: Correct `inspect.isdatadescriptor` to look for `__set__` or `__delete__`. Patch by Aaron Hall.

- bpo-29209: Removed the `doctype()` method and the html parameter of the constructor of `XMLParser`. The `doctype()` method defined in a subclass will no longer be called. Deprecated methods `getchildren()` and `getiterator()` in the `ElementTree` module emit now a `DeprecationWarning` instead of `PendingDeprecationWarning`.

- bpo-33453: Fix dataclasses to work if using literal string type annotations or if using PEP 563 “Postponed Evaluation of Annotations”. Only specific string prefixes are detected for both ClassVar (“ClassVar” and “typing.ClassVar”) and InitVar (“InitVar” and “dataclasses.InitVar”).

- bpo-28556: Minor fixes in typing module: add annotations to `NamedTuple.__new__`, pass `*args` and `**kwds` in `Generic.__new__`. Original PRs by Paulius Šarka and Chad Dombrova.

- bpo-33365: Print the header values besides the header keys instead just the header keys if debuglevel is set to >0 in `http.client`. Patch by Marco Strigl.

- bpo-20087: Updated alias mapping with glibc 2.27 supported locales.

- bpo-33422: Fix trailing quotation marks getting deleted when looking up byte/string literals on pydoc. Patch by Andrés Delfino.

- bpo-28167: The function `platform.linux_distribution` and `platform.dist` now trigger a `DeprecationWarning` and have been marked for removal in Python 3.8

- bpo-33281: Fix ctypes.util.find_library regression on macOS.

- bpo-33311: Text and html output generated by cgitb does not display parentheses if the current call is done directly in the module. Patch by Stéphane Blondon.

- bpo-27300: The file classes in tempfile now accept an errors parameter that complements the already existing encoding. Patch by Stephan Hohe.

- bpo-32933: `unittest.mock.mock_open()` now supports iteration over the file contents. Patch by Tony Flury.

- bpo-33217: Raise `TypeError` when looking up non-Enum objects in Enum classes and Enum members.

- bpo-33197: Update error message when constructing invalid inspect.Parameters Patch by Dong-hee Na.

- bpo-33383: Fixed crash in the get() method of the `dbm.ndbm` database object when it is called with a single argument.

- bpo-33375: The warnings module now finds the Python file associated with a warning from the code object, rather than the frame’s global namespace. This is consistent with how tracebacks and pdb find filenames, and should work better for dynamically executed code.

- bpo-33336: `imaplib` now allows `MOVE` command in `IMAP4.uid()` (RFC 6851: IMAP MOVE Extension) and potentially as a name of supported method of `IMAP4` object.

- bpo-32455: Added jump parameter to `dis.stack_effect()`.

- bpo-27485: Rename and deprecate undocumented functions in `urllib.parse()`.

- bpo-33332: Add `signal.valid_signals()` to expose the POSIX sigfillset() functionality.

- bpo-33251: `ConfigParser.items()` was fixed so that key-value pairs passed in via `vars` are not included in the resulting output.

- bpo-33329: Fix multiprocessing regression on newer glibcs

- bpo-33334: `dis.stack_effect()` now supports all defined opcodes including NOP and EXTENDED_ARG.

- bpo-991266: Fix quoting of the `Comment` attribute of `http.cookies.SimpleCookie`.

- bpo-33131: Upgrade bundled version of pip to 10.0.1.

- bpo-33308: Fixed a crash in the `parser` module when converting an ST object to a tree of tuples or lists with `line_info=False` and `col_info=True`.

- bpo-23403: lib2to3 now uses pickle protocol 4 for pre-computed grammars.

- bpo-33266: lib2to3 now recognizes `rf'...'` strings.

- bpo-11594: Ensure line-endings are respected when using lib2to3.

- bpo-33254: Have `importlib.resources.contents()` and `importlib.abc.ResourceReader.contents()` return an iterable instead of an iterator.

- bpo-33265: `contextlib.ExitStack` and `contextlib.AsyncExitStack` now use a method instead of a wrapper function for exit callbacks.

- bpo-33263: Fix FD leak in `_SelectorSocketTransport` Patch by Vlad Starostin.

- bpo-33256: Fix display of `<module>` call in the html produced by `cgitb.html()`. Patch by Stéphane Blondon.

- bpo-33144: `random.Random()` and its subclassing mechanism got optimized to check only once at class/subclass instantiation time whether its `getrandbits()` method can be relied on by other methods, including `randrange()`, for the generation of arbitrarily large random integers. Patch by Wolfgang Maier.

- bpo-33185: Fixed regression when running pydoc with the `-m` switch. (The regression was introduced in 3.7.0b3 by the resolution of bpo-33053)

  This fix also changed pydoc to add `os.getcwd()` to `sys.path` when necessary, rather than adding `"."`.

- bpo-29613: Added support for the `SameSite` cookie flag to the `http.cookies` module.

- bpo-33169: Delete entries of `None` in `sys.path_importer_cache` when `importlib.machinery.invalidate_caches()` is called.

- bpo-33203: `random.Random.choice()` now raises `IndexError` for empty sequences consistently even when called from subclasses without a `getrandbits()` implementation.

- bpo-33224: Update difflib.mdiff() for PEP 479. Convert an uncaught StopIteration in a generator into a return-statement.

- bpo-33209: End framing at the end of C implementation of `pickle.Pickler.dump()`.

- bpo-32861: The urllib.robotparser’s `__str__` representation now includes wildcard entries and the “Crawl-delay” and “Request-rate” fields. Also removes extra newlines that were being appended to the end of the string. Patch by Michael Lazar.

- bpo-23403: `DEFAULT_PROTOCOL` in `pickle` was bumped to 4. Protocol 4 is described in PEP 3154 and available since Python 3.4. It offers better performance and smaller size compared to protocol 3 introduced in Python 3.0.

- bpo-20104: Improved error handling and fixed a reference leak in `os.posix_spawn()`.

- bpo-33106: Deleting a key from a read-only dbm database raises module specific error instead of KeyError.

- bpo-33175: In dataclasses, Field.__set_name__ now looks up the __set_name__ special method on the class, not the instance, of the default value.

- bpo-32380: Create functools.singledispatchmethod to support generic single dispatch on descriptors and methods.

- bpo-33141: Have Field objects pass through __set_name__ to their default values, if they have their own __set_name__.

- bpo-33096: Allow ttk.Treeview.insert to insert iid that has a false boolean value. Note iid=0 and iid=False would be same. Patch by Garvit Khatri.

- bpo-32873: Treat type variables and special typing forms as immutable by copy and pickle. This fixes several minor issues and inconsistencies, and improves backwards compatibility with Python 3.6.

- bpo-33134: When computing dataclass’s __hash__, use the lookup table to contain the function which returns the __hash__ value. This is an improvement over looking up a string, and then testing that string to see what to do.

- bpo-33127: The ssl module now compiles with LibreSSL 2.7.1.

- bpo-32505: Raise TypeError if a member variable of a dataclass is of type Field, but doesn’t have a type annotation.

- bpo-33078: Fix the failure on OSX caused by the tests relying on sem_getvalue

- bpo-33116: Add ‘Field’ to dataclasses.__all__.

- bpo-32896: Fix an error where subclassing a dataclass with a field that uses a default_factory would generate an incorrect class.

- bpo-33100: Dataclasses: If a field has a default value that’s a MemberDescriptorType, then it’s from that field being in __slots__, not an actual default value.

- bpo-32953: If a non-dataclass inherits from a frozen dataclass, allow attributes to be added to the derived class. Only attributes from the frozen dataclass cannot be assigned to. Require all dataclasses in a hierarchy to be either all frozen or all non-frozen.

- bpo-33097: Raise RuntimeError when `executor.submit` is called during interpreter shutdown.

- bpo-32968: Modulo and floor division involving Fraction and float should return float.

- bpo-33061: Add missing `NoReturn` to `__all__` in typing.py

- bpo-33078: Fix the size handling in multiprocessing.Queue when a pickling error occurs.

- bpo-33064: lib2to3 now properly supports trailing commas after `*args` and `**kwargs` in function signatures.

- bpo-33056: FIX properly close leaking fds in concurrent.futures.ProcessPoolExecutor.

- bpo-33021: Release the GIL during fstat() calls, avoiding hang of all threads when calling mmap.mmap(), os.urandom(), and random.seed(). Patch by Nir Soffer.

- bpo-31804: Avoid failing in multiprocessing.Process if the standard streams are closed or None at exit.

- bpo-33034: Providing an explicit error message when casting the port property to anything that is not an integer value using `urlparse()` and `urlsplit()`. Patch by Matt Eaton.

- bpo-30249: Improve struct.unpack_from() exception messages for problems with the buffer size and offset.

- bpo-33037: Skip sending/receiving data after SSL transport closing.

- bpo-27683: Fix a regression in `ipaddress` that result of `hosts()` is empty when the network is constructed by a tuple containing an integer mask and only 1 bit left for addresses.

- bpo-22674: Add the strsignal() function in the signal module that returns the system description of the given signal, as returned by strsignal(3).

- bpo-32999: Fix C implementation of `ABC.__subclasscheck__(cls, subclass)` crashed when `subclass` is not a type object.

- bpo-33009: Fix inspect.signature() for single-parameter partialmethods.

- bpo-32969: Expose several missing constants in zlib and fix corresponding documentation.

- bpo-32056: Improved exceptions raised for invalid number of channels and sample width when read an audio file in modules `aifc`, `wave` and `sunau`.

- bpo-32970: Improved disassembly of the MAKE_FUNCTION instruction.

- bpo-32844: Fix wrong redirection of a low descriptor (0 or 1) to stderr in subprocess if another low descriptor is closed.

- bpo-32960: For dataclasses, disallow inheriting frozen from non-frozen classes, and also disallow inheriting non-frozen from frozen classes. This restriction will be relaxed at a future date.

- bpo-32713: Fixed tarfile.itn handling of out-of-bounds float values. Patch by Joffrey Fuhrer.

- bpo-32257: The ssl module now contains OP_NO_RENEGOTIATION constant, available with OpenSSL 1.1.0h or 1.1.1.

- bpo-32951: Direct instantiation of SSLSocket and SSLObject objects is now prohibited. The constructors were never documented, tested, or designed as public constructors. Users were suppose to use ssl.wrap_socket() or SSLContext.

- bpo-32929: Remove the tri-state parameter “hash”, and add the boolean “unsafe_hash”. If unsafe_hash is True, add a __hash__ function, but if a __hash__ exists, raise TypeError. If unsafe_hash is False, add a __hash__ based on the values of eq= and frozen=. The unsafe_hash=False behavior is the same as the old hash=None behavior. unsafe_hash=False is the default, just as hash=None used to be.

- bpo-32947: Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround for TLSv1.3 for future compatibility with OpenSSL 1.1.1.

- bpo-32146: Document the interaction between frozen executables and the spawn and forkserver start methods in multiprocessing.

- bpo-30622: The ssl module now detects missing NPN support in LibreSSL.

- bpo-32922: dbm.open() now encodes filename with the filesystem encoding rather than default encoding.

- bpo-32759: Free unused arenas in multiprocessing.heap.

- bpo-32859: In `os.dup2`, don’t check every call whether the `dup3` syscall exists or not.

- bpo-32556: nt._getfinalpathname, nt._getvolumepathname and nt._getdiskusage now correctly convert from bytes.

- bpo-21060: Rewrite confusing message from setup.py upload from “No dist file created in earlier command” to the more helpful “Must create and upload files in one command”.

- bpo-32857: In `tkinter`, `after_cancel(None)` now raises a `ValueError` instead of canceling the first scheduled function. Patch by Cheryl Sabella.

- bpo-32852: Make sure sys.argv remains as a list when running trace.

- bpo-31333: `_abc` module is added. It is a speedup module with C implementations for various functions and methods in `abc`. Creating an ABC subclass and calling `isinstance` or `issubclass` with an ABC subclass are up to 1.5x faster. In addition, this makes Python start-up up to 10% faster.

  Note that the new implementation hides internal registry and caches, previously accessible via private attributes `_abc_registry`, `_abc_cache`, and `_abc_negative_cache`. There are three debugging helper methods that can be used instead `_dump_registry`, `_abc_registry_clear`, and `_abc_caches_clear`.

- bpo-32841: Fixed `asyncio.Condition` issue which silently ignored cancellation after notifying and cancelling a conditional lock. Patch by Bar Harel.

- bpo-32819: ssl.match_hostname() has been simplified and no longer depends on re and ipaddress module for wildcard and IP addresses. Error reporting for invalid wildcards has been improved.

- bpo-19675: `multiprocessing.Pool` no longer leaks processes if its initialization fails.

- bpo-32394: socket: Remove TCP_FASTOPEN,TCP_KEEPCNT,TCP_KEEPIDLE,TCP_KEEPINTVL flags on older version Windows during run-time.

- bpo-31787: Fixed refleaks of `__init__()` methods in various modules. (Contributed by Oren Milman)

- bpo-30157: Fixed guessing quote and delimiter in csv.Sniffer.sniff() when only the last field is quoted. Patch by Jake Davis.

- bpo-30688: Added support of `\N{name}` escapes in regular expressions. Based on patch by Jonathan Eunice.

- bpo-32792: collections.ChainMap() preserves the order of the underlying mappings.

- bpo-32775: `fnmatch.translate()` no longer produces patterns which contain set operations. Sets starting with ‘[’ or containing ‘–’, ‘&&’, ‘~~’ or ‘||’ will be interpreted differently in regular expressions in future versions. Currently they emit warnings. fnmatch.translate() now avoids producing patterns containing such sets by accident.

- bpo-32622: Implement native fast sendfile for Windows proactor event loop.

- bpo-32777: Fix a rare but potential pre-exec child process deadlock in subprocess on POSIX systems when marking file descriptors inheritable on exec in the child process. This bug appears to have been introduced in 3.4.

- bpo-32647: The ctypes module used to depend on indirect linking for dlopen. The shared extension is now explicitly linked against libdl on platforms with dl.

- bpo-32749: A `dbm.dumb` database opened with flags ‘r’ is now read-only. `dbm.dumb.open()` with flags ‘r’ and ‘w’ no longer creates a database if it does not exist.

- bpo-32741: Implement `asyncio.TimerHandle.when()` method.

- bpo-32691: Use mod_spec.parent when running modules with pdb

- bpo-32734: Fixed `asyncio.Lock()` safety issue which allowed acquiring and locking the same lock multiple times, without it being free. Patch by Bar Harel.

- bpo-32727: Do not include name field in SMTP envelope from address. Patch by Stéphane Wirtel

- bpo-31453: Add TLSVersion constants and SSLContext.maximum_version / minimum_version attributes. The new API wraps OpenSSL 1.1 https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_set_min_proto_version.html feature.

- bpo-24334: Internal implementation details of ssl module were cleaned up. The SSLSocket has one less layer of indirection. Owner and session information are now handled by the SSLSocket and SSLObject constructor. Channel binding implementation has been simplified.

- bpo-31848: Fix the error handling in Aifc_read.initfp() when the SSND chunk is not found. Patch by Zackery Spytz.

- bpo-32585: Add Ttk spinbox widget to `tkinter.ttk`. Patch by Alan D Moore.

- bpo-32512: `profile` CLI accepts `-m module_name` as an alternative to script path.

- bpo-8525: help() on a type now displays builtin subclasses. This is intended primarily to help with notification of more specific exception subclasses.

  Patch by Sanyam Khurana.

- bpo-31639: http.server now exposes a ThreadingHTTPServer class and uses it when the module is run with `-m` to cope with web browsers pre-opening sockets.

- bpo-29877: compileall: import ProcessPoolExecutor only when needed, preventing hangs on low resource platforms

- bpo-32221: Various functions returning tuple containing IPv6 addresses now omit `%scope` part since the same information is already encoded in scopeid tuple item. Especially this speeds up `socket.recvfrom()` when it receives multicast packet since useless resolving of network interface name is omitted.

- bpo-32147: `binascii.unhexlify()` is now up to 2 times faster. Patch by Sergey Fedoseev.

- bpo-30693: The TarFile class now recurses directories in a reproducible way.

- bpo-30693: The ZipFile class now recurses directories in a reproducible way.

- bpo-31680: Added `curses.ncurses_version`.

- bpo-31908: Fix output of cover files for `trace` module command-line tool. Previously emitted cover files only when `--missing` option was used. Patch by Michael Selik.

- bpo-31608: Raise a `TypeError` instead of crashing if a `collections.deque` subclass returns a non-deque from `__new__`. Patch by Oren Milman.

- bpo-31425: Add support for sockets of the AF_QIPCRTR address family, supported by the Linux kernel. This is used to communicate with services, such as GPS or radio, running on Qualcomm devices. Patch by Bjorn Andersson.

- bpo-22005: Implemented unpickling instances of `datetime`, `date` and `time` pickled by Python 2. `encoding='latin1'` should be used for successful decoding.

- bpo-27645: `sqlite3.Connection` now exposes a `backup` method, if the underlying SQLite library is at version 3.6.11 or higher. Patch by Lele Gaifax.

- bpo-16865: Support arrays >=2GiB in `ctypes`. Patch by Segev Finer.

- bpo-31508: Removed support of arguments in `tkinter.ttk.Treeview.selection`. It was deprecated in 3.6. Use specialized methods like `selection_set` for changing the selection.

- bpo-29456: Fix bugs in hangul normalization: u1176, u11a7 and u11c3

### Documentation

- bpo-21257: Document `http.client.parse_headers()`.

- bpo-34764: Improve example of iter() with 2nd sentinel argument.

- bpo-35564: Explicitly set master_doc variable in conf.py for compliance with Sphinx 2.0

- bpo-35511: Specified that profile.Profile class doesn’t not support enable or disable methods. Also, elaborated that Profile object as a context manager is only supported in cProfile module.

- bpo-10536: Enhance the gettext docs. Patch by Éric Araujo

- bpo-35089: Remove mention of `typing.io` and `typing.re`. Their types should be imported from `typing` directly.

- bpo-35038: Fix the documentation about an unexisting `f_restricted` attribute in the frame object. Patch by Stéphane Wirtel

- bpo-35042: Replace PEP XYZ by the pep role and allow to use the direct links to the PEPs.

- bpo-35044: Fix the documentation with the role `exc` for the appropriated exception. Patch by Stéphane Wirtel

- bpo-35035: Rename documentation for `email.utils` to `email.utils.rst`.

- bpo-34967: Use app.add_object_type() instead of the deprecated Sphinx function app.description_unit()

- bpo-34913: Add documentation about the new command line interface of the gzip module.

- bpo-32174: chm document displays non-ASCII charaters properly on some MBCS Windows systems.

- bpo-11233: Create availability directive for documentation. Original patch by Georg Brandl.

- bpo-34790: Document how passing coroutines to asyncio.wait() can be confusing.

- bpo-34552: Make clear that `==` operator sometimes is equivalent to `is`. The `<`, `<=`, `>` and `>=` operators are only defined where they make sense.

- bpo-28617: Fixed info in the stdtypes docs concerning the types that support membership tests.

- bpo-20177: Migrate datetime.date.fromtimestamp to Argument Clinic. Patch by Tim Hoffmann.

- bpo-34065: Fix wrongly written basicConfig documentation markup syntax

- bpo-33460: replaced ellipsis with correct error codes in tutorial chapter 3.

- bpo-33847: Add ‘@’ operator entry to index.

- bpo-33409: Clarified the relationship between PEP 538’s PYTHONCOERCECLOCALE and PEP 540’s PYTHONUTF8 mode.

- bpo-33197: Add versionadded tag to the documentation of ParameterKind.description

- bpo-17045: Improve the C-API doc for PyTypeObject. This includes adding several quick-reference tables and a lot of missing slot/typedef entries. The existing entries were also cleaned up with a slightly more consistent format.

- bpo-33736: Improve the documentation of `asyncio.open_connection()`, `asyncio.start_server()` and their UNIX socket counterparts.

- bpo-23859: Document that `asyncio.wait()` does not cancel its futures on timeout.

- bpo-32436: Document PEP 567 changes to asyncio.

- bpo-33604: Update HMAC md5 default to a DeprecationWarning, bump removal to 3.8.

- bpo-33594: Document `getargspec`, `from_function` and `from_builtin` as deprecated in their respective docstring, and include version since deprecation in DeprecationWarning message.

- bpo-33503: Fix broken pypi link

- bpo-33421: Add missing documentation for `typing.AsyncContextManager`.

- bpo-33487: BZ2file now emit a DeprecationWarning when buffering=None is passed, the deprecation message and documentation also now explicitly state it is deprecated since 3.0.

- bpo-33378: Add Korean language switcher for https://docs.python.org/3/

- bpo-33276: Clarify that the `__path__` attribute on modules cannot be just any value.

- bpo-33201: Modernize documentation for writing C extension types.

- bpo-33195: Deprecate `Py_UNICODE` usage in `c-api/arg` document. `Py_UNICODE` related APIs are deprecated since Python 3.3, but it is missed in the document.

- bpo-33126: Document PyBuffer_ToContiguous().

- bpo-27212: Modify documentation for the `islice()` recipe to consume initial values up to the start index.

- bpo-28247: Update `zipapp` documentation to describe how to make standalone applications.

- bpo-18802: Documentation changes for ipaddress. Patch by Jon Foster and Berker Peksag.

- bpo-27428: Update documentation to clarify that `WindowsRegistryFinder` implements `MetaPathFinder`. (Patch by Himanshu Lakhara)

- bpo-28124: The ssl module function ssl.wrap_socket() has been de-emphasized and deprecated in favor of the more secure and efficient SSLContext.wrap_socket() method.

- bpo-17232: Clarify docs for -O and -OO. Patch by Terry Reedy.

- bpo-32436: Add documentation for the contextvars module (PEP 567).

- bpo-32800: Update link to w3c doc for xml default namespaces.

- bpo-11015: Update `test.support` documentation.

- bpo-32613: Update the faq/windows.html to use the py command from PEP 397 instead of python.

- bpo-8722: Document `__getattr__()` behavior when property `get()` method raises `AttributeError`.

- bpo-32614: Modify RE examples in documentation to use raw strings to prevent `DeprecationWarning` and add text to REGEX HOWTO to highlight the deprecation.

- bpo-20709: Remove the paragraph where we explain that os.utime() does not support a directory as path under Windows. Patch by Jan-Philip Gehrcke

- bpo-32722: Remove the bad example in the tutorial of the Generator Expression. Patch by Stéphane Wirtel

- bpo-31972: Improve docstrings for `pathlib.PurePath` subclasses.

- bpo-30607: Use the externalized `python-docs-theme` package when building the documentation.

- bpo-8243: Add a note about curses.addch and curses.addstr exception behavior when writing outside a window, or pad.

- bpo-32337: Update documentation related with `dict` order.

- bpo-25041: Document `AF_PACKET` in the `socket` module.

- bpo-31432: Clarify meaning of CERT_NONE, CERT_OPTIONAL, and CERT_REQUIRED flags for ssl.SSLContext.verify_mode.

### Tests

- bpo-35772: Fix sparse file tests of test_tarfile on ppc64 with the tmpfs filesystem. Fix the function testing if the filesystem supports sparse files: create a file which contains data and “holes”, instead of creating a file which contains no data. tmpfs effective block size is a page size (tmpfs lives in the page cache). RHEL uses 64 KiB pages on aarch64, ppc64, ppc64le, only s390x and x86_64 use 4 KiB pages, whereas the test punch holes of 4 KiB.

- bpo-35045: Make ssl tests less strict and also accept TLSv1 as system default. The changes unbreaks test_min_max_version on Fedora 29.

- bpo-32710: `test_asyncio/test_sendfile.py` now resets the event loop policy using `tearDownModule()` as done in other tests, to prevent a warning when running tests on Windows.

- bpo-33717: test.pythoninfo now logs information of all clocks, not only time.time() and time.perf_counter().

- bpo-35488: Add a test to pathlib’s Path.match() to verify it does not support glob-style ** recursive pattern matching.

- bpo-31731: Fix a race condition in `check_interrupted_write()` of test_io: create directly the thread with SIGALRM signal blocked, rather than blocking the signal later from the thread. Previously, it was possible that the thread gets the signal before the signal is blocked.

- bpo-35424: Fix test_multiprocessing_main_handling: use `multiprocessing.Pool` with a context manager and then explicitly join the pool.

- bpo-35519: Rename `test.bisect` module to `test.bisect_cmd` to avoid conflict with `bisect` module when running directly a test like `./python Lib/test/test_xmlrpc.py`.

- bpo-35513: Replace `time.time()` with `time.monotonic()` in tests to measure time delta.

- bpo-34279: `test.support.run_unittest()` no longer raise `TestDidNotRun` if the test result contains skipped tests. The exception is now only raised if no test have been run and no test have been skipped.

- bpo-35412: Add testcase to `test_future4`: check unicode literal.

- bpo-26704: Added test demonstrating double-patching of an instance method. Patch by Anthony Sottile.

- bpo-33725: test_multiprocessing_fork may crash on recent versions of macOS. Until the issue is resolved, skip the test on macOS.

- bpo-35352: Modify test_asyncio to use the certificate set from the test directory.

- bpo-35317: Fix `mktime()` overflow error in `test_email`: run `test_localtime_daylight_true_dst_true()` and `test_localtime_daylight_false_dst_true()` with a specific timezone.

- bpo-21263: After several reports that test_gdb does not work properly on macOS and since gdb is not shipped by default anymore, test_gdb is now skipped on macOS when LLVM Clang has been used to compile Python. Patch by Lysandros Nikolaou

- bpo-34279: regrtest issue a warning when no tests have been executed in a particular test file. Also, a new final result state is issued if no test have been executed across all test files. Patch by Pablo Galindo.

- bpo-34962: make docstest in Doc now passes., and is enforced in CI

- bpo-23596: Use argparse for the command line of the gzip module. Patch by Antony Lee

- bpo-34537: Fix `test_gdb.test_strings()` when `LC_ALL=C` and GDB was compiled with Python 3.6 or earlier.

- bpo-34587: test_socket: Remove RDSTest.testCongestion(). The test tries to fill the receiver’s socket buffer and expects an error. But the RDS protocol doesn’t require that. Moreover, the Linux implementation of RDS expects that the producer of the messages reduces its rate, it’s not the role of the receiver to trigger an error. The test fails on Fedora 28 by design, so just remove it.

- bpo-34661: Fix test_shutil if unzip doesn’t support -t.

- bpo-34200: Fixed non-deterministic flakiness of test_pkg by not using the scary test.support.module_cleanup() logic to save and restore sys.modules contents between test cases.

- bpo-34569: The experimental PEP 554 data channels now correctly pass negative PyLong objects between subinterpreters on 32-bit systems. Patch by Michael Felt.

- bpo-34594: Fix usage of hardcoded `errno` values in the tests.

- bpo-34579: Fix test_embed for AIX Patch by Michael Felt

- bpo-34542: Use 3072 RSA keys and SHA-256 signature for test certs and keys.

- bpo-11193: Remove special condition for AIX in `test_subprocess.test_undecodable_env`

- bpo-34347: Fix `test_utf8_mode.test_cmd_line` for AIX

- bpo-34490: On AIX with AF_UNIX family sockets getsockname() does not provide ‘sockname’, so skip calls to transport.get_extra_info(‘sockname’)

- bpo-34391: Fix ftplib test for TLS 1.3 by reading from data socket.

- bpo-11192: Fix `test_socket` on AIX 6.1 and later IPv6 zone id supports only supported by inet_pton6_zone() Switch to runtime-based platform.system() to establish current platform rather than build-time based sys.platform()

- bpo-34399: Update all RSA keys and DH params to use at least 2048 bits.

- bpo-34373: Fix `test_mktime` and `test_pthread_getcpuclickid` tests for AIX Add range checking for `_PyTime_localtime` for AIX Patch by Michael Felt

- bpo-11191: Skip the distutils test ‘test_search_cpp’ when using XLC as compiler patch by aixtools (Michael Felt)

- Improved an error message when mock assert_has_calls fails.

- bpo-33746: Fix test_unittest when run in verbose mode.

- bpo-33901: Fix test_dbm_gnu on macOS with gdbm 1.15: add a larger value to make sure that the file size changes.

- bpo-33873: Fix a bug in `regrtest` that caused an extra test to run if –huntrleaks/-R was used. Exit with error in case that invalid parameters are specified to –huntrleaks/-R (at least one warmup run and one repetition must be used).

- bpo-33562: Check that a global asyncio event loop policy is not left behind by any tests.

- bpo-33655: Ignore test_posix_fallocate failures on BSD platforms that might be due to running on ZFS.

- bpo-32962: Fixed test_gdb when Python is compiled with flags -mcet -fcf-protection -O0.

- bpo-33358: Fix `test_embed.test_pre_initialization_sys_options()` when the interpreter is built with `--enable-shared`.

- bpo-32872: Avoid regrtest compatibility issue with namespace packages.

- bpo-32517: Fix failing `test_asyncio` on macOS 10.12.2+ due to transport of `KqueueSelector` loop was not being closed.

- bpo-32663: Making sure the `SMTPUTF8SimTests` class of tests gets run in test_smtplib.py.

- bpo-27643: Test_C test case needs “signed short” bitfields, but the IBM XLC compiler (on AIX) does not support this Skip the code and test when AIX and XLC are used

  Applicable to Python2-2.7 and later

- bpo-19417: Add test_bdb.py.

- bpo-31809: Add tests to verify connection with secp ECDH curves.

### Build

- bpo-34691: The _contextvars module is now built into the core Python library on Windows.

- bpo-35683: Improved Azure Pipelines build steps and now verifying layouts correctly

- bpo-35642: Remove asynciomodule.c from pythoncore.vcxproj

- bpo-35550: Fix incorrect Solaris #ifdef checks to look for __sun && __SVR4 instead of sun when compiling.

- bpo-35499: `make profile-opt` no longer replaces `CFLAGS_NODIST` with `CFLAGS`. It now adds profile-guided optimization (PGO) flags to `CFLAGS_NODIST`: existing `CFLAGS_NODIST` flags are kept.

- bpo-35257: Avoid leaking the linker flags from Link Time Optimizations (LTO) into distutils when compiling C extensions.

- bpo-35351: When building Python with clang and LTO, LTO flags are no longer passed into CFLAGS to build third-party C extensions through distutils.

- bpo-35139: Fix a compiler error when statically linking `pyexpat` in `Modules/Setup`.

- bpo-35059: PCbuild: Set InlineFunctionExpansion to OnlyExplicitInline (“/Ob1” option) in pyproject.props in Debug mode to expand functions marked as inline. This change should make Python compiled in Debug mode a little bit faster on Windows.

- bpo-35011: Restores the use of pyexpatns.h to isolate our embedded copy of the expat C library so that its symbols do not conflict at link or dynamic loading time with an embedding application or other extension modules with their own version of libexpat.

- bpo-28015: Have –with-lto works correctly with clang.

- bpo-34765: Update the outdated install-sh file to the latest revision from automake v1.16.1

- bpo-34585: Check for floating-point byte order in configure.ac using compilation tests instead of executing code, so that these checks work in cross-compiled builds.

- bpo-34710: Fixed SSL module build with OpenSSL & pedantic CFLAGS.

- bpo-34582: Add JUnit XML output for regression tests and update Azure DevOps builds.

- bpo-34081: Make Sphinx warnings as errors in the Docs Makefile.

- bpo-34555: Fix for case where it was not possible to have both `HAVE_LINUX_VM_SOCKETS_H` and `HAVE_SOCKADDR_ALG` be undefined.

- bpo-33015: Fix an undefined behaviour in the pthread implementation of `PyThread_start_new_thread()`: add a function wrapper to always return `NULL`.

- bpo-34245: The Python shared library is now installed with write permission (mode 0755), which is the standard way of installing such libraries.

- bpo-34121: Fix detection of C11 atomic support on clang.

- bpo-32430: Rename Modules/Setup.dist to Modules/Setup, and remove the necessity to copy the former manually to the latter when updating the local source tree.

- bpo-30345: Add -g to LDFLAGS when compiling with LTO to get debug symbols.

- bpo-5755: Move `-Wstrict-prototypes` option to `CFLAGS_NODIST` from `OPT`. This option emitted annoying warnings when building extension modules written in C++.

- bpo-33614: Ensures module definition files for the stable ABI on Windows are correctly regenerated.

- bpo-33648: The –with-c-locale-warning configuration flag has been removed. It has had no effect for about a year.

- bpo-33522: Enable CI builds on Visual Studio Team Services at https://python.visualstudio.com/cpython

- bpo-33512: configure’s check for “long double” has been simplified

- bpo-33483: C compiler is now correctly detected from the standard environment variables. –without-gcc and –with-icc options have been removed.

- bpo-33394: Enable the verbose build for extension modules, when GNU make is passed macros on the command line.

- bpo-33393: Update config.guess and config.sub files.

- bpo-33377: Add new triplets for mips r6 and riscv variants (used in extension suffixes).

- bpo-32232: By default, modules configured in `Modules/Setup` are no longer built with `-DPy_BUILD_CORE`. Instead, modules that specifically need that preprocessor definition include it in their individual entries.

- bpo-33182: The embedding tests can once again be built with clang 6.0

- bpo-33163: Upgrade pip to 9.0.3 and setuptools to v39.0.1.

- bpo-33012: gcc 8 has added a new warning heuristic to detect invalid function casts and a stock python build seems to hit that warning quite often. The most common is the cast of a METH_NOARGS function (that uses just one argument) to a PyCFunction. Fix this by adding a dummy argument to all functions that implement METH_NOARGS.

- bpo-32898: Fix the python debug build when using COUNT_ALLOCS.

- bpo-29442: Replace optparse with argparse in setup.py

### Windows

- bpo-35890: Fix API calling consistency of GetVersionEx and wcstok.

- bpo-32560: The `py` launcher now forwards its `STARTUPINFO` structure to child processes.

- bpo-35854: Fix EnvBuilder and –symlinks in venv on Windows

- bpo-35811: Avoid propagating venv settings when launching via py.exe

- bpo-35797: Fix default executable used by the multiprocessing module

- bpo-35758: Allow building on ARM with MSVC.

- bpo-29734: Fix handle leaks in os.stat on Windows.

- bpo-35596: Use unchecked PYCs for the embeddable distro to avoid zipimport restrictions.

- bpo-35596: Fix vcruntime140.dll being added to embeddable distro multiple times.

- bpo-35402: Update Windows build to use Tcl and Tk 8.6.9

- bpo-35401: Updates Windows build to OpenSSL 1.1.0j

- bpo-34977: venv on Windows will now use a python.exe redirector rather than copying the actual binaries from the base environment.

- bpo-34977: Adds support for building a Windows App Store package

- bpo-35067: Remove _distutils_findvs module and use vswhere.exe instead.

- bpo-32557: Allow shutil.disk_usage to take a file path on Windows

- bpo-34770: Fix a possible null pointer dereference in pyshellext.cpp.

- bpo-34603: Fix returning structs from functions produced by MSVC

- bpo-34581: Guard MSVC-specific code in socketmodule.c with `#ifdef _MSC_VER`.

- bpo-34532: Fixes exit code of list version arguments for py.exe.

- bpo-34062: Fixed the ‘–list’ and ‘–list-paths’ arguments for the py.exe launcher

- bpo-34225: Ensure INCLUDE and LIB directories do not end with a backslash.

- bpo-34011: A suite of code has been changed which copied across DLLs and init.tcl from the running Python location into a venv being created. These copies are needed only when running from a Python source build, and the copying code is now only run when that is the case, rather than whenever a venv is created.

- bpo-34006: Revert line length limit for Windows help docs. The line-length limit is not needed because the pages appear in a separate app rather than on a browser tab. It can also interact badly with the DPI setting.

- bpo-31546: Restore running PyOS_InputHook while waiting for user input at the prompt. The restores integration of interactive GUI windows (such as Matplotlib figures) with the prompt on Windows.

- bpo-30237: Output error when ReadConsole is canceled by CancelSynchronousIo instead of crashing.

- bpo-33895: GIL is released while calling functions that acquire Windows loader lock.

- bpo-33720: Reduces maximum marshal recursion depth on release builds.

- bpo-29097: Fix bug where `datetime.fromtimestamp()` erroneously throws an `OSError` on Windows for values between 0 and 86400. Patch by Ammar Askar.

- bpo-33316: PyThread_release_lock always fails

- bpo-33184: Update Windows installer to use OpenSSL 1.1.0h.

- bpo-32890: Fix usage of GetLastError() instead of errno in os.execve() and os.truncate().

- bpo-33016: Fix potential use of uninitialized memory in nt._getfinalpathname

- bpo-32903: Fix a memory leak in os.chdir() on Windows if the current directory is set to a UNC path.

- bpo-32901: Update Tcl and Tk versions to 8.6.8

- bpo-31966: Fixed WindowsConsoleIO.write() for writing empty data.

- bpo-32409: Ensures activate.bat can handle Unicode contents.

- bpo-32457: Improves handling of denormalized executable path when launching Python.

- bpo-32370: Use the correct encoding for ipconfig output in the uuid module. Patch by Segev Finer.

- bpo-29248: Fix `os.readlink()` on Windows, which was mistakenly treating the `PrintNameOffset` field of the reparse data buffer as a number of characters instead of bytes. Patch by Craig Holmquist and SSE4.

- bpo-1104: Correctly handle string length in `msilib.SummaryInfo.GetProperty()` to prevent it from truncating the last character.

### macOS

- bpo-35401: Update macOS installer to use OpenSSL 1.1.0j.

- bpo-35025: Properly guard the use of the `CLOCK_GETTIME` et al. macros in `timemodule` on macOS.

- bpo-24658: On macOS, fix reading from and writing into a file with a size larger than 2 GiB.

- bpo-34405: Update to OpenSSL 1.1.0i for macOS installer builds.

- bpo-33635: In macOS stat on some file descriptors (/dev/fd/3 f.e) will result in bad file descriptor OSError. Guard against this exception was added in is_dir, is_file and similar methods. DirEntry.is_dir can also throw this exception so _RecursiveWildcardSelector._iterate_directories was also extended with the same error ignoring pattern.

- bpo-13631: The .editrc file in user’s home directory is now processed correctly during the readline initialization through editline emulation on macOS.

- bpo-33184: Update macOS installer build to use OpenSSL 1.1.0h.

- bpo-32726: Build and link with private copy of Tcl/Tk 8.6 for the macOS 10.6+ installer. The 10.9+ installer variant already does this. This means that the Python 3.7 provided by the python.org macOS installers no longer need or use any external versions of Tcl/Tk, either system-provided or user-installed, such as ActiveTcl.

- bpo-32901: Update macOS 10.9+ installer to Tcl/Tk 8.6.8.

- bpo-31903: In `_scproxy`, drop the GIL when calling into `SystemConfiguration` to avoid deadlocks.

### IDLE

- bpo-35770: IDLE macosx deletes Options => Configure IDLE. It previously deleted Window => Zoom Height by mistake. (Zoom Height is now on the Options menu). On Mac, the settings dialog is accessed via Preferences on the IDLE menu.

- bpo-35769: Change IDLE’s new file name from ‘Untitled’ to ‘untitled’

- bpo-35660: Fix imports in idlelib.window.

- bpo-35641: Proper format `calltip` when the function has no docstring.

- bpo-33987: Use ttk Frame for ttk widgets.

- bpo-34055: Fix erroneous ‘smart’ indents and newlines in IDLE Shell.

- bpo-35591: Find Selection now works when selection not found.

- bpo-35196: Speed up squeezer line counting.

- bpo-35598: Update config_key: use PEP 8 names and ttk widgets, make some objects global, and add tests.

- bpo-28097: Add Previous/Next History entries to Shell menu.

- bpo-35208: Squeezer now properly counts wrapped lines before newlines.

- bpo-35555: Gray out Code Context menu entry when it’s not applicable.

- bpo-35521: Document the IDLE editor code context feature. Add some internal references within the IDLE doc.

- bpo-22703: The Code Context menu label now toggles between Show/Hide Code Context. The Zoom Height menu now toggles between Zoom/Restore Height. Zoom Height has moved from the Window menu to the Options menu.

- bpo-35213: Where appropriate, use ‘macOS’ in idlelib.

- bpo-34864: On macOS, warn if the system preference “Prefer tabs when opening documents” is set to “Always”.

- bpo-34864: Document two IDLE on MacOS issues. The System Preferences Dock “prefer tabs always” setting disables some IDLE features. Menus are a bit different than as described for Windows and Linux.

- bpo-35202: Remove unused imports from lib/idlelib

- bpo-33000: Document that IDLE’s shell has no line limit. A program that runs indefinitely can overfill memory.

- bpo-23220: Explain how IDLE’s Shell displays output.

- bpo-35099: Improve the doc about IDLE running user code. The section is renamed from “IDLE – console differences” is renamed “Running user code”. It mostly covers the implications of using custom sys.stdxxx objects.

- bpo-35097: Add IDLE doc subsection explaining editor windows. Topics include opening, title and status bar, .py* extension, and running.

- bpo-35093: Document the IDLE document viewer in the IDLE doc. Add a paragraph in “Help and preferences”, “Help sources” subsection.

- bpo-35088: Update idlelib.help.copy_string docstring. We now use git and backporting instead of hg and forward merging.

- bpo-35087: Update idlelib help files for the current doc build. The main change is the elimination of chapter-section numbers.

- bpo-34548: Use configured color theme for read-only text views.

- bpo-1529353: Enable “squeezing” of long outputs in the shell, to avoid performance degradation and to clean up the history without losing it. Squeezed outputs may be copied, viewed in a separate window, and “unsqueezed”.

- bpo-34047: Fixed mousewheel scrolling direction on macOS.

- bpo-34275: Make IDLE calltips always visible on Mac. Some MacOS-tk combinations need .update_idletasks(). Patch by Kevin Walzer.

- bpo-34120: Fix unresponsiveness after closing certain windows and dialogs.

- bpo-33975: Avoid small type when running htests. Since part of the purpose of human-viewed tests is to determine that widgets look right, it is important that they look the same for testing as when running IDLE.

- bpo-33905: Add test for idlelib.stackview.StackBrowser.

- bpo-33924: Change mainmenu.menudefs key ‘windows’ to ‘window’. Every other menudef key is lowercase version of main menu entry.

- bpo-33906: Rename idlelib.windows as window Match Window on the main menu and remove last plural module name.

- bpo-33917: Fix and document idlelib/idle_test/template.py. The revised file compiles, runs, and tests OK. idle_test/README.txt explains how to use it to create new IDLE test files.

- bpo-33904: IDLE: In rstrip, rename class RstripExtension as Rstrip

- bpo-33907: For consistency and clarity, rename an IDLE module and classes. Module calltips and its class CallTips are now calltip and Calltip. In module calltip_w, class CallTip is now CalltipWindow.

- bpo-33856: Add “help” in the welcome message of IDLE

- bpo-33839: IDLE: refactor ToolTip and CallTip and add documentation and tests

- bpo-33855: Minimally test all IDLE modules. Add missing files, import module, instantiate classes, and check coverage. Check existing files.

- bpo-33656: On Windows, add API call saying that tk scales for DPI. On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary unchanged, and a monitor resolution greater than 96 DPI, this should make text and lines sharper. It should otherwise have no effect.

- bpo-33768: Clicking on a context line moves that line to the top of the editor window.

- bpo-33763: IDLE: Use read-only text widget for code context instead of label widget.

- bpo-33664: Scroll IDLE editor text by lines. Previously, the mouse wheel and scrollbar slider moved text by a fixed number of pixels, resulting in partial lines at the top of the editor box. The change also applies to the shell and grep output windows, but not to read-only text views.

- bpo-33679: Enable theme-specific color configuration for Code Context. Use the Highlights tab to see the setting for built-in themes or add settings to custom themes.

- bpo-33642: Display up to maxlines non-blank lines for Code Context. If there is no current context, show a single blank line.

- bpo-33628: IDLE: Cleanup codecontext.py and its test.

- bpo-33564: IDLE’s code context now recognizes async as a block opener.

- bpo-21474: Update word/identifier definition from ascii to unicode. In text and entry boxes, this affects selection by double-click, movement left/right by control-left/right, and deletion left/right by control-BACKSPACE/DEL.

- bpo-33204: IDLE: consistently color invalid string prefixes. A ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’. Consistently color as much of the prefix, starting at the right, as is valid. Revise and extend colorizer test.

- bpo-32984: Set `__file__` while running a startup file. Like Python, IDLE optionally runs one startup file in the Shell window before presenting the first interactive input prompt. For IDLE, `-s` runs a file named in environmental variable `IDLESTARTUP` or `PYTHONSTARTUP`; `-r file` runs `file`. Python sets `__file__` to the startup file name before running the file and unsets it before the first prompt. IDLE now does the same when run normally, without the `-n` option.

- bpo-32940: Simplify and rename StringTranslatePseudoMapping in pyparse.

- bpo-32916: Change `str` to `code` in pyparse.

- bpo-32905: Remove unused code in pyparse module.

- bpo-32874: Add tests for pyparse.

- bpo-32837: Using the system and place-dependent default encoding for open() is a bad idea for IDLE’s system and location-independent files.

- bpo-32826: Add “encoding=utf-8” to open() in IDLE’s test_help_about. GUI test test_file_buttons() only looks at initial ascii-only lines, but failed on systems where open() defaults to ‘ascii’ because readline() internally reads and decodes far enough ahead to encounter a non-ascii character in CREDITS.txt.

- bpo-32831: Add docstrings and tests for codecontext.

- bpo-32765: Update configdialog General tab docstring to add new widgets to the widget list.

### Tools/Demos

- bpo-35884: Add a benchmark script for timing various ways to access variables: `Tools/scripts/var_access_benchmark.py`.

- bpo-34989: python-gdb.py now handles errors on computing the line number of a Python frame.

- bpo-20260: Argument Clinic now has non-bitwise unsigned int converters.

- bpo-32962: python-gdb now catches `UnicodeDecodeError` exceptions when calling `string()`.

- bpo-32962: python-gdb now catches ValueError on read_var(): when Python has no debug symbols for example.

- bpo-33189: pygettext.py now recognizes only literal strings as docstrings and translatable strings, and rejects bytes literals and f-string expressions.

- bpo-31920: Fixed handling directories as arguments in the `pygettext` script. Based on patch by Oleg Krasnikov.

- bpo-29673: Fix pystackv and pystack gdbinit macros.

- bpo-25427: Remove the pyvenv script in favor of `python3 -m venv` in order to lower confusion as to what Python interpreter a virtual environment will be created for.

- bpo-32885: Add an `-n` flag for `Tools/scripts/pathfix.py` to disable automatic backup creation (files with `~` suffix).

- bpo-32222: Fix pygettext not extracting docstrings for functions with type annotated arguments. Patch by Toby Harradine.

- bpo-31583: Fix 2to3 for using with –add-suffix option but without –output-dir option for relative path to files in current directory.

### C API

- bpo-35713: The `PyByteArray_Init()` and `PyByteArray_Fini()` functions have been removed. They did nothing since Python 2.7.4 and Python 3.2.0, were excluded from the limited API (stable ABI), and were not documented.

- bpo-33817: Fixed `_PyBytes_Resize()` for empty bytes objects.

- bpo-35322: Fix memory leak in `PyUnicode_EncodeLocale()` and `PyUnicode_EncodeFSDefault()` on error handling.

- bpo-35059: The following C macros have been converted to static inline functions: `Py_INCREF()`, `Py_DECREF()`, `Py_XINCREF()`, `Py_XDECREF()`, `PyObject_INIT()`, `PyObject_INIT_VAR()`.

- bpo-35296: `make install` now also installs the internal API: `Include/internal/*.h` header files.

- bpo-35081: Internal APIs surrounded by `#ifdef Py_BUILD_CORE` have been moved from `Include/*.h` headers to new header files `Include/internal/pycore_*.h`.

- bpo-35259: Conditionally declare `Py_FinalizeEx()` (new in 3.6) based on Py_LIMITED_API. Patch by Arthur Neufeld.

- bpo-35081: The `_PyObject_GC_TRACK()` and `_PyObject_GC_UNTRACK()` macros have been removed from the public C API.

- bpo-35134: Creation of a new `Include/cpython/` subdirectory.

- bpo-34725: Adds _Py_SetProgramFullPath so embedders may override sys.executable

- bpo-34910: Ensure that `PyObject_Print()` always returns `-1` on error. Patch by Zackery Spytz.

- bpo-34523: Py_DecodeLocale() and Py_EncodeLocale() now use the UTF-8 encoding on Windows if Py_LegacyWindowsFSEncodingFlag is zero.

- bpo-34193: Fix pluralization in TypeError messages in getargs.c and typeobject.c: ‘1 argument’ instead of ‘1 arguments’ and ‘1 element’ instead of ‘1 elements’.

- bpo-34127: Return grammatically correct error message based on argument count. Patch by Karthikeyan Singaravelan.

- bpo-23927: Fixed `SystemError` in `PyArg_ParseTupleAndKeywords()` when the `w*` format unit is used for optional parameter.

- bpo-32455: Added `PyCompile_OpcodeStackEffectWithJump()`.

- bpo-34008: Py_Main() can again be called after Py_Initialize(), as in Python 3.6.

- bpo-32500: Fixed error messages for `PySequence_Size()`, `PySequence_GetItem()`, `PySequence_SetItem()` and `PySequence_DelItem()` called with a mapping and `PyMapping_Size()` called with a sequence.

- bpo-33818: `PyExceptionClass_Name()` will now return `const char *` instead of `char *`.

- bpo-33042: Embedding applications may once again call PySys_ResetWarnOptions, PySys_AddWarnOption, and PySys_AddXOption prior to calling Py_Initialize.

- bpo-32374: Document that m_traverse for multi-phase initialized modules can be called with m_state=NULL, and add a sanity check

- bpo-30863: `PyUnicode_AsWideChar()` and `PyUnicode_AsWideCharString()` no longer cache the `wchar_t*` representation of string objects.

## Python 3.7.0 final

Release date: 2018-06-27

### Library

- bpo-33851: Fix `ast.get_docstring()` for a node that lacks a docstring.

### C API

- bpo-33932: Calling Py_Initialize() twice does nothing, instead of failing with a fatal error: restore the Python 3.6 behaviour.

## Python 3.7.0 release candidate 1

Release date: 2018-06-12

### Core and Builtins

- bpo-33803: Fix a crash in hamt.c caused by enabling GC tracking for an object that hadn’t all of its fields set to NULL.

- bpo-33706: Fix a crash in Python initialization when parsing the command line options. Thanks Christoph Gohlke for the bug report and the fix!

- bpo-30654: Fixed reset of the SIGINT handler to SIG_DFL on interpreter shutdown even when there was a custom handler set previously. Patch by Philipp Kerling.

- bpo-31849: Fix signed/unsigned comparison warning in pyhash.c.

### Library

- bpo-30167: Prevent site.main() exception if PYTHONSTARTUP is set. Patch by Steve Weber.

- bpo-33812: Datetime instance d with non-None tzinfo, but with d.tzinfo.utcoffset(d) returning None is now treated as naive by the astimezone() method.

- bpo-30805: Avoid race condition with debug logging

- bpo-33694: asyncio: Fix a race condition causing data loss on pause_reading()/resume_reading() when using the ProactorEventLoop.

- bpo-32493: Correct test for `uuid_enc_be` availability in `configure.ac`. Patch by Michael Felt.

- bpo-33792: Add asyncio.WindowsSelectorEventLoopPolicy and asyncio.WindowsProactorEventLoopPolicy.

- bpo-33778: Update `unicodedata`’s database to Unicode version 11.0.0.

- bpo-33770: improve base64 exception message for encoded inputs of invalid length

- bpo-33769: asyncio/start_tls: Fix error message; cancel callbacks in case of an unhandled error; mark SSLTransport as closed if it is aborted.

- bpo-33767: The concatenation (`+`) and repetition (`*`) sequence operations now raise `TypeError` instead of `SystemError` when performed on `mmap.mmap` objects. Patch by Zackery Spytz.

- bpo-33734: asyncio/ssl: Fix AttributeError, increase default handshake timeout

- bpo-11874: Use a better regex when breaking usage into wrappable parts. Avoids bogus assertion errors from custom metavar strings.

- bpo-33582: Emit a deprecation warning for inspect.formatargspec

### Documentation

- bpo-33409: Clarified the relationship between PEP 538’s PYTHONCOERCECLOCALE and PEP 540’s PYTHONUTF8 mode.

- bpo-33736: Improve the documentation of `asyncio.open_connection()`, `asyncio.start_server()` and their UNIX socket counterparts.

- bpo-31432: Clarify meaning of CERT_NONE, CERT_OPTIONAL, and CERT_REQUIRED flags for ssl.SSLContext.verify_mode.

### Build

- bpo-5755: Move `-Wstrict-prototypes` option to `CFLAGS_NODIST` from `OPT`. This option emitted annoying warnings when building extension modules written in C++.

### Windows

- bpo-33720: Reduces maximum marshal recursion depth on release builds.

### IDLE

- bpo-33656: On Windows, add API call saying that tk scales for DPI. On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary unchanged, and a monitor resolution greater than 96 DPI, this should make text and lines sharper. It should otherwise have no effect.

- bpo-33768: Clicking on a context line moves that line to the top of the editor window.

- bpo-33763: IDLE: Use read-only text widget for code context instead of label widget.

- bpo-33664: Scroll IDLE editor text by lines. Previously, the mouse wheel and scrollbar slider moved text by a fixed number of pixels, resulting in partial lines at the top of the editor box. The change also applies to the shell and grep output windows, but not to read-only text views.

- bpo-33679: Enable theme-specific color configuration for Code Context. Use the Highlights tab to see the setting for built-in themes or add settings to custom themes.

- bpo-33642: Display up to maxlines non-blank lines for Code Context. If there is no current context, show a single blank line.

## Python 3.7.0 beta 5

Release date: 2018-05-30

### Core and Builtins

- bpo-33622: Fixed a leak when the garbage collector fails to add an object with the `__del__` method or referenced by it into the `gc.garbage` list. `PyGC_Collect()` can now be called when an exception is set and preserves it.

- bpo-33509: Fix module_globals parameter of warnings.warn_explicit(): don’t crash if module_globals is not a dict.

- bpo-20104: The new `os.posix_spawn` added in 3.7.0b1 was removed as we are still working on what the API should look like. Expect this in 3.8 instead.

- bpo-33475: Fixed miscellaneous bugs in converting annotations to strings and optimized parentheses in the string representation.

- bpo-33391: Fix a leak in set_symmetric_difference().

- bpo-28055: Fix unaligned accesses in siphash24(). Patch by Rolf Eike Beer.

- bpo-32911: Due to unexpected compatibility issues discovered during downstream beta testing, reverted bpo-29463. `docstring` field is removed from Module, ClassDef, FunctionDef, and AsyncFunctionDef ast nodes which was added in 3.7a1. Docstring expression is restored as a first statement in their body. Based on patch by Inada Naoki.

- bpo-21983: Fix a crash in `ctypes.cast()` in case the type argument is a ctypes structured data type. Patch by Eryk Sun and Oren Milman.

### Library

- bpo-32751: When cancelling the task due to a timeout, `asyncio.wait_for()` will now wait until the cancellation is complete.

- bpo-32684: Fix gather to propagate cancellation of itself even with return_exceptions.

- bpo-33654: Support protocol type switching in SSLTransport.set_protocol().

- bpo-33674: Pause the transport as early as possible to further reduce the risk of data_received() being called before connection_made().

- bpo-33674: Fix a race condition in SSLProtocol.connection_made() of asyncio.sslproto: start immediately the handshake instead of using call_soon(). Previously, data_received() could be called before the handshake started, causing the handshake to hang or fail.

- bpo-31647: Fixed bug where calling write_eof() on a _SelectorSocketTransport after it’s already closed raises AttributeError.

- bpo-32610: Make asyncio.all_tasks() return only pending tasks.

- bpo-32410: Avoid blocking on file IO in sendfile fallback code

- bpo-33469: Fix RuntimeError after closing loop that used run_in_executor

- bpo-33672: Fix Task.__repr__ crash with Cython’s bogus coroutines

- bpo-33654: Fix transport.set_protocol() to support switching between asyncio.Protocol and asyncio.BufferedProtocol. Fix loop.start_tls() to work with asyncio.BufferedProtocols.

- bpo-33652: Pickles of type variables and subscripted generics are now future-proof and compatible with older Python versions.

- bpo-32493: Fixed `uuid.uuid1()` on FreeBSD.

- bpo-33618: Finalize and document preliminary and experimental TLS 1.3 support with OpenSSL 1.1.1

- bpo-33623: Fix possible SIGSGV when asyncio.Future is created in __del__

- bpo-30877: Fixed a bug in the Python implementation of the JSON decoder that prevented the cache of parsed strings from clearing after finishing the decoding. Based on patch by c-fos.

- bpo-33570: Change TLS 1.3 cipher suite settings for compatibility with OpenSSL 1.1.1-pre6 and newer. OpenSSL 1.1.1 will have TLS 1.3 ciphers enabled by default.

- bpo-28556: Do not simplify arguments to `typing.Union`. Now `Union[Manager, Employee]` is not simplified to `Employee` at runtime. Such simplification previously caused several bugs and limited possibilities for introspection.

- bpo-33540: Add a new `block_on_close` class attribute to `ForkingMixIn` and `ThreadingMixIn` classes of `socketserver`.

- bpo-33548: tempfile._candidate_tempdir_list should consider common TEMP locations

- bpo-33109: argparse subparsers are once again not required by default, reverting the change in behavior introduced by bpo-26510 in 3.7.0a2.

- bpo-33536: dataclasses.make_dataclass now checks for invalid field names and duplicate fields. Also, added a check for invalid field specifications.

- bpo-33542: Prevent `uuid.get_node` from using a DUID instead of a MAC on Windows. Patch by Zvi Effron

- bpo-26819: Fix race condition with `ReadTransport.resume_reading` in Windows proactor event loop.

- Fix failure in `typing.get_type_hints()` when ClassVar was provided as a string forward reference.

- bpo-33505: Optimize asyncio.ensure_future() by reordering if checks: 1.17x faster.

- bpo-33497: Add errors param to cgi.parse_multipart and make an encoding in FieldStorage use the given errors (needed for Twisted). Patch by Amber Brown.

- bpo-33495: Change dataclasses.Fields repr to use the repr of each of its members, instead of str. This makes it more clear what each field actually represents. This is especially true for the ‘type’ member.

- bpo-33453: Fix dataclasses to work if using literal string type annotations or if using PEP 563 “Postponed Evaluation of Annotations”. Only specific string prefixes are detected for both ClassVar (“ClassVar” and “typing.ClassVar”) and InitVar (“InitVar” and “dataclasses.InitVar”).

- bpo-28556: Minor fixes in typing module: add annotations to `NamedTuple.__new__`, pass `*args` and `**kwds` in `Generic.__new__`. Original PRs by Paulius Šarka and Chad Dombrova.

- bpo-20087: Updated alias mapping with glibc 2.27 supported locales.

- bpo-33422: Fix trailing quotation marks getting deleted when looking up byte/string literals on pydoc. Patch by Andrés Delfino.

- bpo-28167: The function `platform.linux_distribution` and `platform.dist` now trigger a `DeprecationWarning` and have been marked for removal in Python 3.8

- bpo-33197: Update error message when constructing invalid inspect.Parameters Patch by Dong-hee Na.

- bpo-33263: Fix FD leak in `_SelectorSocketTransport` Patch by Vlad Starostin.

- bpo-32861: The urllib.robotparser’s `__str__` representation now includes wildcard entries and the “Crawl-delay” and “Request-rate” fields. Patch by Michael Lazar.

- bpo-32257: The ssl module now contains OP_NO_RENEGOTIATION constant, available with OpenSSL 1.1.0h or 1.1.1.

- bpo-16865: Support arrays >=2GiB in `ctypes`. Patch by Segev Finer.

### Documentation

- bpo-23859: Document that `asyncio.wait()` does not cancel its futures on timeout.

- bpo-32436: Document PEP 567 changes to asyncio.

- bpo-33604: Update HMAC md5 default to a DeprecationWarning, bump removal to 3.8.

- bpo-33503: Fix broken pypi link

- bpo-33421: Add missing documentation for `typing.AsyncContextManager`.

### Tests

- bpo-33655: Ignore test_posix_fallocate failures on BSD platforms that might be due to running on ZFS.

- bpo-32604: Remove the _xxsubinterpreters module (meant for testing) and associated helpers. This module was originally added recently in 3.7b1.

### Build

- bpo-33614: Ensures module definition files for the stable ABI on Windows are correctly regenerated.

- bpo-33522: Enable CI builds on Visual Studio Team Services at https://python.visualstudio.com/cpython

- bpo-33012: Add `-Wno-cast-function-type` for gcc 8 for silencing warnings about function casts like casting to PyCFunction in method definition lists.

### macOS

- bpo-13631: The .editrc file in user’s home directory is now processed correctly during the readline initialization through editline emulation on macOS.

### IDLE

- bpo-33628: IDLE: Cleanup codecontext.py and its test.

- bpo-33564: IDLE’s code context now recognizes async as a block opener.

- bpo-32831: Add docstrings and tests for codecontext.

## Python 3.7.0 beta 4

Release date: 2018-05-02

### Core and Builtins

- bpo-33363: Raise a SyntaxError for `async with` and `async for` statements outside of async functions.

- bpo-33128: Fix a bug that causes PathFinder to appear twice on sys.meta_path. Patch by Pablo Galindo Salgado.

- bpo-33312: Fixed clang ubsan (undefined behavior sanitizer) warnings in dictobject.c by adjusting how the internal struct _dictkeysobject shared keys structure is declared.

- bpo-33231: Fix potential memory leak in `normalizestring()`.

- bpo-33205: Change dict growth function from `round_up_to_power_2(used*2+hashtable_size/2)` to `round_up_to_power_2(used*3)`. Previously, dict is shrinked only when `used == 0`. Now dict has more chance to be shrinked.

- bpo-29922: Improved error messages in ‘async with’ when `__aenter__()` or `__aexit__()` return non-awaitable object.

- bpo-33199: Fix `ma_version_tag` in dict implementation is uninitialized when copying from key-sharing dict.

### Library

- bpo-33281: Fix ctypes.util.find_library regression on macOS.

- bpo-33383: Fixed crash in the get() method of the `dbm.ndbm` database object when it is called with a single argument.

- bpo-33329: Fix multiprocessing regression on newer glibcs

- bpo-991266: Fix quoting of the `Comment` attribute of `http.cookies.SimpleCookie`.

- bpo-33131: Upgrade bundled version of pip to 10.0.1.

- bpo-33308: Fixed a crash in the `parser` module when converting an ST object to a tree of tuples or lists with `line_info=False` and `col_info=True`.

- bpo-33266: lib2to3 now recognizes `rf'...'` strings.

- bpo-11594: Ensure line-endings are respected when using lib2to3.

- bpo-33254: Have `importlib.resources.contents()` and `importlib.abc.ResourceReader.contents()` return an iterable instead of an iterator.

- bpo-33256: Fix display of `<module>` call in the html produced by `cgitb.html()`. Patch by Stéphane Blondon.

- bpo-33185: Fixed regression when running pydoc with the `-m` switch. (The regression was introduced in 3.7.0b3 by the resolution of bpo-33053) This fix also changed pydoc to add `os.getcwd()` to `sys.path` when necessary, rather than adding `"."`.

- bpo-33169: Delete entries of `None` in `sys.path_importer_cache` when `importlib.machinery.invalidate_caches()` is called.

- bpo-33217: Deprecate looking up non-Enum objects in Enum classes and Enum members (will raise `TypeError` in 3.8+).

- bpo-33203: `random.Random.choice()` now raises `IndexError` for empty sequences consistently even when called from subclasses without a `getrandbits()` implementation.

- bpo-33224: Update difflib.mdiff() for PEP 479. Convert an uncaught StopIteration in a generator into a return-statement.

- bpo-33209: End framing at the end of C implementation of `pickle.Pickler.dump()`.

- bpo-20104: Improved error handling and fixed a reference leak in `os.posix_spawn()`.

- bpo-33175: In dataclasses, Field.__set_name__ now looks up the __set_name__ special method on the class, not the instance, of the default value.

- bpo-33097: Raise RuntimeError when `executor.submit` is called during interpreter shutdown.

- bpo-31908: Fix output of cover files for `trace` module command-line tool. Previously emitted cover files only when `--missing` option was used. Patch by Michael Selik.

### Documentation

- bpo-33378: Add Korean language switcher for https://docs.python.org/3/

- bpo-33276: Clarify that the `__path__` attribute on modules cannot be just any value.

- bpo-33201: Modernize documentation for writing C extension types.

- bpo-33195: Deprecate `Py_UNICODE` usage in `c-api/arg` document. `Py_UNICODE` related APIs are deprecated since Python 3.3, but it is missed in the document.

- bpo-8243: Add a note about curses.addch and curses.addstr exception behavior when writing outside a window, or pad.

- bpo-32337: Update documentation related with `dict` order.

### Tests

- bpo-33358: Fix `test_embed.test_pre_initialization_sys_options()` when the interpreter is built with `--enable-shared`.

### Build

- bpo-33394: Enable the verbose build for extension modules, when GNU make is passed macros on the command line.

- bpo-33393: Update config.guess and config.sub files.

- bpo-33377: Add new triplets for mips r6 and riscv variants (used in extension suffixes).

- bpo-32232: By default, modules configured in `Modules/Setup` are no longer built with `-DPy_BUILD_CORE`. Instead, modules that specifically need that preprocessor definition include it in their individual entries.

- bpo-33182: The embedding tests can once again be built with clang 6.0

### Windows

- bpo-33184: Update Windows installer to use OpenSSL 1.1.0h.

### macOS

- bpo-33184: Update macOS installer build to use OpenSSL 1.1.0h.

### IDLE

- bpo-21474: Update word/identifier definition from ascii to unicode. In text and entry boxes, this affects selection by double-click, movement left/right by control-left/right, and deletion left/right by control-BACKSPACE/DEL.

- bpo-33204: IDLE: consistently color invalid string prefixes. A ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’. Consistently color as much of the prefix, starting at the right, as is valid. Revise and extend colorizer test.

### Tools/Demos

- bpo-33189: pygettext.py now recognizes only literal strings as docstrings and translatable strings, and rejects bytes literals and f-string expressions.

- bpo-31920: Fixed handling directories as arguments in the `pygettext` script. Based on patch by Oleg Krasnikov.

- bpo-29673: Fix pystackv and pystack gdbinit macros.

- bpo-31583: Fix 2to3 for using with –add-suffix option but without –output-dir option for relative path to files in current directory.

## Python 3.7.0 beta 3

Release date: 2018-03-29

### Security

- bpo-33136: Harden ssl module against LibreSSL CVE-2018-8970. X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test ensures that NULL bytes are not allowed.

- bpo-33001: Minimal fix to prevent buffer overrun in os.symlink on Windows

- bpo-32981: Regexes in difflib and poplib were vulnerable to catastrophic backtracking. These regexes formed potential DOS vectors (REDOS). They have been refactored. This resolves CVE-2018-1060 and CVE-2018-1061. Patch by Jamie Davis.

### Core and Builtins

- bpo-33053: When using the -m switch, sys.path[0] is now explicitly expanded as the starting working directory, rather than being left as the empty path (which allows imports from the current working directory at the time of the import)

- bpo-33018: Improve consistency of errors raised by `issubclass()` when called with a non-class and an abstract base class as the first and second arguments, respectively. Patch by Josh Bronson.

- bpo-33041: Fixed jumping when the function contains an `async for` loop.

- bpo-33026: Fixed jumping out of “with” block by setting f_lineno.

- bpo-33005: Fix a crash on fork when using a custom memory allocator (ex: using PYTHONMALLOC env var). _PyGILState_Reinit() and _PyInterpreterState_Enable() now use the default RAW memory allocator to allocate a new interpreters mutex on fork.

- bpo-17288: Prevent jumps from ‘return’ and ‘exception’ trace events.

- bpo-32836: Don’t use temporary variables in cases of list/dict/set comprehensions

### Library

- bpo-33141: Have Field objects pass through __set_name__ to their default values, if they have their own __set_name__.

- bpo-33096: Allow ttk.Treeview.insert to insert iid that has a false boolean value. Note iid=0 and iid=False would be same. Patch by Garvit Khatri.

- bpo-32873: Treat type variables and special typing forms as immutable by copy and pickle. This fixes several minor issues and inconsistencies, and improves backwards compatibility with Python 3.6.

- bpo-33134: When computing dataclass’s __hash__, use the lookup table to contain the function which returns the __hash__ value. This is an improvement over looking up a string, and then testing that string to see what to do.

- bpo-33127: The ssl module now compiles with LibreSSL 2.7.1.

- bpo-32505: Raise TypeError if a member variable of a dataclass is of type Field, but doesn’t have a type annotation.

- bpo-33078: Fix the failure on OSX caused by the tests relying on sem_getvalue

- bpo-33116: Add ‘Field’ to dataclasses.__all__.

- bpo-32896: Fix an error where subclassing a dataclass with a field that uses a default_factory would generate an incorrect class.

- bpo-33100: Dataclasses: If a field has a default value that’s a MemberDescriptorType, then it’s from that field being in __slots__, not an actual default value.

- bpo-32953: If a non-dataclass inherits from a frozen dataclass, allow attributes to be added to the derived class. Only attributes from the frozen dataclass cannot be assigned to. Require all dataclasses in a hierarchy to be either all frozen or all non-frozen.

- bpo-33061: Add missing `NoReturn` to `__all__` in typing.py

- bpo-33078: Fix the size handling in multiprocessing.Queue when a pickling error occurs.

- bpo-33064: lib2to3 now properly supports trailing commas after `*args` and `**kwargs` in function signatures.

- bpo-33056: FIX properly close leaking fds in concurrent.futures.ProcessPoolExecutor.

- bpo-33021: Release the GIL during fstat() calls, avoiding hang of all threads when calling mmap.mmap(), os.urandom(), and random.seed(). Patch by Nir Soffer.

- bpo-31804: Avoid failing in multiprocessing.Process if the standard streams are closed or None at exit.

- bpo-33037: Skip sending/receiving data after SSL transport closing.

- bpo-27683: Fix a regression in `ipaddress` that result of `hosts()` is empty when the network is constructed by a tuple containing an integer mask and only 1 bit left for addresses.

- bpo-32999: Fix C implementation of `ABC.__subclasscheck__(cls, subclass)` crashed when `subclass` is not a type object.

- bpo-33009: Fix inspect.signature() for single-parameter partialmethods.

- bpo-32969: Expose several missing constants in zlib and fix corresponding documentation.

- bpo-32056: Improved exceptions raised for invalid number of channels and sample width when read an audio file in modules `aifc`, `wave` and `sunau`.

- bpo-32844: Fix wrong redirection of a low descriptor (0 or 1) to stderr in subprocess if another low descriptor is closed.

- bpo-32857: In `tkinter`, `after_cancel(None)` now raises a `ValueError` instead of canceling the first scheduled function. Patch by Cheryl Sabella.

- bpo-31639: http.server now exposes a ThreadedHTTPServer class and uses it when the module is run with `-m` to cope with web browsers pre-opening sockets.

- bpo-27645: `sqlite3.Connection` now exposes a `backup` method, if the underlying SQLite library is at version 3.6.11 or higher. Patch by Lele Gaifax.

### Documentation

- bpo-33126: Document PyBuffer_ToContiguous().

- bpo-27212: Modify documentation for the `islice()` recipe to consume initial values up to the start index.

- bpo-28247: Update `zipapp` documentation to describe how to make standalone applications.

- bpo-18802: Documentation changes for ipaddress. Patch by Jon Foster and Berker Peksag.

- bpo-27428: Update documentation to clarify that `WindowsRegistryFinder` implements `MetaPathFinder`. (Patch by Himanshu Lakhara)

### Tests

- bpo-32872: Avoid regrtest compatibility issue with namespace packages.

- bpo-32517: Fix failing `test_asyncio` on macOS 10.12.2+ due to transport of `KqueueSelector` loop was not being closed.

- bpo-19417: Add test_bdb.py.

### Build

- bpo-33163: Upgrade pip to 9.0.3 and setuptools to v39.0.1.

### Windows

- bpo-33016: Fix potential use of uninitialized memory in nt._getfinalpathname

- bpo-32903: Fix a memory leak in os.chdir() on Windows if the current directory is set to a UNC path.

### macOS

- bpo-32726: Build and link with private copy of Tcl/Tk 8.6 for the macOS 10.6+ installer. The 10.9+ installer variant already does this. This means that the Python 3.7 provided by the python.org macOS installers no longer need or use any external versions of Tcl/Tk, either system-provided or user-installed, such as ActiveTcl.

### IDLE

- bpo-32984: Set `__file__` while running a startup file. Like Python, IDLE optionally runs one startup file in the Shell window before presenting the first interactive input prompt. For IDLE, `-s` runs a file named in environmental variable `IDLESTARTUP` or `PYTHONSTARTUP`; `-r file` runs `file`. Python sets `__file__` to the startup file name before running the file and unsets it before the first prompt. IDLE now does the same when run normally, without the `-n` option.

- bpo-32940: Simplify and rename StringTranslatePseudoMapping in pyparse.

### Tools/Demos

- bpo-32885: Add an `-n` flag for `Tools/scripts/pathfix.py` to disable automatic backup creation (files with `~` suffix).

### C API

- bpo-33042: Embedding applications may once again call PySys_ResetWarnOptions, PySys_AddWarnOption, and PySys_AddXOption prior to calling Py_Initialize.

- bpo-32374: Document that m_traverse for multi-phase initialized modules can be called with m_state=NULL, and add a sanity check

## Python 3.7.0 beta 2

Release date: 2018-02-27

### Security

- bpo-28414: The ssl module now allows users to perform their own IDN en/decoding when using SNI.

### Core and Builtins

- bpo-32889: Update Valgrind suppression list to account for the rename of `Py_ADDRESS_IN_RANG` to `address_in_range`.

- bpo-31356: Remove the new API added in bpo-31356 (gc.ensure_disabled() context manager).

- bpo-32305: For namespace packages, ensure that both `__file__` and `__spec__.origin` are set to None.

- bpo-32303: Make sure `__spec__.loader` matches `__loader__` for namespace packages.

- bpo-32711: Fix the warning messages for Python/ast_unparse.c. Patch by Stéphane Wirtel

- bpo-32583: Fix possible crashing in builtin Unicode decoders caused by write out-of-bound errors when using customized decode error handlers.

### Library

- bpo-32960: For dataclasses, disallow inheriting frozen from non-frozen classes, and also disallow inheriting non-frozen from frozen classes. This restriction will be relaxed at a future date.

- bpo-32713: Fixed tarfile.itn handling of out-of-bounds float values. Patch by Joffrey Fuhrer.

- bpo-32951: Direct instantiation of SSLSocket and SSLObject objects is now prohibited. The constructors were never documented, tested, or designed as public constructors. Users were suppose to use ssl.wrap_socket() or SSLContext.

- bpo-32929: Remove the tri-state parameter “hash”, and add the boolean “unsafe_hash”. If unsafe_hash is True, add a __hash__ function, but if a __hash__ exists, raise TypeError. If unsafe_hash is False, add a __hash__ based on the values of eq= and frozen=. The unsafe_hash=False behavior is the same as the old hash=None behavior. unsafe_hash=False is the default, just as hash=None used to be.

- bpo-32947: Add OP_ENABLE_MIDDLEBOX_COMPAT and test workaround for TLSv1.3 for future compatibility with OpenSSL 1.1.1.

- bpo-30622: The ssl module now detects missing NPN support in LibreSSL.

- bpo-32922: dbm.open() now encodes filename with the filesystem encoding rather than default encoding.

- bpo-32859: In `os.dup2`, don’t check every call whether the `dup3` syscall exists or not.

- bpo-32556: nt._getfinalpathname, nt._getvolumepathname and nt._getdiskusage now correctly convert from bytes.

- bpo-25988: Emit a `DeprecationWarning` when using or importing an ABC directly from `collections` rather than from `collections.abc`.

- bpo-21060: Rewrite confusing message from setup.py upload from “No dist file created in earlier command” to the more helpful “Must create and upload files in one command”.

- bpo-32852: Make sure sys.argv remains as a list when running trace.

- bpo-31333: `_abc` module is added. It is a speedup module with C implementations for various functions and methods in `abc`. Creating an ABC subclass and calling `isinstance` or `issubclass` with an ABC subclass are up to 1.5x faster. In addition, this makes Python start-up up to 10% faster. Note that the new implementation hides internal registry and caches, previously accessible via private attributes `_abc_registry`, `_abc_cache`, and `_abc_negative_cache`. There are three debugging helper methods that can be used instead `_dump_registry`, `_abc_registry_clear`, and `_abc_caches_clear`.

- bpo-32841: Fixed `asyncio.Condition` issue which silently ignored cancellation after notifying and cancelling a conditional lock. Patch by Bar Harel.

- bpo-32819: ssl.match_hostname() has been simplified and no longer depends on re and ipaddress module for wildcard and IP addresses. Error reporting for invalid wildcards has been improved.

- bpo-32394: socket: Remove TCP_FASTOPEN,TCP_KEEPCNT,TCP_KEEPIDLE,TCP_KEEPINTVL flags on older version Windows during run-time.

- bpo-31787: Fixed refleaks of `__init__()` methods in various modules. (Contributed by Oren Milman)

- bpo-30157: Fixed guessing quote and delimiter in csv.Sniffer.sniff() when only the last field is quoted. Patch by Jake Davis.

- bpo-32792: collections.ChainMap() preserves the order of the underlying mappings.

- bpo-32775: `fnmatch.translate()` no longer produces patterns which contain set operations. Sets starting with ‘[’ or containing ‘–’, ‘&&’, ‘~~’ or ‘||’ will be interpreted differently in regular expressions in future versions. Currently they emit warnings. fnmatch.translate() now avoids producing patterns containing such sets by accident.

- bpo-32622: Implement native fast sendfile for Windows proactor event loop.

- bpo-32777: Fix a rare but potential pre-exec child process deadlock in subprocess on POSIX systems when marking file descriptors inheritable on exec in the child process. This bug appears to have been introduced in 3.4.

- bpo-32647: The ctypes module used to depend on indirect linking for dlopen. The shared extension is now explicitly linked against libdl on platforms with dl.

- bpo-32741: Implement `asyncio.TimerHandle.when()` method.

- bpo-32691: Use mod_spec.parent when running modules with pdb

- bpo-32734: Fixed `asyncio.Lock()` safety issue which allowed acquiring and locking the same lock multiple times, without it being free. Patch by Bar Harel.

- bpo-32727: Do not include name field in SMTP envelope from address. Patch by Stéphane Wirtel

- bpo-31453: Add TLSVersion constants and SSLContext.maximum_version / minimum_version attributes. The new API wraps OpenSSL 1.1 https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_set_min_proto_version.html feature.

- bpo-24334: Internal implementation details of ssl module were cleaned up. The SSLSocket has one less layer of indirection. Owner and session information are now handled by the SSLSocket and SSLObject constructor. Channel binding implementation has been simplified.

- bpo-31848: Fix the error handling in Aifc_read.initfp() when the SSND chunk is not found. Patch by Zackery Spytz.

- bpo-32585: Add Ttk spinbox widget to `tkinter.ttk`. Patch by Alan D Moore.

- bpo-32221: Various functions returning tuple containing IPv6 addresses now omit `%scope` part since the same information is already encoded in scopeid tuple item. Especially this speeds up `socket.recvfrom()` when it receives multicast packet since useless resolving of network interface name is omitted.

- bpo-30693: The TarFile class now recurses directories in a reproducible way.

- bpo-30693: The ZipFile class now recurses directories in a reproducible way.

### Documentation

- bpo-28124: The ssl module function ssl.wrap_socket() has been de-emphasized and deprecated in favor of the more secure and efficient SSLContext.wrap_socket() method.

- bpo-17232: Clarify docs for -O and -OO. Patch by Terry Reedy.

- bpo-32436: Add documentation for the contextvars module (PEP 567).

- bpo-32800: Update link to w3c doc for xml default namespaces.

- bpo-11015: Update `test.support` documentation.

- bpo-8722: Document `__getattr__()` behavior when property `get()` method raises `AttributeError`.

- bpo-32614: Modify RE examples in documentation to use raw strings to prevent `DeprecationWarning` and add text to REGEX HOWTO to highlight the deprecation.

- bpo-31972: Improve docstrings for `pathlib.PurePath` subclasses.

### Tests

- bpo-31809: Add tests to verify connection with secp ECDH curves.

### Build

- bpo-32898: Fix the python debug build when using COUNT_ALLOCS.

### Windows

- bpo-32901: Update Tcl and Tk versions to 8.6.8

- bpo-31966: Fixed WindowsConsoleIO.write() for writing empty data.

- bpo-32409: Ensures activate.bat can handle Unicode contents.

- bpo-32457: Improves handling of denormalized executable path when launching Python.

- bpo-32370: Use the correct encoding for ipconfig output in the uuid module. Patch by Segev Finer.

- bpo-29248: Fix `os.readlink()` on Windows, which was mistakenly treating the `PrintNameOffset` field of the reparse data buffer as a number of characters instead of bytes. Patch by Craig Holmquist and SSE4.

### macOS

- bpo-32901: Update macOS 10.9+ installer to Tcl/Tk 8.6.8.

### IDLE

- bpo-32916: Change `str` to `code` in pyparse.

- bpo-32905: Remove unused code in pyparse module.

- bpo-32874: Add tests for pyparse.

- bpo-32837: Using the system and place-dependent default encoding for open() is a bad idea for IDLE’s system and location-independent files.

- bpo-32826: Add “encoding=utf-8” to open() in IDLE’s test_help_about. GUI test test_file_buttons() only looks at initial ascii-only lines, but failed on systems where open() defaults to ‘ascii’ because readline() internally reads and decodes far enough ahead to encounter a non-ascii character in CREDITS.txt.

- bpo-32765: Update configdialog General tab docstring to add new widgets to the widget list.

### Tools/Demos

- bpo-32222: Fix pygettext not extracting docstrings for functions with type annotated arguments. Patch by Toby Harradine.

## Python 3.7.0 beta 1

Release date: 2018-01-30

### Core and Builtins

- bpo-32703: Fix coroutine’s ResourceWarning when there’s an active error set when it’s being finalized.

- bpo-32650: Pdb and other debuggers dependent on bdb.py will correctly step over (next command) native coroutines. Patch by Pablo Galindo.

- bpo-28685: Optimize list.sort() and sorted() by using type specialized comparisons when possible.

- bpo-32685: Improve suggestion when the Python 2 form of print statement is either present on the same line as the header of a compound statement or else terminated by a semi-colon instead of a newline. Patch by Nitish Chandra.

- bpo-32697: Python now explicitly preserves the definition order of keyword-only parameters. It’s always preserved their order, but this behavior was never guaranteed before; this behavior is now guaranteed and tested.

- bpo-32690: The locals() dictionary now displays in the lexical order that variables were defined. Previously, the order was reversed.

- bpo-32677: Add `.isascii()` method to `str`, `bytes` and `bytearray`. It can be used to test that string contains only ASCII characters.

- bpo-32670: Enforce PEP 479 for all code. This means that manually raising a StopIteration exception from a generator is prohibited for all code, regardless of whether ‘from __future__ import generator_stop’ was used or not.

- bpo-32591: Added built-in support for tracking the origin of coroutine objects; see sys.set_coroutine_origin_tracking_depth and CoroutineType.cr_origin. This replaces the asyncio debug mode’s use of coroutine wrapping for native coroutine objects.

- bpo-31368: Expose preadv and pwritev system calls in the os module. Patch by Pablo Galindo

- bpo-32544: `hasattr(obj, name)` and `getattr(obj, name, default)` are about 4 times faster than before when `name` is not found and `obj` doesn’t override `__getattr__` or `__getattribute__`.

- bpo-26163: Improved frozenset() hash to create more distinct hash values when faced with datasets containing many similar values.

- bpo-32550: Remove the STORE_ANNOTATION bytecode.

- bpo-20104: Expose posix_spawn as a low level API in the os module. (removed before 3.7.0rc1)

- bpo-24340: Fixed estimation of the code stack size.

- bpo-32436: Implement PEP 567 Context Variables.

- bpo-18533: `repr()` on a dict containing its own `values()` or `items()` no longer raises `RecursionError`; OrderedDict similarly. Instead, use `...`, as for other recursive structures. Patch by Ben North.

- bpo-20891: Py_Initialize() now creates the GIL. The GIL is no longer created “on demand” to fix a race condition when PyGILState_Ensure() is called in a non-Python thread.

- bpo-32028: Leading whitespace is now correctly ignored when generating suggestions for converting Py2 print statements to Py3 builtin print function calls. Patch by Sanyam Khurana.

- bpo-31179: Make dict.copy() up to 5.5 times faster.

- bpo-31113: Get rid of recursion in the compiler for normal control flow.

### Library

- bpo-25988: Deprecate exposing the contents of collections.abc in the regular collections module.

- bpo-31429: The default cipher suite selection of the ssl module now uses a blacklist approach rather than a hard-coded whitelist. Python no longer re-enables ciphers that have been blocked by OpenSSL security update. Default cipher suite selection can be configured on compile time.

- bpo-30306: contextlib.contextmanager now releases the arguments passed to the underlying generator as soon as the context manager is entered. Previously it would keep them alive for as long as the context manager was alive, even when not being used as a function decorator. Patch by Martin Teichmann.

- bpo-21417: Added support for setting the compression level for zipfile.ZipFile.

- bpo-32251: Implement asyncio.BufferedProtocol (provisional API).

- bpo-32513: In dataclasses, allow easier overriding of dunder methods without specifying decorator parameters.

- bpo-32660: `termios` makes available `FIONREAD`, `FIONCLEX`, `FIOCLEX`, `FIOASYNC` and `FIONBIO` also under Solaris/derivatives.

- bpo-27931: Fix email address header parsing error when the username is an empty quoted string. Patch by Xiang Zhang.

- bpo-32659: Under Solaris and derivatives, `os.stat_result` provides a st_fstype attribute.

- bpo-32662: Implement Server.start_serving(), Server.serve_forever(), and Server.is_serving() methods. Add ‘start_serving’ keyword parameter to loop.create_server() and loop.create_unix_server().

- bpo-32391: Implement `asyncio.StreamWriter.wait_closed()` and `asyncio.StreamWriter.is_closing()` methods

- bpo-32643: Make Task._step, Task._wakeup and Future._schedule_callbacks methods private.

- bpo-32630: Refactor decimal module to use contextvars to store decimal context.

- bpo-32622: Add `asyncio.AbstractEventLoop.sendfile()` method.

- bpo-32304: distutils’ upload command no longer corrupts tar files ending with a CR byte, and no longer tries to convert CR to CRLF in any of the upload text fields.

- bpo-32502: uuid.uuid1 no longer raises an exception if a 64-bit hardware address is encountered.

- bpo-32596: `concurrent.futures` imports `ThreadPoolExecutor` and `ProcessPoolExecutor` lazily (using PEP 562). It makes `import asyncio` about 15% faster because asyncio uses only `ThreadPoolExecutor` by default.

- bpo-31801: Add `_ignore_` to `Enum` so temporary variables can be used during class construction without being turned into members.

- bpo-32576: Use queue.SimpleQueue() in places where it can be invoked from a weakref callback.

- bpo-32574: Fix memory leak in asyncio.Queue, when the queue has limited size and it is full, the cancelation of queue.put() can cause a memory leak. Patch by: José Melero.

- bpo-32521: The nis module is now compatible with new libnsl and headers location.

- bpo-32467: collections.abc.ValuesView now inherits from collections.abc.Collection.

- bpo-32473: Improve ABCMeta._dump_registry() output readability

- bpo-32102: New argument `capture_output` for subprocess.run

- bpo-32521: glibc has removed Sun RPC. Use replacement libtirpc headers and library in nis module.

- bpo-32493: UUID module fixes build for FreeBSD/OpenBSD

- bpo-32503: Pickling with protocol 4 no longer creates too small frames.

- bpo-29237: Create enum for pstats sorting options

- bpo-32454: Add close(fd) function to the socket module.

- bpo-25942: The subprocess module is now more graceful when handling a Ctrl-C KeyboardInterrupt during subprocess.call, subprocess.run, or a Popen context manager. It now waits a short amount of time for the child (presumed to have also gotten the SIGINT) to exit, before continuing the KeyboardInterrupt exception handling. This still includes a SIGKILL in the call() and run() APIs, but at least the child had a chance first.

- bpo-32433: The hmac module now has hmac.digest(), which provides an optimized HMAC digest.

- bpo-28134: Sockets now auto-detect family, type and protocol from file descriptor by default.

- bpo-32404: Fix bug where `datetime.datetime.fromtimestamp()` did not call __new__ in `datetime.datetime` subclasses.

- bpo-32403: Improved speed of `datetime.date` and `datetime.datetime` alternate constructors.

- bpo-32228: Ensure that `truncate()` preserves the file position (as reported by `tell()`) after writes longer than the buffer size.

- bpo-32410: Implement `loop.sock_sendfile` for asyncio event loop.

- bpo-22908: Added seek and tell to the ZipExtFile class. This only works if the file object used to open the zipfile is seekable.

- bpo-32373: Add socket.getblocking() method.

- bpo-32248: Add `importlib.resources` and `importlib.abc.ResourceReader` as the unified API for reading resources contained within packages. Loaders wishing to support resource reading must implement the `get_resource_reader()` method. File-based and zipimport-based loaders both implement these APIs. `importlib.abc.ResourceLoader` is deprecated in favor of these new APIs.

- bpo-32320: collections.namedtuple() now supports default values.

- bpo-29302: Add contextlib.AsyncExitStack. Patch by Alexander Mohr and Ilya Kulakov.

- bpo-31961: Removed in Python 3.7.0b2. The args argument of subprocess.Popen can now be a path-like object. If args is given as a sequence, it’s first element can now be a path-like object as well.

- bpo-31900: The `locale.localeconv()` function now sets temporarily the `LC_CTYPE` locale to the `LC_NUMERIC` locale to decode `decimal_point` and `thousands_sep` byte strings if they are non-ASCII or longer than 1 byte, and the `LC_NUMERIC` locale is different than the `LC_CTYPE` locale. This temporary change affects other threads. Same change for the `str.format()` method when formatting a number (`int`, `float`, `float` and subclasses) with the `n` type (ex: `'{:n}'.format(1234)`).

- bpo-31853: Use super().method instead of socket.method in SSLSocket. They were there most likely for legacy reasons.

- bpo-31399: The ssl module now uses OpenSSL’s X509_VERIFY_PARAM_set1_host() and X509_VERIFY_PARAM_set1_ip() API to verify hostname and IP addresses. Subject common name fallback can be disabled with SSLContext.hostname_checks_common_name.

- bpo-14976: Add a queue.SimpleQueue class, an unbounded FIFO queue with a reentrant C implementation of put().

### Documentation

- bpo-32724: Add references to some commands in the documentation of Pdb. Patch by Stéphane Wirtel

- bpo-32649: Complete the C API documentation, profiling and tracing part with the newly added per-opcode events.

- bpo-17799: Explain real behaviour of sys.settrace and sys.setprofile and their C-API counterparts regarding which type of events are received in each function. Patch by Pablo Galindo Salgado.

### Tests

- bpo-32721: Fix test_hashlib to not fail if the _md5 module is not built.

- bpo-28414: Add test cases for IDNA 2003 and 2008 host names. IDNA 2003 internationalized host names are working since bpo-31399 has landed. IDNA 2008 are still broken.

- bpo-32604: Add a new “_xxsubinterpreters” extension module that exposes the existing subinterpreter C-API and a new cross-interpreter data sharing mechanism. The module is primarily intended for more thorough testing of the existing subinterpreter support. Note that the _xxsubinterpreters module has been removed in 3.7.0rc1.

- bpo-32602: Add test certs and test for ECDSA cert and EC/RSA dual mode.

- bpo-32549: On Travis CI, Python now Compiles and uses a local copy of OpenSSL 1.1.0g for testing.

### Build

- bpo-32635: Fix segfault of the crypt module when libxcrypt is provided instead of libcrypt at the system.

- bpo-32598: Use autoconf to detect OpenSSL libs, headers and supported features. The ax_check_openssl M4 macro uses pkg-config to locate OpenSSL and falls back to manual search.

- bpo-32593: Drop support of FreeBSD 9 and older.

- bpo-29708: If the `SOURCE_DATE_EPOCH` environment variable is set, `py_compile` will always create hash-based `.pyc` files.

### Windows

- bpo-32588: Create standalone _distutils_findvs module and add missing _queue module to installer.

- bpo-29911: Ensure separate Modify and Uninstall buttons are displayed.

- bpo-32507: Use app-local UCRT install rather than the proper update for old versions of Windows.

### macOS

- bpo-32726: Provide an additional, more modern macOS installer variant that supports macOS 10.9+ systems in 64-bit mode only. Upgrade the supplied third-party libraries to OpenSSL 1.1.0g and to SQLite 3.22.0. The 10.9+ installer now links with and supplies its own copy of Tcl/Tk 8.6.

- bpo-28440: No longer add /Library/Python/3.x/site-packages to sys.path for macOS framework builds to avoid future conflicts.

### C API

- bpo-32681: Fix uninitialized variable ‘res’ in the C implementation of os.dup2. Patch by Stéphane Wirtel

- bpo-10381: Add C API access to the `datetime.timezone` constructor and `datetime.timzone.UTC` singleton.

## Python 3.7.0 alpha 4

Release date: 2018-01-08

### Core and Builtins

- bpo-31975: The default warning filter list now starts with a “default::DeprecationWarning:__main__” entry, so deprecation warnings are once again shown by default in single-file scripts and at the interactive prompt.

- bpo-32226: `__class_getitem__` is now an automatic class method.

- bpo-32399: Add AIX uuid library support for RFC4122 using uuid_create() in libc.a

- bpo-32390: Fix the compilation failure on AIX after the f_fsid field has been added to the object returned by os.statvfs() (bpo-32143). Original patch by Michael Felt.

- bpo-32379: Make MRO computation faster when a class inherits from a single base.

- bpo-32259: The error message of a TypeError raised when unpack non-iterable is now more specific.

- bpo-27169: The `__debug__` constant is now optimized out at compile time. This fixes also bpo-22091.

- bpo-32329: The `-R` option now turns on hash randomization when the `PYTHONHASHSEED` environment variable is set to `0`. Previously, the option was ignored. Moreover, `sys.flags.hash_randomization` is now properly set to 0 when hash randomization is turned off by `PYTHONHASHSEED=0`.

- bpo-30416: The optimizer is now protected from spending much time doing complex calculations and consuming much memory for creating large constants in constant folding. Increased limits for constants that can be produced in constant folding.

- bpo-32282: Fix an unnecessary ifdef in the include of VersionHelpers.h in socketmodule on Windows.

- bpo-30579: Implement TracebackType.__new__ to allow Python-level creation of traceback objects, and make TracebackType.tb_next mutable.

- bpo-32260: Don’t byte swap the input keys to the SipHash algorithm on big-endian platforms. This should ensure siphash gives consistent results across platforms.

- bpo-31506: Improve the error message logic for object.__new__ and object.__init__. Patch by Sanyam Khurana.

- bpo-20361: `-b` and `-bb` now inject `'default::BytesWarning'` and `error::BytesWarning` entries into `sys.warnoptions`, ensuring that they take precedence over any other warning filters configured via the `-W` option or the `PYTHONWARNINGS` environment variable.

- bpo-32230: `-X dev` now injects a `'default'` entry into sys.warnoptions, ensuring that it behaves identically to actually passing `-Wdefault` at the command line.

- bpo-29240: Add a new UTF-8 mode: implementation of the PEP 540.

- bpo-32226: PEP 560: Add support for `__mro_entries__` and `__class_getitem__`. Implemented by Ivan Levkivskyi.

- bpo-32225: PEP 562: Add support for module `__getattr__` and `__dir__`. Implemented by Ivan Levkivskyi.

- bpo-31901: The `atexit` module now has its callback stored per interpreter.

- bpo-31650: Implement PEP 552 (Deterministic pycs). Python now supports invalidating bytecode cache files bashed on a source content hash rather than source last-modified time.

- bpo-29469: Move constant folding from bytecode layer to AST layer. Original patch by Eugene Toder.

### Library

- bpo-32506: Now that dict is defined as keeping insertion order, drop OrderedDict and just use plain dict.

- bpo-32279: Add params to dataclasses.make_dataclasses(): init, repr, eq, order, hash, and frozen. Pass them through to dataclass().

- bpo-32278: Make type information optional on dataclasses.make_dataclass(). If omitted, the string ‘typing.Any’ is used.

- bpo-32499: Add dataclasses.is_dataclass(obj), which returns True if obj is a dataclass or an instance of one.

- bpo-32468: Improve frame repr() to mention filename, code name and current line number.

- bpo-23749: asyncio: Implement loop.start_tls()

- bpo-32441: Return the new file descriptor (i.e., the second argument) from `os.dup2`. Previously, `None` was always returned.

- bpo-32422: `functools.lru_cache` uses less memory (3 words for each cached key) and takes about 1/3 time for cyclic GC.

- bpo-31721: Prevent Python crash from happening when Future._log_traceback is set to True manually. Now it can only be set to False, or a ValueError is raised.

- bpo-32415: asyncio: Add Task.get_loop() and Future.get_loop()

- bpo-26133: Don’t unsubscribe signals in asyncio UNIX event loop on interpreter shutdown.

- bpo-32363: Make asyncio.Task.set_exception() and set_result() raise NotImplementedError. Task._step() and Future.__await__() raise proper exceptions when they are in an invalid state, instead of raising an AssertionError.

- bpo-32357: Optimize asyncio.iscoroutine() and loop.create_task() for non-native coroutines (e.g. async/await compiled with Cython). ‘loop.create_task(python_coroutine)’ used to be 20% faster than ‘loop.create_task(cython_coroutine)’. Now, the latter is as fast.

- bpo-32356: asyncio.transport.resume_reading() and pause_reading() are now idempotent. New transport.is_reading() method is added.

- bpo-32355: Optimize asyncio.gather(); now up to 15% faster.

- bpo-32351: Use fastpath in asyncio.sleep if delay<0 (2x boost)

- bpo-32348: Optimize asyncio.Future schedule/add/remove callback. The optimization shows 3-6% performance improvements of async/await code.

- bpo-32331: Fix socket.settimeout() and socket.setblocking() to keep socket.type as is. Fix socket.socket() constructor to reset any bit flags applied to socket’s type. This change only affects OSes that have SOCK_NONBLOCK and/or SOCK_CLOEXEC.

- bpo-32248: Add `importlib.abc.ResourceReader` as an ABC for loaders to provide a unified API for reading resources contained within packages. Also add `importlib.resources` as the port of `importlib_resources`.

- bpo-32311: Implement asyncio.create_task(coro) shortcut

- bpo-32327: Convert asyncio functions that were documented as coroutines to coroutines. Affected functions: loop.sock_sendall, loop.sock_recv, loop.sock_accept, loop.getaddrinfo, loop.getnameinfo.

- bpo-32323: `urllib.parse.urlsplit()` does not convert zone-id (scope) to lower case for scoped IPv6 addresses in hostnames now.

- bpo-32302: Fix bdist_wininst of distutils for CRT v142: it binary compatible with CRT v140.

- bpo-29711: Fix `stop_serving` in asyncio proactor loop kill all listening servers

- bpo-32308: `re.sub()` now replaces empty matches adjacent to a previous non-empty match.

- bpo-29970: Abort asyncio SSLProtocol connection if handshake not complete within 10s

- bpo-32314: Implement asyncio.run().

- bpo-17852: Revert incorrect fix based on misunderstanding of _Py_PyAtExit() semantics.

- bpo-32296: Implement asyncio._get_running_loop() and get_event_loop() in C. This makes them 4x faster.

- bpo-32250: Implement `asyncio.current_task()` and `asyncio.all_tasks()`. Add helpers intended to be used by alternative task implementations: `asyncio._register_task`, `asyncio._enter_task`, `asyncio._leave_task` and `asyncio._unregister_task`. Deprecate `asyncio.Task.current_task()` and `asyncio.Task.all_tasks()`.

- bpo-32255: A single empty field is now always quoted when written into a CSV file. This allows to distinguish an empty row from a row consisting of a single empty field. Patch by Licht Takeuchi.

- bpo-32277: Raise `NotImplementedError` instead of `SystemError` on platforms where `chmod(..., follow_symlinks=False)` is not supported. Patch by Anthony Sottile.

- bpo-30050: New argument warn_on_full_buffer to signal.set_wakeup_fd lets you control whether Python prints a warning on stderr when the wakeup fd buffer overflows.

- bpo-29137: The `fpectl` library has been removed. It was never enabled by default, never worked correctly on x86-64, and it changed the Python ABI in ways that caused unexpected breakage of C extensions.

- bpo-32273: Move asyncio.test_utils to test.test_asyncio.

- bpo-32272: Remove asyncio.async() function.

- bpo-32269: Add asyncio.get_running_loop() function.

- bpo-32265: All class and static methods of builtin types now are correctly classified by inspect.classify_class_attrs() and grouped in pydoc ouput. Added types.ClassMethodDescriptorType for unbound class methods of builtin types.

- bpo-32253: Deprecate `yield from lock`, `await lock`, `with (yield from lock)` and `with await lock` for asyncio synchronization primitives.

- bpo-22589: Changed MIME type of .bmp from ‘image/x-ms-bmp’ to ‘image/bmp’

- bpo-32193: Convert asyncio to use async/await syntax. Old styled `yield from` is still supported too.

- bpo-32206: Add support to run modules with pdb

- bpo-32227: `functools.singledispatch` now supports registering implementations using type annotations.

- bpo-15873: Added new alternate constructors `datetime.datetime.fromisoformat()`, `datetime.time.fromisoformat()` and `datetime.date.fromisoformat()` as the inverse operation of each classes’s respective `isoformat` methods.

- bpo-32199: The getnode() ip getter now uses ‘ip link’ instead of ‘ip link list’.

- bpo-32143: os.statvfs() includes the f_fsid field from statvfs(2)

- bpo-26439: Fix ctypes.util.find_library() for AIX by implementing ctypes._aix.find_library() Patch by: Michael Felt

- bpo-31993: The pickler now uses less memory when serializing large bytes and str objects into a file. Pickles created with protocol 4 will require less memory for unpickling large bytes and str objects.

- bpo-27456: Ensure TCP_NODELAY is set on Linux. Tests by Victor Stinner.

- bpo-31778: ast.literal_eval() is now more strict. Addition and subtraction of arbitrary numbers no longer allowed.

- bpo-31802: Importing native path module (`posixpath`, `ntpath`) now works even if the `os` module still is not imported.

- bpo-30241: Add contextlib.AbstractAsyncContextManager. Patch by Jelle Zijlstra.

- bpo-31699: Fix deadlocks in `concurrent.futures.ProcessPoolExecutor` when task arguments or results cause pickling or unpickling errors. This should make sure that calls to the `ProcessPoolExecutor` API always eventually return.

- bpo-15216: `TextIOWrapper.reconfigure()` supports changing encoding, errors, and newline.

### Documentation

- bpo-32418: Add get_loop() method to Server and AbstractServer classes.

### Tests

- bpo-32252: Fix faulthandler_suppress_crash_report() used to prevent core dump files when testing crashes. getrlimit() returns zero on success.

- bpo-32002: Adjust C locale coercion testing for the empty locale and POSIX locale cases to more readily adjust to platform dependent behaviour.

### Windows

- bpo-19764: Implement support for `subprocess.Popen(close_fds=True)` on Windows. Patch by Segev Finer.

### Tools/Demos

- bpo-24960: 2to3 and lib2to3 can now read pickled grammar files using pkgutil.get_data() rather than probing the filesystem. This lets 2to3 and lib2to3 work when run from a zipfile.

### C API

- bpo-32030: Py_Initialize() doesn’t reset the memory allocators to default if the `PYTHONMALLOC` environment variable is not set.

- bpo-29084: Undocumented C API for OrderedDict has been excluded from the limited C API. It was added by mistake and actually never worked in the limited C API.

- bpo-32264: Moved the pygetopt.h header into internal/, since it has no public APIs.

- bpo-32241: `Py_SetProgramName()` and `Py_SetPythonHome()` now take the `const wchar *` arguments instead of `wchar *`.

## Python 3.7.0 alpha 3

Release date: 2017-12-05

### Core and Builtins

- bpo-32176: co_flags.CO_NOFREE is now always set correctly by the code object constructor based on freevars and cellvars, rather than needing to be set correctly by the caller. This ensures it will be cleared automatically when additional cell references are injected into a modified code object and function.

- bpo-10544: Yield expressions are now deprecated in comprehensions and generator expressions. They are still permitted in the definition of the outermost iterable, as that is evaluated directly in the enclosing scope.

- bpo-32137: The repr of deeply nested dict now raises a RecursionError instead of crashing due to a stack overflow.

- bpo-32096: Revert memory allocator changes in the C API: move structures back from _PyRuntime to Objects/obmalloc.c. The memory allocators are once again initialized statically, and so PyMem_RawMalloc() and Py_DecodeLocale() can be called before _PyRuntime_Initialize().

- bpo-32043: Add a new “developer mode”: new “-X dev” command line option to enable debug checks at runtime.

- bpo-32023: SyntaxError is now correctly raised when a generator expression without parenthesis is used instead of an inheritance list in a class definition. The duplication of the parentheses can be omitted only on calls.

- bpo-32012: SyntaxError is now correctly raised when a generator expression without parenthesis is passed as an argument, but followed by a trailing comma. A generator expression always needs to be directly inside a set of parentheses and cannot have a comma on either side.

- bpo-28180: A new internal `_Py_SetLocaleFromEnv(category)` helper function has been added in order to improve the consistency of behaviour across different `libc` implementations (e.g. Android doesn’t support setting the locale from the environment by default).

- bpo-31949: Fixed several issues in printing tracebacks (PyTraceBack_Print()). Setting sys.tracebacklimit to 0 or less now suppresses printing tracebacks. Setting sys.tracebacklimit to None now causes using the default limit. Setting sys.tracebacklimit to an integer larger than LONG_MAX now means using the limit LONG_MAX rather than the default limit. Fixed integer overflows in the case of more than 2**31 traceback items on Windows. Fixed output errors handling.

- bpo-30696: Fix the interactive interpreter looping endlessly when no memory.

- bpo-20047: Bytearray methods partition() and rpartition() now accept only bytes-like objects as separator, as documented. In particular they now raise TypeError rather of returning a bogus result when an integer is passed as a separator.

- bpo-21720: BytesWarning no longer emitted when the fromlist argument of `__import__()` or the `__all__` attribute of the module contain bytes instances.

- bpo-31845: Environment variables are once more read correctly at interpreter startup.

- bpo-28936: Ensure that lexically first syntax error involving a parameter and `global` or `nonlocal` is detected first at a given scope. Patch by Ivan Levkivskyi.

- bpo-31825: Fixed OverflowError in the ‘unicode-escape’ codec and in codecs.escape_decode() when decode an escaped non-ascii byte.

- bpo-31618: The per-frame tracing logic added in 3.7a1 has been altered so that `frame->f_lineno` is updated before either `"line"` or `"opcode"` events are emitted. Previously, opcode events were emitted first, and therefore would occasionally see stale line numbers on the frame. The behavior of this feature has changed slightly as a result: when both `f_trace_lines` and `f_trace_opcodes` are enabled, line events now occur first.

- bpo-28603: Print the full context/cause chain of exceptions on interpreter exit, even if an exception in the chain is unhashable or compares equal to later ones. Patch by Zane Bitter.

- bpo-31786: Fix timeout rounding in the select module to round correctly negative timeouts between -1.0 and 0.0. The functions now block waiting for events as expected. Previously, the call was incorrectly non-blocking. Patch by Pablo Galindo.

- bpo-31781: Prevent crashes when calling methods of an uninitialized `zipimport.zipimporter` object. Patch by Oren Milman.

- bpo-30399: Standard repr() of BaseException with a single argument no longer contains redundant trailing comma.

- bpo-31626: Fixed a bug in debug memory allocator. There was a write to freed memory after shrinking a memory block.

- bpo-30817: `PyErr_PrintEx()` clears now the ignored exception that may be raised by `_PySys_SetObjectId()`, for example when no memory.

### Library

- bpo-28556: Two minor fixes for `typing` module: allow shallow copying instances of generic classes, improve interaction of `__init_subclass__` with generics. Original PRs by Ivan Levkivskyi.

- bpo-32214: PEP 557, Data Classes. Provides a decorator which adds boilerplate methods to classes which use type annotations so specify fields.

- bpo-27240: The header folding algorithm for the new email policies has been rewritten, which also fixes bpo-30788, bpo-31831, and bpo-32182. In particular, RFC2231 folding is now done correctly.

- bpo-32186: io.FileIO.readall() and io.FileIO.read() now release the GIL when getting the file size. Fixed hang of all threads with inaccessible NFS server. Patch by Nir Soffer.

- bpo-321010: Add `sys.flags.dev_mode` flag

- bpo-32154: The `asyncio.windows_utils.socketpair()` function has been removed: use directly `socket.socketpair()` which is available on all platforms since Python 3.5 (before, it wasn’t available on Windows). `asyncio.windows_utils.socketpair()` was just an alias to `socket.socketpair` on Python 3.5 and newer.

- bpo-32089: warnings: In development (-X dev) and debug mode (pydebug build), use the “default” action for ResourceWarning, rather than the “always” action, in the default warnings filters.

- bpo-32107: `uuid.getnode()` now preferentially returns universally administered MAC addresses if available, over locally administered MAC addresses. This makes a better guarantee for global uniqueness of UUIDs returned from `uuid.uuid1()`. If only locally administered MAC addresses are available, the first such one found is returned.

- bpo-23033: Wildcard is now supported in hostname when it is one and only character in the left most segment of hostname in second argument of `ssl.match_hostname()`. Patch by Mandeep Singh.

- bpo-12239: Make `msilib.SummaryInformation.GetProperty()` return `None` when the value of property is `VT_EMPTY`. Initial patch by Mark Mc Mahon.

- bpo-28334: Use `os.path.expanduser()` to find the `~/.netrc` file in `netrc.netrc`. If it does not exist, `FileNotFoundError` is raised. Patch by Dimitri Merejkowsky.

- bpo-32121: Made `tracemalloc.Traceback` behave more like the traceback module, sorting the frames from oldest to most recent. `Traceback.format()` now accepts negative limit, truncating the result to the `abs(limit)` oldest frames. To get the old behaviour, one can use the new most_recent_first argument to `Traceback.format()`. (Patch by Jesse Bakker.)

- bpo-31325: Fix wrong usage of `collections.namedtuple()` in the `RobotFileParser.parse()` method. Initial patch by Robin Wellner.

- bpo-12382: `msilib.OpenDatabase()` now raises a better exception message when it couldn’t open or create an MSI file. Initial patch by William Tisäter.

- bpo-19610: `setup()` now warns about invalid types for some fields. The `distutils.dist.Distribution` class now warns when `classifiers`, `keywords` and `platforms` fields are not specified as a list or a string.

- bpo-32071: Added the `-k` command-line option to `python -m unittest` to run only tests that match the given pattern(s).

- bpo-10049: Added nullcontext no-op context manager to contextlib. This provides a simpler and faster alternative to ExitStack() when handling optional context managers.

- bpo-28684: The new test.support.skip_unless_bind_unix_socket() decorator is used here to skip asyncio tests that fail because the platform lacks a functional bind() function for unix domain sockets (as it is the case for non root users on the recent Android versions that run now SELinux in enforcing mode).

- bpo-32110: `codecs.StreamReader.read(n)` now returns not more than n characters/bytes for non-negative n. This makes it compatible with `read()` methods of other file-like objects.

- bpo-27535: The warnings module doesn’t leak memory anymore in the hidden warnings registry for the “ignore” action of warnings filters. warn_explicit() function doesn’t add the warning key to the registry anymore for the “ignore” action.

- bpo-32088: warnings: When Python is build is debug mode (`Py_DEBUG`), `DeprecationWarning`, `PendingDeprecationWarning` and `ImportWarning` warnings are now displayed by default.

- bpo-1647489: Fixed searching regular expression patterns that could match an empty string. Non-empty string can now be correctly found after matching an empty string.

- bpo-25054: Added support of splitting on a pattern that could match an empty string.

- bpo-32072: Fixed issues with binary plists: Fixed saving bytearrays. Identical objects will be saved only once. Equal references will be load as identical objects. Added support for saving and loading recursive data structures.

- bpo-32069: Drop legacy SSL transport from asyncio, ssl.MemoryBIO is always used anyway.

- bpo-32066: asyncio: Support pathlib.Path in create_unix_connection; sock arg should be optional

- bpo-32046: Updates 2to3 to convert from operator.isCallable(obj) to callable(obj). Patch by Dong-hee Na.

- bpo-32018: inspect.signature should follow PEP 8, if the parameter has an annotation and a default value. Patch by Dong-hee Na.

- bpo-32025: Add time.thread_time() and time.thread_time_ns()

- bpo-32037: Integers that fit in a signed 32-bit integer will be now pickled with protocol 0 using the INT opcode. This will decrease the size of a pickle, speed up pickling and unpickling, and make these integers be unpickled as int instances in Python 2.

- bpo-32034: Make asyncio.IncompleteReadError and LimitOverrunError pickleable.

- bpo-32015: Fixed the looping of asyncio in the case of reconnection the socket during waiting async read/write from/to the socket.

- bpo-32011: Restored support of loading marshal files with the TYPE_INT64 code. These files can be produced in Python 2.7.

- bpo-28369: Enhance add_reader/writer check that socket is not used by some transport. Before, only cases when add_reader/writer were called with an int FD were supported. Now the check is implemented correctly for all file-like objects.

- bpo-31976: Fix race condition when flushing a file is slow, which can cause a segfault if closing the file from another thread.

- bpo-31985: Formally deprecated aifc.openfp, sunau.openfp, and wave.openfp. Since change 7bc817d5ba917528e8bd07ec461c635291e7b06a in 1993, openfp in each of the three modules had been pointing to that module’s open function as a matter of backwards compatibility, though it had been both untested and undocumented.

- bpo-21862: cProfile command line now accepts `-m module_name` as an alternative to script path. Patch by Sanyam Khurana.

- bpo-31970: Reduce performance overhead of asyncio debug mode.

- bpo-31843: database argument of sqlite3.connect() now accepts a path-like object, instead of just a string.

- bpo-31945: Add Configurable blocksize to `HTTPConnection` and `HTTPSConnection` for improved upload throughput. Patch by Nir Soffer.

- bpo-31943: Add a `cancelled()` method to `asyncio.Handle`. Patch by Marat Sharafutdinov.

- bpo-9678: Fixed determining the MAC address in the uuid module: Using ifconfig on NetBSD and OpenBSD. Using arp on Linux, FreeBSD, NetBSD and OpenBSD. Based on patch by Takayuki Shimizukawa.

- bpo-30057: Fix potential missed signal in signal.signal().

- bpo-31933: Fix Blake2 params leaf_size and node_offset on big endian platforms. Patch by Jack O’Connor.

- bpo-21423: Add an initializer argument to {Process,Thread}PoolExecutor

- bpo-31927: Fixed compilation of the socket module on NetBSD 8. Fixed assertion failure or reading arbitrary data when parse a AF_BLUETOOTH address on NetBSD and DragonFly BSD.

- bpo-27666: Fixed stack corruption in curses.box() and curses.ungetmouse() when the size of types chtype or mmask_t is less than the size of C long. curses.box() now accepts characters as arguments. Based on patch by Steve Fink.

- bpo-31917: Add 3 new clock identifiers: `time.CLOCK_BOOTTIME`, `time.CLOCK_PROF` and `time.CLOCK_UPTIME`.

- bpo-31897: plistlib now catches more errors when read binary plists and raises InvalidFileException instead of unexpected exceptions.

- bpo-25720: Fix the method for checking pad state of curses WINDOW. Patch by Masayuki Yamamoto.

- bpo-31893: Fixed the layout of the kqueue_event structure on OpenBSD and NetBSD. Fixed the comparison of the kqueue_event objects.

- bpo-31891: Fixed building the curses module on NetBSD.

- bpo-31884: added required constants to subprocess module for setting priority on windows

- bpo-28281: Remove year (1-9999) limits on the Calendar.weekday() function. Patch by Mark Gollahon.

- bpo-31702: crypt.mksalt() now allows to specify the number of rounds for SHA-256 and SHA-512 hashing.

- bpo-30639: `inspect.getfile()` no longer computes the repr of unknown objects to display in an error message, to protect against badly behaved custom reprs.

- bpo-30768: Fix the pthread+semaphore implementation of PyThread_acquire_lock_timed() when called with timeout > 0 and intr_flag=0: recompute the timeout if sem_timedwait() is interrupted by a signal (EINTR). See also the PEP 475.

- bpo-31854: Add `mmap.ACCESS_DEFAULT` constant.

- bpo-31834: Use optimized code for BLAKE2 only with SSSE3+. The pure SSE2 implementation is slower than the pure C reference implementation.

- bpo-28292: Calendar.itermonthdates() will now consistently raise an exception when a date falls outside of the 0001-01-01 through 9999-12-31 range. To support applications that cannot tolerate such exceptions, the new methods itermonthdays3() and itermonthdays4() are added. The new methods return tuples and are not restricted by the range supported by datetime.date.

- bpo-28564: The shutil.rmtree() function has been sped up to 20–40%. This was done using the os.scandir() function.

- bpo-28416: Instances of pickle.Pickler subclass with the persistent_id() method and pickle.Unpickler subclass with the persistent_load() method no longer create reference cycles.

- bpo-31653: Don’t release the GIL if we can acquire a multiprocessing semaphore immediately.

- bpo-28326: Fix multiprocessing.Process when stdout and/or stderr is closed or None.

- bpo-20825: Add `subnet_of` and `superset_of` containment tests to `ipaddress.IPv6Network` and `ipaddress.IPv4Network`. Patch by Michel Albert and Cheryl Sabella.

- bpo-31827: Remove the os.stat_float_times() function. It was introduced in Python 2.3 for backward compatibility with Python 2.2, and was deprecated since Python 3.1.

- bpo-31756: Add a `subprocess.Popen(text=False)` keyword argument to `subprocess` functions to be more explicit about when the library should attempt to decode outputs into text. Patch by Andrew Clegg.

- bpo-31819: Add AbstractEventLoop.sock_recv_into().

- bpo-31457: If nested log adapters are used, the inner `process()` methods are no longer omitted.

- bpo-31457: The `manager` property on LoggerAdapter objects is now properly settable.

- bpo-31806: Fix timeout rounding in time.sleep(), threading.Lock.acquire() and socket.socket.settimeout() to round correctly negative timeouts between -1.0 and 0.0. The functions now block waiting for events as expected. Previously, the call was incorrectly non-blocking. Patch by Pablo Galindo.

- bpo-31803: time.clock() and time.get_clock_info(‘clock’) now emit a DeprecationWarning warning.

- bpo-31800: Extended support for parsing UTC offsets. strptime ‘%z’ can now parse the output generated by datetime.isoformat, including seconds and microseconds.

- bpo-28603: traceback: Fix a TypeError that occurred during printing of exception tracebacks when either the current exception or an exception in its context/cause chain is unhashable. Patch by Zane Bitter.

- bpo-30541: Add new function to seal a mock and prevent the automatically creation of child mocks. Patch by Mario Corchero.

- bpo-31784: Implement the PEP 564, add new 6 new functions with nanosecond resolution to the `time` module: `clock_gettime_ns()`, `clock_settime_ns()`, `monotonic_ns()`, `perf_counter_ns()`, `process_time_ns()`, `time_ns()`.

- bpo-30143: 2to3 now generates a code that uses abstract collection classes from collections.abc rather than collections.

- bpo-31770: Prevent a crash when calling the `__init__()` method of a `sqlite3.Cursor` object more than once. Patch by Oren Milman.

- bpo-31764: Prevent a crash in `sqlite3.Cursor.close()` in case the `Cursor` object is uninitialized. Patch by Oren Milman.

- bpo-31752: Fix possible crash in timedelta constructor called with custom integers.

- bpo-31620: an empty asyncio.Queue now doesn’t leak memory when queue.get pollers timeout

- bpo-31690: Allow the flags re.ASCII, re.LOCALE, and re.UNICODE to be used as group flags for regular expressions.

- bpo-30349: FutureWarning is now emitted if a regular expression contains character set constructs that will change semantically in the future (nested sets and set operations).

- bpo-31664: Added support for the Blowfish hashing in the crypt module.

- bpo-31632: Fix method set_protocol() of class _SSLProtocolTransport in asyncio module. This method was previously modifying a wrong reference to the protocol.

- bpo-15037: Added a workaround for getkey() in curses for ncurses 5.7 and earlier.

- bpo-31307: Allow use of bytes objects for arguments to `configparser.ConfigParser.read()`. Patch by Vincent Michel.

- bpo-31334: Fix `poll.poll([timeout])` in the `select` module for arbitrary negative timeouts on all OSes where it can only be a non-negative integer or -1. Patch by Riccardo Coccioli.

- bpo-31310: multiprocessing’s semaphore tracker should be launched again if crashed.

- bpo-31308: Make multiprocessing’s forkserver process immune to Ctrl-C and other user interruptions. If it crashes, restart it when necessary.

- bpo-31245: Added support for AF_UNIX socket in asyncio `create_datagram_endpoint`.

- bpo-30553: Add HTTP/2 status code 421 (Misdirected Request) to `http.HTTPStatus`. Patch by Vitor Pereira.

### Documentation

- bpo-32105: Added asyncio.BaseEventLoop.connect_accepted_socket versionadded marker.

### Tests

- bpo-31380: Skip test_httpservers test_undecodable_file on macOS: fails on APFS.

- bpo-31705: Skip test_socket.test_sha256() on Linux kernel older than 4.5. The test fails with ENOKEY on kernel 3.10 (on ppc64le). A fix was merged into the kernel 4.5.

- bpo-32138: Skip on Android test_faulthandler tests that raise SIGSEGV and remove the test.support.requires_android_level decorator.

- bpo-32136: The runtime embedding tests have been split out from `Lib/test/test_capi.py` into a new `Lib/test/test_embed.py` file.

- bpo-28668: test.support.requires_multiprocessing_queue is removed. Skip tests with test.support.import_module(‘multiprocessing.synchronize’) instead when the semaphore implementation is broken or missing.

- bpo-32126: Skip test_get_event_loop_new_process in test.test_asyncio.test_events when sem_open() is not functional.

- bpo-31174: Fix test_tools.test_unparse: DirectoryTestCase now stores the names sample to always test the same files. It prevents false alarms when hunting reference leaks.

### Build

- bpo-28538: Revert the previous changes, the if_nameindex structure is defined by Unified Headers.

- bpo-28762: Revert the last commit, the F_LOCK macro is defined by Android Unified Headers.

- bpo-29040: Support building Android with Unified Headers. The first NDK release to support Unified Headers is android-ndk-r14.

- bpo-32059: `detect_modules()` in `setup.py` now also searches the sysroot paths when cross-compiling.

- bpo-31957: Fixes Windows SDK version detection when building for Windows.

- bpo-31609: Fixes quotes in PCbuild/clean.bat

- bpo-31934: Abort the build when building out of a not clean source tree.

- bpo-31926: Fixed Argument Clinic sometimes causing compilation errors when there was more than one function and/or method in a .c file with the same name.

- bpo-28791: Update Windows builds to use SQLite 3.21.0.

- bpo-28791: Update OS X installer to use SQLite 3.21.0.

- bpo-28643: Record profile-opt build progress with stamp files.

- bpo-31866: Finish removing support for AtheOS.

### Windows

- bpo-1102: Return `None` when `View.Fetch()` returns `ERROR_NO_MORE_ITEMS` instead of raising `MSIError`. Initial patch by Anthony Tuininga.

- bpo-31944: Fixes Modify button in Apps and Features dialog.

- bpo-20486: Implement the `Database.Close()` method to help closing MSI database objects.

- bpo-31857: Make the behavior of USE_STACKCHECK deterministic in a multi-threaded environment.

### macOS

- bpo-31392: Update macOS installer to use OpenSSL 1.0.2m

### IDLE

- bpo-32207: Improve tk event exception tracebacks in IDLE. When tk event handling is driven by IDLE’s run loop, a confusing and distracting queue.EMPTY traceback context is no longer added to tk event exception tracebacks. The traceback is now the same as when event handling is driven by user code. Patch based on a suggestion by Serhiy Storchaka.

- bpo-32164: Delete unused file idlelib/tabbedpages.py. Use of TabbedPageSet in configdialog was replaced by ttk.Notebook.

- bpo-32100: IDLE: Fix old and new bugs in pathbrowser; improve tests. Patch mostly by Cheryl Sabella.

- bpo-31858: IDLE – Restrict shell prompt manipulation to the shell. Editor and output windows only see an empty last prompt line. This simplifies the code and fixes a minor bug when newline is inserted. Sys.ps1, if present, is read on Shell start-up, but is not set or changed.

- bpo-31860: The font sample in the IDLE configuration dialog is now editable. Changes persist while IDLE remains open

- bpo-31836: Test_code_module now passes if run after test_idle, which sets ps1. The code module uses sys.ps1 if present or sets it to ‘>>> ‘ if not. Test_code_module now properly tests both behaviors. Ditto for ps2.

- bpo-28603: Fix a TypeError that caused a shell restart when printing a traceback that includes an exception that is unhashable. Patch by Zane Bitter.

- bpo-13802: Use non-Latin characters in the IDLE’s Font settings sample. Even if one selects a font that defines a limited subset of the unicode Basic Multilingual Plane, tcl/tk will use other fonts that define a character. The expanded example give users of non-Latin characters a better idea of what they might see in IDLE’s shell and editors. To make room for the expanded sample, frames on the Font tab are re-arranged. The Font/Tabs help explains a bit about the additions.

### Tools/Demos

- bpo-32159: Remove CVS and Subversion tools: remove svneol.py and treesync.py scripts. CPython migrated from CVS to Subversion, to Mercurial, and then to Git. CVS and Subversion are no longer used to develop CPython.

- bpo-30722: Make redemo work with Python 3.6 and newer versions. Also, remove the `LOCALE` option since it doesn’t work with string patterns in Python 3. Patch by Christoph Sarnowski.

### C API

- bpo-20891: Fix PyGILState_Ensure(). When PyGILState_Ensure() is called in a non-Python thread before PyEval_InitThreads(), only call PyEval_InitThreads() after calling PyThreadState_New() to fix a crash.

- bpo-32125: The `Py_UseClassExceptionsFlag` flag has been removed. It was deprecated and wasn’t used anymore since Python 2.0.

- bpo-25612: Move the current exception state from the frame object to the co-routine. This simplifies the interpreter and fixes a couple of obscure bugs caused by having swap exception state when entering or exiting a generator.

- bpo-23699: Add Py_RETURN_RICHCOMPARE macro to reduce boilerplate code in rich comparison functions.

- bpo-30697: The `PyExc_RecursionErrorInst` singleton is removed and `PyErr_NormalizeException()` does not use it anymore. This singleton is persistent and its members being never cleared may cause a segfault during finalization of the interpreter. See also bpo-22898.

## Python 3.7.0 alpha 2

Release date: 2017-10-16

### Core and Builtins

- bpo-31558: `gc.freeze()` is a new API that allows for moving all objects currently tracked by the garbage collector to a permanent generation, effectively removing them from future collection events. This can be used to protect those objects from having their PyGC_Head mutated. In effect, this enables great copy-on-write stability at fork().

- bpo-31642: Restored blocking “from package import module” by setting sys.modules[“package.module”] to None.

- bpo-31708: Allow use of asynchronous generator expressions in synchronous functions.

- bpo-31709: Drop support of asynchronous __aiter__.

- bpo-30404: The -u option now makes the stdout and stderr streams unbuffered rather than line-buffered.

- bpo-31619: Fixed a ValueError when convert a string with large number of underscores to integer with binary base.

- bpo-31602: Fix an assertion failure in `zipimporter.get_source()` in case of a bad `zlib.decompress()`. Patch by Oren Milman.

- bpo-31592: Fixed an assertion failure in Python parser in case of a bad `unicodedata.normalize()`. Patch by Oren Milman.

- bpo-31588: Raise a `TypeError` with a helpful error message when class creation fails due to a metaclass with a bad `__prepare__()` method. Patch by Oren Milman.

- bpo-31574: Importlib was instrumented with two dtrace probes to profile import timing.

- bpo-31566: Fix an assertion failure in `_warnings.warn()` in case of a bad `__name__` global. Patch by Oren Milman.

- bpo-31506: Improved the error message logic for object.__new__ and object.__init__.

- bpo-31505: Fix an assertion failure in `json`, in case `_json.make_encoder()` received a bad `encoder()` argument. Patch by Oren Milman.

- bpo-31492: Fix assertion failures in case of failing to import from a module with a bad `__name__` attribute, and in case of failing to access an attribute of such a module. Patch by Oren Milman.

- bpo-31478: Fix an assertion failure in `_random.Random.seed()` in case the argument has a bad `__abs__()` method. Patch by Oren Milman.

- bpo-31336: Speed up class creation by 10-20% by reducing the overhead in the necessary special method lookups. Patch by Stefan Behnel.

- bpo-31415: Add `-X importtime` option to show how long each import takes. It can be used to optimize application’s startup time. Support the `PYTHONPROFILEIMPORTTIME` as an equivalent way to enable this.

- bpo-31410: Optimized calling wrapper and classmethod descriptors.

- bpo-31353: PEP 553 - Add a new built-in called `breakpoint()` which calls `sys.breakpointhook()`. By default this imports `pdb` and calls `pdb.set_trace()`, but users may override `sys.breakpointhook()` to call whatever debugger they want. The original value of the hook is saved in `sys.__breakpointhook__`.

- bpo-17852: Maintain a list of open buffered files, flush them before exiting the interpreter. Based on a patch from Armin Rigo.

- bpo-31315: Fix an assertion failure in imp.create_dynamic(), when spec.name is not a string. Patch by Oren Milman.

- bpo-31311: Fix a crash in the `__setstate__()` method of `ctypes._CData`, in case of a bad `__dict__`. Patch by Oren Milman.

- bpo-31293: Fix crashes in true division and multiplication of a timedelta object by a float with a bad as_integer_ratio() method. Patch by Oren Milman.

- bpo-31285: Fix an assertion failure in `warnings.warn_explicit`, when the return value of the received loader’s get_source() has a bad splitlines() method. Patch by Oren Milman.

- bpo-30406: Make `async` and `await` proper keywords, as specified in PEP 492.

### Library

- bpo-30058: Fixed buffer overflow in select.kqueue.control().

- bpo-31672: `idpattern` in `string.Template` matched some non-ASCII characters. Now it uses `-i` regular expression local flag to avoid non-ASCII characters.

- bpo-31701: On Windows, faulthandler.enable() now ignores MSC and COM exceptions.

- bpo-31728: Prevent crashes in `_elementtree` due to unsafe cleanup of `Element.text` and `Element.tail`. Patch by Oren Milman.

- bpo-31671: Now `re.compile()` converts passed RegexFlag to normal int object before compiling. bm_regex_compile benchmark shows 14% performance improvements.

- bpo-30397: The types of compiled regular objects and match objects are now exposed as `re.Pattern` and `re.Match`. This adds information in pydoc output for the re module.

- bpo-31675: Fixed memory leaks in Tkinter’s methods splitlist() and split() when pass a string larger than 2 GiB.

- bpo-31673: Fixed typo in the name of Tkinter’s method adderrorinfo().

- bpo-31648: Improvements to path predicates in ElementTree: Allow whitespace around predicate parts, i.e. “[a = ‘text’]” instead of requiring the less readable “[a=’text’]”. Add support for text comparison of the current node, like “[.=’text’]”. Patch by Stefan Behnel.

- bpo-30806: Fix the string representation of a netrc object.

- bpo-31638: Add optional argument `compressed` to `zipapp.create_archive`, and add option `--compress` to the command line interface of `zipapp`.

- bpo-25351: Avoid venv activate failures with undefined variables

- bpo-20519: Avoid ctypes use (if possible) and improve import time for uuid.

- bpo-28293: The regular expression cache is no longer completely dumped when it is full.

- bpo-31596: Added pthread_getcpuclockid() to the time module

- bpo-27494: Make 2to3 accept a trailing comma in generator expressions. For example, `set(x for x in [],)` is now allowed.

- bpo-30347: Stop crashes when concurrently iterate over itertools.groupby() iterators.

- bpo-30346: An iterator produced by itertools.groupby() iterator now becomes exhausted after advancing the groupby iterator.

- bpo-31556: Cancel asyncio.wait_for future faster if timeout <= 0

- bpo-31540: Allow passing a context object in `concurrent.futures.ProcessPoolExecutor` constructor. Also, free job resources in `concurrent.futures.ProcessPoolExecutor` earlier to improve memory usage when a worker waits for new jobs.

- bpo-31516: `threading.current_thread()` should not return a dummy thread at shutdown.

- bpo-31525: In the sqlite module, require the sqlite3_prepare_v2 API. Thus, the sqlite module now requires sqlite version at least 3.3.9.

- bpo-26510: argparse subparsers are now required by default. This matches behaviour in Python 2. For optional subparsers, use the new parameter `add_subparsers(required=False)`. Patch by Anthony Sottile. (As of 3.7.0rc1, the default was changed to not required as had been the case since Python 3.3.)

- bpo-27541: Reprs of subclasses of some collection and iterator classes (`bytearray`, `array.array`, `collections.deque`, `collections.defaultdict`, `itertools.count`, `itertools.repeat`) now contain actual type name insteads of hardcoded name of the base class.

- bpo-31351: python -m ensurepip now exits with non-zero exit code if pip bootstrapping has failed.

- bpo-31389: `pdb.set_trace()` now takes an optional keyword-only argument `header`. If given, this is printed to the console just before debugging begins.

### Documentation

- bpo-31537: Fix incorrect usage of `get_history_length` in readline documentation example code. Patch by Brad Smith.

- bpo-30085: The operator functions without double underscores are preferred for clarity. The one with underscores are only kept for back-compatibility.

### Build

- bpo-31696: Improve compiler version information in `sys.version` when Python is built with Clang.

- bpo-31625: Stop using ranlib on static libraries. Instead, we assume ar supports the ‘s’ flag.

- bpo-31624: Remove support for BSD/OS.

- bpo-22140: Prevent double substitution of prefix in python-config.sh.

- bpo-31569: Correct PCBuild/ case to PCbuild/ in build scripts and documentation.

- bpo-31536: Avoid wholesale rebuild after `make regen-all` if nothing changed.

### IDLE

- bpo-31460: Simplify the API of IDLE’s Module Browser. Passing a widget instead of an flist with a root widget opens the option of creating a browser frame that is only part of a window. Passing a full file name instead of pieces assumed to come from a .py file opens the possibility of browsing python files that do not end in .py.

- bpo-31649: IDLE - Make _htest, _utest parameters keyword only.

- bpo-31559: Remove test order dependence in idle_test.test_browser.

- bpo-31459: Rename IDLE’s module browser from Class Browser to Module Browser. The original module-level class and method browser became a module browser, with the addition of module-level functions, years ago. Nested classes and functions were added yesterday. For back-compatibility, the virtual event <<open-class-browser>>, which appears on the Keys tab of the Settings dialog, is not changed. Patch by Cheryl Sabella.

- bpo-31500: Default fonts now are scaled on HiDPI displays.

- bpo-1612262: IDLE module browser now shows nested classes and functions. Original patches for code and tests by Guilherme Polo and Cheryl Sabella, respectively.

### C API

- bpo-28280: Make `PyMapping_Keys()`, `PyMapping_Values()` and `PyMapping_Items()` always return a `list` (rather than a `list` or a `tuple`). Patch by Oren Milman.

- bpo-31532: Fix memory corruption due to allocator mix in getpath.c between Py_GetPath() and Py_SetPath()

- bpo-25658: Implement PEP 539 for Thread Specific Storage (TSS) API: it is a new Thread Local Storage (TLS) API to CPython which would supersede use of the existing TLS API within the CPython interpreter, while deprecating the existing API. PEP written by Erik M. Bray, patch by Masayuki Yamamoto.

## Python 3.7.0 alpha 1

Release date: 2017-09-19

### Security

- bpo-29781: SSLObject.version() now correctly returns None when handshake over BIO has not been performed yet.

- bpo-29505: Add fuzz tests for float(str), int(str), unicode(str); for oss-fuzz.

- bpo-30947: Upgrade libexpat embedded copy from version 2.2.1 to 2.2.3 to get security fixes.

- bpo-30730: Prevent environment variables injection in subprocess on Windows. Prevent passing other environment variables and command arguments.

- bpo-30694: Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes of multiple security vulnerabilities including: CVE-2017-9233 (External entity infinite loop DoS), CVE-2016-9063 (Integer overflow, re-fix), CVE-2016-0718 (Fix regression bugs from 2.2.0’s fix to CVE-2016-0718) and CVE-2012-0876 (Counter hash flooding with SipHash). Note: the CVE-2016-5300 (Use os-specific entropy sources like getrandom) doesn’t impact Python, since Python already gets entropy from the OS to set the expat secret using `XML_SetHashSalt()`.

- bpo-30500: Fix urllib.parse.splithost() to correctly parse fragments. For example, `splithost('//127.0.0.1#@evil.com/')` now correctly returns the `127.0.0.1` host, instead of treating `@evil.com` as the host in an authentication (`login@host`).

- bpo-29591: Update expat copy from 2.1.1 to 2.2.0 to get fixes of CVE-2016-0718 and CVE-2016-4472. See https://sourceforge.net/p/expat/bugs/537/ for more information.

### Core and Builtins

- bpo-31490: Fix an assertion failure in `ctypes` class definition, in case the class has an attribute whose name is specified in `_anonymous_` but not in `_fields_`. Patch by Oren Milman.

- bpo-31471: Fix an assertion failure in `subprocess.Popen()` on Windows, in case the env argument has a bad keys() method. Patch by Oren Milman.

- bpo-31418: Fix an assertion failure in `PyErr_WriteUnraisable()` in case of an exception with a bad `__module__` attribute. Patch by Oren Milman.

- bpo-31416: Fix assertion failures in case of a bad warnings.filters or warnings.defaultaction. Patch by Oren Milman.

- bpo-28411: Change direct usage of PyInterpreterState.modules to PyImport_GetModuleDict(). Also introduce more uniformity in other code that deals with sys.modules. This helps reduce complications when working on sys.modules.

- bpo-28411: Switch to the abstract API when dealing with `PyInterpreterState.modules`. This allows later support for all dict subclasses and other Mapping implementations. Also add a `PyImport_GetModule()` function to reduce a bunch of duplicated code.

- bpo-31411: Raise a TypeError instead of SystemError in case warnings.onceregistry is not a dictionary. Patch by Oren Milman.

- bpo-31344: For finer control of tracing behaviour when testing the interpreter, two new frame attributes have been added to control the emission of particular trace events: `f_trace_lines` (`True` by default) to turn off per-line trace events; and `f_trace_opcodes` (`False` by default) to turn on per-opcode trace events.

- bpo-31373: Fix several possible instances of undefined behavior due to floating-point demotions.

- bpo-30465: Location information (`lineno` and `col_offset`) in f-strings is now (mostly) correct. This fixes tools like flake8 from showing warnings on the wrong line (typically the first line of the file).

- bpo-30860: Consolidate CPython’s global runtime state under a single struct. This improves discoverability of the runtime state.

- bpo-31347: Fix possible undefined behavior in _PyObject_FastCall_Prepend.

- bpo-31343: Include sys/sysmacros.h for major(), minor(), and makedev(). GNU C libray plans to remove the functions from sys/types.h.

- bpo-31291: Fix an assertion failure in `zipimport.zipimporter.get_data` on Windows, when the return value of `pathname.replace('/','\\')` isn’t a string. Patch by Oren Milman.

- bpo-31271: Fix an assertion failure in the write() method of `io.TextIOWrapper`, when the encoder doesn’t return a bytes object. Patch by Oren Milman.

- bpo-31243: Fix a crash in some methods of `io.TextIOWrapper`, when the decoder’s state is invalid. Patch by Oren Milman.

- bpo-30721: `print` now shows correct usage hint for using Python 2 redirection syntax. Patch by Sanyam Khurana.

- bpo-31070: Fix a race condition in importlib _get_module_lock().

- bpo-30747: Add a non-dummy implementation of _Py_atomic_store and _Py_atomic_load on MSVC.

- bpo-31095: Fix potential crash during GC caused by `tp_dealloc` which doesn’t call `PyObject_GC_UnTrack()`.

- bpo-31071: Avoid masking original TypeError in call with * unpacking when other arguments are passed.

- bpo-30978: str.format_map() now passes key lookup exceptions through. Previously any exception was replaced with a KeyError exception.

- bpo-30808: Use _Py_atomic API for concurrency-sensitive signal state.

- bpo-30876: Relative import from unloaded package now reimports the package instead of failing with SystemError. Relative import from non-package now fails with ImportError rather than SystemError.

- bpo-30703: Improve signal delivery. Avoid using Py_AddPendingCall from signal handler, to avoid calling signal-unsafe functions. The tests I’m adding here fail without the rest of the patch, on Linux and OS X. This means our signal delivery logic had defects (some signals could be lost).

- bpo-30765: Avoid blocking in pthread_mutex_lock() when PyThread_acquire_lock() is asked not to block.

- bpo-31161: Make sure the ‘Missing parentheses’ syntax error message is only applied to SyntaxError, not to subclasses. Patch by Martijn Pieters.

- bpo-30814: Fixed a race condition when import a submodule from a package.

- bpo-30736: The internal unicodedata database has been upgraded to Unicode 10.0.

- bpo-30604: Move co_extra_freefuncs from per-thread to per-interpreter to avoid crashes.

- bpo-30597: `print` now shows expected input in custom error message when used as a Python 2 statement. Patch by Sanyam Khurana.

- bpo-30682: Removed a too-strict assertion that failed for certain f-strings, such as eval(“f’\n’”) and eval(“f’\r’”).

- bpo-30501: The compiler now produces more optimal code for complex condition expressions in the “if”, “while” and “assert” statement, the “if” expression, and generator expressions and comprehensions.

- bpo-28180: Implement PEP 538 (legacy C locale coercion). This means that when a suitable coercion target locale is available, both the core interpreter and locale-aware C extensions will assume the use of UTF-8 as the default text encoding, rather than ASCII.

- bpo-30486: Allows setting cell values for __closure__. Patch by Lisa Roach.

- bpo-30537: itertools.islice now accepts integer-like objects (having an __index__ method) as start, stop, and slice arguments

- bpo-25324: Tokens needed for parsing in Python moved to C. `COMMENT`, `NL` and `ENCODING`. This way the tokens and tok_names in the token module don’t get changed when you import the tokenize module.

- bpo-29104: Fixed parsing backslashes in f-strings.

- bpo-27945: Fixed various segfaults with dict when input collections are mutated during searching, inserting or comparing. Based on patches by Duane Griffin and Tim Mitchell.

- bpo-25794: Fixed type.__setattr__() and type.__delattr__() for non-interned attribute names. Based on patch by Eryk Sun.

- bpo-30039: If a KeyboardInterrupt happens when the interpreter is in the middle of resuming a chain of nested ‘yield from’ or ‘await’ calls, it’s now correctly delivered to the innermost frame.

- bpo-28974: `object.__format__(x, '')` is now equivalent to `str(x)` rather than `format(str(self), '')`.

- bpo-30024: Circular imports involving absolute imports with binding a submodule to a name are now supported.

- bpo-12414: sys.getsizeof() on a code object now returns the sizes which includes the code struct and sizes of objects which it references. Patch by Dong-hee Na.

- bpo-29839: len() now raises ValueError rather than OverflowError if __len__() returned a large negative integer.

- bpo-11913: README.rst is now included in the list of distutils standard READMEs and therefore included in source distributions.

- bpo-29914: Fixed default implementations of __reduce__ and __reduce_ex__(). object.__reduce__() no longer takes arguments, object.__reduce_ex__() now requires one argument.

- bpo-29949: Fix memory usage regression of set and frozenset object.

- bpo-29935: Fixed error messages in the index() method of tuple, list and deque when pass indices of wrong type.

- bpo-29816: Shift operation now has less opportunity to raise OverflowError. ValueError always is raised rather than OverflowError for negative counts. Shifting zero with non-negative count always returns zero.

- bpo-24821: Fixed the slowing down to 25 times in the searching of some unlucky Unicode characters.

- bpo-29102: Add a unique ID to PyInterpreterState. This makes it easier to identify each subinterpreter.

- bpo-29894: The deprecation warning is emitted if __complex__ returns an instance of a strict subclass of complex. In a future versions of Python this can be an error.

- bpo-29859: Show correct error messages when any of the pthread_* calls in thread_pthread.h fails.

- bpo-29849: Fix a memory leak when an ImportError is raised during from import.

- bpo-28856: Fix an oversight that %b format for bytes should support objects follow the buffer protocol.

- bpo-29723: The `sys.path[0]` initialization change for bpo-29139 caused a regression by revealing an inconsistency in how sys.path is initialized when executing `__main__` from a zipfile, directory, or other import location. The interpreter now consistently avoids ever adding the import location’s parent directory to `sys.path`, and ensures no other `sys.path` entries are inadvertently modified when inserting the import location named on the command line.

- bpo-29568: Escaped percent “%%” in the format string for classic string formatting no longer allows any characters between two percents.

- bpo-29714: Fix a regression that bytes format may fail when containing zero bytes inside.

- bpo-29695: bool(), float(), list() and tuple() no longer take keyword arguments. The first argument of int() can now be passes only as positional argument.

- bpo-28893: Set correct __cause__ for errors about invalid awaitables returned from __aiter__ and __anext__.

- bpo-28876: `bool(range)` works even if `len(range)` raises `OverflowError`.

- bpo-29683: Fixes to memory allocation in _PyCode_SetExtra. Patch by Brian Coleman.

- bpo-29684: Fix minor regression of PyEval_CallObjectWithKeywords. It should raise TypeError when kwargs is not a dict. But it might cause segv when args=NULL and kwargs is not a dict.

- bpo-28598: Support __rmod__ for subclasses of str being called before str.__mod__. Patch by Martijn Pieters.

- bpo-29607: Fix stack_effect computation for CALL_FUNCTION_EX. Patch by Matthieu Dartiailh.

- bpo-29602: Fix incorrect handling of signed zeros in complex constructor for complex subclasses and for inputs having a __complex__ method. Patch by Serhiy Storchaka.

- bpo-29347: Fixed possibly dereferencing undefined pointers when creating weakref objects.

- bpo-29463: Add `docstring` field to Module, ClassDef, FunctionDef, and AsyncFunctionDef ast nodes. docstring is not first stmt in their body anymore. It affects `co_firstlineno` and `co_lnotab` of code object for module and class. (Reverted in bpo-32911.)

- bpo-29438: Fixed use-after-free problem in key sharing dict.

- bpo-29546: Set the ‘path’ and ‘name’ attribute on ImportError for `from ... import ...`.

- bpo-29546: Improve from-import error message with location

- bpo-29478: If max_line_length=None is specified while using the Compat32 policy, it is no longer ignored. Patch by Mircea Cosbuc.

- bpo-29319: Prevent RunMainFromImporter overwriting sys.path[0].

- bpo-29337: Fixed possible BytesWarning when compare the code objects. Warnings could be emitted at compile time.

- bpo-29327: Fixed a crash when pass the iterable keyword argument to sorted().

- bpo-29034: Fix memory leak and use-after-free in os module (path_converter).

- bpo-29159: Fix regression in bytes(x) when x.__index__() raises Exception.

- bpo-29049: Call _PyObject_GC_TRACK() lazily when calling Python function. Calling function is up to 5% faster.

- bpo-28927: bytes.fromhex() and bytearray.fromhex() now ignore all ASCII whitespace, not only spaces. Patch by Robert Xiao.

- bpo-28932: Do not include <sys/random.h> if it does not exist.

- bpo-25677: Correct the positioning of the syntax error caret for indented blocks. Based on patch by Michael Layzell.

- bpo-29000: Fixed bytes formatting of octals with zero padding in alternate form.

- bpo-18896: Python function can now have more than 255 parameters. collections.namedtuple() now supports tuples with more than 255 elements.

- bpo-28596: The preferred encoding is UTF-8 on Android. Patch written by Chi Hsuan Yen.

- bpo-22257: Clean up interpreter startup (see PEP 432).

- bpo-26919: On Android, operating system data is now always encoded/decoded to/from UTF-8, instead of the locale encoding to avoid inconsistencies with os.fsencode() and os.fsdecode() which are already using UTF-8.

- bpo-28991: functools.lru_cache() was susceptible to an obscure reentrancy bug triggerable by a monkey-patched len() function.

- bpo-28147: Fix a memory leak in split-table dictionaries: setattr() must not convert combined table into split table. Patch written by INADA Naoki.

- bpo-28739: f-string expressions are no longer accepted as docstrings and by ast.literal_eval() even if they do not include expressions.

- bpo-28512: Fixed setting the offset attribute of SyntaxError by PyErr_SyntaxLocationEx() and PyErr_SyntaxLocationObject().

- bpo-28918: Fix the cross compilation of xxlimited when Python has been built with Py_DEBUG defined.

- bpo-23722: Rather than silently producing a class that doesn’t support zero-argument `super()` in methods, failing to pass the new `__classcell__` namespace entry up to `type.__new__` now results in a `DeprecationWarning` and a class that supports zero-argument `super()`.

- bpo-28797: Modifying the class __dict__ inside the __set_name__ method of a descriptor that is used inside that class no longer prevents calling the __set_name__ method of other descriptors.

- bpo-28799: Remove the `PyEval_GetCallStats()` function and deprecate the untested and undocumented `sys.callstats()` function. Remove the `CALL_PROFILE` special build: use the `sys.setprofile()` function, `cProfile` or `profile` to profile function calls.

- bpo-12844: More than 255 arguments can now be passed to a function.

- bpo-28782: Fix a bug in the implementation `yield from` when checking if the next instruction is YIELD_FROM. Regression introduced by WORDCODE (bpo-26647).

- bpo-28774: Fix error position of the unicode error in ASCII and Latin1 encoders when a string returned by the error handler contains multiple non-encodable characters (non-ASCII for the ASCII codec, characters out of the U+0000-U+00FF range for Latin1).

- bpo-28731: Optimize _PyDict_NewPresized() to create correct size dict. Improve speed of dict literal with constant keys up to 30%.

- bpo-28532: Show sys.version when -V option is supplied twice.

- bpo-27100: The with-statement now checks for __enter__ before it checks for __exit__. This gives less confusing error messages when both methods are missing. Patch by Jonathan Ellington.

- bpo-28746: Fix the set_inheritable() file descriptor method on platforms that do not have the ioctl FIOCLEX and FIONCLEX commands.

- bpo-26920: Fix not getting the locale’s charset upon initializing the interpreter, on platforms that do not have langinfo.

- bpo-28648: Fixed crash in Py_DecodeLocale() in debug build on Mac OS X when decode astral characters. Patch by Xiang Zhang.

- bpo-28665: Improve speed of the STORE_DEREF opcode by 40%.

- bpo-19398: Extra slash no longer added to sys.path components in case of empty compile-time PYTHONPATH components.

- bpo-28621: Sped up converting int to float by reusing faster bits counting implementation. Patch by Adrian Wielgosik.

- bpo-28580: Optimize iterating split table values. Patch by Xiang Zhang.

- bpo-28583: PyDict_SetDefault didn’t combine split table when needed. Patch by Xiang Zhang.

- bpo-28128: Deprecation warning for invalid str and byte escape sequences now prints better information about where the error occurs. Patch by Serhiy Storchaka and Eric Smith.

- bpo-28509: dict.update() no longer allocate unnecessary large memory.

- bpo-28426: Fixed potential crash in PyUnicode_AsDecodedObject() in debug build.

- bpo-28517: Fixed of-by-one error in the peephole optimizer that caused keeping unreachable code.

- bpo-28214: Improved exception reporting for problematic __set_name__ attributes.

- bpo-23782: Fixed possible memory leak in _PyTraceback_Add() and exception loss in PyTraceBack_Here().

- bpo-28183: Optimize and cleanup dict iteration.

- bpo-26081: Added C implementation of asyncio.Future. Original patch by Yury Selivanov.

- bpo-28379: Added sanity checks and tests for PyUnicode_CopyCharacters(). Patch by Xiang Zhang.

- bpo-28376: The type of long range iterator is now registered as Iterator. Patch by Oren Milman.

- bpo-28376: Creating instances of range_iterator by calling range_iterator type now is disallowed. Calling iter() on range instance is the only way. Patch by Oren Milman.

- bpo-26906: Resolving special methods of uninitialized type now causes implicit initialization of the type instead of a fail.

- bpo-18287: PyType_Ready() now checks that tp_name is not NULL. Original patch by Niklas Koep.

- bpo-24098: Fixed possible crash when AST is changed in process of compiling it.

- bpo-28201: Dict reduces possibility of 2nd conflict in hash table when hashes have same lower bits.

- bpo-28350: String constants with null character no longer interned.

- bpo-26617: Fix crash when GC runs during weakref callbacks.

- bpo-27942: String constants now interned recursively in tuples and frozensets.

- bpo-28289: ImportError.__init__ now resets not specified attributes.

- bpo-21578: Fixed misleading error message when ImportError called with invalid keyword args.

- bpo-28203: Fix incorrect type in complex(1.0, {2:3}) error message. Patch by Soumya Sharma.

- bpo-28086: Single var-positional argument of tuple subtype was passed unscathed to the C-defined function. Now it is converted to exact tuple.

- bpo-28214: Now __set_name__ is looked up on the class instead of the instance.

- bpo-27955: Fallback on reading /dev/urandom device when the getrandom() syscall fails with EPERM, for example when blocked by SECCOMP.

- bpo-28192: Don’t import readline in isolated mode.

- bpo-27441: Remove some redundant assignments to ob_size in longobject.c. Thanks Oren Milman.

- bpo-27222: Clean up redundant code in long_rshift function. Thanks Oren Milman.

- Upgrade internal unicode databases to Unicode version 9.0.0.

- bpo-28131: Fix a regression in zipimport’s compile_source(). zipimport should use the same optimization level as the interpreter.

- bpo-28126: Replace Py_MEMCPY with memcpy(). Visual Studio can properly optimize memcpy().

- bpo-28120: Fix dict.pop() for splitted dictionary when trying to remove a “pending key” (Not yet inserted in split-table). Patch by Xiang Zhang.

- bpo-26182: Raise DeprecationWarning when async and await keywords are used as variable/attribute/class/function name.

- bpo-26182: Fix a refleak in code that raises DeprecationWarning.

- bpo-28721: Fix asynchronous generators aclose() and athrow() to handle StopAsyncIteration propagation properly.

- bpo-26110: Speed-up method calls: add LOAD_METHOD and CALL_METHOD opcodes.

### Library

- bpo-31499: xml.etree: Fix a crash when a parser is part of a reference cycle.

- bpo-31482: `random.seed()` now works with bytes in version=1

- bpo-28556: typing.get_type_hints now finds the right globalns for classes and modules by default (when no `globalns` was specified by the caller).

- bpo-28556: Speed improvements to the `typing` module. Original PRs by Ivan Levkivskyi and Mitar.

- bpo-31544: The C accelerator module of ElementTree ignored exceptions raised when looking up TreeBuilder target methods in XMLParser().

- bpo-31234: socket.create_connection() now fixes manually a reference cycle: clear the variable storing the last exception on success.

- bpo-31457: LoggerAdapter objects can now be nested.

- bpo-31431: SSLContext.check_hostname now automatically sets SSLContext.verify_mode to ssl.CERT_REQUIRED instead of failing with a ValueError.

- bpo-31233: socketserver.ThreadingMixIn now keeps a list of non-daemonic threads to wait until all these threads complete in server_close().

- bpo-28638: Changed the implementation strategy for collections.namedtuple() to substantially reduce the use of exec() in favor of precomputed methods. As a result, the verbose parameter and _source attribute are no longer supported. The benefits include 1) having a smaller memory footprint for applications using multiple named tuples, 2) faster creation of the named tuple class (approx 4x to 6x depending on how it is measured), and 3) minor speed-ups for instance creation using __new__, _make, and _replace. (The primary patch contributor is Jelle Zijlstra with further improvements by INADA Naoki, Serhiy Storchaka, and Raymond Hettinger.)

- bpo-31400: Improves SSL error handling to avoid losing error numbers.

- bpo-27629: Make return types of SSLContext.wrap_bio() and SSLContext.wrap_socket() customizable.

- bpo-28958: ssl.SSLContext() now uses OpenSSL error information when a context cannot be instantiated.

- bpo-28182: The SSL module now raises SSLCertVerificationError when OpenSSL fails to verify the peer’s certificate. The exception contains more information about the error.

- bpo-27340: SSLSocket.sendall() now uses memoryview to create slices of data. This fixes support for all bytes-like object. It is also more efficient and avoids costly copies.

- bpo-14191: A new function `argparse.ArgumentParser.parse_intermixed_args` provides the ability to parse command lines where there user intermixes options and positional arguments.

- bpo-31178: Fix string concatenation bug in rare error path in the subprocess module

- bpo-31350: Micro-optimize `asyncio._get_running_loop()` to become up to 10% faster.

- bpo-31170: expat: Update libexpat from 2.2.3 to 2.2.4. Fix copying of partial characters for UTF-8 input (libexpat bug 115): https://github.com/libexpat/libexpat/issues/115

- bpo-29136: Add TLS 1.3 cipher suites and OP_NO_TLSv1_3.

- bpo-1198569: `string.Template` subclasses can optionally define `braceidpattern` if they want to specify different placeholder patterns inside and outside the braces. If None (the default) it falls back to `idpattern`.

- bpo-31326: concurrent.futures.ProcessPoolExecutor.shutdown() now explicitly closes the call queue. Moreover, shutdown(wait=True) now also join the call queue thread, to prevent leaking a dangling thread.

- bpo-27144: The `map()` and `as_completed()` iterators in `concurrent.futures` now avoid keeping a reference to yielded objects.

- bpo-31281: Fix `fileinput.FileInput(files, inplace=True)` when `files` contain `pathlib.Path` objects.

- bpo-10746: Fix ctypes producing wrong PEP 3118 type codes for integer types.

- bpo-27584: `AF_VSOCK` has been added to the socket interface which allows communication between virtual machines and their host.

- bpo-22536: The subprocess module now sets the filename when FileNotFoundError is raised on POSIX systems due to the executable or cwd not being found.

- bpo-29741: Update some methods in the _pyio module to also accept integer types. Patch by Oren Milman.

- bpo-31249: concurrent.futures: WorkItem.run() used by ThreadPoolExecutor now breaks a reference cycle between an exception object and the WorkItem object.

- bpo-31247: xmlrpc.server now explicitly breaks reference cycles when using sys.exc_info() in code handling exceptions.

- bpo-23835: configparser: reading defaults in the `ConfigParser()` constructor is now using `read_dict()`, making its behavior consistent with the rest of the parser. Non-string keys and values in the defaults dictionary are now being implicitly converted to strings. Patch by James Tocknell.

- bpo-31238: pydoc: the stop() method of the private ServerThread class now waits until DocServer.serve_until_quit() completes and then explicitly sets its docserver attribute to None to break a reference cycle.

- bpo-5001: Many asserts in `multiprocessing` are now more informative, and some error types have been changed to more specific ones.

- bpo-31109: Convert zipimport to use Argument Clinic.

- bpo-30102: The ssl and hashlib modules now call OPENSSL_add_all_algorithms_noconf() on OpenSSL < 1.1.0. The function detects CPU features and enables optimizations on some CPU architectures such as POWER8. Patch is based on research from Gustavo Serra Scalet.

- bpo-18966: Non-daemonic threads created by a multiprocessing.Process are now joined on child exit.

- bpo-31183: `dis` now works with asynchronous generator and coroutine objects. Patch by George Collins based on diagnosis by Luciano Ramalho.

- bpo-5001: There are a number of uninformative asserts in the `multiprocessing` module, as noted in issue 5001. This change fixes two of the most potentially problematic ones, since they are in error-reporting code, in the `multiprocessing.managers.convert_to_error` function. (It also makes more informative a ValueError message.) The only potentially problematic change is that the AssertionError is now a TypeError; however, this should also help distinguish it from an AssertionError being reported by the function/its caller (such as in issue 31169). - Patch by Allen W. Smith (drallensmith on github).

- bpo-31185: Fixed miscellaneous errors in asyncio speedup module.

- bpo-31151: socketserver.ForkingMixIn.server_close() now waits until all child processes completed to prevent leaking zombie processes.

- bpo-31072: Add an `include_file` parameter to `zipapp.create_archive()`

- bpo-24700: Optimize array.array comparison. It is now from 10x up to 70x faster when comparing arrays holding values of the same integer type.

- bpo-31135: ttk: fix the destroy() method of LabeledScale and OptionMenu classes. Call the parent destroy() method even if the used attribute doesn’t exist. The LabeledScale.destroy() method now also explicitly clears label and scale attributes to help the garbage collector to destroy all widgets.

- bpo-31107: Fix `copyreg._slotnames()` mangled attribute calculation for classes whose name begins with an underscore. Patch by Shane Harvey.

- bpo-31080: Allow `logging.config.fileConfig` to accept kwargs and/or args.

- bpo-30897: `pathlib.Path` objects now include an `is_mount()` method (only implemented on POSIX). This is similar to `os.path.ismount(p)`. Patch by Cooper Ry Lees.

- bpo-31061: Fixed a crash when using asyncio and threads.

- bpo-30987: Added support for CAN ISO-TP protocol in the socket module.

- bpo-30522: Added a `setStream` method to `logging.StreamHandler` to allow the stream to be set after creation.

- bpo-30502: Fix handling of long oids in ssl. Based on patch by Christian Heimes.

- bpo-5288: Support tzinfo objects with sub-minute offsets.

- bpo-30919: Fix shared memory performance regression in multiprocessing in 3.x. Shared memory used anonymous memory mappings in 2.x, while 3.x mmaps actual files. Try to be careful to do as little disk I/O as possible.

- bpo-26732: Fix too many fds in processes started with the “forkserver” method. A child process would inherit as many fds as the number of still-running children.

- bpo-29403: Fix `unittest.mock`’s autospec to not fail on method-bound builtin functions. Patch by Aaron Gallagher.

- bpo-30961: Fix decrementing a borrowed reference in tracemalloc.

- bpo-19896: Fix multiprocessing.sharedctypes to recognize typecodes `'q'` and `'Q'`.

- bpo-30946: Remove obsolete code in readline module for platforms where GNU readline is older than 2.1 or where select() is not available.

- bpo-25684: Change `ttk.OptionMenu` radiobuttons to be unique across instances of `OptionMenu`.

- bpo-30886: Fix multiprocessing.Queue.join_thread(): it now waits until the thread completes, even if the thread was started by the same process which created the queue.

- bpo-29854: Fix segfault in readline when using readline’s history-size option. Patch by Nir Soffer.

- bpo-30794: Added multiprocessing.Process.kill method to terminate using the SIGKILL signal on Unix.

- bpo-30319: socket.close() now ignores ECONNRESET error.

- bpo-30828: Fix out of bounds write in `asyncio.CFuture.remove_done_callback()`.

- bpo-30302: Use keywords in the `repr` of `datetime.timedelta`.

- bpo-30807: signal.setitimer() may disable the timer when passed a tiny value. Tiny values (such as 1e-6) are valid non-zero values for setitimer(), which is specified as taking microsecond-resolution intervals. However, on some platform, our conversion routine could convert 1e-6 into a zero interval, therefore disabling the timer instead of (re-)scheduling it.

- bpo-30441: Fix bug when modifying os.environ while iterating over it

- bpo-29585: Avoid importing `sysconfig` from `site` to improve startup speed. Python startup is about 5% faster on Linux and 30% faster on macOS.

- bpo-29293: Add missing parameter “n” on multiprocessing.Condition.notify(). The doc claims multiprocessing.Condition behaves like threading.Condition, but its notify() method lacked the optional “n” argument (to specify the number of sleepers to wake up) that threading.Condition.notify() accepts.

- bpo-30532: Fix email header value parser dropping folding white space in certain cases.

- bpo-30596: Add a `close()` method to `multiprocessing.Process`.

- bpo-9146: Fix a segmentation fault in _hashopenssl when standard hash functions such as md5 are not available in the linked OpenSSL library. As in some special FIPS-140 build environments.

- bpo-29169: Update zlib to 1.2.11.

- bpo-30119: ftplib.FTP.putline() now throws ValueError on commands that contains CR or LF. Patch by Dong-hee Na.

- bpo-30879: os.listdir() and os.scandir() now emit bytes names when called with bytes-like argument.

- bpo-30746: Prohibited the ‘=’ character in environment variable names in `os.putenv()` and `os.spawn*()`.

- bpo-30664: The description of a unittest subtest now preserves the order of keyword arguments of TestCase.subTest().

- bpo-21071: struct.Struct.format type is now `str` instead of `bytes`.

- bpo-29212: Fix concurrent.futures.thread.ThreadPoolExecutor threads to have a non repr() based thread name by default when no thread_name_prefix is supplied. They will now identify themselves as “ThreadPoolExecutor-y_n”.

- bpo-29755: Fixed the lgettext() family of functions in the gettext module. They now always return bytes.

- bpo-30616: Functional API of enum allows to create empty enums. Patched by Dong-hee Na

- bpo-30038: Fix race condition between signal delivery and wakeup file descriptor. Patch by Nathaniel Smith.

- bpo-23894: lib2to3 now recognizes `rb'...'` and `f'...'` strings.

- bpo-24744: pkgutil.walk_packages function now raises ValueError if path is a string. Patch by Sanyam Khurana.

- bpo-24484: Avoid race condition in multiprocessing cleanup.

- bpo-30589: Fix multiprocessing.Process.exitcode to return the opposite of the signal number when the process is killed by a signal (instead of 255) when using the “forkserver” method.

- bpo-28994: The traceback no longer displayed for SystemExit raised in a callback registered by atexit.

- bpo-30508: Don’t log exceptions if Task/Future “cancel()” method was called.

- bpo-30645: Fix path calculation in `imp.load_package()`, fixing it for cases when a package is only shipped with bytecodes. Patch by Alexandru Ardelean.

- bpo-11822: The dis.dis() function now is able to disassemble nested code objects.

- bpo-30624: selectors does not take KeyboardInterrupt and SystemExit into account, leaving a fd in a bad state in case of error. Patch by Giampaolo Rodola’.

- bpo-30595: multiprocessing.Queue.get() with a timeout now polls its reader in non-blocking mode if it succeeded to acquire the lock but the acquire took longer than the timeout.

- bpo-28556: Updates to typing module: Add generic AsyncContextManager, add support for ContextManager on all versions. Original PRs by Jelle Zijlstra and Ivan Levkivskyi

- bpo-30605: re.compile() no longer raises a BytesWarning when compiling a bytes instance with misplaced inline modifier. Patch by Roy Williams.

- bpo-29870: Fix ssl sockets leaks when connection is aborted in asyncio/ssl implementation. Patch by Michaël Sghaïer.

- bpo-29743: Closing transport during handshake process leaks open socket. Patch by Nikolay Kim

- bpo-27585: Fix waiter cancellation in asyncio.Lock. Patch by Mathieu Sornay.

- bpo-30014: modify() method of poll(), epoll() and devpoll() based classes of selectors module is around 10% faster. Patch by Giampaolo Rodola’.

- bpo-30418: On Windows, subprocess.Popen.communicate() now also ignore EINVAL on stdin.write() if the child process is still running but closed the pipe.

- bpo-30463: Addded empty __slots__ to abc.ABC. This allows subclassers to deny __dict__ and __weakref__ creation. Patch by Aaron Hall.

- bpo-30520: Loggers are now pickleable.

- bpo-30557: faulthandler now correctly filters and displays exception codes on Windows

- bpo-30526: Add TextIOWrapper.reconfigure() and a TextIOWrapper.write_through attribute.

- bpo-30245: Fix possible overflow when organize struct.pack_into error message. Patch by Yuan Liu.

- bpo-30378: Fix the problem that logging.handlers.SysLogHandler cannot handle IPv6 addresses.

- bpo-16500: Allow registering at-fork handlers.

- bpo-30470: Deprecate invalid ctypes call protection on Windows. Patch by Mariatta Wijaya.

- bpo-30414: multiprocessing.Queue._feed background running thread do not break from main loop on exception.

- bpo-30003: Fix handling escape characters in HZ codec. Based on patch by Ma Lin.

- bpo-30149: inspect.signature() now supports callables with variable-argument parameters wrapped with partialmethod. Patch by Dong-hee Na.

- bpo-30436: importlib.find_spec() raises ModuleNotFoundError instead of AttributeError if the specified parent module is not a package (i.e. lacks a __path__ attribute).

- bpo-30301: Fix AttributeError when using SimpleQueue.empty() under spawn and forkserver start methods.

- bpo-30375: Warnings emitted when compile a regular expression now always point to the line in the user code. Previously they could point into inners of the re module if emitted from inside of groups or conditionals.

- bpo-30329: imaplib and poplib now catch the Windows socket WSAEINVAL error (code 10022) on shutdown(SHUT_RDWR): An invalid operation was attempted. This error occurs sometimes on SSL connections.

- bpo-29196: Removed previously deprecated in Python 2.4 classes Plist, Dict and _InternalDict in the plistlib module. Dict values in the result of functions readPlist() and readPlistFromBytes() are now normal dicts. You no longer can use attribute access to access items of these dictionaries.

- bpo-9850: The `macpath` is now deprecated and will be removed in Python 3.8.

- bpo-30299: Compiling regular expression in debug mode on CPython now displays the compiled bytecode in human readable form.

- bpo-30048: Fixed `Task.cancel()` can be ignored when the task is running coroutine and the coroutine returned without any more `await`.

- bpo-30266: contextlib.AbstractContextManager now supports anti-registration by setting __enter__ = None or __exit__ = None, following the pattern introduced in bpo-25958. Patch by Jelle Zijlstra.

- bpo-30340: Enhanced regular expressions optimization. This increased the performance of matching some patterns up to 25 times.

- bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. Now allowed several subsequential inline modifiers at the start of the pattern (e.g. `'(?i)(?s)...'`). In verbose mode whitespaces and comments now are allowed before and between inline modifiers (e.g. `'(?x) (?i) (?s)...'`).

- bpo-30285: Optimized case-insensitive matching and searching of regular expressions.

- bpo-29990: Fix range checking in GB18030 decoder. Original patch by Ma Lin.

- bpo-29979: rewrite cgi.parse_multipart, reusing the FieldStorage class and making its results consistent with those of FieldStorage for multipart/form-data requests. Patch by Pierre Quentel.

- bpo-30243: Removed the __init__ methods of _json’s scanner and encoder. Misusing them could cause memory leaks or crashes. Now scanner and encoder objects are completely initialized in the __new__ methods.

- bpo-30215: Compiled regular expression objects with the re.LOCALE flag no longer depend on the locale at compile time. Only the locale at matching time affects the result of matching.

- bpo-30185: Avoid KeyboardInterrupt tracebacks in forkserver helper process when Ctrl-C is received.

- bpo-30103: binascii.b2a_uu() and uu.encode() now support using `'`'` as zero instead of space.

- bpo-28556: Various updates to typing module: add typing.NoReturn type, use WrapperDescriptorType, minor bug-fixes. Original PRs by Jim Fasarakis-Hilliard and Ivan Levkivskyi.

- bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux.

- bpo-30228: The seek() and tell() methods of io.FileIO now set the internal seekable attribute to avoid one syscall on open() (in buffered or text mode).

- bpo-30190: unittest’s assertAlmostEqual and assertNotAlmostEqual provide a better message in case of failure which includes the difference between left and right arguments. (patch by Giampaolo Rodola’)

- bpo-30101: Add support for curses.A_ITALIC.

- bpo-29822: inspect.isabstract() now works during __init_subclass__. Patch by Nate Soares.

- bpo-29960: Preserve generator state when _random.Random.setstate() raises an exception. Patch by Bryan Olson.

- bpo-30070: Fixed leaks and crashes in errors handling in the parser module.

- bpo-22352: Column widths in the output of dis.dis() are now adjusted for large line numbers and instruction offsets.

- bpo-30061: Fixed crashes in IOBase methods __next__() and readlines() when readline() or __next__() respectively return non-sizeable object. Fixed possible other errors caused by not checking results of PyObject_Size(), PySequence_Size(), or PyMapping_Size().

- bpo-30218: Fix PathLike support for shutil.unpack_archive. Patch by Jelle Zijlstra.

- bpo-10076: Compiled regular expression and match objects in the re module now support copy.copy() and copy.deepcopy() (they are considered atomic).

- bpo-30068: _io._IOBase.readlines will check if it’s closed first when hint is present.

- bpo-29694: Fixed race condition in pathlib mkdir with flags parents=True. Patch by Armin Rigo.

- bpo-29692: Fixed arbitrary unchaining of RuntimeError exceptions in contextlib.contextmanager. Patch by Siddharth Velankar.

- bpo-26187: Test that sqlite3 trace callback is not called multiple times when schema is changing. Indirectly fixed by switching to use sqlite3_prepare_v2() in bpo-9303. Patch by Aviv Palivoda.

- bpo-30017: Allowed calling the close() method of the zip entry writer object multiple times. Writing to a closed writer now always produces a ValueError.

- bpo-29998: Pickling and copying ImportError now preserves name and path attributes.

- bpo-29995: re.escape() now escapes only regex special characters.

- bpo-29962: Add math.remainder operation, implementing remainder as specified in IEEE 754.

- bpo-29649: Improve struct.pack_into() exception messages for problems with the buffer size and offset. Patch by Andrew Nester.

- bpo-29654: Support If-Modified-Since HTTP header (browser cache). Patch by Pierre Quentel.

- bpo-29931: Fixed comparison check for ipaddress.ip_interface objects. Patch by Sanjay Sundaresan.

- bpo-29953: Fixed memory leaks in the replace() method of datetime and time objects when pass out of bound fold argument.

- bpo-29942: Fix a crash in itertools.chain.from_iterable when encountering long runs of empty iterables.

- bpo-10030: Sped up reading encrypted ZIP files by 2 times.

- bpo-29204: Element.getiterator() and the html parameter of XMLParser() were deprecated only in the documentation (since Python 3.2 and 3.4 correspondingly). Now using them emits a deprecation warning.

- bpo-27863: Fixed multiple crashes in ElementTree caused by race conditions and wrong types.

- bpo-25996: Added support of file descriptors in os.scandir() on Unix. os.fwalk() is sped up by 2 times by using os.scandir().

- bpo-28699: Fixed a bug in pools in multiprocessing.pool that raising an exception at the very first of an iterable may swallow the exception or make the program hang. Patch by Davin Potts and Xiang Zhang.

- bpo-23890: unittest.TestCase.assertRaises() now manually breaks a reference cycle to not keep objects alive longer than expected.

- bpo-29901: The zipapp module now supports general path-like objects, not just pathlib.Path.

- bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True) when the OS gives priority to errors such as EACCES over EEXIST.

- bpo-29861: Release references to tasks, their arguments and their results as soon as they are finished in multiprocessing.Pool.

- bpo-19930: The mode argument of os.makedirs() no longer affects the file permission bits of newly-created intermediate-level directories.

- bpo-29884: faulthandler: Restore the old sigaltstack during teardown. Patch by Christophe Zeitouny.

- bpo-25455: Fixed crashes in repr of recursive buffered file-like objects.

- bpo-29800: Fix crashes in partial.__repr__ if the keys of partial.keywords are not strings. Patch by Michael Seifert.

- bpo-8256: Fixed possible failing or crashing input() if attributes “encoding” or “errors” of sys.stdin or sys.stdout are not set or are not strings.

- bpo-28692: Using non-integer value for selecting a plural form in gettext is now deprecated.

- bpo-26121: Use C library implementation for math functions erf() and erfc().

- bpo-29619: os.stat() and os.DirEntry.inode() now convert inode (st_ino) using unsigned integers.

- bpo-28298: Fix a bug that prevented array ‘Q’, ‘L’ and ‘I’ from accepting big intables (objects that have __int__) as elements.

- bpo-29645: Speed up importing the webbrowser module. webbrowser.register() is now thread-safe.

- bpo-28231: The zipfile module now accepts path-like objects for external paths.

- bpo-26915: index() and count() methods of collections.abc.Sequence now check identity before checking equality when do comparisons.

- bpo-28682: Added support for bytes paths in os.fwalk().

- bpo-29728: Add new `socket.TCP_NOTSENT_LOWAT` (Linux 3.12) constant. Patch by Nathaniel J. Smith.

- bpo-29623: Allow use of path-like object as a single argument in ConfigParser.read(). Patch by David Ellis.

- bpo-9303: Migrate sqlite3 module to _v2 API. Patch by Aviv Palivoda.

- bpo-28963: Fix out of bound iteration in asyncio.Future.remove_done_callback implemented in C.

- bpo-29704: asyncio.subprocess.SubprocessStreamProtocol no longer closes before all pipes are closed.

- bpo-29271: Fix Task.current_task and Task.all_tasks implemented in C to accept None argument as their pure Python implementation.

- bpo-29703: Fix asyncio to support instantiation of new event loops in child processes.

- bpo-29615: SimpleXMLRPCDispatcher no longer chains KeyError (or any other exception) to exception(s) raised in the dispatched methods. Patch by Petr Motejlek.

- bpo-7769: Method register_function() of xmlrpc.server.SimpleXMLRPCDispatcher and its subclasses can now be used as a decorator.

- bpo-29376: Fix assertion error in threading._DummyThread.is_alive().

- bpo-28624: Add a test that checks that cwd parameter of Popen() accepts PathLike objects. Patch by Sayan Chowdhury.

- bpo-28518: Start a transaction implicitly before a DML statement. Patch by Aviv Palivoda.

- bpo-29742: get_extra_info() raises exception if get called on closed ssl transport. Patch by Nikolay Kim.

- bpo-16285: urllib.parse.quote is now based on RFC 3986 and hence includes ‘~’ in the set of characters that is not quoted by default. Patch by Christian Theune and Ratnadeep Debnath.

- bpo-29532: Altering a kwarg dictionary passed to functools.partial() no longer affects a partial object after creation.

- bpo-29110: Fix file object leak in aifc.open() when file is given as a filesystem path and is not in valid AIFF format. Patch by Anthony Zhang.

- bpo-22807: Add uuid.SafeUUID and uuid.UUID.is_safe to relay information from the platform about whether generated UUIDs are generated with a multiprocessing safe method.

- bpo-29576: Improve some deprecations in importlib. Some deprecated methods now emit DeprecationWarnings and have better descriptive messages.

- bpo-29534: Fixed different behaviour of Decimal.from_float() for _decimal and _pydecimal. Thanks Andrew Nester.

- bpo-10379: locale.format_string now supports the ‘monetary’ keyword argument, and locale.format is deprecated.

- bpo-29851: importlib.reload() now raises ModuleNotFoundError if the module lacks a spec.

- bpo-28556: Various updates to typing module: typing.Counter, typing.ChainMap, improved ABC caching, etc. Original PRs by Jelle Zijlstra, Ivan Levkivskyi, Manuel Krebber, and Łukasz Langa.

- bpo-29100: Fix datetime.fromtimestamp() regression introduced in Python 3.6.0: check minimum and maximum years.

- bpo-29416: Prevent infinite loop in pathlib.Path.mkdir

- bpo-29444: Fixed out-of-bounds buffer access in the group() method of the match object. Based on patch by WGH.

- bpo-29377: Add WrapperDescriptorType, MethodWrapperType, and MethodDescriptorType built-in types to types module. Original patch by Manuel Krebber.

- bpo-29218: Unused install_misc command is now removed. It has been documented as unused since 2000. Patch by Eric N. Vander Weele.

- bpo-29368: The extend() method is now called instead of the append() method when unpickle collections.deque and other list-like objects. This can speed up unpickling to 2 times.

- bpo-29338: The help of a builtin or extension class now includes the constructor signature if __text_signature__ is provided for the class.

- bpo-29335: Fix subprocess.Popen.wait() when the child process has exited to a stopped instead of terminated state (ex: when under ptrace).

- bpo-29290: Fix a regression in argparse that help messages would wrap at non-breaking spaces.

- bpo-28735: Fixed the comparison of mock.MagickMock with mock.ANY.

- bpo-29197: Removed deprecated function ntpath.splitunc().

- bpo-29210: Removed support of deprecated argument “exclude” in tarfile.TarFile.add().

- bpo-29219: Fixed infinite recursion in the repr of uninitialized ctypes.CDLL instances.

- bpo-29192: Removed deprecated features in the http.cookies module.

- bpo-29193: A format string argument for string.Formatter.format() is now positional-only.

- bpo-29195: Removed support of deprecated undocumented keyword arguments in methods of regular expression objects.

- bpo-28969: Fixed race condition in C implementation of functools.lru_cache. KeyError could be raised when cached function with full cache was simultaneously called from different threads with the same uncached arguments.

- bpo-20804: The unittest.mock.sentinel attributes now preserve their identity when they are copied or pickled.

- bpo-29142: In urllib.request, suffixes in no_proxy environment variable with leading dots could match related hostnames again (e.g. .b.c matches a.b.c). Patch by Milan Oberkirch.

- bpo-28961: Fix unittest.mock._Call helper: don’t ignore the name parameter anymore. Patch written by Jiajun Huang.

- bpo-15812: inspect.getframeinfo() now correctly shows the first line of a context. Patch by Sam Breese.

- bpo-28985: Update authorizer constants in sqlite3 module. Patch by Dingyuan Wang.

- bpo-29079: Prevent infinite loop in pathlib.resolve() on Windows

- bpo-13051: Fixed recursion errors in large or resized curses.textpad.Textbox. Based on patch by Tycho Andersen.

- bpo-9770: curses.ascii predicates now work correctly with negative integers.

- bpo-28427: old keys should not remove new values from WeakValueDictionary when collecting from another thread.

- bpo-28923: Remove editor artifacts from Tix.py.

- bpo-28871: Fixed a crash when deallocate deep ElementTree.

- bpo-19542: Fix bugs in WeakValueDictionary.setdefault() and WeakValueDictionary.pop() when a GC collection happens in another thread.

- bpo-20191: Fixed a crash in resource.prlimit() when passing a sequence that doesn’t own its elements as limits.

- bpo-16255: subprocess.Popen uses /system/bin/sh on Android as the shell, instead of /bin/sh.

- bpo-28779: multiprocessing.set_forkserver_preload() would crash the forkserver process if a preloaded module instantiated some multiprocessing objects such as locks.

- bpo-26937: The chown() method of the tarfile.TarFile class does not fail now when the grp module cannot be imported, as for example on Android platforms.

- bpo-28847: dbm.dumb now supports reading read-only files and no longer writes the index file when it is not changed. A deprecation warning is now emitted if the index file is missed and recreated in the ‘r’ and ‘w’ modes (will be an error in future Python releases).

- bpo-27030: Unknown escapes consisting of `'\'` and an ASCII letter in re.sub() replacement templates regular expressions now are errors.

- bpo-28835: Fix a regression introduced in warnings.catch_warnings(): call warnings.showwarning() if it was overridden inside the context manager.

- bpo-27172: To assist with upgrades from 2.7, the previously documented deprecation of `inspect.getfullargspec()` has been reversed. This decision may be revisited again after the Python 2.7 branch is no longer officially supported.

- bpo-28740: Add sys.getandroidapilevel(): return the build time API version of Android as an integer. Function only available on Android.

- bpo-26273: Add new `socket.TCP_CONGESTION` (Linux 2.6.13) and `socket.TCP_USER_TIMEOUT` (Linux 2.6.37) constants. Patch written by Omar Sandoval.

- bpo-28752: Restored the __reduce__() methods of datetime objects.

- bpo-28727: Regular expression patterns, _sre.SRE_Pattern objects created by re.compile(), become comparable (only x==y and x!=y operators). This change should fix the bpo-18383: don’t duplicate warning filters when the warnings module is reloaded (thing usually only done in unit tests).

- bpo-20572: Remove the subprocess.Popen.wait endtime parameter. It was deprecated in 3.4 and undocumented prior to that.

- bpo-25659: In ctypes, prevent a crash calling the from_buffer() and from_buffer_copy() methods on abstract classes like Array.

- bpo-28548: In the “http.server” module, parse the protocol version if possible, to avoid using HTTP 0.9 in some error responses.

- bpo-19717: Makes Path.resolve() succeed on paths that do not exist. Patch by Vajrasky Kok

- bpo-28563: Fixed possible DoS and arbitrary code execution when handle plural form selections in the gettext module. The expression parser now supports exact syntax supported by GNU gettext.

- bpo-28387: Fixed possible crash in _io.TextIOWrapper deallocator when the garbage collector is invoked in other thread. Based on patch by Sebastian Cufre.

- bpo-27517: LZMA compressor and decompressor no longer raise exceptions if given empty data twice. Patch by Benjamin Fogle.

- bpo-28549: Fixed segfault in curses’s addch() with ncurses6.

- bpo-28449: tarfile.open() with mode “r” or “r:” now tries to open a tar file with compression before trying to open it without compression. Otherwise it had 50% chance failed with ignore_zeros=True.

- bpo-23262: The webbrowser module now supports Firefox 36+ and derived browsers. Based on patch by Oleg Broytman.

- bpo-24241: The webbrowser in an X environment now prefers using the default browser directly. Also, the webbrowser register() function now has a documented ‘preferred’ argument, to specify browsers to be returned by get() with no arguments. Patch by David Steele

- bpo-27939: Fixed bugs in tkinter.ttk.LabeledScale and tkinter.Scale caused by representing the scale as float value internally in Tk. tkinter.IntVar now works if float value is set to underlying Tk variable.

- bpo-28255: calendar.TextCalendar.prweek() no longer prints a space after a weeks’s calendar. calendar.TextCalendar.pryear() no longer prints redundant newline after a year’s calendar. Based on patch by Xiang Zhang.

- bpo-28255: calendar.TextCalendar.prmonth() no longer prints a space at the start of new line after printing a month’s calendar. Patch by Xiang Zhang.

- bpo-20491: The textwrap.TextWrapper class now honors non-breaking spaces. Based on patch by Kaarle Ritvanen.

- bpo-28353: os.fwalk() no longer fails on broken links.

- bpo-28430: Fix iterator of C implemented asyncio.Future doesn’t accept non-None value is passed to it.send(val).

- bpo-27025: Generated names for Tkinter widgets now start by the “!” prefix for readability.

- bpo-25464: Fixed HList.header_exists() in tkinter.tix module by addin a workaround to Tix library bug.

- bpo-28488: shutil.make_archive() no longer adds entry “./” to ZIP archive.

- bpo-25953: re.sub() now raises an error for invalid numerical group reference in replacement template even if the pattern is not found in the string. Error message for invalid group reference now includes the group index and the position of the reference. Based on patch by SilentGhost.

- bpo-28469: timeit now uses the sequence 1, 2, 5, 10, 20, 50,… instead of 1, 10, 100,… for autoranging.

- bpo-28115: Command-line interface of the zipfile module now uses argparse. Added support of long options.

- bpo-18219: Optimize csv.DictWriter for large number of columns. Patch by Mariatta Wijaya.

- bpo-28448: Fix C implemented asyncio.Future didn’t work on Windows.

- bpo-23214: In the “io” module, the argument to BufferedReader and BytesIO’s read1() methods is now optional and can be -1, matching the BufferedIOBase specification.

- bpo-28480: Fix error building socket module when multithreading is disabled.

- bpo-28240: timeit: remove `-c/--clock` and `-t/--time` command line options which were deprecated since Python 3.3.

- bpo-28240: timeit now repeats the benchmarks 5 times instead of only 3 to make benchmarks more reliable.

- bpo-28240: timeit autorange now uses a single loop iteration if the benchmark takes less than 10 seconds, instead of 10 iterations. “python3 -m timeit -s ‘import time’ ‘time.sleep(1)’” now takes 4 seconds instead of 40 seconds.

- Distutils.sdist now looks for README and setup.py files with case sensitivity. This behavior matches that found in Setuptools 6.0 and later. See setuptools 100 for rationale.

- bpo-24452: Make webbrowser support Chrome on Mac OS X. Patch by Ned Batchelder.

- bpo-20766: Fix references leaked by pdb in the handling of SIGINT handlers.

- bpo-27998: Fixed bytes path support in os.scandir() on Windows. Patch by Eryk Sun.

- bpo-28317: The disassembler now decodes FORMAT_VALUE argument.

- bpo-28380: unittest.mock Mock autospec functions now properly support assert_called, assert_not_called, and assert_called_once.

- bpo-28229: lzma module now supports pathlib.

- bpo-28321: Fixed writing non-BMP characters with binary format in plistlib.

- bpo-28225: bz2 module now supports pathlib. Initial patch by Ethan Furman.

- bpo-28227: gzip now supports pathlib. Patch by Ethan Furman.

- bpo-28332: Deprecated silent truncations in socket.htons and socket.ntohs. Original patch by Oren Milman.

- bpo-27358: Optimized merging var-keyword arguments and improved error message when passing a non-mapping as a var-keyword argument.

- bpo-28257: Improved error message when passing a non-iterable as a var-positional argument. Added opcode BUILD_TUPLE_UNPACK_WITH_CALL.

- bpo-28322: Fixed possible crashes when unpickle itertools objects from incorrect pickle data. Based on patch by John Leitch.

- bpo-28228: imghdr now supports pathlib.

- bpo-28226: compileall now supports pathlib.

- bpo-28314: Fix function declaration (C flags) for the getiterator() method of xml.etree.ElementTree.Element.

- bpo-28148: Stop using localtime() and gmtime() in the time module. Introduced platform independent _PyTime_localtime API that is similar to POSIX localtime_r, but available on all platforms. Patch by Ed Schouten.

- bpo-28253: Fixed calendar functions for extreme months: 0001-01 and 9999-12. Methods itermonthdays() and itermonthdays2() are reimplemented so that they don’t call itermonthdates() which can cause datetime.date under/overflow.

- bpo-28275: Fixed possible use after free in the decompress() methods of the LZMADecompressor and BZ2Decompressor classes. Original patch by John Leitch.

- bpo-27897: Fixed possible crash in sqlite3.Connection.create_collation() if pass invalid string-like object as a name. Patch by Xiang Zhang.

- bpo-18844: random.choices() now has k as a keyword-only argument to improve the readability of common cases and come into line with the signature used in other languages.

- bpo-18893: Fix invalid exception handling in Lib/ctypes/macholib/dyld.py. Patch by Madison May.

- bpo-27611: Fixed support of default root window in the tkinter.tix module. Added the master parameter in the DisplayStyle constructor.

- bpo-27348: In the traceback module, restore the formatting of exception messages like “Exception: None”. This fixes a regression introduced in 3.5a2.

- bpo-25651: Allow falsy values to be used for msg parameter of subTest().

- bpo-27778: Fix a memory leak in os.getrandom() when the getrandom() is interrupted by a signal and a signal handler raises a Python exception.

- bpo-28200: Fix memory leak on Windows in the os module (fix path_converter() function).

- bpo-25400: RobotFileParser now correctly returns default values for crawl_delay and request_rate. Initial patch by Peter Wirtz.

- bpo-27932: Prevent memory leak in win32_ver().

- Fix UnboundLocalError in socket._sendfile_use_sendfile.

- bpo-28075: Check for ERROR_ACCESS_DENIED in Windows implementation of os.stat(). Patch by Eryk Sun.

- bpo-22493: Warning message emitted by using inline flags in the middle of regular expression now contains a (truncated) regex pattern. Patch by Tim Graham.

- bpo-25270: Prevent codecs.escape_encode() from raising SystemError when an empty bytestring is passed.

- bpo-28181: Get antigravity over HTTPS. Patch by Kaartic Sivaraam.

- bpo-25895: Enable WebSocket URL schemes in urllib.parse.urljoin. Patch by Gergely Imreh and Markus Holtermann.

- bpo-28114: Fix a crash in parse_envlist() when env contains byte strings. Patch by Eryk Sun.

- bpo-27599: Fixed buffer overrun in binascii.b2a_qp() and binascii.a2b_qp().

- bpo-27906: Fix socket accept exhaustion during high TCP traffic. Patch by Kevin Conway.

- bpo-28174: Handle when SO_REUSEPORT isn’t properly supported. Patch by Seth Michael Larson.

- bpo-26654: Inspect functools.partial in asyncio.Handle.__repr__. Patch by iceboy.

- bpo-26909: Fix slow pipes IO in asyncio. Patch by INADA Naoki.

- bpo-28176: Fix callbacks race in asyncio.SelectorLoop.sock_connect.

- bpo-27759: Fix selectors incorrectly retain invalid file descriptors. Patch by Mark Williams.

- bpo-28325: Remove vestigial MacOS 9 macurl2path module and its tests.

- bpo-28368: Refuse monitoring processes if the child watcher has no loop attached. Patch by Vincent Michel.

- bpo-28369: Raise RuntimeError when transport’s FD is used with add_reader, add_writer, etc.

- bpo-28370: Speedup asyncio.StreamReader.readexactly. Patch by Коренберг Марк.

- bpo-28371: Deprecate passing asyncio.Handles to run_in_executor.

- bpo-28372: Fix asyncio to support formatting of non-python coroutines.

- bpo-28399: Remove UNIX socket from FS before binding. Patch by Коренберг Марк.

- bpo-27972: Prohibit Tasks to await on themselves.

- bpo-24142: Reading a corrupt config file left configparser in an invalid state. Original patch by Florian Höch.

- bpo-29581: ABCMeta.__new__ now accepts `**kwargs`, allowing abstract base classes to use keyword parameters in __init_subclass__. Patch by Nate Soares.

- bpo-25532: inspect.unwrap() will now only try to unwrap an object sys.getrecursionlimit() times, to protect against objects which create a new object on every attribute access.

- bpo-30177: path.resolve(strict=False) no longer cuts the path after the first element not present in the filesystem. Patch by Antoine Pietri.

### Documentation

- bpo-31294: Fix incomplete code snippet in the ZeroMQSocketListener and ZeroMQSocketHandler examples and adapt them to Python 3.

- bpo-21649: Add RFC 7525 and Mozilla server side TLS links to SSL documentation.

- bpo-31128: Allow the pydoc server to bind to arbitrary hostnames.

- bpo-30803: Clarify doc on truth value testing. Original patch by Peter Thomassen.

- bpo-30176: Add missing attribute related constants in curses documentation.

- bpo-30052: the link targets for `bytes()` and `bytearray()` are now their respective type definitions, rather than the corresponding builtin function entries. Use bytes and bytearray to reference the latter. In order to ensure this and future cross-reference updates are applied automatically, the daily documentation builds now disable the default output caching features in Sphinx.

- bpo-26985: Add missing info of code object in inspect documentation.

- bpo-19824: Improve the documentation for, and links to, template strings by emphasizing their utility for internationalization, and by clarifying some usage constraints. (See also: bpo-20314, bpo-12518)

- bpo-28929: Link the documentation to its source file on GitHub.

- bpo-25008: Document smtpd.py as effectively deprecated and add a pointer to aiosmtpd, a third-party asyncio-based replacement.

- bpo-26355: Add canonical header link on each page to corresponding major version of the documentation. Patch by Matthias Bussonnier.

- bpo-29349: Fix Python 2 syntax in code for building the documentation.

- bpo-23722: The data model reference and the porting section in the 3.6 What’s New guide now cover the additional `__classcell__` handling needed for custom metaclasses to fully support PEP 487 and zero-argument `super()`.

- bpo-28513: Documented command-line interface of zipfile.

### Tests

- bpo-29639: test.support.HOST is now “localhost”, a new HOSTv4 constant has been added for your `127.0.0.1` needs, similar to the existing HOSTv6 constant.

- bpo-31320: Silence traceback in test_ssl

- bpo-31346: Prefer PROTOCOL_TLS_CLIENT and PROTOCOL_TLS_SERVER protocols for SSLContext.

- bpo-25674: Remove sha256.tbs-internet.com ssl test

- bpo-30715: Address ALPN callback changes for OpenSSL 1.1.0f. The latest version behaves like OpenSSL 1.0.2 and no longer aborts handshake.

- bpo-30822: regrtest: Exclude tzdata from regrtest –all. When running the test suite using –use=all / -u all, exclude tzdata since it makes test_datetime too slow (15-20 min on some buildbots) which then times out on some buildbots. Fix also regrtest command line parser to allow passing -u extralargefile to run test_zipfile64.

- bpo-30695: Add the `set_nomemory(start, stop)` and `remove_mem_hooks()` functions to the _testcapi module.

- bpo-30357: test_thread: setUp() now uses support.threading_setup() and support.threading_cleanup() to wait until threads complete to avoid random side effects on following tests. Initial patch written by Grzegorz Grzywacz.

- bpo-30197: Enhanced functions swap_attr() and swap_item() in the test.support module. They now work when delete replaced attribute or item inside the with statement. The old value of the attribute or item (or None if it doesn’t exist) now will be assigned to the target of the “as” clause, if there is one.

- bpo-24932: Use proper command line parsing in _testembed

- bpo-28950: Disallow -j0 to be combined with -T/-l in regrtest command line arguments.

- bpo-28683: Fix the tests that bind() a unix socket and raise PermissionError on Android for a non-root user.

- bpo-26936: Fix the test_socket failures on Android - getservbyname(), getservbyport() and getaddrinfo() are broken on some Android API levels.

- bpo-28666: Now test.support.rmtree is able to remove unwritable or unreadable directories.

- bpo-23839: Various caches now are cleared before running every test file.

- bpo-26944: Fix test_posix for Android where ‘id -G’ is entirely wrong or missing the effective gid.

- bpo-28409: regrtest: fix the parser of command line arguments.

- bpo-28217: Adds _testconsole module to test console input.

- bpo-26939: Add the support.setswitchinterval() function to fix test_functools hanging on the Android armv7 qemu emulator.

### Build

- bpo-31354: Allow –with-lto to be used on all builds, not just `make profile-opt`.

- bpo-31370: Remove support for building –without-threads. This option is not really useful anymore in the 21st century. Removing lots of conditional paths allows us to simplify the code base, including in difficult to maintain low-level internal code.

- bpo-31341: Per PEP 11, support for the IRIX operating system was removed.

- bpo-30854: Fix compile error when compiling –without-threads. Patch by Masayuki Yamamoto.

- bpo-30687: Locate msbuild.exe on Windows when building rather than vcvarsall.bat

- bpo-20210: Support the disabled marker in Setup files. Extension modules listed after this marker are not built at all, neither by the Makefile nor by setup.py.

- bpo-29941: Add `--with-assertions` configure flag to explicitly enable C `assert()` checks. Defaults to off. `--with-pydebug` implies `--with-assertions`.

- bpo-28787: Fix out-of-tree builds of Python when configured with `--with--dtrace`.

- bpo-29243: Prevent unnecessary rebuilding of Python during `make test`, `make install` and some other make targets when configured with `--enable-optimizations`.

- bpo-23404: Don’t regenerate generated files based on file modification time anymore: the action is now explicit. Replace `make touch` with `make regen-all`.

- bpo-29643: Fix `--enable-optimization` didn’t work.

- bpo-27593: sys.version and the platform module python_build(), python_branch(), and python_revision() functions now use git information rather than hg when building from a repo.

- bpo-29572: Update Windows build and OS X installers to use OpenSSL 1.0.2k.

- bpo-27659: Prohibit implicit C function declarations: use `-Werror=implicit-function-declaration` when possible (GCC and Clang, but it depends on the compiler version). Patch written by Chi Hsuan Yen.

- bpo-29384: Remove old Be OS helper scripts.

- bpo-26851: Set Android compilation and link flags.

- bpo-28768: Fix implicit declaration of function _setmode. Patch by Masayuki Yamamoto

- bpo-29080: Removes hard dependency on hg.exe from PCBuild/build.bat

- bpo-23903: Added missed names to PC/python3.def.

- bpo-28762: lockf() is available on Android API level 24, but the F_LOCK macro is not defined in android-ndk-r13.

- bpo-28538: Fix the compilation error that occurs because if_nameindex() is available on Android API level 24, but the if_nameindex structure is not defined.

- bpo-20211: Do not add the directory for installing C header files and the directory for installing object code libraries to the cross compilation search paths. Original patch by Thomas Petazzoni.

- bpo-28849: Do not define sys.implementation._multiarch on Android.

- bpo-10656: Fix out-of-tree building on AIX. Patch by Tristan Carel and Michael Haubenwallner.

- bpo-26359: Rename –with-optimiations to –enable-optimizations.

- bpo-28444: Fix missing extensions modules when cross compiling.

- bpo-28208: Update Windows build and OS X installers to use SQLite 3.14.2.

- bpo-28248: Update Windows build and OS X installers to use OpenSSL 1.0.2j.

- bpo-21124: Fix building the _struct module on Cygwin by passing `NULL` instead of `&PyType_Type` to PyVarObject_HEAD_INIT. Patch by Masayuki Yamamoto.

- bpo-13756: Fix building extensions modules on Cygwin. Patch by Roumen Petrov, based on original patch by Jason Tishler.

- bpo-21085: Add configure check for siginfo_t.si_band, which Cygwin does not provide. Patch by Masayuki Yamamoto with review and rebase by Erik Bray.

- bpo-28258: Fixed build with Estonian locale (python-config and distclean targets in Makefile). Patch by Arfrever Frehtes Taifersar Arahesis.

- bpo-26661: setup.py now detects system libffi with multiarch wrapper.

- bpo-27979: A full copy of libffi is no longer bundled for use when building _ctypes on non-OSX UNIX platforms. An installed copy of libffi is now required when building _ctypes on such platforms.

- bpo-15819: Remove redundant include search directory option for building outside the source tree.

- bpo-28676: Prevent missing ‘getentropy’ declaration warning on macOS. Patch by Gareth Rees.

### Windows

- bpo-31392: Update Windows build to use OpenSSL 1.1.0f

- bpo-30389: Adds detection of Visual Studio 2017 to distutils on Windows.

- bpo-31358: zlib is no longer bundled in the CPython source, instead it is downloaded on demand just like bz2, lzma, OpenSSL, Tcl/Tk, and SQLite.

- bpo-31340: Change to building with MSVC v141 (included with Visual Studio 2017)

- bpo-30581: os.cpu_count() now returns the correct number of processors on Windows when the number of logical processors is greater than 64.

- bpo-30916: Pre-build OpenSSL, Tcl and Tk and include the binaries in the build.

- bpo-30731: Add a missing xmlns to python.manifest so that it matches the schema.

- bpo-30291: Allow requiring 64-bit interpreters from py.exe using -64 suffix. Contributed by Steve (Gadget) Barnes.

- bpo-30362: Adds list options (-0, -0p) to py.exe launcher. Contributed by Steve Barnes.

- bpo-23451: Fix socket deprecation warnings in socketmodule.c. Patch by Segev Finer.

- bpo-30450: The build process on Windows no longer depends on Subversion, instead pulling external code from GitHub via a Python script. If Python 3.6 is not found on the system (via `py -3.6`), NuGet is used to download a copy of 32-bit Python.

- bpo-29579: Removes readme.txt from the installer.

- bpo-25778: winreg does not truncate string correctly (Patch by Eryk Sun)

- bpo-28896: Deprecate WindowsRegistryFinder and disable it by default

- bpo-28522: Fixes mishandled buffer reallocation in getpathp.c

- bpo-28402: Adds signed catalog files for stdlib on Windows.

- bpo-28333: Enables Unicode for ps1/ps2 and input() prompts. (Patch by Eryk Sun)

- bpo-28251: Improvements to help manuals on Windows.

- bpo-28110: launcher.msi has different product codes between 32-bit and 64-bit

- bpo-28161: Opening CON for write access fails

- bpo-28162: WindowsConsoleIO readall() fails if first line starts with Ctrl+Z

- bpo-28163: WindowsConsoleIO fileno() passes wrong flags to _open_osfhandle

- bpo-28164: _PyIO_get_console_type fails for various paths

- bpo-28137: Renames Windows path file to ._pth

- bpo-28138: Windows ._pth file should allow import site

### IDLE

- bpo-31493: IDLE code context – fix code update and font update timers. Canceling timers prevents a warning message when test_idle completes.

- bpo-31488: IDLE - Update non-key options in former extension classes. When applying configdialog changes, call .reload for each feature class. Change ParenMatch so updated options affect existing instances attached to existing editor windows.

- bpo-31477: IDLE - Improve rstrip entry in doc. Strip trailing whitespace strips more than blank spaces. Multiline string literals are not skipped.

- bpo-31480: IDLE - make tests pass with zzdummy extension disabled by default.

- bpo-31421: Document how IDLE runs tkinter programs. IDLE calls tcl/tk update in the background in order to make live interaction and experimentation with tkinter applications much easier.

- bpo-31414: IDLE – fix tk entry box tests by deleting first. Adding to an int entry is not the same as deleting and inserting because int(‘’) will fail.

- bpo-31051: Rearrange IDLE configdialog GenPage into Window, Editor, and Help sections.

- bpo-30617: IDLE - Add docstrings and tests for outwin subclass of editor. Move some data and functions from the class to module level. Patch by Cheryl Sabella.

- bpo-31287: IDLE - Do not modify tkinter.message in test_configdialog.

- bpo-27099: Convert IDLE’s built-in ‘extensions’ to regular features. About 10 IDLE features were implemented as supposedly optional extensions. Their different behavior could be confusing or worse for users and not good for maintenance. Hence the conversion. The main difference for users is that user configurable key bindings for builtin features are now handled uniformly. Now, editing a binding in a keyset only affects its value in the keyset. All bindings are defined together in the system-specific default keysets in config-extensions.def. All custom keysets are saved as a whole in config-extension.cfg. All take effect as soon as one clicks Apply or Ok. The affected events are ‘<<force-open-completions>>’, ‘<<expand-word>>’, ‘<<force-open-calltip>>’, ‘<<flash-paren>>’, ‘<<format-paragraph>>’, ‘<<run-module>>’, ‘<<check-module>>’, and ‘<<zoom-height>>’. Any (global) customizations made before 3.6.3 will not affect their keyset-specific customization after 3.6.3. and vice versa. Initial patch by Charles Wohlganger.

- bpo-31206: IDLE: Factor HighPage(Frame) class from ConfigDialog. Patch by Cheryl Sabella.

- bpo-31001: Add tests for configdialog highlight tab. Patch by Cheryl Sabella.

- bpo-31205: IDLE: Factor KeysPage(Frame) class from ConfigDialog. The slightly modified tests continue to pass. Patch by Cheryl Sabella.

- bpo-31130: IDLE – stop leaks in test_configdialog. Initial patch by Victor Stinner.

- bpo-31002: Add tests for configdialog keys tab. Patch by Cheryl Sabella.

- bpo-19903: IDLE: Calltips use `inspect.signature` instead of `inspect.getfullargspec`. This improves calltips for builtins converted to use Argument Clinic. Patch by Louie Lu.

- bpo-31083: IDLE - Add an outline of a TabPage class in configdialog. Update existing classes to match outline. Initial patch by Cheryl Sabella.

- bpo-31050: Factor GenPage(Frame) class from ConfigDialog. The slightly modified tests continue to pass. Patch by Cheryl Sabella.

- bpo-31004: IDLE - Factor FontPage(Frame) class from ConfigDialog. Slightly modified tests continue to pass. Fix General tests. Patch mostly by Cheryl Sabella.

- bpo-30781: IDLE - Use ttk widgets in ConfigDialog. Patches by Terry Jan Reedy and Cheryl Sabella.

- bpo-31060: IDLE - Finish rearranging methods of ConfigDialog Grouping methods pertaining to each tab and the buttons will aid writing tests and improving the tabs and will enable splitting the groups into classes.

- bpo-30853: IDLE – Factor a VarTrace class out of ConfigDialog. Instance tracers manages pairs consisting of a tk variable and a callback function. When tracing is turned on, setting the variable calls the function. Test coverage for the new class is 100%.

- bpo-31003: IDLE: Add more tests for General tab.

- bpo-30993: IDLE - Improve configdialog font page and tests. In configdialog: Document causal pathways in create_font_tab docstring. Simplify some attribute names. Move set_samples calls to var_changed_font (idea from Cheryl Sabella). Move related functions to positions after the create widgets function. In test_configdialog: Fix test_font_set so not order dependent. Fix renamed test_indent_scale so it tests the widget. Adjust tests for movement of set_samples call. Add tests for load functions. Put all font tests in one class and tab indent tests in another. Except for two lines, these tests completely cover the related functions.

- bpo-30981: IDLE – Add more configdialog font page tests.

- bpo-28523: IDLE: replace ‘colour’ with ‘color’ in configdialog.

- bpo-30917: Add tests for idlelib.config.IdleConf. Increase coverage from 46% to 96%. Patch by Louie Lu.

- bpo-30934: Document coverage details for idlelib tests. Add section to idlelib/idle-test/README.txt. Include check that branches are taken both ways. Exclude IDLE-specific code that does not run during unit tests.

- bpo-30913: IDLE: Document ConfigDialog tk Vars, methods, and widgets in docstrings This will facilitate improving the dialog and splitting up the class. Original patch by Cheryl Sabella.

- bpo-30899: IDLE: Add tests for ConfigParser subclasses in config. Patch by Louie Lu.

- bpo-30881: IDLE: Add docstrings to browser.py. Patch by Cheryl Sabella.

- bpo-30851: IDLE: Remove unused variables in configdialog. One is a duplicate, one is set but cannot be altered by users. Patch by Cheryl Sabella.

- bpo-30870: IDLE: In Settings dialog, select font with Up, Down keys as well as mouse. Initial patch by Louie Lu.

- bpo-8231: IDLE: call config.IdleConf.GetUserCfgDir only once.

- bpo-30779: IDLE: Factor ConfigChanges class from configdialog, put in config; test. * In config, put dump test code in a function; run it and unittest in ‘if __name__ == ‘__main__’. * Add class config.ConfigChanges based on changes_class_v4.py on bpo issue. * Add class test_config.ChangesTest, partly using configdialog_tests_v1.py. * Revise configdialog to use ConfigChanges; see tracker msg297804. * Revise test_configdialog to match configdialog changes. * Remove configdialog functions unused or moved to ConfigChanges. Cheryl Sabella contributed parts of the patch.

- bpo-30777: IDLE: configdialog - Add docstrings and fix comments. Patch by Cheryl Sabella.

- bpo-30495: IDLE: Improve textview with docstrings, PEP8 names, and more tests. Patch by Cheryl Sabella.

- bpo-30723: IDLE: Make several improvements to parenmatch. Add ‘parens’ style to highlight both opener and closer. Make ‘default’ style, which is not default, a synonym for ‘opener’. Make time-delay work the same with all styles. Add help for config dialog extensions tab, including help for parenmatch. Add new tests. Original patch by Charles Wohlganger.

- bpo-30674: IDLE: add docstrings to grep module. Patch by Cheryl Sabella

- bpo-21519: IDLE’s basic custom key entry dialog now detects duplicates properly. Original patch by Saimadhav Heblikar.

- bpo-29910: IDLE no longer deletes a character after commenting out a region by a key shortcut. Add `return 'break'` for this and other potential conflicts between IDLE and default key bindings.

- bpo-30728: Review and change idlelib.configdialog names. Lowercase method and attribute names. Replace ‘colour’ with ‘color’, expand overly cryptic names, delete unneeded underscores. Replace `import *` with specific imports. Patches by Cheryl Sabella.

- bpo-6739: IDLE: Verify user-entered key sequences by trying to bind them with tk. Add tests for all 3 validation functions. Original patch by G Polo. Tests added by Cheryl Sabella.

- bpo-15786: Fix several problems with IDLE’s autocompletion box. The following should now work: clicking on selection box items; using the scrollbar; selecting an item by hitting Return. Hangs on MacOSX should no longer happen. Patch by Louie Lu.

- bpo-25514: Add doc subsubsection about IDLE failure to start. Popup no-connection message directs users to this section.

- bpo-30642: Fix reference leaks in IDLE tests. Patches by Louie Lu and Terry Jan Reedy.

- bpo-30495: Add docstrings for textview.py and use PEP8 names. Patches by Cheryl Sabella and Terry Jan Reedy.

- bpo-30290: Help-about: use pep8 names and add tests. Increase coverage to 100%. Patches by Louie Lu, Cheryl Sabella, and Terry Jan Reedy.

- bpo-30303: Add _utest option to textview; add new tests. Increase coverage to 100%. Patches by Louie Lu and Terry Jan Reedy.

- bpo-29071: IDLE colors f-string prefixes (but not invalid ur prefixes).

- bpo-28572: Add 10% to coverage of IDLE’s test_configdialog. Update and augment description of the configuration system.

### Tools/Demos

- bpo-30983: gdb integration commands (py-bt, etc.) work on optimized shared builds now, too. PEP 523 introduced _PyEval_EvalFrameDefault which inlines PyEval_EvalFrameEx on non-debug shared builds. This broke the ability to use py-bt, py-up, and a few other Python-specific gdb integrations. The problem is fixed by only looking for _PyEval_EvalFrameDefault frames in python-gdb.py. Original patch by Bruno “Polaco” Penteado.

- bpo-29748: Added the slice index converter in Argument Clinic.

- bpo-24037: Argument Clinic now uses the converter `bool(accept={int})` rather than `int` for semantical booleans. This avoids repeating the default value for Python and C and will help in converting to `bool` in future.

- bpo-29367: python-gdb.py now supports also `method-wrapper` (`wrapperobject`) objects.

- bpo-28023: Fix python-gdb.py didn’t support new dict implementation.

- bpo-15369: The pybench and pystone microbenchmark have been removed from Tools. Please use the new Python benchmark suite https://github.com/python/performance which is more reliable and includes a portable version of pybench working on Python 2 and Python 3.

- bpo-28102: The zipfile module CLI now prints usage to stderr. Patch by Stephen J. Turnbull.

### C API

- bpo-31338: Added the `Py_UNREACHABLE()` macro for code paths which are never expected to be reached. This and a few other useful macros are now documented in the C API manual.

- bpo-30832: Remove own implementation for thread-local storage. CPython has provided the own implementation for thread-local storage (TLS) on Python/thread.c, it’s used in the case which a platform has not supplied native TLS. However, currently all supported platforms (Windows and pthreads) have provided native TLS and defined the Py_HAVE_NATIVE_TLS macro with unconditional in any case.

- bpo-30708: PyUnicode_AsWideCharString() now raises a ValueError if the second argument is NULL and the wchar_t* string contains null characters.

- bpo-16500: Deprecate PyOS_AfterFork() and add PyOS_BeforeFork(), PyOS_AfterFork_Parent() and PyOS_AfterFork_Child().

- bpo-6532: The type of results of PyThread_start_new_thread() and PyThread_get_thread_ident(), and the id parameter of PyThreadState_SetAsyncExc() changed from “long” to “unsigned long”.

- bpo-27867: Function PySlice_GetIndicesEx() is deprecated and replaced with a macro if Py_LIMITED_API is not set or set to the value between 0x03050400 and 0x03060000 (not including) or 0x03060100 or higher. Added functions PySlice_Unpack() and PySlice_AdjustIndices().

- bpo-29083: Fixed the declaration of some public API functions. PyArg_VaParse() and PyArg_VaParseTupleAndKeywords() were not available in limited API. PyArg_ValidateKeywordArguments(), PyArg_UnpackTuple() and Py_BuildValue() were not available in limited API of version < 3.3 when PY_SSIZE_T_CLEAN is defined.

- bpo-28769: The result of PyUnicode_AsUTF8AndSize() and PyUnicode_AsUTF8() is now of type `const char *` rather of `char *`.

- bpo-29058: All stable API extensions added after Python 3.2 are now available only when Py_LIMITED_API is set to the PY_VERSION_HEX value of the minimum Python version supporting this API.

- bpo-28822: The index parameters start and end of PyUnicode_FindChar() are now adjusted to behave like `str[start:end]`.

- bpo-28808: PyUnicode_CompareWithASCIIString() now never raises exceptions.

- bpo-28761: The fields name and doc of structures PyMemberDef, PyGetSetDef, PyStructSequence_Field, PyStructSequence_Desc, and wrapperbase are now of type `const char *` rather of `char *`.

- bpo-28748: Private variable _Py_PackageContext is now of type `const char *` rather of `char *`.

- bpo-19569: Compiler warnings are now emitted if use most of deprecated functions.

- bpo-28426: Deprecated undocumented functions PyUnicode_AsEncodedObject(), PyUnicode_AsDecodedObject(), PyUnicode_AsDecodedUnicode() and PyUnicode_AsEncodedUnicode().

## Python 3.6.6 final

Release date: 2018-06-27

There were no new changes in version 3.6.6.

## Python 3.6.6 release candidate 1

Release date: 2018-06-11

### Core and Builtins

- bpo-33786: Fix asynchronous generators to handle GeneratorExit in athrow() correctly

- bpo-30654: Fixed reset of the SIGINT handler to SIG_DFL on interpreter shutdown even when there was a custom handler set previously. Patch by Philipp Kerling.

- bpo-33622: Fixed a leak when the garbage collector fails to add an object with the `__del__` method or referenced by it into the `gc.garbage` list. `PyGC_Collect()` can now be called when an exception is set and preserves it.

- bpo-31849: Fix signed/unsigned comparison warning in pyhash.c.

- bpo-33391: Fix a leak in set_symmetric_difference().

- bpo-28055: Fix unaligned accesses in siphash24(). Patch by Rolf Eike Beer.

- bpo-33231: Fix potential memory leak in `normalizestring()`.

- bpo-29922: Improved error messages in ‘async with’ when `__aenter__()` or `__aexit__()` return non-awaitable object.

- bpo-33199: Fix `ma_version_tag` in dict implementation is uninitialized when copying from key-sharing dict.

- bpo-33041: Fixed jumping when the function contains an `async for` loop.

- bpo-32282: Fix an unnecessary ifdef in the include of VersionHelpers.h in socketmodule on Windows.

- bpo-21983: Fix a crash in `ctypes.cast()` in case the type argument is a ctypes structured data type. Patch by Eryk Sun and Oren Milman.

### Library

- bpo-30167: Prevent site.main() exception if PYTHONSTARTUP is set. Patch by Steve Weber.

- bpo-33812: Datetime instance d with non-None tzinfo, but with d.tzinfo.utcoffset(d) returning None is now treated as naive by the astimezone() method.

- bpo-30805: Avoid race condition with debug logging

- bpo-33767: The concatenation (`+`) and repetition (`*`) sequence operations now raise `TypeError` instead of `SystemError` when performed on `mmap.mmap` objects. Patch by Zackery Spytz.

- bpo-32684: Fix gather to propagate cancellation of itself even with return_exceptions.

- bpo-33674: Fix a race condition in SSLProtocol.connection_made() of asyncio.sslproto: start immediately the handshake instead of using call_soon(). Previously, data_received() could be called before the handshake started, causing the handshake to hang or fail.

- bpo-31647: Fixed bug where calling write_eof() on a _SelectorSocketTransport after it’s already closed raises AttributeError.

- bpo-33672: Fix Task.__repr__ crash with Cython’s bogus coroutines

- bpo-33469: Fix RuntimeError after closing loop that used run_in_executor

- bpo-11874: Use a better regex when breaking usage into wrappable parts. Avoids bogus assertion errors from custom metavar strings.

- bpo-30877: Fixed a bug in the Python implementation of the JSON decoder that prevented the cache of parsed strings from clearing after finishing the decoding. Based on patch by c-fos.

- bpo-33548: tempfile._candidate_tempdir_list should consider common TEMP locations

- bpo-33542: Prevent `uuid.get_node` from using a DUID instead of a MAC on Windows. Patch by Zvi Effron

- bpo-26819: Fix race condition with `ReadTransport.resume_reading` in Windows proactor event loop.

- bpo-28556: Minor fixes in typing module: add annotations to `NamedTuple.__new__`, pass `*args` and `**kwds` in `Generic.__new__`. Original PRs by Paulius Šarka and Chad Dombrova.

- bpo-20087: Updated alias mapping with glibc 2.27 supported locales.

- bpo-33422: Fix trailing quotation marks getting deleted when looking up byte/string literals on pydoc. Patch by Andrés Delfino.

- bpo-33197: Update error message when constructing invalid inspect.Parameters Patch by Dong-hee Na.

- bpo-33383: Fixed crash in the get() method of the `dbm.ndbm` database object when it is called with a single argument.

- bpo-33329: Fix multiprocessing regression on newer glibcs

- bpo-991266: Fix quoting of the `Comment` attribute of `http.cookies.SimpleCookie`.

- bpo-33131: Upgrade bundled version of pip to 10.0.1.

- bpo-33308: Fixed a crash in the `parser` module when converting an ST object to a tree of tuples or lists with `line_info=False` and `col_info=True`.

- bpo-33263: Fix FD leak in `_SelectorSocketTransport` Patch by Vlad Starostin.

- bpo-33256: Fix display of `<module>` call in the html produced by `cgitb.html()`. Patch by Stéphane Blondon.

- bpo-33203: `random.Random.choice()` now raises `IndexError` for empty sequences consistently even when called from subclasses without a `getrandbits()` implementation.

- bpo-33224: Update difflib.mdiff() for PEP 479. Convert an uncaught StopIteration in a generator into a return-statement.

- bpo-33209: End framing at the end of C implementation of `pickle.Pickler.dump()`.

- bpo-32861: The urllib.robotparser’s `__str__` representation now includes wildcard entries and the “Crawl-delay” and “Request-rate” fields. Patch by Michael Lazar.

- bpo-33096: Allow ttk.Treeview.insert to insert iid that has a false boolean value. Note iid=0 and iid=False would be same. Patch by Garvit Khatri.

- bpo-33127: The ssl module now compiles with LibreSSL 2.7.1.

- bpo-33021: Release the GIL during fstat() calls, avoiding hang of all threads when calling mmap.mmap(), os.urandom(), and random.seed(). Patch by Nir Soffer.

- bpo-27683: Fix a regression in `ipaddress` that result of `hosts()` is empty when the network is constructed by a tuple containing an integer mask and only 1 bit left for addresses.

- bpo-32844: Fix wrong redirection of a low descriptor (0 or 1) to stderr in subprocess if another low descriptor is closed.

- bpo-31908: Fix output of cover files for `trace` module command-line tool. Previously emitted cover files only when `--missing` option was used. Patch by Michael Selik.

- bpo-31457: If nested log adapters are used, the inner `process()` methods are no longer omitted.

- bpo-16865: Support arrays >=2GiB in `ctypes`. Patch by Segev Finer.

- bpo-31238: pydoc: the stop() method of the private ServerThread class now waits until DocServer.serve_until_quit() completes and then explicitly sets its docserver attribute to None to break a reference cycle.

### Documentation

- bpo-33503: Fix broken pypi link

- bpo-33421: Add missing documentation for `typing.AsyncContextManager`.

- bpo-33378: Add Korean language switcher for https://docs.python.org/3/

- bpo-33276: Clarify that the `__path__` attribute on modules cannot be just any value.

- bpo-33201: Modernize documentation for writing C extension types.

- bpo-33195: Deprecate `Py_UNICODE` usage in `c-api/arg` document. `Py_UNICODE` related APIs are deprecated since Python 3.3, but it is missed in the document.

- bpo-33126: Document PyBuffer_ToContiguous().

- bpo-27212: Modify documentation for the `islice()` recipe to consume initial values up to the start index.

- bpo-28247: Update `zipapp` documentation to describe how to make standalone applications.

- bpo-18802: Documentation changes for ipaddress. Patch by Jon Foster and Berker Peksag.

- bpo-27428: Update documentation to clarify that `WindowsRegistryFinder` implements `MetaPathFinder`. (Patch by Himanshu Lakhara)

- bpo-8243: Add a note about curses.addch and curses.addstr exception behavior when writing outside a window, or pad.

- bpo-31432: Clarify meaning of CERT_NONE, CERT_OPTIONAL, and CERT_REQUIRED flags for ssl.SSLContext.verify_mode.

### Tests

- bpo-33655: Ignore test_posix_fallocate failures on BSD platforms that might be due to running on ZFS.

- bpo-19417: Add test_bdb.py.

### Build

- bpo-5755: Move `-Wstrict-prototypes` option to `CFLAGS_NODIST` from `OPT`. This option emitted annoying warnings when building extension modules written in C++.

- bpo-33614: Ensures module definition files for the stable ABI on Windows are correctly regenerated.

- bpo-33522: Enable CI builds on Visual Studio Team Services at https://python.visualstudio.com/cpython

- bpo-33012: Add `-Wno-cast-function-type` for gcc 8 for silencing warnings about function casts like casting to PyCFunction in method definition lists.

- bpo-33394: Enable the verbose build for extension modules, when GNU make is passed macros on the command line.

### Windows

- bpo-33184: Update Windows installer to OpenSSL 1.0.2o.

### macOS

- bpo-33184: Update macOS installer build to use OpenSSL 1.0.2o.

### IDLE

- bpo-33656: On Windows, add API call saying that tk scales for DPI. On Windows 8.1+ or 10, with DPI compatibility properties of the Python binary unchanged, and a monitor resolution greater than 96 DPI, this should make text and lines sharper. It should otherwise have no effect.

- bpo-33768: Clicking on a context line moves that line to the top of the editor window.

- bpo-33763: IDLE: Use read-only text widget for code context instead of label widget.

- bpo-33664: Scroll IDLE editor text by lines. Previously, the mouse wheel and scrollbar slider moved text by a fixed number of pixels, resulting in partial lines at the top of the editor box. The change also applies to the shell and grep output windows, but not to read-only text views.

- bpo-33679: Enable theme-specific color configuration for Code Context. Use the Highlights tab to see the setting for built-in themes or add settings to custom themes.

- bpo-33642: Display up to maxlines non-blank lines for Code Context. If there is no current context, show a single blank line.

- bpo-33628: IDLE: Cleanup codecontext.py and its test.

- bpo-33564: IDLE’s code context now recognizes async as a block opener.

- bpo-29706: IDLE now colors async and await as keywords in 3.6. They become full keywords in 3.7.

- bpo-21474: Update word/identifier definition from ascii to unicode. In text and entry boxes, this affects selection by double-click, movement left/right by control-left/right, and deletion left/right by control-BACKSPACE/DEL.

- bpo-33204: IDLE: consistently color invalid string prefixes. A ‘u’ string prefix cannot be paired with either ‘r’ or ‘f’. Consistently color as much of the prefix, starting at the right, as is valid. Revise and extend colorizer test.

- bpo-32831: Add docstrings and tests for codecontext.

### Tools/Demos

- bpo-33189: pygettext.py now recognizes only literal strings as docstrings and translatable strings, and rejects bytes literals and f-string expressions.

- bpo-31920: Fixed handling directories as arguments in the `pygettext` script. Based on patch by Oleg Krasnikov.

- bpo-29673: Fix pystackv and pystack gdbinit macros.

- bpo-32885: Add an `-n` flag for `Tools/scripts/pathfix.py` to disable automatic backup creation (files with `~` suffix).

- bpo-31583: Fix 2to3 for using with –add-suffix option but without –output-dir option for relative path to files in current directory.

### C API

- bpo-32374: Document that m_traverse for multi-phase initialized modules can be called with m_state=NULL, and add a sanity check

## Python 3.6.5 final

Release date: 2018-03-28

### Tests

- bpo-32872: Avoid regrtest compatibility issue with namespace packages.

### Build

- bpo-33163: Upgrade pip to 9.0.3 and setuptools to v39.0.1.

## Python 3.6.5 release candidate 1

Release date: 2018-03-13

### Security

- bpo-33001: Minimal fix to prevent buffer overrun in os.symlink on Windows

- bpo-32981: Regexes in difflib and poplib were vulnerable to catastrophic backtracking. These regexes formed potential DOS vectors (REDOS). They have been refactored. This resolves CVE-2018-1060 and CVE-2018-1061. Patch by Jamie Davis.

### Core and Builtins

- bpo-33026: Fixed jumping out of “with” block by setting f_lineno.

- bpo-17288: Prevent jumps from ‘return’ and ‘exception’ trace events.

- bpo-32889: Update Valgrind suppression list to account for the rename of `Py_ADDRESS_IN_RANG` to `address_in_range`.

- bpo-32650: Pdb and other debuggers dependent on bdb.py will correctly step over (next command) native coroutines. Patch by Pablo Galindo.

- bpo-32685: Improve suggestion when the Python 2 form of print statement is either present on the same line as the header of a compound statement or else terminated by a semi-colon instead of a newline. Patch by Nitish Chandra.

- bpo-32583: Fix possible crashing in builtin Unicode decoders caused by write out-of-bound errors when using customized decode error handlers.

- bpo-26163: Improved frozenset() hash to create more distinct hash values when faced with datasets containing many similar values.

- bpo-27169: The `__debug__` constant is now optimized out at compile time. This fixes also bpo-22091.

- bpo-32329: `sys.flags.hash_randomization` is now properly set to 0 when hash randomization is turned off by `PYTHONHASHSEED=0`.

- bpo-30416: The optimizer is now protected from spending much time doing complex calculations and consuming much memory for creating large constants in constant folding.

- bpo-18533: `repr()` on a dict containing its own `values()` or `items()` no longer raises `RecursionError`; OrderedDict similarly. Instead, use `...`, as for other recursive structures. Patch by Ben North.

- bpo-32028: Leading whitespace is now correctly ignored when generating suggestions for converting Py2 print statements to Py3 builtin print function calls. Patch by Sanyam Khurana.

- bpo-32137: The repr of deeply nested dict now raises a RecursionError instead of crashing due to a stack overflow.

### Library

- bpo-33064: lib2to3 now properly supports trailing commas after `*args` and `**kwargs` in function signatures.

- bpo-31804: Avoid failing in multiprocessing.Process if the standard streams are closed or None at exit.

- bpo-33037: Skip sending/receiving data after SSL transport closing.

- bpo-30353: Fix ctypes pass-by-value for structs on 64-bit Cygwin/MinGW.

- bpo-33009: Fix inspect.signature() for single-parameter partialmethods.

- bpo-32969: Expose several missing constants in zlib and fix corresponding documentation.

- bpo-32713: Fixed tarfile.itn handling of out-of-bounds float values. Patch by Joffrey Fuhrer.

- bpo-30622: The ssl module now detects missing NPN support in LibreSSL.

- bpo-32922: dbm.open() now encodes filename with the filesystem encoding rather than default encoding.

- bpo-32859: In `os.dup2`, don’t check every call whether the `dup3` syscall exists or not.

- bpo-21060: Rewrite confusing message from setup.py upload from “No dist file created in earlier command” to the more helpful “Must create and upload files in one command”.

- bpo-32857: In `tkinter`, `after_cancel(None)` now raises a `ValueError` instead of canceling the first scheduled function. Patch by Cheryl Sabella.

- bpo-32852: Make sure sys.argv remains as a list when running trace.

- bpo-32841: Fixed `asyncio.Condition` issue which silently ignored cancellation after notifying and cancelling a conditional lock. Patch by Bar Harel.

- bpo-31787: Fixed refleaks of `__init__()` methods in various modules. (Contributed by Oren Milman)

- bpo-30157: Fixed guessing quote and delimiter in csv.Sniffer.sniff() when only the last field is quoted. Patch by Jake Davis.

- bpo-32394: socket: Remove TCP_FASTOPEN, TCP_KEEPCNT flags on older version Windows during run-time.

- bpo-32777: Fix a rare but potential pre-exec child process deadlock in subprocess on POSIX systems when marking file descriptors inheritable on exec in the child process. This bug appears to have been introduced in 3.4.

- bpo-32647: The ctypes module used to depend on indirect linking for dlopen. The shared extension is now explicitly linked against libdl on platforms with dl.

- bpo-32734: Fixed `asyncio.Lock()` safety issue which allowed acquiring and locking the same lock multiple times, without it being free. Patch by Bar Harel.

- bpo-32727: Do not include name field in SMTP envelope from address. Patch by Stéphane Wirtel

- bpo-27931: Fix email address header parsing error when the username is an empty quoted string. Patch by Xiang Zhang.

- bpo-32304: distutils’ upload command no longer corrupts tar files ending with a CR byte, and no longer tries to convert CR to CRLF in any of the upload text fields.

- bpo-32502: uuid.uuid1 no longer raises an exception if a 64-bit hardware address is encountered.

- bpo-31848: Fix the error handling in Aifc_read.initfp() when the SSND chunk is not found. Patch by Zackery Spytz.

- bpo-32555: On FreeBSD and Solaris, os.strerror() now always decode the byte string from the current locale encoding, rather than using ASCII/surrogateescape in some cases.

- bpo-32521: The nis module is now compatible with new libnsl and headers location.

- bpo-32473: Improve ABCMeta._dump_registry() output readability

- bpo-32521: glibc has removed Sun RPC. Use replacement libtirpc headers and library in nis module.

- bpo-32228: Ensure that `truncate()` preserves the file position (as reported by `tell()`) after writes longer than the buffer size.

- bpo-26133: Don’t unsubscribe signals in asyncio UNIX event loop on interpreter shutdown.

- bpo-32185: The SSL module no longer sends IP addresses in SNI TLS extension on platforms with OpenSSL 1.0.2+ or inet_pton.

- bpo-32323: `urllib.parse.urlsplit()` does not convert zone-id (scope) to lower case for scoped IPv6 addresses in hostnames now.

- bpo-32302: Fix bdist_wininst of distutils for CRT v142: it binary compatible with CRT v140.

- bpo-32255: A single empty field is now always quoted when written into a CSV file. This allows to distinguish an empty row from a row consisting of a single empty field. Patch by Licht Takeuchi.

- bpo-32277: Raise `NotImplementedError` instead of `SystemError` on platforms where `chmod(..., follow_symlinks=False)` is not supported. Patch by Anthony Sottile.

- bpo-32199: The getnode() ip getter now uses ‘ip link’ instead of ‘ip link list’.

- bpo-27456: Ensure TCP_NODELAY is set on Linux. Tests by Victor Stinner.

- bpo-31900: The `locale.localeconv()` function now sets temporarily the `LC_CTYPE` locale to the `LC_NUMERIC` locale to decode `decimal_point` and `thousands_sep` byte strings if they are non-ASCII or longer than 1 byte, and the `LC_NUMERIC` locale is different than the `LC_CTYPE` locale. This temporary change affects other threads. Same change for the `str.format()` method when formatting a number (`int`, `float`, `float` and subclasses) with the `n` type (ex: `'{:n}'.format(1234)`).

- bpo-31802: Importing native path module (`posixpath`, `ntpath`) now works even if the `os` module still is not imported.

### Documentation

- bpo-17232: Clarify docs for -O and -OO. Patch by Terry Reedy.

- bpo-32800: Update link to w3c doc for xml default namespaces.

- bpo-8722: Document `__getattr__()` behavior when property `get()` method raises `AttributeError`.

- bpo-32614: Modify RE examples in documentation to use raw strings to prevent `DeprecationWarning` and add text to REGEX HOWTO to highlight the deprecation.

- bpo-31972: Improve docstrings for `pathlib.PurePath` subclasses.

- bpo-17799: Explain real behaviour of sys.settrace and sys.setprofile and their C-API counterparts regarding which type of events are received in each function. Patch by Pablo Galindo Salgado.

### Tests

- bpo-32517: Fix failing `test_asyncio` on macOS 10.12.2+ due to transport of `KqueueSelector` loop was not being closed.

- bpo-32721: Fix test_hashlib to not fail if the _md5 module is not built.

- bpo-32252: Fix faulthandler_suppress_crash_report() used to prevent core dump files when testing crashes. getrlimit() returns zero on success.

- bpo-31518: Debian Unstable has disabled TLS 1.0 and 1.1 for SSLv23_METHOD(). Change TLS/SSL protocol of some tests to PROTOCOL_TLS or PROTOCOL_TLSv1_2 to make them pass on Debian.

### Build

- bpo-32635: Fix segfault of the crypt module when libxcrypt is provided instead of libcrypt at the system.

### Windows

- bpo-33016: Fix potential use of uninitialized memory in nt._getfinalpathname

- bpo-32903: Fix a memory leak in os.chdir() on Windows if the current directory is set to a UNC path.

- bpo-31966: Fixed WindowsConsoleIO.write() for writing empty data.

- bpo-32409: Ensures activate.bat can handle Unicode contents.

- bpo-32457: Improves handling of denormalized executable path when launching Python.

- bpo-32370: Use the correct encoding for ipconfig output in the uuid module. Patch by Segev Finer.

- bpo-29248: Fix `os.readlink()` on Windows, which was mistakenly treating the `PrintNameOffset` field of the reparse data buffer as a number of characters instead of bytes. Patch by Craig Holmquist and SSE4.

- bpo-32588: Create standalone _distutils_findvs module.

### macOS

- bpo-32726: Provide an additional, more modern macOS installer variant that supports macOS 10.9+ systems in 64-bit mode only. Upgrade the supplied third-party libraries to OpenSSL 1.0.2n, XZ 5.2.3, and SQLite 3.22.0. The 10.9+ installer now links with and supplies its own copy of Tcl/Tk 8.6.8.

### IDLE

- bpo-32984: Set `__file__` while running a startup file. Like Python, IDLE optionally runs one startup file in the Shell window before presenting the first interactive input prompt. For IDLE, `-s` runs a file named in environmental variable `IDLESTARTUP` or `PYTHONSTARTUP`; `-r file` runs `file`. Python sets `__file__` to the startup file name before running the file and unsets it before the first prompt. IDLE now does the same when run normally, without the `-n` option.

- bpo-32940: Simplify and rename StringTranslatePseudoMapping in pyparse.

- bpo-32916: Change `str` to `code` in pyparse.

- bpo-32905: Remove unused code in pyparse module.

- bpo-32874: Add tests for pyparse.

- bpo-32837: Using the system and place-dependent default encoding for open() is a bad idea for IDLE’s system and location-independent files.

- bpo-32826: Add “encoding=utf-8” to open() in IDLE’s test_help_about. GUI test test_file_buttons() only looks at initial ascii-only lines, but failed on systems where open() defaults to ‘ascii’ because readline() internally reads and decodes far enough ahead to encounter a non-ascii character in CREDITS.txt.

- bpo-32765: Update configdialog General tab docstring to add new widgets to the widget list.

### Tools/Demos

- bpo-24960: 2to3 and lib2to3 can now read pickled grammar files using pkgutil.get_data() rather than probing the filesystem. This lets 2to3 and lib2to3 work when run from a zipfile.

- bpo-32222: Fix pygettext not extracting docstrings for functions with type annotated arguments. Patch by Toby Harradine.

### C API

- bpo-29084: Undocumented C API for OrderedDict has been excluded from the limited C API. It was added by mistake and actually never worked in the limited C API.

## Python 3.6.4 final

Release date: 2017-12-18

There were no new code changes in version 3.6.4 since v3.6.4rc1.

## Python 3.6.4 release candidate 1

Release date: 2017-12-05

### Core and Builtins

- bpo-32176: co_flags.CO_NOFREE is now always set correctly by the code object constructor based on freevars and cellvars, rather than needing to be set correctly by the caller. This ensures it will be cleared automatically when additional cell references are injected into a modified code object and function.

- bpo-31949: Fixed several issues in printing tracebacks (PyTraceBack_Print()). Setting sys.tracebacklimit to 0 or less now suppresses printing tracebacks. Setting sys.tracebacklimit to None now causes using the default limit. Setting sys.tracebacklimit to an integer larger than LONG_MAX now means using the limit LONG_MAX rather than the default limit. Fixed integer overflows in the case of more than 2**31 traceback items on Windows. Fixed output errors handling.

- bpo-30696: Fix the interactive interpreter looping endlessly when no memory.

- bpo-20047: Bytearray methods partition() and rpartition() now accept only bytes-like objects as separator, as documented. In particular they now raise TypeError rather of returning a bogus result when an integer is passed as a separator.

- bpo-31852: Fix a segmentation fault caused by a combination of the async soft keyword and continuation lines.

- bpo-21720: BytesWarning no longer emitted when the fromlist argument of `__import__()` or the `__all__` attribute of the module contain bytes instances.

- bpo-31825: Fixed OverflowError in the ‘unicode-escape’ codec and in codecs.escape_decode() when decode an escaped non-ascii byte.

- bpo-28603: Print the full context/cause chain of exceptions on interpreter exit, even if an exception in the chain is unhashable or compares equal to later ones. Patch by Zane Bitter.

- bpo-31786: Fix timeout rounding in the select module to round correctly negative timeouts between -1.0 and 0.0. The functions now block waiting for events as expected. Previously, the call was incorrectly non-blocking. Patch by Pablo Galindo.

- bpo-31642: Restored blocking “from package import module” by setting sys.modules[“package.module”] to None.

- bpo-31626: Fixed a bug in debug memory allocator. There was a write to freed memory after shrinking a memory block.

- bpo-31619: Fixed a ValueError when convert a string with large number of underscores to integer with binary base.

- bpo-31592: Fixed an assertion failure in Python parser in case of a bad `unicodedata.normalize()`. Patch by Oren Milman.

- bpo-31588: Raise a `TypeError` with a helpful error message when class creation fails due to a metaclass with a bad `__prepare__()` method. Patch by Oren Milman.

- bpo-31566: Fix an assertion failure in `_warnings.warn()` in case of a bad `__name__` global. Patch by Oren Milman.

- bpo-31505: Fix an assertion failure in `json`, in case `_json.make_encoder()` received a bad `encoder()` argument. Patch by Oren Milman.

- bpo-31492: Fix assertion failures in case of failing to import from a module with a bad `__name__` attribute, and in case of failing to access an attribute of such a module. Patch by Oren Milman.

- bpo-31490: Fix an assertion failure in `ctypes` class definition, in case the class has an attribute whose name is specified in `_anonymous_` but not in `_fields_`. Patch by Oren Milman.

- bpo-31478: Fix an assertion failure in `_random.Random.seed()` in case the argument has a bad `__abs__()` method. Patch by Oren Milman.

- bpo-31315: Fix an assertion failure in imp.create_dynamic(), when spec.name is not a string. Patch by Oren Milman.

- bpo-31311: Fix a crash in the `__setstate__()` method of `ctypes._CData`, in case of a bad `__dict__`. Patch by Oren Milman.

- bpo-31293: Fix crashes in true division and multiplication of a timedelta object by a float with a bad as_integer_ratio() method. Patch by Oren Milman.

- bpo-31285: Fix an assertion failure in `warnings.warn_explicit`, when the return value of the received loader’s get_source() has a bad splitlines() method. Patch by Oren Milman.

- bpo-30817: `PyErr_PrintEx()` clears now the ignored exception that may be raised by `_PySys_SetObjectId()`, for example when no memory.

### Library

- bpo-28556: Two minor fixes for `typing` module: allow shallow copying instances of generic classes, improve interaction of `__init_subclass__` with generics. Original PRs by Ivan Levkivskyi.

- bpo-27240: The header folding algorithm for the new email policies has been rewritten, which also fixes bpo-30788, bpo-31831, and bpo-32182. In particular, RFC2231 folding is now done correctly.

- bpo-32186: io.FileIO.readall() and io.FileIO.read() now release the GIL when getting the file size. Fixed hang of all threads with inaccessible NFS server. Patch by Nir Soffer.

- bpo-12239: Make `msilib.SummaryInformation.GetProperty()` return `None` when the value of property is `VT_EMPTY`. Initial patch by Mark Mc Mahon.

- bpo-31325: Fix wrong usage of `collections.namedtuple()` in the `RobotFileParser.parse()` method. Initial patch by Robin Wellner.

- bpo-12382: `msilib.OpenDatabase()` now raises a better exception message when it couldn’t open or create an MSI file. Initial patch by William Tisäter.

- bpo-32110: `codecs.StreamReader.read(n)` now returns not more than n characters/bytes for non-negative n. This makes it compatible with `read()` methods of other file-like objects.

- bpo-32072: Fixed issues with binary plists: Fixed saving bytearrays. Identical objects will be saved only once. Equal references will be load as identical objects. Added support for saving and loading recursive data structures.

- bpo-32034: Make asyncio.IncompleteReadError and LimitOverrunError pickleable.

- bpo-32015: Fixed the looping of asyncio in the case of reconnection the socket during waiting async read/write from/to the socket.

- bpo-32011: Restored support of loading marshal files with the TYPE_INT64 code. These files can be produced in Python 2.7.

- bpo-31970: Reduce performance overhead of asyncio debug mode.

- bpo-9678: Fixed determining the MAC address in the uuid module: Using ifconfig on NetBSD and OpenBSD. Using arp on Linux, FreeBSD, NetBSD and OpenBSD. Based on patch by Takayuki Shimizukawa.

- bpo-30057: Fix potential missed signal in signal.signal().

- bpo-31933: Fix Blake2 params leaf_size and node_offset on big endian platforms. Patch by Jack O’Connor.

- bpo-31927: Fixed compilation of the socket module on NetBSD 8. Fixed assertion failure or reading arbitrary data when parse a AF_BLUETOOTH address on NetBSD and DragonFly BSD.

- bpo-27666: Fixed stack corruption in curses.box() and curses.ungetmouse() when the size of types chtype or mmask_t is less than the size of C long. curses.box() now accepts characters as arguments. Based on patch by Steve Fink.

- bpo-31897: plistlib now catches more errors when read binary plists and raises InvalidFileException instead of unexpected exceptions.

- bpo-25720: Fix the method for checking pad state of curses WINDOW. Patch by Masayuki Yamamoto.

- bpo-31893: Fixed the layout of the kqueue_event structure on OpenBSD and NetBSD. Fixed the comparison of the kqueue_event objects.

- bpo-31891: Fixed building the curses module on NetBSD.

- bpo-28416: Instances of pickle.Pickler subclass with the persistent_id() method and pickle.Unpickler subclass with the persistent_load() method no longer create reference cycles.

- bpo-28326: Fix multiprocessing.Process when stdout and/or stderr is closed or None.

- bpo-31457: If nested log adapters are used, the inner `process()` methods are no longer omitted.

- bpo-31457: The `manager` property on LoggerAdapter objects is now properly settable.

- bpo-31806: Fix timeout rounding in time.sleep(), threading.Lock.acquire() and socket.socket.settimeout() to round correctly negative timeouts between -1.0 and 0.0. The functions now block waiting for events as expected. Previously, the call was incorrectly non-blocking. Patch by Pablo Galindo.

- bpo-28603: traceback: Fix a TypeError that occurred during printing of exception tracebacks when either the current exception or an exception in its context/cause chain is unhashable. Patch by Zane Bitter.

- bpo-30058: Fixed buffer overflow in select.kqueue.control().

- bpo-31770: Prevent a crash when calling the `__init__()` method of a `sqlite3.Cursor` object more than once. Patch by Oren Milman.

- bpo-31672: `idpattern` in `string.Template` matched some non-ASCII characters. Now it uses `-i` regular expression local flag to avoid non-ASCII characters.

- bpo-31764: Prevent a crash in `sqlite3.Cursor.close()` in case the `Cursor` object is uninitialized. Patch by Oren Milman.

- bpo-31752: Fix possible crash in timedelta constructor called with custom integers.

- bpo-31701: On Windows, faulthandler.enable() now ignores MSC and COM exceptions.

- bpo-31728: Prevent crashes in `_elementtree` due to unsafe cleanup of `Element.text` and `Element.tail`. Patch by Oren Milman.

- bpo-31620: an empty asyncio.Queue now doesn’t leak memory when queue.get pollers timeout

- bpo-31632: Fix method set_protocol() of class _SSLProtocolTransport in asyncio module. This method was previously modifying a wrong reference to the protocol.

- bpo-31675: Fixed memory leaks in Tkinter’s methods splitlist() and split() when pass a string larger than 2 GiB.

- bpo-31673: Fixed typo in the name of Tkinter’s method adderrorinfo().

- bpo-30806: Fix the string representation of a netrc object.

- bpo-15037: Added a workaround for getkey() in curses for ncurses 5.7 and earlier.

- bpo-25351: Avoid venv activate failures with undefined variables

- bpo-25532: inspect.unwrap() will now only try to unwrap an object sys.getrecursionlimit() times, to protect against objects which create a new object on every attribute access.

- bpo-30347: Stop crashes when concurrently iterate over itertools.groupby() iterators.

- bpo-31516: `threading.current_thread()` should not return a dummy thread at shutdown.

- bpo-31351: python -m ensurepip now exits with non-zero exit code if pip bootstrapping has failed.

- bpo-31482: `random.seed()` now works with bytes in version=1

- bpo-31334: Fix `poll.poll([timeout])` in the `select` module for arbitrary negative timeouts on all OSes where it can only be a non-negative integer or -1. Patch by Riccardo Coccioli.

- bpo-31310: multiprocessing’s semaphore tracker should be launched again if crashed.

- bpo-31308: Make multiprocessing’s forkserver process immune to Ctrl-C and other user interruptions. If it crashes, restart it when necessary.

### Documentation

- bpo-32105: Added asyncio.BaseEventLoop.connect_accepted_socket versionadded marker.

- bpo-31537: Fix incorrect usage of `get_history_length` in readline documentation example code. Patch by Brad Smith.

- bpo-30085: The operator functions without double underscores are preferred for clarity. The one with underscores are only kept for back-compatibility.

### Tests

- bpo-31380: Skip test_httpservers test_undecodable_file on macOS: fails on APFS.

- bpo-31705: Skip test_socket.test_sha256() on Linux kernel older than 4.5. The test fails with ENOKEY on kernel 3.10 (on ppc64le). A fix was merged into the kernel 4.5.

- bpo-31174: Fix test_tools.test_unparse: DirectoryTestCase now stores the names sample to always test the same files. It prevents false alarms when hunting reference leaks.

- bpo-30695: Add the `set_nomemory(start, stop)` and `remove_mem_hooks()` functions to the _testcapi module.

### Build

- bpo-32059: `detect_modules()` in `setup.py` now also searches the sysroot paths when cross-compiling.

- bpo-31957: Fixes Windows SDK version detection when building for Windows.

- bpo-31609: Fixes quotes in PCbuild/clean.bat

- bpo-31934: Abort the build when building out of a not clean source tree.

- bpo-31926: Fixed Argument Clinic sometimes causing compilation errors when there was more than one function and/or method in a .c file with the same name.

- bpo-28791: Update Windows builds to use SQLite 3.21.0.

- bpo-28791: Update OS X installer to use SQLite 3.21.0.

- bpo-22140: Prevent double substitution of prefix in python-config.sh.

- bpo-31536: Avoid wholesale rebuild after `make regen-all` if nothing changed.

### Windows

- bpo-1102: Return `None` when `View.Fetch()` returns `ERROR_NO_MORE_ITEMS` instead of raising `MSIError`. Initial patch by Anthony Tuininga.

- bpo-31944: Fixes Modify button in Apps and Features dialog.

### macOS

- bpo-31392: Update macOS installer to use OpenSSL 1.0.2m

### IDLE

- bpo-32207: Improve tk event exception tracebacks in IDLE. When tk event handling is driven by IDLE’s run loop, a confusing and distracting queue.EMPTY traceback context is no longer added to tk event exception tracebacks. The traceback is now the same as when event handling is driven by user code. Patch based on a suggestion by Serhiy Storchaka.

- bpo-32164: Delete unused file idlelib/tabbedpages.py. Use of TabbedPageSet in configdialog was replaced by ttk.Notebook.

- bpo-32100: IDLE: Fix old and new bugs in pathbrowser; improve tests. Patch mostly by Cheryl Sabella.

- bpo-31858: IDLE – Restrict shell prompt manipulation to the shell. Editor and output windows only see an empty last prompt line. This simplifies the code and fixes a minor bug when newline is inserted. Sys.ps1, if present, is read on Shell start-up, but is not set or changed.

- bpo-31860: The font sample in the IDLE configuration dialog is now editable. Changes persist while IDLE remains open

- bpo-31836: Test_code_module now passes if run after test_idle, which sets ps1. The code module uses sys.ps1 if present or sets it to ‘>>> ‘ if not. Test_code_module now properly tests both behaviors. Ditto for ps2.

- bpo-28603: Fix a TypeError that caused a shell restart when printing a traceback that includes an exception that is unhashable. Patch by Zane Bitter.

- bpo-13802: Use non-Latin characters in the IDLE’s Font settings sample. Even if one selects a font that defines a limited subset of the unicode Basic Multilingual Plane, tcl/tk will use other fonts that define a character. The expanded example give users of non-Latin characters a better idea of what they might see in IDLE’s shell and editors. To make room for the expanded sample, frames on the Font tab are re-arranged. The Font/Tabs help explains a bit about the additions.

- bpo-31460: Simplify the API of IDLE’s Module Browser. Passing a widget instead of an flist with a root widget opens the option of creating a browser frame that is only part of a window. Passing a full file name instead of pieces assumed to come from a .py file opens the possibility of browsing python files that do not end in .py.

- bpo-31649: IDLE - Make _htest, _utest parameters keyword only.

- bpo-31559: Remove test order dependence in idle_test.test_browser.

- bpo-31459: Rename IDLE’s module browser from Class Browser to Module Browser. The original module-level class and method browser became a module browser, with the addition of module-level functions, years ago. Nested classes and functions were added yesterday. For back-compatibility, the virtual event <<open-class-browser>>, which appears on the Keys tab of the Settings dialog, is not changed. Patch by Cheryl Sabella.

- bpo-31500: Default fonts now are scaled on HiDPI displays.

- bpo-1612262: IDLE module browser now shows nested classes and functions. Original patches for code and tests by Guilherme Polo and Cheryl Sabella, respectively.

### Tools/Demos

- bpo-30722: Make redemo work with Python 3.6 and newer versions. Also, remove the `LOCALE` option since it doesn’t work with string patterns in Python 3. Patch by Christoph Sarnowski.

### C API

- bpo-20891: Fix PyGILState_Ensure(). When PyGILState_Ensure() is called in a non-Python thread before PyEval_InitThreads(), only call PyEval_InitThreads() after calling PyThreadState_New() to fix a crash.

- bpo-31532: Fix memory corruption due to allocator mix in getpath.c between Py_GetPath() and Py_SetPath()

- bpo-30697: The `PyExc_RecursionErrorInst` singleton is removed and `PyErr_NormalizeException()` does not use it anymore. This singleton is persistent and its members being never cleared may cause a segfault during finalization of the interpreter. See also bpo-22898.

## Python 3.6.3 final

Release date: 2017-10-03

### Library

- bpo-31641: Re-allow arbitrary iterables in `concurrent.futures.as_completed()`. Fixes regression in 3.6.3rc1.

### Build

- bpo-31662: Fix typos in Windows `uploadrelease.bat` script. Fix Windows Doc build issues in `Doc/make.bat`.

- bpo-31423: Fix building the PDF documentation with newer versions of Sphinx.

## Python 3.6.3 release candidate 1

Release date: 2017-09-18

### Security

- bpo-29781: SSLObject.version() now correctly returns None when handshake over BIO has not been performed yet.

- bpo-30947: Upgrade libexpat embedded copy from version 2.2.1 to 2.2.3 to get security fixes.

### Core and Builtins

- bpo-31471: Fix an assertion failure in `subprocess.Popen()` on Windows, in case the env argument has a bad keys() method. Patch by Oren Milman.

- bpo-31418: Fix an assertion failure in `PyErr_WriteUnraisable()` in case of an exception with a bad `__module__` attribute. Patch by Oren Milman.

- bpo-31416: Fix assertion failures in case of a bad warnings.filters or warnings.defaultaction. Patch by Oren Milman.

- bpo-31411: Raise a TypeError instead of SystemError in case warnings.onceregistry is not a dictionary. Patch by Oren Milman.

- bpo-31373: Fix several possible instances of undefined behavior due to floating-point demotions.

- bpo-30465: Location information (`lineno` and `col_offset`) in f-strings is now (mostly) correct. This fixes tools like flake8 from showing warnings on the wrong line (typically the first line of the file).

- bpo-31343: Include sys/sysmacros.h for major(), minor(), and makedev(). GNU C libray plans to remove the functions from sys/types.h.

- bpo-31291: Fix an assertion failure in `zipimport.zipimporter.get_data` on Windows, when the return value of `pathname.replace('/','\\')` isn’t a string. Patch by Oren Milman.

- bpo-31271: Fix an assertion failure in the write() method of `io.TextIOWrapper`, when the encoder doesn’t return a bytes object. Patch by Oren Milman.

- bpo-31243: Fix a crash in some methods of `io.TextIOWrapper`, when the decoder’s state is invalid. Patch by Oren Milman.

- bpo-30721: `print` now shows correct usage hint for using Python 2 redirection syntax. Patch by Sanyam Khurana.

- bpo-31070: Fix a race condition in importlib _get_module_lock().

- bpo-31095: Fix potential crash during GC caused by `tp_dealloc` which doesn’t call `PyObject_GC_UnTrack()`.

- bpo-31071: Avoid masking original TypeError in call with * unpacking when other arguments are passed.

- bpo-30978: str.format_map() now passes key lookup exceptions through. Previously any exception was replaced with a KeyError exception.

- bpo-30808: Use _Py_atomic API for concurrency-sensitive signal state.

- bpo-30876: Relative import from unloaded package now reimports the package instead of failing with SystemError. Relative import from non-package now fails with ImportError rather than SystemError.

- bpo-30703: Improve signal delivery. Avoid using Py_AddPendingCall from signal handler, to avoid calling signal-unsafe functions. The tests I’m adding here fail without the rest of the patch, on Linux and OS X. This means our signal delivery logic had defects (some signals could be lost).

- bpo-30765: Avoid blocking in pthread_mutex_lock() when PyThread_acquire_lock() is asked not to block.

- bpo-31161: Make sure the ‘Missing parentheses’ syntax error message is only applied to SyntaxError, not to subclasses. Patch by Martijn Pieters.

- bpo-30814: Fixed a race condition when import a submodule from a package.

- bpo-30597: `print` now shows expected input in custom error message when used as a Python 2 statement. Patch by Sanyam Khurana.

### Library

- bpo-31499: xml.etree: Fix a crash when a parser is part of a reference cycle.

- bpo-28556: typing.get_type_hints now finds the right globalns for classes and modules by default (when no `globalns` was specified by the caller).

- bpo-28556: Speed improvements to the `typing` module. Original PRs by Ivan Levkivskyi and Mitar.

- bpo-31544: The C accelerator module of ElementTree ignored exceptions raised when looking up TreeBuilder target methods in XMLParser().

- bpo-31234: socket.create_connection() now fixes manually a reference cycle: clear the variable storing the last exception on success.

- bpo-31457: LoggerAdapter objects can now be nested.

- bpo-31400: Improves SSL error handling to avoid losing error numbers.

- bpo-28958: ssl.SSLContext() now uses OpenSSL error information when a context cannot be instantiated.

- bpo-27340: SSLSocket.sendall() now uses memoryview to create slices of data. This fixes support for all bytes-like object. It is also more efficient and avoids costly copies.

- bpo-31178: Fix string concatenation bug in rare error path in the subprocess module

- bpo-31350: Micro-optimize `asyncio._get_running_loop()` to become up to 10% faster.

- bpo-31170: expat: Update libexpat from 2.2.3 to 2.2.4. Fix copying of partial characters for UTF-8 input (libexpat bug 115): https://github.com/libexpat/libexpat/issues/115

- bpo-29136: Add TLS 1.3 cipher suites and OP_NO_TLSv1_3.

- bpo-29212: Fix concurrent.futures.thread.ThreadPoolExecutor threads to have a non repr() based thread name by default when no thread_name_prefix is supplied. They will now identify themselves as “ThreadPoolExecutor-y_n”.

- bpo-9146: Fix a segmentation fault in _hashopenssl when standard hash functions such as md5 are not available in the linked OpenSSL library. As in some special FIPS-140 build environments.

- bpo-27144: The `map()` and `as_completed()` iterators in `concurrent.futures` now avoid keeping a reference to yielded objects.

- bpo-10746: Fix ctypes producing wrong PEP 3118 type codes for integer types.

- bpo-22536: The subprocess module now sets the filename when FileNotFoundError is raised on POSIX systems due to the executable or cwd not being found.

- bpo-31249: concurrent.futures: WorkItem.run() used by ThreadPoolExecutor now breaks a reference cycle between an exception object and the WorkItem object.

- bpo-31247: xmlrpc.server now explicitly breaks reference cycles when using sys.exc_info() in code handling exceptions.

- bpo-30102: The ssl and hashlib modules now call OPENSSL_add_all_algorithms_noconf() on OpenSSL < 1.1.0. The function detects CPU features and enables optimizations on some CPU architectures such as POWER8. Patch is based on research from Gustavo Serra Scalet.

- bpo-31185: Fixed miscellaneous errors in asyncio speedup module.

- bpo-31135: ttk: fix the destroy() method of LabeledScale and OptionMenu classes. Call the parent destroy() method even if the used attribute doesn’t exist. The LabeledScale.destroy() method now also explicitly clears label and scale attributes to help the garbage collector to destroy all widgets.

- bpo-31107: Fix `copyreg._slotnames()` mangled attribute calculation for classes whose name begins with an underscore. Patch by Shane Harvey.

- bpo-31061: Fixed a crash when using asyncio and threads.

- bpo-30502: Fix handling of long oids in ssl. Based on patch by Christian Heimes.

- bpo-30119: ftplib.FTP.putline() now throws ValueError on commands that contains CR or LF. Patch by Dong-hee Na.

- bpo-30595: multiprocessing.Queue.get() with a timeout now polls its reader in non-blocking mode if it succeeded to acquire the lock but the acquire took longer than the timeout.

- bpo-29403: Fix `unittest.mock`’s autospec to not fail on method-bound builtin functions. Patch by Aaron Gallagher.

- bpo-30961: Fix decrementing a borrowed reference in tracemalloc.

- bpo-25684: Change `ttk.OptionMenu` radiobuttons to be unique across instances of `OptionMenu`.

- bpo-30886: Fix multiprocessing.Queue.join_thread(): it now waits until the thread completes, even if the thread was started by the same process which created the queue.

- bpo-29854: Fix segfault in readline when using readline’s history-size option. Patch by Nir Soffer.

- bpo-30319: socket.close() now ignores ECONNRESET error.

- bpo-30828: Fix out of bounds write in `asyncio.CFuture.remove_done_callback()`.

- bpo-30807: signal.setitimer() may disable the timer when passed a tiny value. Tiny values (such as 1e-6) are valid non-zero values for setitimer(), which is specified as taking microsecond-resolution intervals. However, on some platform, our conversion routine could convert 1e-6 into a zero interval, therefore disabling the timer instead of (re-)scheduling it.

- bpo-30441: Fix bug when modifying os.environ while iterating over it

- bpo-30532: Fix email header value parser dropping folding white space in certain cases.

- bpo-30879: os.listdir() and os.scandir() now emit bytes names when called with bytes-like argument.

- bpo-30746: Prohibited the ‘=’ character in environment variable names in `os.putenv()` and `os.spawn*()`.

- bpo-29755: Fixed the lgettext() family of functions in the gettext module. They now always return bytes.

### Documentation

- bpo-31294: Fix incomplete code snippet in the ZeroMQSocketListener and ZeroMQSocketHandler examples and adapt them to Python 3.

- bpo-21649: Add RFC 7525 and Mozilla server side TLS links to SSL documentation.

- bpo-30803: Clarify doc on truth value testing. Original patch by Peter Thomassen.

### Tests

- bpo-31320: Silence traceback in test_ssl

- bpo-25674: Remove sha256.tbs-internet.com ssl test

- bpo-30715: Address ALPN callback changes for OpenSSL 1.1.0f. The latest version behaves like OpenSSL 1.0.2 and no longer aborts handshake.

- bpo-30822: regrtest: Exclude tzdata from regrtest –all. When running the test suite using –use=all / -u all, exclude tzdata since it makes test_datetime too slow (15-20 min on some buildbots) which then times out on some buildbots. Fix also regrtest command line parser to allow passing -u extralargefile to run test_zipfile64.

### Build

- bpo-30854: Fix compile error when compiling –without-threads. Patch by Masayuki Yamamoto.

### Windows

- bpo-30389: Adds detection of Visual Studio 2017 to distutils on Windows.

- bpo-31340: Change to building with MSVC v141 (included with Visual Studio 2017)

- bpo-30581: os.cpu_count() now returns the correct number of processors on Windows when the number of logical processors is greater than 64.

- bpo-30731: Add a missing xmlns to python.manifest so that it matches the schema.

### IDLE

- bpo-31493: IDLE code context – fix code update and font update timers. Canceling timers prevents a warning message when test_idle completes.

- bpo-31488: IDLE - Update non-key options in former extension classes. When applying configdialog changes, call .reload for each feature class. Change ParenMatch so updated options affect existing instances attached to existing editor windows.

- bpo-31477: IDLE - Improve rstrip entry in doc. Strip trailing whitespace strips more than blank spaces. Multiline string literals are not skipped.

- bpo-31480: IDLE - make tests pass with zzdummy extension disabled by default.

- bpo-31421: Document how IDLE runs tkinter programs. IDLE calls tcl/tk update in the background in order to make live interaction and experimentation with tkinter applications much easier.

- bpo-31414: IDLE – fix tk entry box tests by deleting first. Adding to an int entry is not the same as deleting and inserting because int(‘’) will fail.

- bpo-31051: Rearrange IDLE configdialog GenPage into Window, Editor, and Help sections.

- bpo-30617: IDLE - Add docstrings and tests for outwin subclass of editor. Move some data and functions from the class to module level. Patch by Cheryl Sabella.

- bpo-31287: IDLE - Do not modify tkinter.message in test_configdialog.

- bpo-27099: Convert IDLE’s built-in ‘extensions’ to regular features. About 10 IDLE features were implemented as supposedly optional extensions. Their different behavior could be confusing or worse for users and not good for maintenance. Hence the conversion. The main difference for users is that user configurable key bindings for builtin features are now handled uniformly. Now, editing a binding in a keyset only affects its value in the keyset. All bindings are defined together in the system-specific default keysets in config-extensions.def. All custom keysets are saved as a whole in config-extension.cfg. All take effect as soon as one clicks Apply or Ok. The affected events are ‘<<force-open-completions>>’, ‘<<expand-word>>’, ‘<<force-open-calltip>>’, ‘<<flash-paren>>’, ‘<<format-paragraph>>’, ‘<<run-module>>’, ‘<<check-module>>’, and ‘<<zoom-height>>’. Any (global) customizations made before 3.6.3 will not affect their keyset-specific customization after 3.6.3. and vice versa. Initial patch by Charles Wohlganger.

- bpo-31206: IDLE: Factor HighPage(Frame) class from ConfigDialog. Patch by Cheryl Sabella.

- bpo-31001: Add tests for configdialog highlight tab. Patch by Cheryl Sabella.

- bpo-31205: IDLE: Factor KeysPage(Frame) class from ConfigDialog. The slightly modified tests continue to pass. Patch by Cheryl Sabella.

- bpo-31130: IDLE – stop leaks in test_configdialog. Initial patch by Victor Stinner.

- bpo-31002: Add tests for configdialog keys tab. Patch by Cheryl Sabella.

- bpo-19903: IDLE: Calltips use `inspect.signature` instead of `inspect.getfullargspec`. This improves calltips for builtins converted to use Argument Clinic. Patch by Louie Lu.

- bpo-31083: IDLE - Add an outline of a TabPage class in configdialog. Update existing classes to match outline. Initial patch by Cheryl Sabella.

- bpo-31050: Factor GenPage(Frame) class from ConfigDialog. The slightly modified tests continue to pass. Patch by Cheryl Sabella.

- bpo-31004: IDLE - Factor FontPage(Frame) class from ConfigDialog. Slightly modified tests continue to pass. Fix General tests. Patch mostly by Cheryl Sabella.

- bpo-30781: IDLE - Use ttk widgets in ConfigDialog. Patches by Terry Jan Reedy and Cheryl Sabella.

- bpo-31060: IDLE - Finish rearranging methods of ConfigDialog Grouping methods pertaining to each tab and the buttons will aid writing tests and improving the tabs and will enable splitting the groups into classes.

- bpo-30853: IDLE – Factor a VarTrace class out of ConfigDialog. Instance tracers manages pairs consisting of a tk variable and a callback function. When tracing is turned on, setting the variable calls the function. Test coverage for the new class is 100%.

- bpo-31003: IDLE: Add more tests for General tab.

- bpo-30993: IDLE - Improve configdialog font page and tests. In configdialog: Document causal pathways in create_font_tab docstring. Simplify some attribute names. Move set_samples calls to var_changed_font (idea from Cheryl Sabella). Move related functions to positions after the create widgets function. In test_configdialog: Fix test_font_set so not order dependent. Fix renamed test_indent_scale so it tests the widget. Adjust tests for movement of set_samples call. Add tests for load functions. Put all font tests in one class and tab indent tests in another. Except for two lines, these tests completely cover the related functions.

- bpo-30981: IDLE – Add more configdialog font page tests.

- bpo-28523: IDLE: replace ‘colour’ with ‘color’ in configdialog.

- bpo-30917: Add tests for idlelib.config.IdleConf. Increase coverage from 46% to 96%. Patch by Louie Lu.

- bpo-30934: Document coverage details for idlelib tests. Add section to idlelib/idle-test/README.txt. Include check that branches are taken both ways. Exclude IDLE-specific code that does not run during unit tests.

- bpo-30913: IDLE: Document ConfigDialog tk Vars, methods, and widgets in docstrings This will facilitate improving the dialog and splitting up the class. Original patch by Cheryl Sabella.

- bpo-30899: IDLE: Add tests for ConfigParser subclasses in config. Patch by Louie Lu.

- bpo-30881: IDLE: Add docstrings to browser.py. Patch by Cheryl Sabella.

- bpo-30851: IDLE: Remove unused variables in configdialog. One is a duplicate, one is set but cannot be altered by users. Patch by Cheryl Sabella.

- bpo-30870: IDLE: In Settings dialog, select font with Up, Down keys as well as mouse. Initial patch by Louie Lu.

- bpo-8231: IDLE: call config.IdleConf.GetUserCfgDir only once.

- bpo-30779: IDLE: Factor ConfigChanges class from configdialog, put in config; test. * In config, put dump test code in a function; run it and unittest in ‘if __name__ == ‘__main__’. * Add class config.ConfigChanges based on changes_class_v4.py on bpo issue. * Add class test_config.ChangesTest, partly using configdialog_tests_v1.py. * Revise configdialog to use ConfigChanges; see tracker msg297804. * Revise test_configdialog to match configdialog changes. * Remove configdialog functions unused or moved to ConfigChanges. Cheryl Sabella contributed parts of the patch.

- bpo-30777: IDLE: configdialog - Add docstrings and fix comments. Patch by Cheryl Sabella.

- bpo-30495: IDLE: Improve textview with docstrings, PEP8 names, and more tests. Patch by Cheryl Sabella.

- bpo-30723: IDLE: Make several improvements to parenmatch. Add ‘parens’ style to highlight both opener and closer. Make ‘default’ style, which is not default, a synonym for ‘opener’. Make time-delay work the same with all styles. Add help for config dialog extensions tab, including help for parenmatch. Add new tests. Original patch by Charles Wohlganger.

- bpo-30674: IDLE: add docstrings to grep module. Patch by Cheryl Sabella

- bpo-21519: IDLE’s basic custom key entry dialog now detects duplicates properly. Original patch by Saimadhav Heblikar.

- bpo-29910: IDLE no longer deletes a character after commenting out a region by a key shortcut. Add `return 'break'` for this and other potential conflicts between IDLE and default key bindings.

- bpo-30728: Review and change idlelib.configdialog names. Lowercase method and attribute names. Replace ‘colour’ with ‘color’, expand overly cryptic names, delete unneeded underscores. Replace `import *` with specific imports. Patches by Cheryl Sabella.

- bpo-6739: IDLE: Verify user-entered key sequences by trying to bind them with tk. Add tests for all 3 validation functions. Original patch by G Polo. Tests added by Cheryl Sabella.

### Tools/Demos

- bpo-30983: gdb integration commands (py-bt, etc.) work on optimized shared builds now, too. PEP 523 introduced _PyEval_EvalFrameDefault which inlines PyEval_EvalFrameEx on non-debug shared builds. This broke the ability to use py-bt, py-up, and a few other Python-specific gdb integrations. The problem is fixed by only looking for _PyEval_EvalFrameDefault frames in python-gdb.py. Original patch by Bruno “Polaco” Penteado.

## Python 3.6.2 final

Release date: 2017-07-17

No changes since release candidate 2

## Python 3.6.2 release candidate 2

Release date: 2017-07-07

### Security

- bpo-30730: Prevent environment variables injection in subprocess on Windows. Prevent passing other environment variables and command arguments.

- bpo-30694: Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes of multiple security vulnerabilities including: CVE-2017-9233 (External entity infinite loop DoS), CVE-2016-9063 (Integer overflow, re-fix), CVE-2016-0718 (Fix regression bugs from 2.2.0’s fix to CVE-2016-0718) and CVE-2012-0876 (Counter hash flooding with SipHash). Note: the CVE-2016-5300 (Use os-specific entropy sources like getrandom) doesn’t impact Python, since Python already gets entropy from the OS to set the expat secret using `XML_SetHashSalt()`.

- bpo-30500: Fix urllib.parse.splithost() to correctly parse fragments. For example, `splithost('//127.0.0.1#@evil.com/')` now correctly returns the `127.0.0.1` host, instead of treating `@evil.com` as the host in an authentication (`login@host`).

## Python 3.6.2 release candidate 1

Release date: 2017-06-17

### Core and Builtins

- bpo-30682: Removed a too-strict assertion that failed for certain f-strings, such as eval(“f’\n’”) and eval(“f’\r’”).

- bpo-30604: Move co_extra_freefuncs to not be per-thread to avoid crashes

- bpo-29104: Fixed parsing backslashes in f-strings.

- bpo-27945: Fixed various segfaults with dict when input collections are mutated during searching, inserting or comparing. Based on patches by Duane Griffin and Tim Mitchell.

- bpo-25794: Fixed type.__setattr__() and type.__delattr__() for non-interned attribute names. Based on patch by Eryk Sun.

- bpo-30039: If a KeyboardInterrupt happens when the interpreter is in the middle of resuming a chain of nested ‘yield from’ or ‘await’ calls, it’s now correctly delivered to the innermost frame.

- bpo-12414: sys.getsizeof() on a code object now returns the sizes which includes the code struct and sizes of objects which it references. Patch by Dong-hee Na.

- bpo-29949: Fix memory usage regression of set and frozenset object.

- bpo-29935: Fixed error messages in the index() method of tuple, list and deque when pass indices of wrong type.

- bpo-29859: Show correct error messages when any of the pthread_* calls in thread_pthread.h fails.

- bpo-28876: `bool(range)` works even if `len(range)` raises `OverflowError`.

- bpo-29600: Fix wrapping coroutine return values in StopIteration.

- bpo-28856: Fix an oversight that %b format for bytes should support objects follow the buffer protocol.

- bpo-29714: Fix a regression that bytes format may fail when containing zero bytes inside.

- bpo-29478: If max_line_length=None is specified while using the Compat32 policy, it is no longer ignored. Patch by Mircea Cosbuc.

### Library

- bpo-30616: Functional API of enum allows to create empty enums. Patched by Dong-hee Na

- bpo-30038: Fix race condition between signal delivery and wakeup file descriptor. Patch by Nathaniel Smith.

- bpo-23894: lib2to3 now recognizes `rb'...'` and `f'...'` strings.

- bpo-23890: unittest.TestCase.assertRaises() now manually breaks a reference cycle to not keep objects alive longer than expected.

- bpo-30149: inspect.signature() now supports callables with variable-argument parameters wrapped with partialmethod. Patch by Dong-hee Na.

- bpo-30645: Fix path calculation in imp.load_package(), fixing it for cases when a package is only shipped with bytecodes. Patch by Alexandru Ardelean.

- bpo-29931: Fixed comparison check for ipaddress.ip_interface objects. Patch by Sanjay Sundaresan.

- bpo-30605: re.compile() no longer raises a BytesWarning when compiling a bytes instance with misplaced inline modifier. Patch by Roy Williams.

### Security

- bpo-29591: Update expat copy from 2.1.1 to 2.2.0 to get fixes of CVE-2016-0718 and CVE-2016-4472. See https://sourceforge.net/p/expat/bugs/537/ for more information.

### Library

- bpo-24484: Avoid race condition in multiprocessing cleanup (#2159)

- bpo-28994: The traceback no longer displayed for SystemExit raised in a callback registered by atexit.

- bpo-30508: Don’t log exceptions if Task/Future “cancel()” method was called.

- bpo-28556: Updates to typing module: Add generic AsyncContextManager, add support for ContextManager on all versions. Original PRs by Jelle Zijlstra and Ivan Levkivskyi

- bpo-29870: Fix ssl sockets leaks when connection is aborted in asyncio/ssl implementation. Patch by Michaël Sghaïer.

- bpo-29743: Closing transport during handshake process leaks open socket. Patch by Nikolay Kim

- bpo-27585: Fix waiter cancellation in asyncio.Lock. Patch by Mathieu Sornay.

- bpo-30418: On Windows, subprocess.Popen.communicate() now also ignore EINVAL on stdin.write() if the child process is still running but closed the pipe.

- bpo-29822: inspect.isabstract() now works during __init_subclass__. Patch by Nate Soares.

- bpo-29581: ABCMeta.__new__ now accepts `**kwargs`, allowing abstract base classes to use keyword parameters in __init_subclass__. Patch by Nate Soares.

- bpo-30557: faulthandler now correctly filters and displays exception codes on Windows

- bpo-30378: Fix the problem that logging.handlers.SysLogHandler cannot handle IPv6 addresses.

- bpo-29960: Preserve generator state when _random.Random.setstate() raises an exception. Patch by Bryan Olson.

- bpo-30414: multiprocessing.Queue._feed background running thread do not break from main loop on exception.

- bpo-30003: Fix handling escape characters in HZ codec. Based on patch by Ma Lin.

- bpo-30301: Fix AttributeError when using SimpleQueue.empty() under spawn and forkserver start methods.

- bpo-30329: imaplib and poplib now catch the Windows socket WSAEINVAL error (code 10022) on shutdown(SHUT_RDWR): An invalid operation was attempted. This error occurs sometimes on SSL connections.

- bpo-30375: Warnings emitted when compile a regular expression now always point to the line in the user code. Previously they could point into inners of the re module if emitted from inside of groups or conditionals.

- bpo-30048: Fixed `Task.cancel()` can be ignored when the task is running coroutine and the coroutine returned without any more `await`.

- bpo-30266: contextlib.AbstractContextManager now supports anti-registration by setting __enter__ = None or __exit__ = None, following the pattern introduced in bpo-25958. Patch by Jelle Zijlstra.

- bpo-30298: Weaken the condition of deprecation warnings for inline modifiers. Now allowed several subsequential inline modifiers at the start of the pattern (e.g. `'(?i)(?s)...'`). In verbose mode whitespaces and comments now are allowed before and between inline modifiers (e.g. `'(?x) (?i) (?s)...'`).

- bpo-29990: Fix range checking in GB18030 decoder. Original patch by Ma Lin.

- bpo-26293: Change resulted because of zipfile breakage. (See also: bpo-29094)

- bpo-30243: Removed the __init__ methods of _json’s scanner and encoder. Misusing them could cause memory leaks or crashes. Now scanner and encoder objects are completely initialized in the __new__ methods.

- bpo-30185: Avoid KeyboardInterrupt tracebacks in forkserver helper process when Ctrl-C is received.

- bpo-28556: Various updates to typing module: add typing.NoReturn type, use WrapperDescriptorType, minor bug-fixes. Original PRs by Jim Fasarakis-Hilliard and Ivan Levkivskyi.

- bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux.

- bpo-30070: Fixed leaks and crashes in errors handling in the parser module.

- bpo-30061: Fixed crashes in IOBase methods __next__() and readlines() when readline() or __next__() respectively return non-sizeable object. Fixed possible other errors caused by not checking results of PyObject_Size(), PySequence_Size(), or PyMapping_Size().

- bpo-30017: Allowed calling the close() method of the zip entry writer object multiple times. Writing to a closed writer now always produces a ValueError.

- bpo-30068: _io._IOBase.readlines will check if it’s closed first when hint is present.

- bpo-29694: Fixed race condition in pathlib mkdir with flags parents=True. Patch by Armin Rigo.

- bpo-29692: Fixed arbitrary unchaining of RuntimeError exceptions in contextlib.contextmanager. Patch by Siddharth Velankar.

- bpo-29998: Pickling and copying ImportError now preserves name and path attributes.

- bpo-29953: Fixed memory leaks in the replace() method of datetime and time objects when pass out of bound fold argument.

- bpo-29942: Fix a crash in itertools.chain.from_iterable when encountering long runs of empty iterables.

- bpo-27863: Fixed multiple crashes in ElementTree caused by race conditions and wrong types.

- bpo-28699: Fixed a bug in pools in multiprocessing.pool that raising an exception at the very first of an iterable may swallow the exception or make the program hang. Patch by Davin Potts and Xiang Zhang.

- bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True) when the OS gives priority to errors such as EACCES over EEXIST.

- bpo-29861: Release references to tasks, their arguments and their results as soon as they are finished in multiprocessing.Pool.

- bpo-29884: faulthandler: Restore the old sigaltstack during teardown. Patch by Christophe Zeitouny.

- bpo-25455: Fixed crashes in repr of recursive buffered file-like objects.

- bpo-29800: Fix crashes in partial.__repr__ if the keys of partial.keywords are not strings. Patch by Michael Seifert.

- bpo-29742: get_extra_info() raises exception if get called on closed ssl transport. Patch by Nikolay Kim.

- bpo-8256: Fixed possible failing or crashing input() if attributes “encoding” or “errors” of sys.stdin or sys.stdout are not set or are not strings.

- bpo-28298: Fix a bug that prevented array ‘Q’, ‘L’ and ‘I’ from accepting big intables (objects that have __int__) as elements. Patch by Oren Milman.

- bpo-28231: The zipfile module now accepts path-like objects for external paths.

- bpo-26915: index() and count() methods of collections.abc.Sequence now check identity before checking equality when do comparisons.

- bpo-29615: SimpleXMLRPCDispatcher no longer chains KeyError (or any other exception) to exception(s) raised in the dispatched methods. Patch by Petr Motejlek.

- bpo-30177: path.resolve(strict=False) no longer cuts the path after the first element not present in the filesystem. Patch by Antoine Pietri.

### IDLE

- bpo-15786: Fix several problems with IDLE’s autocompletion box. The following should now work: clicking on selection box items; using the scrollbar; selecting an item by hitting Return. Hangs on MacOSX should no longer happen. Patch by Louie Lu.

- bpo-25514: Add doc subsubsection about IDLE failure to start. Popup no-connection message directs users to this section.

- bpo-30642: Fix reference leaks in IDLE tests. Patches by Louie Lu and Terry Jan Reedy.

- bpo-30495: Add docstrings for textview.py and use PEP8 names. Patches by Cheryl Sabella and Terry Jan Reedy.

- bpo-30290: Help-about: use pep8 names and add tests. Increase coverage to 100%. Patches by Louie Lu, Cheryl Sabella, and Terry Jan Reedy.

- bpo-30303: Add _utest option to textview; add new tests. Increase coverage to 100%. Patches by Louie Lu and Terry Jan Reedy.

### C API

- bpo-27867: Function PySlice_GetIndicesEx() no longer replaced with a macro if Py_LIMITED_API is not set.

### Build

- bpo-29941: Add `--with-assertions` configure flag to explicitly enable C `assert()` checks. Defaults to off. `--with-pydebug` implies `--with-assertions`.

- bpo-28787: Fix out-of-tree builds of Python when configured with `--with--dtrace`.

- bpo-29243: Prevent unnecessary rebuilding of Python during `make test`, `make install` and some other make targets when configured with `--enable-optimizations`.

- bpo-23404: Don’t regenerate generated files based on file modification time anymore: the action is now explicit. Replace `make touch` with `make regen-all`.

- bpo-29643: Fix `--enable-optimization` didn’t work.

### Documentation

- bpo-30176: Add missing attribute related constants in curses documentation.

- bpo-30052: the link targets for `bytes()` and `bytearray()` are now their respective type definitions, rather than the corresponding builtin function entries. Use bytes and bytearray to reference the latter. In order to ensure this and future cross-reference updates are applied automatically, the daily documentation builds now disable the default output caching features in Sphinx.

- bpo-26985: Add missing info of code object in inspect documentation.

### Tools/Demos

- bpo-29367: python-gdb.py now supports also `method-wrapper` (`wrapperobject`) objects.

### Tests

- bpo-30357: test_thread: setUp() now uses support.threading_setup() and support.threading_cleanup() to wait until threads complete to avoid random side effects on following tests. Initial patch written by Grzegorz Grzywacz.

- bpo-30197: Enhanced functions swap_attr() and swap_item() in the test.support module. They now work when delete replaced attribute or item inside the with statement. The old value of the attribute or item (or None if it doesn’t exist) now will be assigned to the target of the “as” clause, if there is one.

### Windows

- bpo-30687: Locate msbuild.exe on Windows when building rather than vcvarsall.bat

- bpo-30450: The build process on Windows no longer depends on Subversion, instead pulling external code from GitHub via a Python script. If Python 3.6 is not found on the system (via `py -3.6`), NuGet is used to download a copy of 32-bit Python.

## Python 3.6.1 final

Release date: 2017-03-21

### Core and Builtins

- bpo-29723: The `sys.path[0]` initialization change for bpo-29139 caused a regression by revealing an inconsistency in how sys.path is initialized when executing `__main__` from a zipfile, directory, or other import location. The interpreter now consistently avoids ever adding the import location’s parent directory to `sys.path`, and ensures no other `sys.path` entries are inadvertently modified when inserting the import location named on the command line.

### Build

- bpo-27593: fix format of git information used in sys.version

- Fix incompatible comment in python.h

## Python 3.6.1 release candidate 1

Release date: 2017-03-04

### Core and Builtins

- bpo-28893: Set correct __cause__ for errors about invalid awaitables returned from __aiter__ and __anext__.

- bpo-29683: Fixes to memory allocation in _PyCode_SetExtra. Patch by Brian Coleman.

- bpo-29684: Fix minor regression of PyEval_CallObjectWithKeywords. It should raise TypeError when kwargs is not a dict. But it might cause segv when args=NULL and kwargs is not a dict.

- bpo-28598: Support __rmod__ for subclasses of str being called before str.__mod__. Patch by Martijn Pieters.

- bpo-29607: Fix stack_effect computation for CALL_FUNCTION_EX. Patch by Matthieu Dartiailh.

- bpo-29602: Fix incorrect handling of signed zeros in complex constructor for complex subclasses and for inputs having a __complex__ method. Patch by Serhiy Storchaka.

- bpo-29347: Fixed possibly dereferencing undefined pointers when creating weakref objects.

- bpo-29438: Fixed use-after-free problem in key sharing dict.

- bpo-29319: Prevent RunMainFromImporter overwriting sys.path[0].

- bpo-29337: Fixed possible BytesWarning when compare the code objects. Warnings could be emitted at compile time.

- bpo-29327: Fixed a crash when pass the iterable keyword argument to sorted().

- bpo-29034: Fix memory leak and use-after-free in os module (path_converter).

- bpo-29159: Fix regression in bytes(x) when x.__index__() raises Exception.

- bpo-28932: Do not include <sys/random.h> if it does not exist.

- bpo-25677: Correct the positioning of the syntax error caret for indented blocks. Based on patch by Michael Layzell.

- bpo-29000: Fixed bytes formatting of octals with zero padding in alternate form.

- bpo-26919: On Android, operating system data is now always encoded/decoded to/from UTF-8, instead of the locale encoding to avoid inconsistencies with os.fsencode() and os.fsdecode() which are already using UTF-8.

- bpo-28991: functools.lru_cache() was susceptible to an obscure reentrancy bug triggerable by a monkey-patched len() function.

- bpo-28739: f-string expressions are no longer accepted as docstrings and by ast.literal_eval() even if they do not include expressions.

- bpo-28512: Fixed setting the offset attribute of SyntaxError by PyErr_SyntaxLocationEx() and PyErr_SyntaxLocationObject().

- bpo-28918: Fix the cross compilation of xxlimited when Python has been built with Py_DEBUG defined.

- bpo-28731: Optimize _PyDict_NewPresized() to create correct size dict. Improve speed of dict literal with constant keys up to 30%.

### Library

- bpo-29169: Update zlib to 1.2.11.

- bpo-29623: Allow use of path-like object as a single argument in ConfigParser.read(). Patch by David Ellis.

- bpo-28963: Fix out of bound iteration in asyncio.Future.remove_done_callback implemented in C.

- bpo-29704: asyncio.subprocess.SubprocessStreamProtocol no longer closes before all pipes are closed.

- bpo-29271: Fix Task.current_task and Task.all_tasks implemented in C to accept None argument as their pure Python implementation.

- bpo-29703: Fix asyncio to support instantiation of new event loops in child processes.

- bpo-29376: Fix assertion error in threading._DummyThread.is_alive().

- bpo-28624: Add a test that checks that cwd parameter of Popen() accepts PathLike objects. Patch by Sayan Chowdhury.

- bpo-28518: Start a transaction implicitly before a DML statement. Patch by Aviv Palivoda.

- bpo-29532: Altering a kwarg dictionary passed to functools.partial() no longer affects a partial object after creation.

- bpo-29110: Fix file object leak in aifc.open() when file is given as a filesystem path and is not in valid AIFF format. Patch by Anthony Zhang.

- bpo-28556: Various updates to typing module: typing.Counter, typing.ChainMap, improved ABC caching, etc. Original PRs by Jelle Zijlstra, Ivan Levkivskyi, Manuel Krebber, and Łukasz Langa.

- bpo-29100: Fix datetime.fromtimestamp() regression introduced in Python 3.6.0: check minimum and maximum years.

- bpo-29519: Fix weakref spewing exceptions during interpreter shutdown when used with a rare combination of multiprocessing and custom codecs.

- bpo-29416: Prevent infinite loop in pathlib.Path.mkdir

- bpo-29444: Fixed out-of-bounds buffer access in the group() method of the match object. Based on patch by WGH.

- bpo-29335: Fix subprocess.Popen.wait() when the child process has exited to a stopped instead of terminated state (ex: when under ptrace).

- bpo-29290: Fix a regression in argparse that help messages would wrap at non-breaking spaces.

- bpo-28735: Fixed the comparison of mock.MagickMock with mock.ANY.

- bpo-29316: Restore the provisional status of typing module, add corresponding note to documentation. Patch by Ivan L.

- bpo-29219: Fixed infinite recursion in the repr of uninitialized ctypes.CDLL instances.

- bpo-29011: Fix an important omission by adding Deque to the typing module.

- bpo-28969: Fixed race condition in C implementation of functools.lru_cache. KeyError could be raised when cached function with full cache was simultaneously called from different threads with the same uncached arguments.

- bpo-29142: In urllib.request, suffixes in no_proxy environment variable with leading dots could match related hostnames again (e.g. .b.c matches a.b.c). Patch by Milan Oberkirch.

- bpo-28961: Fix unittest.mock._Call helper: don’t ignore the name parameter anymore. Patch written by Jiajun Huang.

- bpo-29203: functools.lru_cache() now respects PEP 468 and preserves the order of keyword arguments. f(a=1, b=2) is now cached separately from f(b=2, a=1) since both calls could potentially give different results.

- bpo-15812: inspect.getframeinfo() now correctly shows the first line of a context. Patch by Sam Breese.

- bpo-29094: Offsets in a ZIP file created with extern file object and modes “w” and “x” now are relative to the start of the file.

- bpo-29085: Allow random.Random.seed() to use high quality OS randomness rather than the pid and time.

- bpo-29061: Fixed bug in secrets.randbelow() which would hang when given a negative input. Patch by Brendan Donegan.

- bpo-29079: Prevent infinite loop in pathlib.resolve() on Windows

- bpo-13051: Fixed recursion errors in large or resized curses.textpad.Textbox. Based on patch by Tycho Andersen.

- bpo-29119: Fix weakrefs in the pure python version of collections.OrderedDict move_to_end() method. Contributed by Andra Bogildea.

- bpo-9770: curses.ascii predicates now work correctly with negative integers.

- bpo-28427: old keys should not remove new values from WeakValueDictionary when collecting from another thread.

- bpo-28923: Remove editor artifacts from Tix.py.

- bpo-29055: Neaten-up empty population error on random.choice() by suppressing the upstream exception.

- bpo-28871: Fixed a crash when deallocate deep ElementTree.

- bpo-19542: Fix bugs in WeakValueDictionary.setdefault() and WeakValueDictionary.pop() when a GC collection happens in another thread.

- bpo-20191: Fixed a crash in resource.prlimit() when passing a sequence that doesn’t own its elements as limits.

- bpo-28779: multiprocessing.set_forkserver_preload() would crash the forkserver process if a preloaded module instantiated some multiprocessing objects such as locks.

- bpo-28847: dbm.dumb now supports reading read-only files and no longer writes the index file when it is not changed.

- bpo-26937: The chown() method of the tarfile.TarFile class does not fail now when the grp module cannot be imported, as for example on Android platforms.

### IDLE

- bpo-29071: IDLE colors f-string prefixes (but not invalid ur prefixes).

- bpo-28572: Add 10% to coverage of IDLE’s test_configdialog. Update and augment description of the configuration system.

### Windows

- bpo-29579: Removes readme.txt from the installer

- bpo-29326: Ignores blank lines in ._pth files (Patch by Alexey Izbyshev)

- bpo-28164: Correctly handle special console filenames (patch by Eryk Sun)

- bpo-29409: Implement PEP 529 for io.FileIO (Patch by Eryk Sun)

- bpo-29392: Prevent crash when passing invalid arguments into msvcrt module.

- bpo-25778: winreg does not truncate string correctly (Patch by Eryk Sun)

- bpo-28896: Deprecate WindowsRegistryFinder and disable it by default.

### C API

- bpo-27867: Function PySlice_GetIndicesEx() is replaced with a macro if Py_LIMITED_API is not set or set to the value between 0x03050400 and 0x03060000 (not including) or 0x03060100 or higher.

- bpo-29083: Fixed the declaration of some public API functions. PyArg_VaParse() and PyArg_VaParseTupleAndKeywords() were not available in limited API. PyArg_ValidateKeywordArguments(), PyArg_UnpackTuple() and Py_BuildValue() were not available in limited API of version < 3.3 when PY_SSIZE_T_CLEAN is defined.

- bpo-29058: All stable API extensions added after Python 3.2 are now available only when Py_LIMITED_API is set to the PY_VERSION_HEX value of the minimum Python version supporting this API.

### Documentation

- bpo-28929: Link the documentation to its source file on GitHub.

- bpo-25008: Document smtpd.py as effectively deprecated and add a pointer to aiosmtpd, a third-party asyncio-based replacement.

- bpo-26355: Add canonical header link on each page to corresponding major version of the documentation. Patch by Matthias Bussonnier.

- bpo-29349: Fix Python 2 syntax in code for building the documentation.

### Tests

- bpo-28087: Skip test_asyncore and test_eintr poll failures on macOS. Skip some tests of select.poll when running on macOS due to unresolved issues with the underlying system poll function on some macOS versions.

- bpo-29571: to match the behaviour of the `re.LOCALE` flag, test_re.test_locale_flag now uses `locale.getpreferredencoding(False)` to determine the candidate encoding for the test regex (allowing it to correctly skip the test when the default locale encoding is a multi-byte encoding)

- bpo-28950: Disallow -j0 to be combined with -T/-l in regrtest command line arguments.

- bpo-28683: Fix the tests that bind() a unix socket and raise PermissionError on Android for a non-root user.

- bpo-26939: Add the support.setswitchinterval() function to fix test_functools hanging on the Android armv7 qemu emulator.

### Build

- bpo-27593: sys.version and the platform module python_build(), python_branch(), and python_revision() functions now use git information rather than hg when building from a repo.

- bpo-29572: Update Windows build and OS X installers to use OpenSSL 1.0.2k.

- bpo-26851: Set Android compilation and link flags.

- bpo-28768: Fix implicit declaration of function _setmode. Patch by Masayuki Yamamoto

- bpo-29080: Removes hard dependency on hg.exe from PCBuild/build.bat

- bpo-23903: Added missed names to PC/python3.def.

- bpo-28762: lockf() is available on Android API level 24, but the F_LOCK macro is not defined in android-ndk-r13.

- bpo-28538: Fix the compilation error that occurs because if_nameindex() is available on Android API level 24, but the if_nameindex structure is not defined.

- bpo-20211: Do not add the directory for installing C header files and the directory for installing object code libraries to the cross compilation search paths. Original patch by Thomas Petazzoni.

- bpo-28849: Do not define sys.implementation._multiarch on Android.

## Python 3.6.0 final

Release date: 2016-12-23

No changes since release candidate 2

## Python 3.6.0 release candidate 2

Release date: 2016-12-16

### Core and Builtins

- bpo-28147: Fix a memory leak in split-table dictionaries: setattr() must not convert combined table into split table. Patch written by INADA Naoki.

- bpo-28990: Fix asyncio SSL hanging if connection is closed before handshake is completed. (Patch by HoHo-Ho)

### Tools/Demos

- bpo-28770: Fix python-gdb.py for fastcalls.

### Windows

- bpo-28896: Deprecate WindowsRegistryFinder.

### Build

- bpo-28898: Prevent gdb build errors due to HAVE_LONG_LONG redefinition.

## Python 3.6.0 release candidate 1

Release date: 2016-12-06

### Core and Builtins

- bpo-23722: Rather than silently producing a class that doesn’t support zero-argument `super()` in methods, failing to pass the new `__classcell__` namespace entry up to `type.__new__` now results in a `DeprecationWarning` and a class that supports zero-argument `super()`.

- bpo-28797: Modifying the class __dict__ inside the __set_name__ method of a descriptor that is used inside that class no longer prevents calling the __set_name__ method of other descriptors.

- bpo-28782: Fix a bug in the implementation `yield from` when checking if the next instruction is YIELD_FROM. Regression introduced by WORDCODE (bpo-26647).

### Library

- bpo-27030: Unknown escapes in re.sub() replacement template are allowed again. But they still are deprecated and will be disabled in 3.7.

- bpo-28835: Fix a regression introduced in warnings.catch_warnings(): call warnings.showwarning() if it was overridden inside the context manager.

- bpo-27172: To assist with upgrades from 2.7, the previously documented deprecation of `inspect.getfullargspec()` has been reversed. This decision may be revisited again after the Python 2.7 branch is no longer officially supported.

- bpo-26273: Add new `socket.TCP_CONGESTION` (Linux 2.6.13) and `socket.TCP_USER_TIMEOUT` (Linux 2.6.37) constants. Patch written by Omar Sandoval.

- bpo-24142: Reading a corrupt config file left configparser in an invalid state. Original patch by Florian Höch.

- bpo-28843: Fix asyncio C Task to handle exceptions __traceback__.

### C API

- bpo-28808: PyUnicode_CompareWithASCIIString() now never raises exceptions.

### Documentation

- bpo-23722: The data model reference and the porting section in the What’s New guide now cover the additional `__classcell__` handling needed for custom metaclasses to fully support PEP 487 and zero-argument `super()`.

### Tools/Demos

- bpo-28023: Fix python-gdb.py didn’t support new dict implementation.

## Python 3.6.0 beta 4

Release date: 2016-11-21

### Core and Builtins

- bpo-28532: Show sys.version when -V option is supplied twice.

- bpo-27100: The with-statement now checks for __enter__ before it checks for __exit__. This gives less confusing error messages when both methods are missing. Patch by Jonathan Ellington.

- bpo-28746: Fix the set_inheritable() file descriptor method on platforms that do not have the ioctl FIOCLEX and FIONCLEX commands.

- bpo-26920: Fix not getting the locale’s charset upon initializing the interpreter, on platforms that do not have langinfo.

- bpo-28648: Fixed crash in Py_DecodeLocale() in debug build on Mac OS X when decode astral characters. Patch by Xiang Zhang.

- bpo-19398: Extra slash no longer added to sys.path components in case of empty compile-time PYTHONPATH components.

- bpo-28665: Improve speed of the STORE_DEREF opcode by 40%.

- bpo-28583: PyDict_SetDefault didn’t combine split table when needed. Patch by Xiang Zhang.

- bpo-27243: Change PendingDeprecationWarning -> DeprecationWarning. As it was agreed in the issue, __aiter__ returning an awaitable should result in PendingDeprecationWarning in 3.5 and in DeprecationWarning in 3.6.

- bpo-26182: Fix a refleak in code that raises DeprecationWarning.

- bpo-28721: Fix asynchronous generators aclose() and athrow() to handle StopAsyncIteration propagation properly.

### Library

- bpo-28752: Restored the __reduce__() methods of datetime objects.

- bpo-28727: Regular expression patterns, _sre.SRE_Pattern objects created by re.compile(), become comparable (only x==y and x!=y operators). This change should fix the bpo-18383: don’t duplicate warning filters when the warnings module is reloaded (thing usually only done in unit tests).

- bpo-20572: The subprocess.Popen.wait method’s undocumented endtime parameter now raises a DeprecationWarning.

- bpo-25659: In ctypes, prevent a crash calling the from_buffer() and from_buffer_copy() methods on abstract classes like Array.

- bpo-19717: Makes Path.resolve() succeed on paths that do not exist. Patch by Vajrasky Kok

- bpo-28563: Fixed possible DoS and arbitrary code execution when handle plural form selections in the gettext module. The expression parser now supports exact syntax supported by GNU gettext.

- bpo-28387: Fixed possible crash in _io.TextIOWrapper deallocator when the garbage collector is invoked in other thread. Based on patch by Sebastian Cufre.

- bpo-28600: Optimize loop.call_soon.

- bpo-28613: Fix get_event_loop() return the current loop if called from coroutines/callbacks.

- bpo-28634: Fix asyncio.isfuture() to support unittest.Mock.

- bpo-26081: Fix refleak in _asyncio.Future.__iter__().throw.

- bpo-28639: Fix inspect.isawaitable to always return bool Patch by Justin Mayfield.

- bpo-28652: Make loop methods reject socket kinds they do not support.

- bpo-28653: Fix a refleak in functools.lru_cache.

- bpo-28703: Fix asyncio.iscoroutinefunction to handle Mock objects.

- bpo-28704: Fix create_unix_server to support Path-like objects (PEP 519).

- bpo-28720: Add collections.abc.AsyncGenerator.

### Documentation

- bpo-28513: Documented command-line interface of zipfile.

### Tests

- bpo-28666: Now test.support.rmtree is able to remove unwritable or unreadable directories.

- bpo-23839: Various caches now are cleared before running every test file.

### Build

- bpo-10656: Fix out-of-tree building on AIX. Patch by Tristan Carel and Michael Haubenwallner.

- bpo-26359: Rename –with-optimiations to –enable-optimizations.

- bpo-28676: Prevent missing ‘getentropy’ declaration warning on macOS. Patch by Gareth Rees.

## Python 3.6.0 beta 3

Release date: 2016-10-31

### Core and Builtins

- bpo-28128: Deprecation warning for invalid str and byte escape sequences now prints better information about where the error occurs. Patch by Serhiy Storchaka and Eric Smith.

- bpo-28509: dict.update() no longer allocate unnecessary large memory.

- bpo-28426: Fixed potential crash in PyUnicode_AsDecodedObject() in debug build.

- bpo-28517: Fixed of-by-one error in the peephole optimizer that caused keeping unreachable code.

- bpo-28214: Improved exception reporting for problematic __set_name__ attributes.

- bpo-23782: Fixed possible memory leak in _PyTraceback_Add() and exception loss in PyTraceBack_Here().

- bpo-28471: Fix “Python memory allocator called without holding the GIL” crash in socket.setblocking.

### Library

- bpo-27517: LZMA compressor and decompressor no longer raise exceptions if given empty data twice. Patch by Benjamin Fogle.

- bpo-28549: Fixed segfault in curses’s addch() with ncurses6.

- bpo-28449: tarfile.open() with mode “r” or “r:” now tries to open a tar file with compression before trying to open it without compression. Otherwise it had 50% chance failed with ignore_zeros=True.

- bpo-23262: The webbrowser module now supports Firefox 36+ and derived browsers. Based on patch by Oleg Broytman.

- bpo-27939: Fixed bugs in tkinter.ttk.LabeledScale and tkinter.Scale caused by representing the scale as float value internally in Tk. tkinter.IntVar now works if float value is set to underlying Tk variable.

- bpo-18844: The various ways of specifying weights for random.choices() now produce the same result sequences.

- bpo-28255: calendar.TextCalendar().prmonth() no longer prints a space at the start of new line after printing a month’s calendar. Patch by Xiang Zhang.

- bpo-20491: The textwrap.TextWrapper class now honors non-breaking spaces. Based on patch by Kaarle Ritvanen.

- bpo-28353: os.fwalk() no longer fails on broken links.

- bpo-28430: Fix iterator of C implemented asyncio.Future doesn’t accept non-None value is passed to it.send(val).

- bpo-27025: Generated names for Tkinter widgets now start by the “!” prefix for readability.

- bpo-25464: Fixed HList.header_exists() in tkinter.tix module by addin a workaround to Tix library bug.

- bpo-28488: shutil.make_archive() no longer adds entry “./” to ZIP archive.

- bpo-25953: re.sub() now raises an error for invalid numerical group reference in replacement template even if the pattern is not found in the string. Error message for invalid group reference now includes the group index and the position of the reference. Based on patch by SilentGhost.

- bpo-18219: Optimize csv.DictWriter for large number of columns. Patch by Mariatta Wijaya.

- bpo-28448: Fix C implemented asyncio.Future didn’t work on Windows.

- bpo-28480: Fix error building socket module when multithreading is disabled.

- bpo-24452: Make webbrowser support Chrome on Mac OS X.

- bpo-20766: Fix references leaked by pdb in the handling of SIGINT handlers.

- bpo-28492: Fix how StopIteration exception is raised in _asyncio.Future.

- bpo-28500: Fix asyncio to handle async gens GC from another thread.

- bpo-26923: Fix asyncio.Gather to refuse being cancelled once all children are done. Patch by Johannes Ebke.

- bpo-26796: Don’t configure the number of workers for default threadpool executor. Initial patch by Hans Lawrenz.

- bpo-28544: Implement asyncio.Task in C.

### Windows

- bpo-28522: Fixes mishandled buffer reallocation in getpathp.c

### Build

- bpo-28444: Fix missing extensions modules when cross compiling.

- bpo-28208: Update Windows build and OS X installers to use SQLite 3.14.2.

- bpo-28248: Update Windows build and OS X installers to use OpenSSL 1.0.2j.

### Tests

- bpo-26944: Fix test_posix for Android where ‘id -G’ is entirely wrong or missing the effective gid.

- bpo-28409: regrtest: fix the parser of command line arguments.

## Python 3.6.0 beta 2

Release date: 2016-10-10

### Core and Builtins

- bpo-28183: Optimize and cleanup dict iteration.

- bpo-26081: Added C implementation of asyncio.Future. Original patch by Yury Selivanov.

- bpo-28379: Added sanity checks and tests for PyUnicode_CopyCharacters(). Patch by Xiang Zhang.

- bpo-28376: The type of long range iterator is now registered as Iterator. Patch by Oren Milman.

- bpo-28376: Creating instances of range_iterator by calling range_iterator type now is deprecated. Patch by Oren Milman.

- bpo-28376: The constructor of range_iterator now checks that step is not 0. Patch by Oren Milman.

- bpo-26906: Resolving special methods of uninitialized type now causes implicit initialization of the type instead of a fail.

- bpo-18287: PyType_Ready() now checks that tp_name is not NULL. Original patch by Niklas Koep.

- bpo-24098: Fixed possible crash when AST is changed in process of compiling it.

- bpo-28201: Dict reduces possibility of 2nd conflict in hash table when hashes have same lower bits.

- bpo-28350: String constants with null character no longer interned.

- bpo-26617: Fix crash when GC runs during weakref callbacks.

- bpo-27942: String constants now interned recursively in tuples and frozensets.

- bpo-21578: Fixed misleading error message when ImportError called with invalid keyword args.

- bpo-28203: Fix incorrect type in complex(1.0, {2:3}) error message. Patch by Soumya Sharma.

- bpo-28086: Single var-positional argument of tuple subtype was passed unscathed to the C-defined function. Now it is converted to exact tuple.

- bpo-28214: Now __set_name__ is looked up on the class instead of the instance.

- bpo-27955: Fallback on reading /dev/urandom device when the getrandom() syscall fails with EPERM, for example when blocked by SECCOMP.

- bpo-28192: Don’t import readline in isolated mode.

- Upgrade internal unicode databases to Unicode version 9.0.0.

- bpo-28131: Fix a regression in zipimport’s compile_source(). zipimport should use the same optimization level as the interpreter.

- bpo-28126: Replace Py_MEMCPY with memcpy(). Visual Studio can properly optimize memcpy().

- bpo-28120: Fix dict.pop() for splitted dictionary when trying to remove a “pending key” (Not yet inserted in split-table). Patch by Xiang Zhang.

- bpo-26182: Raise DeprecationWarning when async and await keywords are used as variable/attribute/class/function name.

### Library

- bpo-27998: Fixed bytes path support in os.scandir() on Windows. Patch by Eryk Sun.

- bpo-28317: The disassembler now decodes FORMAT_VALUE argument.

- bpo-26293: Fixed writing ZIP files that starts not from the start of the file. Offsets in ZIP file now are relative to the start of the archive in conforming to the specification.

- bpo-28380: unittest.mock Mock autospec functions now properly support assert_called, assert_not_called, and assert_called_once.

- bpo-27181: remove statistics.geometric_mean and defer until 3.7.

- bpo-28229: lzma module now supports pathlib.

- bpo-28321: Fixed writing non-BMP characters with binary format in plistlib.

- bpo-28225: bz2 module now supports pathlib. Initial patch by Ethan Furman.

- bpo-28227: gzip now supports pathlib. Patch by Ethan Furman.

- bpo-27358: Optimized merging var-keyword arguments and improved error message when passing a non-mapping as a var-keyword argument.

- bpo-28257: Improved error message when passing a non-iterable as a var-positional argument. Added opcode BUILD_TUPLE_UNPACK_WITH_CALL.

- bpo-28322: Fixed possible crashes when unpickle itertools objects from incorrect pickle data. Based on patch by John Leitch.

- bpo-28228: imghdr now supports pathlib.

- bpo-28226: compileall now supports pathlib.

- bpo-28314: Fix function declaration (C flags) for the getiterator() method of xml.etree.ElementTree.Element.

- bpo-28148: Stop using localtime() and gmtime() in the time module. Introduced platform independent _PyTime_localtime API that is similar to POSIX localtime_r, but available on all platforms. Patch by Ed Schouten.

- bpo-28253: Fixed calendar functions for extreme months: 0001-01 and 9999-12. Methods itermonthdays() and itermonthdays2() are reimplemented so that they don’t call itermonthdates() which can cause datetime.date under/overflow.

- bpo-28275: Fixed possible use after free in the decompress() methods of the LZMADecompressor and BZ2Decompressor classes. Original patch by John Leitch.

- bpo-27897: Fixed possible crash in sqlite3.Connection.create_collation() if pass invalid string-like object as a name. Patch by Xiang Zhang.

- bpo-18844: random.choices() now has k as a keyword-only argument to improve the readability of common cases and come into line with the signature used in other languages.

- bpo-18893: Fix invalid exception handling in Lib/ctypes/macholib/dyld.py. Patch by Madison May.

- bpo-27611: Fixed support of default root window in the tkinter.tix module. Added the master parameter in the DisplayStyle constructor.

- bpo-27348: In the traceback module, restore the formatting of exception messages like “Exception: None”. This fixes a regression introduced in 3.5a2.

- bpo-25651: Allow falsy values to be used for msg parameter of subTest().

- bpo-27778: Fix a memory leak in os.getrandom() when the getrandom() is interrupted by a signal and a signal handler raises a Python exception.

- bpo-28200: Fix memory leak on Windows in the os module (fix path_converter() function).

- bpo-25400: RobotFileParser now correctly returns default values for crawl_delay and request_rate. Initial patch by Peter Wirtz.

- bpo-27932: Prevent memory leak in win32_ver().

- Fix UnboundLocalError in socket._sendfile_use_sendfile.

- bpo-28075: Check for ERROR_ACCESS_DENIED in Windows implementation of os.stat(). Patch by Eryk Sun.

- bpo-22493: Warning message emitted by using inline flags in the middle of regular expression now contains a (truncated) regex pattern. Patch by Tim Graham.

- bpo-25270: Prevent codecs.escape_encode() from raising SystemError when an empty bytestring is passed.

- bpo-28181: Get antigravity over HTTPS. Patch by Kaartic Sivaraam.

- bpo-25895: Enable WebSocket URL schemes in urllib.parse.urljoin. Patch by Gergely Imreh and Markus Holtermann.

- bpo-28114: Fix a crash in parse_envlist() when env contains byte strings. Patch by Eryk Sun.

- bpo-27599: Fixed buffer overrun in binascii.b2a_qp() and binascii.a2b_qp().

- bpo-27906: Fix socket accept exhaustion during high TCP traffic. Patch by Kevin Conway.

- bpo-28174: Handle when SO_REUSEPORT isn’t properly supported. Patch by Seth Michael Larson.

- bpo-26654: Inspect functools.partial in asyncio.Handle.__repr__. Patch by iceboy.

- bpo-26909: Fix slow pipes IO in asyncio. Patch by INADA Naoki.

- bpo-28176: Fix callbacks race in asyncio.SelectorLoop.sock_connect.

- bpo-27759: Fix selectors incorrectly retain invalid file descriptors. Patch by Mark Williams.

- bpo-28368: Refuse monitoring processes if the child watcher has no loop attached. Patch by Vincent Michel.

- bpo-28369: Raise RuntimeError when transport’s FD is used with add_reader, add_writer, etc.

- bpo-28370: Speedup asyncio.StreamReader.readexactly. Patch by Коренберг Марк.

- bpo-28371: Deprecate passing asyncio.Handles to run_in_executor.

- bpo-28372: Fix asyncio to support formatting of non-python coroutines.

- bpo-28399: Remove UNIX socket from FS before binding. Patch by Коренберг Марк.

- bpo-27972: Prohibit Tasks to await on themselves.

### Windows

- bpo-28402: Adds signed catalog files for stdlib on Windows.

- bpo-28333: Enables Unicode for ps1/ps2 and input() prompts. (Patch by Eryk Sun)

- bpo-28251: Improvements to help manuals on Windows.

- bpo-28110: launcher.msi has different product codes between 32-bit and 64-bit

- bpo-28161: Opening CON for write access fails

- bpo-28162: WindowsConsoleIO readall() fails if first line starts with Ctrl+Z

- bpo-28163: WindowsConsoleIO fileno() passes wrong flags to _open_osfhandle

- bpo-28164: _PyIO_get_console_type fails for various paths

- bpo-28137: Renames Windows path file to ._pth

- bpo-28138: Windows ._pth file should allow import site

### C API

- bpo-28426: Deprecated undocumented functions PyUnicode_AsEncodedObject(), PyUnicode_AsDecodedObject(), PyUnicode_AsDecodedUnicode() and PyUnicode_AsEncodedUnicode().

### Build

- bpo-28258: Fixed build with Estonian locale (python-config and distclean targets in Makefile). Patch by Arfrever Frehtes Taifersar Arahesis.

- bpo-26661: setup.py now detects system libffi with multiarch wrapper.

- bpo-15819: Remove redundant include search directory option for building outside the source tree.

### Tests

- bpo-28217: Adds _testconsole module to test console input.

## Python 3.6.0 beta 1

Release date: 2016-09-12

### Core and Builtins

- bpo-23722: The __class__ cell used by zero-argument super() is now initialized from type.__new__ rather than __build_class__, so class methods relying on that will now work correctly when called from metaclass methods during class creation. Patch by Martin Teichmann.

- bpo-25221: Fix corrupted result from PyLong_FromLong(0) when Python is compiled with NSMALLPOSINTS = 0.

- bpo-27080: Implement formatting support for PEP 515. Initial patch by Chris Angelico.

- bpo-27199: In tarfile, expose copyfileobj bufsize to improve throughput. Patch by Jason Fried.

- bpo-27948: In f-strings, only allow backslashes inside the braces (where the expressions are). This is a breaking change from the 3.6 alpha releases, where backslashes are allowed anywhere in an f-string. Also, require that expressions inside f-strings be enclosed within literal braces, and not escapes like `f'\x7b"hi"\x7d'`.

- bpo-28046: Remove platform-specific directories from sys.path.

- bpo-28071: Add early-out for differencing from an empty set.

- bpo-25758: Prevents zipimport from unnecessarily encoding a filename (patch by Eryk Sun)

- bpo-25856: The __module__ attribute of extension classes and functions now is interned. This leads to more compact pickle data with protocol 4.

- bpo-27213: Rework CALL_FUNCTION* opcodes to produce shorter and more efficient bytecode. Patch by Demur Rumed, design by Serhiy Storchaka, reviewed by Serhiy Storchaka and Victor Stinner.

- bpo-26331: Implement tokenizing support for PEP 515. Patch by Georg Brandl.

- bpo-27999: Make “global after use” a SyntaxError, and ditto for nonlocal. Patch by Ivan Levkivskyi.

- bpo-28003: Implement PEP 525 – Asynchronous Generators.

- bpo-27985: Implement PEP 526 – Syntax for Variable Annotations. Patch by Ivan Levkivskyi.

- bpo-26058: Add a new private version to the builtin dict type, incremented at each dictionary creation and at each dictionary change. Implementation of the PEP 509.

- bpo-27364: A backslash-character pair that is not a valid escape sequence now generates a DeprecationWarning. Patch by Emanuel Barry.

- bpo-27350: `dict` implementation is changed like PyPy. It is more compact and preserves insertion order. (Concept developed by Raymond Hettinger and patch by Inada Naoki.)

- bpo-27911: Remove unnecessary error checks in `exec_builtin_or_dynamic()`.

- bpo-27078: Added BUILD_STRING opcode. Optimized f-strings evaluation.

- bpo-17884: Python now requires systems with inttypes.h and stdint.h

- bpo-27961: Require platforms to support `long long`. Python hasn’t compiled without `long long` for years, so this is basically a formality.

- bpo-27355: Removed support for Windows CE. It was never finished, and Windows CE is no longer a relevant platform for Python.

- Implement PEP 523.

- bpo-27870: A left shift of zero by a large integer no longer attempts to allocate large amounts of memory.

- bpo-25402: In int-to-decimal-string conversion, improve the estimate of the intermediate memory required, and remove an unnecessarily strict overflow check. Patch by Serhiy Storchaka.

- bpo-27214: In long_invert, be more careful about modifying object returned by long_add, and remove an unnecessary check for small longs. Thanks Oren Milman for analysis and patch.

- bpo-27506: Support passing the bytes/bytearray.translate() “delete” argument by keyword.

- bpo-27812: Properly clear out a generator’s frame’s backreference to the generator to prevent crashes in frame.clear().

- bpo-27811: Fix a crash when a coroutine that has not been awaited is finalized with warnings-as-errors enabled.

- bpo-27587: Fix another issue found by PVS-Studio: Null pointer check after use of ‘def’ in _PyState_AddModule(). Initial patch by Christian Heimes.

- bpo-27792: The modulo operation applied to `bool` and other `int` subclasses now always returns an `int`. Previously the return type depended on the input values. Patch by Xiang Zhang.

- bpo-26984: int() now always returns an instance of exact int.

- bpo-25604: Fix a minor bug in integer true division; this bug could potentially have caused off-by-one-ulp results on platforms with unreliable ldexp implementations.

- bpo-24254: Make class definition namespace ordered by default.

- bpo-27662: Fix an overflow check in `List_New`: the original code was checking against `Py_SIZE_MAX` instead of the correct upper bound of `Py_SSIZE_T_MAX`. Patch by Xiang Zhang.

- bpo-27782: Multi-phase extension module import now correctly allows the `m_methods` field to be used to add module level functions to instances of non-module types returned from `Py_create_mod`. Patch by Xiang Zhang.

- bpo-27936: The round() function accepted a second None argument for some types but not for others. Fixed the inconsistency by accepting None for all numeric types.

- bpo-27487: Warn if a submodule argument to “python -m” or runpy.run_module() is found in sys.modules after parent packages are imported, but before the submodule is executed.

- bpo-27157: Make only type() itself accept the one-argument form. Patch by Eryk Sun and Emanuel Barry.

- bpo-27558: Fix a SystemError in the implementation of “raise” statement. In a brand new thread, raise a RuntimeError since there is no active exception to reraise. Patch written by Xiang Zhang.

- bpo-28008: Implement PEP 530 – asynchronous comprehensions.

- bpo-27942: Fix memory leak in codeobject.c

### Library

- bpo-28732: Fix crash in os.spawnv() with no elements in args

- bpo-28485: Always raise ValueError for negative compileall.compile_dir(workers=…) parameter, even when multithreading is unavailable.

- bpo-28037: Use sqlite3_get_autocommit() instead of setting Connection->inTransaction manually.

- bpo-25283: Attributes tm_gmtoff and tm_zone are now available on all platforms in the return values of time.localtime() and time.gmtime().

- bpo-24454: Regular expression match object groups are now accessible using __getitem__. “mo[x]” is equivalent to “mo.group(x)”.

- bpo-10740: sqlite3 no longer implicitly commit an open transaction before DDL statements.

- bpo-17941: Add a module parameter to collections.namedtuple().

- bpo-22493: Inline flags now should be used only at the start of the regular expression. Deprecation warning is emitted if uses them in the middle of the regular expression.

- bpo-26885: xmlrpc now supports unmarshalling additional data types used by Apache XML-RPC implementation for numerics and None.

- bpo-28070: Fixed parsing inline verbose flag in regular expressions.

- bpo-19500: Add client-side SSL session resumption to the ssl module.

- bpo-28022: Deprecate ssl-related arguments in favor of SSLContext. The deprecation include manual creation of SSLSocket and certfile/keyfile (or similar) in ftplib, httplib, imaplib, smtplib, poplib and urllib.

- bpo-28043: SSLContext has improved default settings: OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION, OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE, OP_SINGLE_ECDH_USE and HIGH ciphers without MD5.

- bpo-24693: Changed some RuntimeError’s in the zipfile module to more appropriate types. Improved some error messages and debugging output.

- bpo-17909: `json.load` and `json.loads` now support binary input encoded as UTF-8, UTF-16 or UTF-32. Patch by Serhiy Storchaka.

- bpo-27137: the pure Python fallback implementation of `functools.partial` now matches the behaviour of its accelerated C counterpart for subclassing, pickling and text representation purposes. Patch by Emanuel Barry and Serhiy Storchaka.

- Fix possible integer overflows and crashes in the mmap module with unusual usage patterns.

- bpo-1703178: Fix the ability to pass the –link-objects option to the distutils build_ext command.

- bpo-28019: itertools.count() no longer rounds non-integer step in range between 1.0 and 2.0 to 1.

- bpo-18401: Pdb now supports the ‘readrc’ keyword argument to control whether .pdbrc files should be read. Patch by Martin Matusiak and Sam Kimbrel.

- bpo-25969: Update the lib2to3 grammar to handle the unpacking generalizations added in 3.5.

- bpo-14977: mailcap now respects the order of the lines in the mailcap files (“first match”), as required by RFC 1542. Patch by Michael Lazar.

- bpo-28082: Convert re flag constants to IntFlag.

- bpo-28025: Convert all ssl module constants to IntEnum and IntFlags. SSLContext properties now return flags and enums.

- bpo-23591: Add Flag, IntFlag, and auto() to enum module.

- bpo-433028: Added support of modifier spans in regular expressions.

- bpo-24594: Validates persist parameter when opening MSI database

- bpo-17582: xml.etree.ElementTree nows preserves whitespaces in attributes (Patch by Duane Griffin. Reviewed and approved by Stefan Behnel.)

- bpo-28047: Fixed calculation of line length used for the base64 CTE in the new email policies.

- bpo-27576: Fix call order in OrderedDict.__init__().

- email.generator.DecodedGenerator now supports the policy keyword.

- bpo-28027: Remove undocumented modules from `Lib/plat-*`: IN, CDROM, DLFCN, TYPES, CDIO, and STROPTS.

- bpo-27445: Don’t pass str(_charset) to MIMEText.set_payload(). Patch by Claude Paroz.

- bpo-24277: The new email API is no longer provisional, and the docs have been reorganized and rewritten to emphasize the new API.

- bpo-22450: urllib now includes an `Accept: */*` header among the default headers. This makes the results of REST API requests more consistent and predictable especially when proxy servers are involved.

- lib2to3.pgen3.driver.load_grammar() now creates a stable cache file between runs given the same Grammar.txt input regardless of the hash randomization setting.

- bpo-28005: Allow ImportErrors in encoding implementation to propagate.

- bpo-26667: Support path-like objects in importlib.util.

- bpo-27570: Avoid zero-length memcpy() etc calls with null source pointers in the “ctypes” and “array” modules.

- bpo-22233: Break email header lines only on the RFC specified CR and LF characters, not on arbitrary unicode line breaks. This also fixes a bug in HTTP header parsing.

- bpo-27331: The email.mime classes now all accept an optional policy keyword.

- bpo-27988: Fix email iter_attachments incorrect mutation of payload list.

- bpo-16113: Add SHA-3 and SHAKE support to hashlib module.

- Eliminate a tautological-pointer-compare warning in _scproxy.c.

- bpo-27776: The `os.urandom()` function does now block on Linux 3.17 and newer until the system urandom entropy pool is initialized to increase the security. This change is part of the PEP 524.

- bpo-27778: Expose the Linux `getrandom()` syscall as a new `os.getrandom()` function. This change is part of the PEP 524.

- bpo-27691: Fix ssl module’s parsing of GEN_RID subject alternative name fields in X.509 certs.

- bpo-18844: Add random.choices().

- bpo-25761: Improved error reporting about truncated pickle data in C implementation of unpickler. UnpicklingError is now raised instead of AttributeError and ValueError in some cases.

- bpo-26798: Add BLAKE2 (blake2b and blake2s) to hashlib.

- bpo-26032: Optimized globbing in pathlib by using os.scandir(); it is now about 1.5–4 times faster.

- bpo-25596: Optimized glob() and iglob() functions in the glob module; they are now about 3–6 times faster.

- bpo-27928: Add scrypt (password-based key derivation function) to hashlib module (requires OpenSSL 1.1.0).

- bpo-27850: Remove 3DES from ssl module’s default cipher list to counter measure sweet32 attack (CVE-2016-2183).

- bpo-27766: Add ChaCha20 Poly1305 to ssl module’s default cipher list. (Required OpenSSL 1.1.0 or LibreSSL).

- bpo-25387: Check return value of winsound.MessageBeep.

- bpo-27866: Add SSLContext.get_ciphers() method to get a list of all enabled ciphers.

- bpo-27744: Add AF_ALG (Linux Kernel crypto) to socket module.

- bpo-26470: Port ssl and hashlib module to OpenSSL 1.1.0.

- bpo-11620: Fix support for SND_MEMORY in winsound.PlaySound. Based on a patch by Tim Lesher.

- bpo-11734: Add support for IEEE 754 half-precision floats to the struct module. Based on a patch by Eli Stevens.

- bpo-27919: Deprecated `extra_path` distribution option in distutils packaging.

- bpo-23229: Add new `cmath` constants: `cmath.inf` and `cmath.nan` to match `math.inf` and `math.nan`, and also `cmath.infj` and `cmath.nanj` to match the format used by complex repr.

- bpo-27842: The csv.DictReader now returns rows of type OrderedDict. (Contributed by Steve Holden.)

- Remove support for passing a file descriptor to os.access. It never worked but previously didn’t raise.

- bpo-12885: Fix error when distutils encounters symlink.

- bpo-27881: Fixed possible bugs when setting sqlite3.Connection.isolation_level. Based on patch by Xiang Zhang.

- bpo-27861: Fixed a crash in sqlite3.Connection.cursor() when a factory creates not a cursor. Patch by Xiang Zhang.

- bpo-19884: Avoid spurious output on OS X with Gnu Readline.

- bpo-27706: Restore deterministic behavior of random.Random().seed() for string seeds using seeding version 1. Allows sequences of calls to random() to exactly match those obtained in Python 2. Patch by Nofar Schnider.

- bpo-10513: Fix a regression in Connection.commit(). Statements should not be reset after a commit.

- bpo-12319: Chunked transfer encoding support added to http.client.HTTPConnection requests. The urllib.request.AbstractHTTPHandler class does not enforce a Content-Length header any more. If a HTTP request has a file or iterable body, but no Content-Length header, the library now falls back to use chunked transfer-encoding.

- A new version of typing.py from https://github.com/python/typing: - Collection (only for 3.6) (bpo-27598) - Add FrozenSet to __all__ (upstream #261) - fix crash in _get_type_vars() (upstream #259) - Remove the dict constraint in ForwardRef._eval_type (upstream #252)

- bpo-27832: Make `_normalize` parameter to `Fraction` constructor keyword-only, so that `Fraction(2, 3, 4)` now raises `TypeError`.

- bpo-27539: Fix unnormalised `Fraction.__pow__` result in the case of negative exponent and negative base.

- bpo-21718: cursor.description is now available for queries using CTEs.

- bpo-27819: In distutils sdists, simply produce the “gztar” (gzipped tar format) distributions on all platforms unless “formats” is supplied.

- bpo-2466: posixpath.ismount now correctly recognizes mount points which the user does not have permission to access.

- bpo-9998: On Linux, ctypes.util.find_library now looks in LD_LIBRARY_PATH for shared libraries.

- bpo-27573: exit message for code.interact is now configurable.

- bpo-27930: Improved behaviour of logging.handlers.QueueListener. Thanks to Paulo Andrade and Petr Viktorin for the analysis and patch.

- bpo-6766: Distributed reference counting added to multiprocessing to support nesting of shared values / proxy objects.

- bpo-21201: Improves readability of multiprocessing error message. Thanks to Wojciech Walczak for patch.

- asyncio: Add set_protocol / get_protocol to Transports.

- bpo-27456: asyncio: Set TCP_NODELAY by default.

### IDLE

- bpo-15308: Add ‘interrupt execution’ (^C) to Shell menu. Patch by Roger Serwy, updated by Bayard Randel.

- bpo-27922: Stop IDLE tests from ‘flashing’ gui widgets on the screen.

- bpo-27891: Consistently group and sort imports within idlelib modules.

- bpo-17642: add larger font sizes for classroom projection.

- Add version to title of IDLE help window.

- bpo-25564: In section on IDLE – console differences, mention that using exec means that __builtins__ is defined for each statement.

- bpo-27821: Fix 3.6.0a3 regression that prevented custom key sets from being selected when no custom theme was defined.

### C API

- bpo-26900: Excluded underscored names and other private API from limited API.

- bpo-26027: Add support for path-like objects in PyUnicode_FSConverter() & PyUnicode_FSDecoder().

### Tests

- bpo-27427: Additional tests for the math module. Patch by Francisco Couzo.

- bpo-27953: Skip math and cmath tests that fail on OS X 10.4 due to a poor libm implementation of tan.

- bpo-26040: Improve test_math and test_cmath coverage and rigour. Patch by Jeff Allen.

- bpo-27787: Call gc.collect() before checking each test for “dangling threads”, since the dangling threads are weak references.

### Build

- bpo-27566: Fix clean target in freeze makefile (patch by Lisa Roach)

- bpo-27705: Update message in validate_ucrtbase.py

- bpo-27976: Deprecate building _ctypes with the bundled copy of libffi on non-OSX UNIX platforms.

- bpo-27983: Cause lack of llvm-profdata tool when using clang as required for PGO linking to be a configure time error rather than make time when `--with-optimizations` is enabled. Also improve our ability to find the llvm-profdata tool on MacOS and some Linuxes.

- bpo-21590: Support for DTrace and SystemTap probes.

- bpo-26307: The profile-opt build now applies PGO to the built-in modules.

- bpo-26359: Add the –with-optimizations flag to turn on LTO and PGO build support when available.

- bpo-27917: Set platform triplets for Android builds.

- bpo-25825: Update references to the $(LIBPL) installation path on AIX. This path was changed in 3.2a4.

- Update OS X installer to use SQLite 3.14.1 and XZ 5.2.2.

- bpo-21122: Fix LTO builds on OS X.

- bpo-17128: Build OS X installer with a private copy of OpenSSL. Also provide a sample Install Certificates command script to install a set of root certificates from the third-party certifi module.

### Tools/Demos

- bpo-27952: Get Tools/scripts/fixcid.py working with Python 3 and the current “re” module, avoid invalid Python backslash escapes, and fix a bug parsing escaped C quote signs.

### Windows

- bpo-28065: Update xz dependency to 5.2.2 and build it from source.

- bpo-25144: Ensures TargetDir is set before continuing with custom install.

- bpo-1602: Windows console doesn’t input or print Unicode (PEP 528)

- bpo-27781: Change file system encoding on Windows to UTF-8 (PEP 529)

- bpo-27731: Opt-out of MAX_PATH on Windows 10

- bpo-6135: Adds encoding and errors parameters to subprocess.

- bpo-27959: Adds oem encoding, alias ansi to mbcs, move aliasmbcs to codec lookup.

- bpo-27982: The functions of the winsound module now accept keyword arguments.

- bpo-20366: Build full text search support into SQLite on Windows.

- bpo-27756: Adds new icons for Python files and processes on Windows. Designs by Cherry Wang.

- bpo-27883: Update sqlite to 3.14.1.0 on Windows.

## Python 3.6.0 alpha 4

Release date: 2016-08-15

### Core and Builtins

- bpo-27704: Optimized creating bytes and bytearray from byte-like objects and iterables. Speed up to 3 times for short objects. Original patch by Naoki Inada.

- bpo-26823: Large sections of repeated lines in tracebacks are now abbreviated as “[Previous line repeated {count} more times]” by the builtin traceback rendering. Patch by Emanuel Barry.

- bpo-27574: Decreased an overhead of parsing keyword arguments in functions implemented with using Argument Clinic.

- bpo-22557: Now importing already imported modules is up to 2.5 times faster.

- bpo-17596: Include <wincrypt.h> to help with Min GW building.

- bpo-17599: On Windows, rename the privately defined REPARSE_DATA_BUFFER structure to avoid conflicting with the definition from Min GW.

- bpo-27507: Add integer overflow check in bytearray.extend(). Patch by Xiang Zhang.

- bpo-27581: Don’t rely on wrapping for overflow check in PySequence_Tuple(). Patch by Xiang Zhang.

- bpo-1621: Avoid signed integer overflow in list and tuple operations. Patch by Xiang Zhang.

- bpo-27419: Standard __import__() no longer look up “__import__” in globals or builtins for importing submodules or “from import”. Fixed a crash if raise a warning about unabling to resolve package from __spec__ or __package__.

- bpo-27083: Respect the PYTHONCASEOK environment variable under Windows.

- bpo-27514: Make having too many statically nested blocks a SyntaxError instead of SystemError.

- bpo-27366: Implemented PEP 487 (Simpler customization of class creation). Upon subclassing, the __init_subclass__ classmethod is called on the base class. Descriptors are initialized with __set_name__ after class creation.

### Library

- bpo-26027: Add PEP 519/__fspath__() support to the os and os.path modules. Includes code from Jelle Zijlstra. (See also: bpo-27524)

- bpo-27598: Add Collections to collections.abc. Patch by Ivan Levkivskyi, docs by Neil Girdhar.

- bpo-25958: Support “anti-registration” of special methods from various ABCs, like __hash__, __iter__ or __len__. All these (and several more) can be set to None in an implementation class and the behavior will be as if the method is not defined at all. (Previously, this mechanism existed only for __hash__, to make mutable classes unhashable.) Code contributed by Andrew Barnert and Ivan Levkivskyi.

- bpo-16764: Support keyword arguments to zlib.decompress(). Patch by Xiang Zhang.

- bpo-27736: Prevent segfault after interpreter re-initialization due to ref count problem introduced in code for bpo-27038 in 3.6.0a3. Patch by Xiang Zhang.

- bpo-25628: The verbose and rename parameters for collections.namedtuple are now keyword-only.

- bpo-12345: Add mathematical constant tau to math and cmath. See also PEP 628.

- bpo-26823: traceback.StackSummary.format now abbreviates large sections of repeated lines as “[Previous line repeated {count} more times]” (this change then further affects other traceback display operations in the module). Patch by Emanuel Barry.

- bpo-27664: Add to concurrent.futures.thread.ThreadPoolExecutor() the ability to specify a thread name prefix.

- bpo-27181: Add geometric_mean and harmonic_mean to statistics module.

- bpo-27573: code.interact now prints an message when exiting.

- bpo-6422: Add autorange method to timeit.Timer objects.

- bpo-27773: Correct some memory management errors server_hostname in _ssl.wrap_socket().

- bpo-26750: unittest.mock.create_autospec() now works properly for subclasses of property() and other data descriptors. Removes the never publicly used, never documented unittest.mock.DescriptorTypes tuple.

- bpo-26754: Undocumented support of general bytes-like objects as path in compile() and similar functions is now deprecated.

- bpo-26800: Undocumented support of general bytes-like objects as paths in os functions is now deprecated.

- bpo-26981: Add _order_ compatibility shim to enum.Enum for Python 2/3 code bases.

- bpo-27661: Added tzinfo keyword argument to datetime.combine.

- In the curses module, raise an error if window.getstr() or window.instr() is passed a negative value.

- bpo-27783: Fix possible usage of uninitialized memory in operator.methodcaller.

- bpo-27774: Fix possible Py_DECREF on unowned object in _sre.

- bpo-27760: Fix possible integer overflow in binascii.b2a_qp.

- bpo-27758: Fix possible integer overflow in the _csv module for large record lengths.

- bpo-27568: Prevent HTTPoxy attack (CVE-2016-1000110). Ignore the HTTP_PROXY variable when REQUEST_METHOD environment is set, which indicates that the script is in CGI mode.

- bpo-7063: Remove dead code from the “array” module’s slice handling. Patch by Chuck.

- bpo-27656: Do not assume sched.h defines any SCHED_* constants.

- bpo-27130: In the “zlib” module, fix handling of large buffers (typically 4 GiB) when compressing and decompressing. Previously, inputs were limited to 4 GiB, and compression and decompression operations did not properly handle results of 4 GiB.

- bpo-24773: Implemented PEP 495 (Local Time Disambiguation).

- Expose the EPOLLEXCLUSIVE constant (when it is defined) in the select module.

- bpo-27567: Expose the EPOLLRDHUP and POLLRDHUP constants in the select module.

- bpo-1621: Avoid signed int negation overflow in the “audioop” module.

- bpo-27533: Release GIL in nt._isdir

- bpo-17711: Fixed unpickling by the persistent ID with protocol 0. Original patch by Alexandre Vassalotti.

- bpo-27522: Avoid an unintentional reference cycle in email.feedparser.

- bpo-27512: Fix a segfault when os.fspath() called an __fspath__() method that raised an exception. Patch by Xiang Zhang.

### IDLE

- bpo-27714: text_textview and test_autocomplete now pass when re-run in the same process. This occurs when test_idle fails when run with the -w option but without -jn. Fix warning from test_config.

- bpo-27621: Put query response validation error messages in the query box itself instead of in a separate messagebox. Redo tests to match. Add Mac OSX refinements. Original patch by Mark Roseman.

- bpo-27620: Escape key now closes Query box as cancelled.

- bpo-27609: IDLE: tab after initial whitespace should tab, not autocomplete. This fixes problem with writing docstrings at least twice indented.

- bpo-27609: Explicitly return None when there are also non-None returns. In a few cases, reverse a condition and eliminate a return.

- bpo-25507: IDLE no longer runs buggy code because of its tkinter imports. Users must include the same imports required to run directly in Python.

- bpo-27173: Add ‘IDLE Modern Unix’ to the built-in key sets. Make the default key set depend on the platform. Add tests for the changes to the config module.

- bpo-27452: add line counter and crc to IDLE configHandler test dump.

### Tests

- bpo-25805: Skip a test in test_pkgutil as needed that doesn’t work when `__name__ == __main__`. Patch by SilentGhost.

- bpo-27472: Add test.support.unix_shell as the path to the default shell.

- bpo-27369: In test_pyexpat, avoid testing an error message detail that changed in Expat 2.2.0.

- bpo-27594: Prevent assertion error when running test_ast with coverage enabled: ensure code object has a valid first line number. Patch suggested by Ivan Levkivskyi.

### Windows

- bpo-27647: Update bundled Tcl/Tk to 8.6.6.

- bpo-27610: Adds PEP 514 metadata to Windows installer

- bpo-27469: Adds a shell extension to the launcher so that drag and drop works correctly.

- bpo-27309: Enables proper Windows styles in python[w].exe manifest.

### Build

- bpo-27713: Suppress spurious build warnings when updating importlib’s bootstrap files. Patch by Xiang Zhang

- bpo-25825: Correct the references to Modules/python.exp, which is required on AIX. The references were accidentally changed in 3.5.0a1.

- bpo-27453: CPP invocation in configure must use CPPFLAGS. Patch by Chi Hsuan Yen.

- bpo-27641: The configure script now inserts comments into the makefile to prevent the pgen and _freeze_importlib executables from being cross-compiled.

- bpo-26662: Set PYTHON_FOR_GEN in configure as the Python program to be used for file generation during the build.

- bpo-10910: Avoid C++ compilation errors on FreeBSD and OS X. Also update FreedBSD version checks for the original ctype UTF-8 workaround.

## Python 3.6.0 alpha 3

Release date: 2016-07-11

### Core and Builtins

- bpo-27473: Fixed possible integer overflow in bytes and bytearray concatenations. Patch by Xiang Zhang.

- bpo-23034: The output of a special Python build with defined COUNT_ALLOCS, SHOW_ALLOC_COUNT or SHOW_TRACK_COUNT macros is now off by default. It can be re-enabled using the “-X showalloccount” option. It now outputs to stderr instead of stdout.

- bpo-27443: __length_hint__() of bytearray iterators no longer return a negative integer for a resized bytearray.

- bpo-27007: The fromhex() class methods of bytes and bytearray subclasses now return an instance of corresponding subclass.

### Library

- bpo-26844: Fix error message for imp.find_module() to refer to ‘path’ instead of ‘name’. Patch by Lev Maximov.

- bpo-23804: Fix SSL zero-length recv() calls to not block and not raise an error about unclean EOF.

- bpo-27466: Change time format returned by http.cookie.time2netscape, confirming the netscape cookie format and making it consistent with documentation.

- bpo-21708: Deprecated dbm.dumb behavior that differs from common dbm behavior: creating a database in ‘r’ and ‘w’ modes and modifying a database in ‘r’ mode.

- bpo-26721: Change the socketserver.StreamRequestHandler.wfile attribute to implement BufferedIOBase. In particular, the write() method no longer does partial writes.

- bpo-22115: Added methods trace_add, trace_remove and trace_info in the tkinter.Variable class. They replace old methods trace_variable, trace, trace_vdelete and trace_vinfo that use obsolete Tcl commands and might not work in future versions of Tcl. Fixed old tracing methods: trace_vdelete() with wrong mode no longer break tracing, trace_vinfo() now always returns a list of pairs of strings, tracing in the “u” mode now works.

- bpo-26243: Only the level argument to zlib.compress() is keyword argument now. The first argument is positional-only.

- bpo-27038: Expose the DirEntry type as os.DirEntry. Code patch by Jelle Zijlstra.

- bpo-27186: Update os.fspath()/PyOS_FSPath() to check the return value of __fspath__() to be either str or bytes.

- bpo-18726: All optional parameters of the dump(), dumps(), load() and loads() functions and JSONEncoder and JSONDecoder class constructors in the json module are now keyword-only.

- bpo-27319: Methods selection_set(), selection_add(), selection_remove() and selection_toggle() of ttk.TreeView now allow passing multiple items as multiple arguments instead of passing them as a tuple. Deprecated undocumented ability of calling the selection() method with arguments.

- bpo-27079: Fixed curses.ascii functions isblank(), iscntrl() and ispunct().

- bpo-27294: Numerical state in the repr for Tkinter event objects is now represented as a combination of known flags.

- bpo-27177: Match objects in the re module now support index-like objects as group indices. Based on patches by Jeroen Demeyer and Xiang Zhang.

- bpo-26754: Some functions (compile() etc) accepted a filename argument encoded as an iterable of integers. Now only strings and byte-like objects are accepted.

- bpo-26536: socket.ioctl now supports SIO_LOOPBACK_FAST_PATH. Patch by Daniel Stokes.

- bpo-27048: Prevents distutils failing on Windows when environment variables contain non-ASCII characters

- bpo-27330: Fixed possible leaks in the ctypes module.

- bpo-27238: Got rid of bare excepts in the turtle module. Original patch by Jelle Zijlstra.

- bpo-27122: When an exception is raised within the context being managed by a contextlib.ExitStack() and one of the exit stack generators catches and raises it in a chain, do not re-raise the original exception when exiting, let the new chained one through. This avoids the PEP 479 bug described in issue25782.

### Security

- bpo-27278: Fix os.urandom() implementation using getrandom() on Linux. Truncate size to INT_MAX and loop until we collected enough random bytes, instead of casting a directly Py_ssize_t to int.

### Library

- bpo-16864: sqlite3.Cursor.lastrowid now supports REPLACE statement. Initial patch by Alex LordThorsen.

- bpo-26386: Fixed ttk.TreeView selection operations with item id’s containing spaces.

- bpo-8637: Honor a pager set by the env var MANPAGER (in preference to one set by the env var PAGER).

### Security

- bpo-22636: Avoid shell injection problems with ctypes.util.find_library().

### Library

- bpo-16182: Fix various functions in the “readline” module to use the locale encoding, and fix get_begidx() and get_endidx() to return code point indexes.

- bpo-27392: Add loop.connect_accepted_socket(). Patch by Jim Fulton.

### IDLE

- bpo-27477: IDLE search dialogs now use ttk widgets.

- bpo-27173: Add ‘IDLE Modern Unix’ to the built-in key sets. Make the default key set depend on the platform. Add tests for the changes to the config module.

- bpo-27452: make command line “idle-test> python test_help.py” work. __file__ is relative when python is started in the file’s directory.

- bpo-27452: add line counter and crc to IDLE configHandler test dump.

- bpo-27380: IDLE: add query.py with base Query dialog and ttk widgets. Module had subclasses SectionName, ModuleName, and HelpSource, which are used to get information from users by configdialog and file =>Load Module. Each subclass has itw own validity checks. Using ModuleName allows users to edit bad module names instead of starting over. Add tests and delete the two files combined into the new one.

- bpo-27372: Test_idle no longer changes the locale.

- bpo-27365: Allow non-ascii chars in IDLE NEWS.txt, for contributor names.

- bpo-27245: IDLE: Cleanly delete custom themes and key bindings. Previously, when IDLE was started from a console or by import, a cascade of warnings was emitted. Patch by Serhiy Storchaka.

- bpo-24137: Run IDLE, test_idle, and htest with tkinter default root disabled. Fix code and tests that fail with this restriction. Fix htests to not create a second and redundant root and mainloop.

- bpo-27310: Fix IDLE.app failure to launch on OS X due to vestigial import.

### C API

- bpo-26754: PyUnicode_FSDecoder() accepted a filename argument encoded as an iterable of integers. Now only strings and byte-like objects are accepted.

### Build

- bpo-28066: Fix the logic that searches build directories for generated include files when building outside the source tree.

- bpo-27442: Expose the Android API level that python was built against, in sysconfig.get_config_vars() as ‘ANDROID_API_LEVEL’.

- bpo-27434: The interpreter that runs the cross-build, found in PATH, must now be of the same feature version (e.g. 3.6) as the source being built.

- bpo-26930: Update Windows builds to use OpenSSL 1.0.2h.

- bpo-23968: Rename the platform directory from plat-$(MACHDEP) to plat-$(PLATFORM_TRIPLET). Rename the config directory (LIBPL) from config-$(LDVERSION) to config-$(LDVERSION)-$(PLATFORM_TRIPLET). Install the platform specific _sysconfigdata module into the platform directory and rename it to include the ABIFLAGS.

- Don’t use largefile support for GNU/Hurd.

### Tools/Demos

- bpo-27332: Fixed the type of the first argument of module-level functions generated by Argument Clinic. Patch by Petr Viktorin.

- bpo-27418: Fixed Tools/importbench/importbench.py.

### Documentation

- bpo-19489: Moved the search box from the sidebar to the header and footer of each page. Patch by Ammar Askar.

- bpo-27285: Update documentation to reflect the deprecation of `pyvenv` and normalize on the term “virtual environment”. Patch by Steve Piercy.

### Tests

- bpo-27027: Added test.support.is_android that is True when this is an Android build.

## Python 3.6.0 alpha 2

Release date: 2016-06-13

### Core and Builtins

- bpo-27095: Simplified MAKE_FUNCTION and removed MAKE_CLOSURE opcodes. Patch by Demur Rumed.

- bpo-27190: Raise NotSupportedError if sqlite3 is older than 3.3.1. Patch by Dave Sawyer.

- bpo-27286: Fixed compiling BUILD_MAP_UNPACK_WITH_CALL opcode. Calling function with generalized unpacking (PEP 448) and conflicting keyword names could cause undefined behavior.

- bpo-27140: Added BUILD_CONST_KEY_MAP opcode.

- bpo-27186: Add support for os.PathLike objects to open() (part of PEP 519).

- bpo-27066: Fixed SystemError if a custom opener (for open()) returns a negative number without setting an exception.

- bpo-26983: float() now always return an instance of exact float. The deprecation warning is emitted if __float__ returns an instance of a strict subclass of float. In a future versions of Python this can be an error.

- bpo-27097: Python interpreter is now about 7% faster due to optimized instruction decoding. Based on patch by Demur Rumed.

- bpo-26647: Python interpreter now uses 16-bit wordcode instead of bytecode. Patch by Demur Rumed.

- bpo-23275: Allow assigning to an empty target list in round brackets: () = iterable.

- bpo-27243: Update the __aiter__ protocol: instead of returning an awaitable that resolves to an asynchronous iterator, the asynchronous iterator should be returned directly. Doing the former will trigger a PendingDeprecationWarning.

### Library

- Comment out socket (SO_REUSEPORT) and posix (O_SHLOCK, O_EXLOCK) constants exposed on the API which are not implemented on GNU/Hurd. They would not work at runtime anyway.

- bpo-27025: Generated names for Tkinter widgets are now more meaningful and recognizable.

- bpo-25455: Fixed crashes in repr of recursive ElementTree.Element and functools.partial objects.

- bpo-27294: Improved repr for Tkinter event objects.

- bpo-20508: Improve exception message of IPv{4,6}Network.__getitem__. Patch by Gareth Rees.

### Security

- bpo-26556: Update expat to 2.1.1, fixes CVE-2015-1283.

- Fix TLS stripping vulnerability in smtplib, CVE-2016-0772. Reported by Team Oststrom.

### Library

- bpo-21386: Implement missing IPv4Address.is_global property. It was documented since 07a5610bae9d. Initial patch by Roger Luethi.

- bpo-27029: Removed deprecated support of universal newlines mode from ZipFile.open().

- bpo-27030: Unknown escapes consisting of `'\'` and an ASCII letter in regular expressions now are errors. The re.LOCALE flag now can be used only with bytes patterns.

- bpo-27186: Add os.PathLike support to DirEntry (part of PEP 519). Initial patch by Jelle Zijlstra.

- bpo-20900: distutils register command now decodes HTTP responses correctly. Initial patch by ingrid.

- bpo-27186: Add os.PathLike support to pathlib, removing its provisional status (part of PEP 519). Initial patch by Dusty Phillips.

- bpo-27186: Add support for os.PathLike objects to os.fsencode() and os.fsdecode() (part of PEP 519).

- bpo-27186: Introduce os.PathLike and os.fspath() (part of PEP 519).

- A new version of typing.py provides several new classes and features: @overload outside stubs, Reversible, DefaultDict, Text, ContextManager, Type[], NewType(), TYPE_CHECKING, and numerous bug fixes (note that some of the new features are not yet implemented in mypy or other static analyzers). Also classes for PEP 492 (Awaitable, AsyncIterable, AsyncIterator) have been added (in fact they made it into 3.5.1 but were never mentioned).

- bpo-25738: Stop http.server.BaseHTTPRequestHandler.send_error() from sending a message body for 205 Reset Content. Also, don’t send Content header fields in responses that don’t have a body. Patch by Susumu Koshiba.

- bpo-21313: Fix the “platform” module to tolerate when sys.version contains truncated build information.

### Security

- bpo-26839: On Linux, `os.urandom()` now calls `getrandom()` with `GRND_NONBLOCK` to fall back on reading `/dev/urandom` if the urandom entropy pool is not initialized yet. Patch written by Colm Buckley.

### Library

- bpo-23883: Added missing APIs to __all__ to match the documented APIs for the following modules: cgi, mailbox, mimetypes, plistlib and smtpd. Patches by Jacek Kołodziej.

- bpo-27164: In the zlib module, allow decompressing raw Deflate streams with a predefined zdict. Based on patch by Xiang Zhang.

- bpo-24291: Fix wsgiref.simple_server.WSGIRequestHandler to completely write data to the client. Previously it could do partial writes and truncate data. Also, wsgiref.handler.ServerHandler can now handle stdout doing partial writes, but this is deprecated.

- bpo-21272: Use _sysconfigdata.py to initialize distutils.sysconfig.

- bpo-19611: `inspect` now reports the implicit `.0` parameters generated by the compiler for comprehension and generator expression scopes as if they were positional-only parameters called `implicit0`. Patch by Jelle Zijlstra.

- bpo-26809: Add `__all__` to `string`. Patch by Emanuel Barry.

- bpo-26373: subprocess.Popen.communicate now correctly ignores BrokenPipeError when the child process dies before .communicate() is called in more/all circumstances.

- signal, socket, and ssl module IntEnum constant name lookups now return a consistent name for values having multiple names. Ex: signal.Signals(6) now refers to itself as signal.SIGALRM rather than flipping between that and signal.SIGIOT based on the interpreter’s hash randomization seed.

- bpo-27167: Clarify the subprocess.CalledProcessError error message text when the child process died due to a signal.

- bpo-25931: Don’t define socketserver.Forking* names on platforms such as Windows that do not support os.fork().

- bpo-21776: distutils.upload now correctly handles HTTPError. Initial patch by Claudiu Popa.

- bpo-26526: Replace custom parse tree validation in the parser module with a simple DFA validator.

- bpo-27114: Fix SSLContext._load_windows_store_certs fails with PermissionError

- bpo-18383: Avoid creating duplicate filters when using filterwarnings and simplefilter. Based on patch by Alex Shkop.

- bpo-23026: winreg.QueryValueEx() now return an integer for REG_QWORD type.

- bpo-26741: subprocess.Popen destructor now emits a ResourceWarning warning if the child process is still running.

- bpo-27056: Optimize pickle.load() and pickle.loads(), up to 10% faster to deserialize a lot of small objects.

- bpo-21271: New keyword only parameters in reset_mock call.

### IDLE

- bpo-5124: Paste with text selected now replaces the selection on X11. This matches how paste works on Windows, Mac, most modern Linux apps, and ttk widgets. Original patch by Serhiy Storchaka.

- bpo-24750: Switch all scrollbars in IDLE to ttk versions. Where needed, minimal tests are added to cover changes.

- bpo-24759: IDLE requires tk 8.5 and availability ttk widgets. Delete now unneeded tk version tests and code for older versions. Add test for IDLE syntax colorizer.

- bpo-27239: idlelib.macosx.isXyzTk functions initialize as needed.

- bpo-27262: move Aqua unbinding code, which enable context menus, to macosx.

- bpo-24759: Make clear in idlelib.idle_test.__init__ that the directory is a private implementation of test.test_idle and tool for maintainers.

- bpo-27196: Stop ‘ThemeChanged’ warnings when running IDLE tests. These persisted after other warnings were suppressed in #20567. Apply Serhiy Storchaka’s update_idletasks solution to four test files. Record this additional advice in idle_test/README.txt

- bpo-20567: Revise idle_test/README.txt with advice about avoiding tk warning messages from tests. Apply advice to several IDLE tests.

- bpo-24225: Update idlelib/README.txt with new file names and event handlers.

- bpo-27156: Remove obsolete code not used by IDLE.

- bpo-27117: Make colorizer htest and turtledemo work with dark themes. Move code for configuring text widget colors to a new function.

- bpo-24225: Rename many `idlelib/*.py` and `idle_test/test_*.py` files. Edit files to replace old names with new names when the old name referred to the module rather than the class it contained. See the issue and IDLE section in What’s New in 3.6 for more.

- bpo-26673: When tk reports font size as 0, change to size 10. Such fonts on Linux prevented the configuration dialog from opening.

- bpo-21939: Add test for IDLE’s percolator. Original patch by Saimadhav Heblikar.

- bpo-21676: Add test for IDLE’s replace dialog. Original patch by Saimadhav Heblikar.

- bpo-18410: Add test for IDLE’s search dialog. Original patch by Westley Martínez.

- bpo-21703: Add test for undo delegator. Patch mostly by Saimadhav Heblikar .

- bpo-27044: Add ConfigDialog.remove_var_callbacks to stop memory leaks.

- bpo-23977: Add more asserts to test_delegator.

### Documentation

- bpo-16484: Change the default PYTHONDOCS URL to “https:”, and fix the resulting links to use lowercase. Patch by Sean Rodman, test by Kaushik Nadikuditi.

- bpo-24136: Document the new PEP 448 unpacking syntax of 3.5.

- bpo-22558: Add remaining doc links to source code for Python-coded modules. Patch by Yoni Lavi.

### Tests

- bpo-25285: regrtest now uses subprocesses when the -j1 command line option is used: each test file runs in a fresh child process. Before, the -j1 option was ignored.

- bpo-25285: Tools/buildbot/test.bat script now uses -j1 by default to run each test file in fresh child process.

### Windows

- bpo-27064: The py.exe launcher now defaults to Python 3. The Windows launcher `py.exe` no longer prefers an installed Python 2 version over Python 3 by default when used interactively.

### Build

- bpo-27229: Fix the cross-compiling pgen rule for in-tree builds. Patch by Xavier de Gaye.

- bpo-26930: Update OS X 10.5+ 32-bit-only installer to build and link with OpenSSL 1.0.2h.

### Windows

- bpo-17500: Remove unused and outdated icons. (See also: https://github.com/python/pythondotorg/issues/945)

### C API

- bpo-27186: Add the PyOS_FSPath() function (part of PEP 519).

- bpo-26282: PyArg_ParseTupleAndKeywords() now supports positional-only parameters.

### Tools/Demos

- bpo-26282: Argument Clinic now supports positional-only and keyword parameters in the same function.

## Python 3.6.0 alpha 1

Release date: 2016-05-16

### Core and Builtins

- bpo-20041: Fixed TypeError when frame.f_trace is set to None. Patch by Xavier de Gaye.

- bpo-26168: Fixed possible refleaks in failing Py_BuildValue() with the “N” format unit.

- bpo-26991: Fix possible refleak when creating a function with annotations.

- bpo-27039: Fixed bytearray.remove() for values greater than 127. Based on patch by Joe Jevnik.

- bpo-23640: int.from_bytes() no longer bypasses constructors for subclasses.

- bpo-27005: Optimized the float.fromhex() class method for exact float. It is now 2 times faster.

- bpo-18531: Single var-keyword argument of dict subtype was passed unscathed to the C-defined function. Now it is converted to exact dict.

- bpo-26811: gc.get_objects() no longer contains a broken tuple with NULL pointer.

- bpo-20120: Use RawConfigParser for .pypirc parsing, removing support for interpolation unintentionally added with move to Python 3. Behavior no longer does any interpolation in .pypirc files, matching behavior in Python 2.7 and Setuptools 19.0.

- bpo-26249: Memory functions of the `PyMem_Malloc()` domain (`PYMEM_DOMAIN_MEM`) now use the pymalloc allocator rather than system `malloc()`. Applications calling `PyMem_Malloc()` without holding the GIL can now crash: use `PYTHONMALLOC=debug` environment variable to validate the usage of memory allocators in your application.

- bpo-26802: Optimize function calls only using unpacking like `func(*tuple)` (no other positional argument, no keyword): avoid copying the tuple. Patch written by Joe Jevnik.

- bpo-26659: Make the builtin slice type support cycle collection.

- bpo-26718: super.__init__ no longer leaks memory if called multiple times. NOTE: A direct call of super.__init__ is not endorsed!

- bpo-27138: Fix the doc comment for FileFinder.find_spec().

- bpo-27147: Mention PEP 420 in the importlib docs.

- bpo-25339: PYTHONIOENCODING now has priority over locale in setting the error handler for stdin and stdout.

- bpo-26494: Fixed crash on iterating exhausting iterators. Affected classes are generic sequence iterators, iterators of str, bytes, bytearray, list, tuple, set, frozenset, dict, OrderedDict, corresponding views and os.scandir() iterator.

- bpo-26574: Optimize `bytes.replace(b'', b'.')` and `bytearray.replace(b'', b'.')`. Patch written by Josh Snider.

- bpo-26581: If coding cookie is specified multiple times on a line in Python source code file, only the first one is taken to account.

- bpo-19711: Add tests for reloading namespace packages.

- bpo-21099: Switch applicable importlib tests to use PEP 451 API.

- bpo-26563: Debug hooks on Python memory allocators now raise a fatal error if functions of the `PyMem_Malloc()` family are called without holding the GIL.

- bpo-26564: On error, the debug hooks on Python memory allocators now use the `tracemalloc` module to get the traceback where a memory block was allocated.

- bpo-26558: The debug hooks on Python memory allocator `PyObject_Malloc()` now detect when functions are called without holding the GIL.

- bpo-26516: Add `PYTHONMALLOC` environment variable to set the Python memory allocators and/or install debug hooks.

- bpo-26516: The `PyMem_SetupDebugHooks()` function can now also be used on Python compiled in release mode.

- bpo-26516: The `PYTHONMALLOCSTATS` environment variable can now also be used on Python compiled in release mode. It now has no effect if set to an empty string.

- bpo-26516: In debug mode, debug hooks are now also installed on Python memory allocators when Python is configured without pymalloc.

- bpo-26464: Fix str.translate() when string is ASCII and first replacements removes character, but next replacement uses a non-ASCII character or a string longer than 1 character. Regression introduced in Python 3.5.0.

- bpo-22836: Ensure exception reports from PyErr_Display() and PyErr_WriteUnraisable() are sensible even when formatting them produces secondary errors. This affects the reports produced by sys.__excepthook__() and when __del__() raises an exception.

- bpo-26302: Correct behavior to reject comma as a legal character for cookie names.

- bpo-26136: Upgrade the warning when a generator raises StopIteration from PendingDeprecationWarning to DeprecationWarning. Patch by Anish Shah.

- bpo-26204: The compiler now ignores all constant statements: bytes, str, int, float, complex, name constants (None, False, True), Ellipsis and ast.Constant; not only str and int. For example, `1.0` is now ignored in `def f(): 1.0`.

- bpo-4806: Avoid masking the original TypeError exception when using star (`*`) unpacking in function calls. Based on patch by Hagen Fürstenau and Daniel Urban.

- bpo-26146: Add a new kind of AST node: `ast.Constant`. It can be used by external AST optimizers, but the compiler does not emit directly such node.

- bpo-23601: Sped-up allocation of dict key objects by using Python’s small object allocator. (Contributed by Julian Taylor.)

- bpo-18018: Import raises ImportError instead of SystemError if a relative import is attempted without a known parent package.

- bpo-25843: When compiling code, don’t merge constants if they are equal but have a different types. For example, `f1, f2 = lambda: 1, lambda: 1.0` is now correctly compiled to two different functions: `f1()` returns `1` (`int`) and `f2()` returns `1.0` (`float`), even if `1` and `1.0` are equal.

- bpo-26107: The format of the `co_lnotab` attribute of code objects changes to support negative line number delta.

- bpo-26154: Add a new private _PyThreadState_UncheckedGet() function to get the current Python thread state, but don’t issue a fatal error if it is NULL. This new function must be used instead of accessing directly the _PyThreadState_Current variable. The variable is no more exposed since Python 3.5.1 to hide the exact implementation of atomic C types, to avoid compiler issues.

- bpo-25791: If __package__ != __spec__.parent or if neither __package__ or __spec__ are defined then ImportWarning is raised.

- bpo-22995: [UPDATE] Comment out the one of the pickleability tests in _PyObject_GetState() due to regressions observed in Cython-based projects.

- bpo-25961: Disallowed null characters in the type name.

- bpo-25973: Fix segfault when an invalid nonlocal statement binds a name starting with two underscores.

- bpo-22995: Instances of extension types with a state that aren’t subclasses of list or dict and haven’t implemented any pickle-related methods (__reduce__, __reduce_ex__, __getnewargs__, __getnewargs_ex__, or __getstate__), can no longer be pickled. Including memoryview.

- bpo-20440: Massive replacing unsafe attribute setting code with special macro Py_SETREF.

- bpo-25766: Special method __bytes__() now works in str subclasses.

- bpo-25421: __sizeof__ methods of builtin types now use dynamic basic size. This allows sys.getsize() to work correctly with their subclasses with __slots__ defined.

- bpo-25709: Fixed problem with in-place string concatenation and utf-8 cache.

- bpo-5319: New Py_FinalizeEx() API allowing Python to set an exit status of 120 on failure to flush buffered streams.

- bpo-25485: telnetlib.Telnet is now a context manager.

- bpo-24097: Fixed crash in object.__reduce__() if slot name is freed inside __getattr__.

- bpo-24731: Fixed crash on converting objects with special methods __bytes__, __trunc__, and __float__ returning instances of subclasses of bytes, int, and float to subclasses of bytes, int, and float correspondingly.

- bpo-25630: Fix a possible segfault during argument parsing in functions that accept filesystem paths.

- bpo-23564: Fixed a partially broken sanity check in the _posixsubprocess internals regarding how fds_to_pass were passed to the child. The bug had no actual impact as subprocess.py already avoided it.

- bpo-25388: Fixed tokenizer crash when processing undecodable source code with a null byte.

- bpo-25462: The hash of the key now is calculated only once in most operations in C implementation of OrderedDict.

- bpo-22995: Default implementation of __reduce__ and __reduce_ex__ now rejects builtin types with not defined __new__.

- bpo-24802: Avoid buffer overreads when int(), float(), compile(), exec() and eval() are passed bytes-like objects. These objects are not necessarily terminated by a null byte, but the functions assumed they were.

- bpo-25555: Fix parser and AST: fill lineno and col_offset of “arg” node when compiling AST from Python objects.

- bpo-24726: Fixed a crash and leaking NULL in repr() of OrderedDict that was mutated by direct calls of dict methods.

- bpo-25449: Iterating OrderedDict with keys with unstable hash now raises KeyError in C implementations as well as in Python implementation.

- bpo-25395: Fixed crash when highly nested OrderedDict structures were garbage collected.

- bpo-25401: Optimize bytes.fromhex() and bytearray.fromhex(): they are now between 2x and 3.5x faster.

- bpo-25399: Optimize bytearray % args using the new private _PyBytesWriter API. Formatting is now between 2.5 and 5 times faster.

- bpo-25274: sys.setrecursionlimit() now raises a RecursionError if the new recursion limit is too low depending at the current recursion depth. Modify also the “lower-water mark” formula to make it monotonic. This mark is used to decide when the overflowed flag of the thread state is reset.

- bpo-24402: Fix input() to prompt to the redirected stdout when sys.stdout.fileno() fails.

- bpo-25349: Optimize bytes % args using the new private _PyBytesWriter API. Formatting is now up to 2 times faster.

- bpo-24806: Prevent builtin types that are not allowed to be subclassed from being subclassed through multiple inheritance.

- bpo-25301: The UTF-8 decoder is now up to 15 times as fast for error handlers: `ignore`, `replace` and `surrogateescape`.

- bpo-24848: Fixed a number of bugs in UTF-7 decoding of misformed data.

- bpo-25267: The UTF-8 encoder is now up to 75 times as fast for error handlers: `ignore`, `replace`, `surrogateescape`, `surrogatepass`. Patch co-written with Serhiy Storchaka.

- bpo-25280: Import trace messages emitted in verbose (-v) mode are no longer formatted twice.

- bpo-25227: Optimize ASCII and latin1 encoders with the `surrogateescape` error handler: the encoders are now up to 3 times as fast. Initial patch written by Serhiy Storchaka.

- bpo-25003: On Solaris 11.3 or newer, os.urandom() now uses the getrandom() function instead of the getentropy() function. The getentropy() function is blocking to generate very good quality entropy, os.urandom() doesn’t need such high-quality entropy.

- bpo-9232: Modify Python’s grammar to allow trailing commas in the argument list of a function declaration. For example, “def f(*, a = 3,): pass” is now legal. Patch from Mark Dickinson.

- bpo-24965: Implement PEP 498 “Literal String Interpolation”. This allows you to embed expressions inside f-strings, which are converted to normal strings at run time. Given x=3, then f’value={x}’ == ‘value=3’. Patch by Eric V. Smith.

- bpo-26478: Fix semantic bugs when using binary operators with dictionary views and tuples.

- bpo-26171: Fix possible integer overflow and heap corruption in zipimporter.get_data().

- bpo-25660: Fix TAB key behaviour in REPL with readline.

- bpo-26288: Optimize PyLong_AsDouble.

- bpo-26289: Optimize floor and modulo division for single-digit longs. Microbenchmarks show 2-2.5x improvement. Built-in ‘divmod’ function is now also ~10% faster. (See also: bpo-26315)

- bpo-25887: Raise a RuntimeError when a coroutine object is awaited more than once.

### Library

- bpo-27057: Fix os.set_inheritable() on Android, ioctl() is blocked by SELinux and fails with EACCESS. The function now falls back to fcntl(). Patch written by Michał Bednarski.

- bpo-27014: Fix infinite recursion using typing.py. Thanks to Kalle Tuure!

- bpo-27031: Removed dummy methods in Tkinter widget classes: tk_menuBar() and tk_bindForTraversal().

- bpo-14132: Fix urllib.request redirect handling when the target only has a query string. Original fix by Ján Janech.

- bpo-17214: The “urllib.request” module now percent-encodes non-ASCII bytes found in redirect target URLs. Some servers send Location header fields with non-ASCII bytes, but “http.client” requires the request target to be ASCII-encodable, otherwise a UnicodeEncodeError is raised. Based on patch by Christian Heimes.

- bpo-27033: The default value of the decode_data parameter for smtpd.SMTPChannel and smtpd.SMTPServer constructors is changed to False.

- bpo-27034: Removed deprecated class asynchat.fifo.

- bpo-26870: Added readline.set_auto_history(), which can stop entries being automatically added to the history list. Based on patch by Tyler Crompton.

- bpo-26039: zipfile.ZipFile.open() can now be used to write data into a ZIP file, as well as for extracting data. Patch by Thomas Kluyver.

- bpo-26892: Honor debuglevel flag in urllib.request.HTTPHandler. Patch contributed by Chi Hsuan Yen.

- bpo-22274: In the subprocess module, allow stderr to be redirected to stdout even when stdout is not redirected. Patch by Akira Li.

- bpo-26807: mock_open ‘files’ no longer error on readline at end of file. Patch from Yolanda Robla.

- bpo-25745: Fixed leaking a userptr in curses panel destructor.

- bpo-26977: Removed unnecessary, and ignored, call to sum of squares helper in statistics.pvariance.

- bpo-26002: Use bisect in statistics.median instead of a linear search. Patch by Upendra Kuma.

- bpo-25974: Make use of new Decimal.as_integer_ratio() method in statistics module. Patch by Stefan Krah.

- bpo-26996: Add secrets module as described in PEP 506.

- bpo-26881: The modulefinder module now supports extended opcode arguments.

- bpo-23815: Fixed crashes related to directly created instances of types in _tkinter and curses.panel modules.

- bpo-17765: weakref.ref() no longer silently ignores keyword arguments. Patch by Georg Brandl.

- bpo-26873: xmlrpc now raises ResponseError on unsupported type tags instead of silently return incorrect result.

- bpo-26915: The __contains__ methods in the collections ABCs now check for identity before checking equality. This better matches the behavior of the concrete classes, allows sensible handling of NaNs, and makes it easier to reason about container invariants.

- bpo-26711: Fixed the comparison of plistlib.Data with other types.

- bpo-24114: Fix an uninitialized variable in `ctypes.util`. The bug only occurs on SunOS when the ctypes implementation searches for the `crle` program. Patch by Xiang Zhang. Tested on SunOS by Kees Bos.

- bpo-26864: In urllib.request, change the proxy bypass host checking against no_proxy to be case-insensitive, and to not match unrelated host names that happen to have a bypassed hostname as a suffix. Patch by Xiang Zhang.

- bpo-24902: Print server URL on http.server startup. Initial patch by Felix Kaiser.

- bpo-25788: fileinput.hook_encoded() now supports an “errors” argument for passing to open. Original patch by Joseph Hackman.

- bpo-26634: recursive_repr() now sets __qualname__ of wrapper. Patch by Xiang Zhang.

- bpo-26804: urllib.request will prefer lower_case proxy environment variables over UPPER_CASE or Mixed_Case ones. Patch contributed by Hans-Peter Jansen.

- bpo-26837: assertSequenceEqual() now correctly outputs non-stringified differing items (like bytes in the -b mode). This affects assertListEqual() and assertTupleEqual().

- bpo-26041: Remove “will be removed in Python 3.7” from deprecation messages of platform.dist() and platform.linux_distribution(). Patch by Kumaripaba Miyurusara Athukorala.

- bpo-26822: itemgetter, attrgetter and methodcaller objects no longer silently ignore keyword arguments.

- bpo-26733: Disassembling a class now disassembles class and static methods. Patch by Xiang Zhang.

- bpo-26801: Fix error handling in `shutil.get_terminal_size()`, catch `AttributeError` instead of `NameError`. Patch written by Emanuel Barry.

- bpo-24838: tarfile’s ustar and gnu formats now correctly calculate name and link field limits for multibyte character encodings like utf-8.

### Security

- bpo-26657: Fix directory traversal vulnerability with http.server on Windows. This fixes a regression that was introduced in 3.3.4rc1 and 3.4.0rc1. Based on patch by Philipp Hagemeister.

### Library

- bpo-26717: Stop encoding Latin-1-ized WSGI paths with UTF-8. Patch by Anthony Sottile.

- bpo-26782: Add STARTUPINFO to subprocess.__all__ on Windows.

- bpo-26404: Add context manager to socketserver. Patch by Aviv Palivoda.

- bpo-26735: Fix `os.urandom()` on Solaris 11.3 and newer when reading more than 1,024 bytes: call `getrandom()` multiple times with a limit of 1024 bytes per call.

- bpo-26585: Eliminate http.server._quote_html() and use html.escape(quote=False). Patch by Xiang Zhang.

- bpo-26685: Raise OSError if closing a socket fails.

- bpo-16329: Add .webm to mimetypes.types_map. Patch by Giampaolo Rodola’.

- bpo-13952: Add .csv to mimetypes.types_map. Patch by Geoff Wilson.

- bpo-26587: the site module now allows .pth files to specify files to be added to sys.path (e.g. zip files).

- bpo-25609: Introduce contextlib.AbstractContextManager and typing.ContextManager.

- bpo-26709: Fixed Y2038 problem in loading binary PLists.

- bpo-23735: Handle terminal resizing with Readline 6.3+ by installing our own SIGWINCH handler. Patch by Eric Price.

- bpo-25951: Change SSLSocket.sendall() to return None, as explicitly documented for plain socket objects. Patch by Aviv Palivoda.

- bpo-26586: In http.server, respond with “413 Request header fields too large” if there are too many header fields to parse, rather than killing the connection and raising an unhandled exception. Patch by Xiang Zhang.

- bpo-26676: Added missing XMLPullParser to ElementTree.__all__.

- bpo-22854: Change BufferedReader.writable() and BufferedWriter.readable() to always return False.

- bpo-26492: Exhausted iterator of array.array now conforms with the behavior of iterators of other mutable sequences: it lefts exhausted even if iterated array is extended.

- bpo-26641: doctest.DocFileTest and doctest.testfile() now support packages (module splitted into multiple directories) for the package parameter.

- bpo-25195: Fix a regression in mock.MagicMock. _Call is a subclass of tuple (changeset 3603bae63c13 only works for classes) so we need to implement __ne__ ourselves. Patch by Andrew Plummer.

- bpo-26644: Raise ValueError rather than SystemError when a negative length is passed to SSLSocket.recv() or read().

- bpo-23804: Fix SSL recv(0) and read(0) methods to return zero bytes instead of up to 1024.

- bpo-26616: Fixed a bug in datetime.astimezone() method.

- bpo-26637: The `importlib` module now emits an `ImportError` rather than a `TypeError` if `__import__()` is tried during the Python shutdown process but `sys.path` is already cleared (set to `None`).

- bpo-21925: `warnings.formatwarning()` now catches exceptions when calling `linecache.getline()` and `tracemalloc.get_object_traceback()` to be able to log `ResourceWarning` emitted late during the Python shutdown process.

- bpo-23848: On Windows, faulthandler.enable() now also installs an exception handler to dump the traceback of all Python threads on any Windows exception, not only on UNIX signals (SIGSEGV, SIGFPE, SIGABRT).

- bpo-26530: Add C functions `_PyTraceMalloc_Track()` and `_PyTraceMalloc_Untrack()` to track memory blocks using the `tracemalloc` module. Add `_PyTraceMalloc_GetTraceback()` to get the traceback of an object.

- bpo-26588: The _tracemalloc now supports tracing memory allocations of multiple address spaces (domains).

- bpo-24266: Ctrl+C during Readline history search now cancels the search mode when compiled with Readline 7.

- bpo-26590: Implement a safe finalizer for the _socket.socket type. It now releases the GIL to close the socket.

- bpo-18787: spwd.getspnam() now raises a PermissionError if the user doesn’t have privileges.

- bpo-26560: Avoid potential ValueError in BaseHandler.start_response. Initial patch by Peter Inglesby.

- bpo-26567: Add a new function `PyErr_ResourceWarning()` function to pass the destroyed object. Add a source attribute to `warnings.WarningMessage`. Add warnings._showwarnmsg() which uses tracemalloc to get the traceback where source object was allocated.

### Security

- bpo-26313: ssl.py _load_windows_store_certs fails if windows cert store is empty. Patch by Baji.

### Library

- bpo-26569: Fix `pyclbr.readmodule()` and `pyclbr.readmodule_ex()` to support importing packages.

- bpo-26499: Account for remaining Content-Length in HTTPResponse.readline() and read1(). Based on patch by Silent Ghost. Also document that HTTPResponse now supports these methods.

- bpo-25320: Handle sockets in directories unittest discovery is scanning. Patch from Victor van den Elzen.

- bpo-16181: cookiejar.http2time() now returns None if year is higher than datetime.MAXYEAR.

- bpo-26513: Fixes platform module detection of Windows Server

- bpo-23718: Fixed parsing time in week 0 before Jan 1. Original patch by Tamás Bence Gedai.

- bpo-26323: Add Mock.assert_called() and Mock.assert_called_once() methods to unittest.mock. Patch written by Amit Saha.

- bpo-20589: Invoking Path.owner() and Path.group() on Windows now raise NotImplementedError instead of ImportError.

- bpo-26177: Fixed the keys() method for Canvas and Scrollbar widgets.

- bpo-15068: Got rid of excessive buffering in fileinput. The bufsize parameter is now deprecated and ignored.

- bpo-19475: Added an optional argument timespec to the datetime isoformat() method to choose the precision of the time component.

- bpo-2202: Fix UnboundLocalError in AbstractDigestAuthHandler.get_algorithm_impls. Initial patch by Mathieu Dupuy.

- bpo-26167: Minimized overhead in copy.copy() and copy.deepcopy(). Optimized copying and deepcopying bytearrays, NotImplemented, slices, short lists, tuples, dicts, sets.

- bpo-25718: Fixed pickling and copying the accumulate() iterator with total is None.

- bpo-26475: Fixed debugging output for regular expressions with the (?x) flag.

- bpo-26482: Allowed pickling recursive dequeues.

- bpo-26335: Make mmap.write() return the number of bytes written like other write methods. Patch by Jakub Stasiak.

- bpo-26457: Fixed the subnets() methods in IP network classes for the case when resulting prefix length is equal to maximal prefix length. Based on patch by Xiang Zhang.

- bpo-26385: Remove the file if the internal open() call in NamedTemporaryFile() fails. Patch by Silent Ghost.

- bpo-26402: Fix XML-RPC client to retry when the server shuts down a persistent connection. This was a regression related to the new http.client.RemoteDisconnected exception in 3.5.0a4.

- bpo-25913: Leading `<~` is optional now in base64.a85decode() with adobe=True. Patch by Swati Jaiswal.

- bpo-26186: Remove an invalid type check in importlib.util.LazyLoader.

- bpo-26367: importlib.__import__() raises ImportError like builtins.__import__() when `level` is specified but without an accompanying package specified.

- bpo-26309: In the “socketserver” module, shut down the request (closing the connected socket) when verify_request() returns false. Patch by Aviv Palivoda.

- bpo-23430: Change the socketserver module to only catch exceptions raised from a request handler that are derived from Exception (instead of BaseException). Therefore SystemExit and KeyboardInterrupt no longer trigger the handle_error() method, and will now to stop a single-threaded server.

### Security

- bpo-25939: On Windows open the cert store readonly in ssl.enum_certificates.

### Library

- bpo-25995: os.walk() no longer uses FDs proportional to the tree depth.

- bpo-25994: Added the close() method and the support of the context manager protocol for the os.scandir() iterator.

- bpo-23992: multiprocessing: make MapResult not fail-fast upon exception.

- bpo-26243: Support keyword arguments to zlib.compress(). Patch by Aviv Palivoda.

- bpo-26117: The os.scandir() iterator now closes file descriptor not only when the iteration is finished, but when it was failed with error.

- bpo-25949: __dict__ for an OrderedDict instance is now created only when needed.

- bpo-25911: Restored support of bytes paths in os.walk() on Windows.

- bpo-26045: Add UTF-8 suggestion to error message when posting a non-Latin-1 string with http.client.

- bpo-26039: Added zipfile.ZipInfo.from_file() and zipinfo.ZipInfo.is_dir(). Patch by Thomas Kluyver.

- bpo-12923: Reset FancyURLopener’s redirect counter even if there is an exception. Based on patches by Brian Brazil and Daniel Rocco.

- bpo-25945: Fixed a crash when unpickle the functools.partial object with wrong state. Fixed a leak in failed functools.partial constructor. “args” and “keywords” attributes of functools.partial have now always types tuple and dict correspondingly.

- bpo-26202: copy.deepcopy() now correctly copies range() objects with non-atomic attributes.

- bpo-23076: Path.glob() now raises a ValueError if it’s called with an invalid pattern. Patch by Thomas Nyberg.

- bpo-19883: Fixed possible integer overflows in zipimport.

- bpo-26227: On Windows, getnameinfo(), gethostbyaddr() and gethostbyname_ex() functions of the socket module now decode the hostname from the ANSI code page rather than UTF-8.

- bpo-26099: The site module now writes an error into stderr if sitecustomize module can be imported but executing the module raise an ImportError. Same change for usercustomize.

- bpo-26147: xmlrpc now works with strings not encodable with used non-UTF-8 encoding.

- bpo-25935: Garbage collector now breaks reference loops with OrderedDict.

- bpo-16620: Fixed AttributeError in msilib.Directory.glob().

- bpo-26013: Added compatibility with broken protocol 2 pickles created in old Python 3 versions (3.4.3 and lower).

- bpo-26129: Deprecated accepting non-integers in grp.getgrgid().

- bpo-25850: Use cross-compilation by default for 64-bit Windows.

- bpo-25822: Add docstrings to the fields of urllib.parse results. Patch contributed by Swati Jaiswal.

- bpo-22642: Convert trace module option parsing mechanism to argparse. Patch contributed by SilentGhost.

- bpo-24705: Fix sysconfig._parse_makefile not expanding ${} vars appearing before $() vars.

- bpo-26069: Remove the deprecated apis in the trace module.

- bpo-22138: Fix mock.patch behavior when patching descriptors. Restore original values after patching. Patch contributed by Sean McCully.

- bpo-25672: In the ssl module, enable the SSL_MODE_RELEASE_BUFFERS mode option if it is safe to do so.

- bpo-26012: Don’t traverse into symlinks for `**` pattern in pathlib.Path.[r]glob().

- bpo-24120: Ignore PermissionError when traversing a tree with pathlib.Path.[r]glob(). Patch by Ulrich Petri.

- bpo-21815: Accept ] characters in the data portion of imap responses, in order to handle the flags with square brackets accepted and produced by servers such as gmail.

- bpo-25447: fileinput now uses sys.stdin as-is if it does not have a buffer attribute (restores backward compatibility).

- bpo-25971: Optimized creating Fractions from floats by 2 times and from Decimals by 3 times.

- bpo-25802: Document as deprecated the remaining implementations of importlib.abc.Loader.load_module().

- bpo-25928: Add Decimal.as_integer_ratio().

- bpo-25447: Copying the lru_cache() wrapper object now always works, independently from the type of the wrapped object (by returning the original object unchanged).

- bpo-25768: Have the functions in compileall return booleans instead of ints and add proper documentation and tests for the return values.

- bpo-24103: Fixed possible use after free in ElementTree.XMLPullParser.

- bpo-25860: os.fwalk() no longer skips remaining directories when error occurs. Original patch by Samson Lee.

- bpo-25914: Fixed and simplified OrderedDict.__sizeof__.

- bpo-25869: Optimized deepcopying ElementTree; it is now 20 times faster.

- bpo-25873: Optimized iterating ElementTree. Iterating elements Element.iter() is now 40% faster, iterating text Element.itertext() is now up to 2.5 times faster.

- bpo-25902: Fixed various refcount issues in ElementTree iteration.

- bpo-22227: The TarFile iterator is reimplemented using generator. This implementation is simpler that using class.

- bpo-25638: Optimized ElementTree.iterparse(); it is now 2x faster. Optimized ElementTree parsing; it is now 10% faster.

- bpo-25761: Improved detecting errors in broken pickle data.

- bpo-25717: Restore the previous behaviour of tolerating most fstat() errors when opening files. This was a regression in 3.5a1, and stopped anonymous temporary files from working in special cases.

- bpo-24903: Fix regression in number of arguments compileall accepts when ‘-d’ is specified. The check on the number of arguments has been dropped completely as it never worked correctly anyway.

- bpo-25764: In the subprocess module, preserve any exception caused by fork() failure when preexec_fn is used.

- bpo-25771: Tweak the exception message for importlib.util.resolve_name() when ‘package’ isn’t specified but necessary.

- bpo-6478: _strptime’s regexp cache now is reset after changing timezone with time.tzset().

- bpo-14285: When executing a package with the “python -m package” option, and package initialization fails, a proper traceback is now reported. The “runpy” module now lets exceptions from package initialization pass back to the caller, rather than raising ImportError.

- bpo-19771: Also in runpy and the “-m” option, omit the irrelevant message “… is a package and cannot be directly executed” if the package could not even be initialized (e.g. due to a bad `*.pyc` file).

- bpo-25177: Fixed problem with the mean of very small and very large numbers. As a side effect, statistics.mean and statistics.variance should be significantly faster.

- bpo-25718: Fixed copying object with state with boolean value is false.

- bpo-10131: Fixed deep copying of minidom documents. Based on patch by Marian Ganisin.

- bpo-7990: dir() on ElementTree.Element now lists properties: “tag”, “text”, “tail” and “attrib”. Original patch by Santoso Wijaya.

- bpo-25725: Fixed a reference leak in pickle.loads() when unpickling invalid data including tuple instructions.

- bpo-25663: In the Readline completer, avoid listing duplicate global names, and search the global namespace before searching builtins.

- bpo-25688: Fixed file leak in ElementTree.iterparse() raising an error.

- bpo-23914: Fixed SystemError raised by unpickler on broken pickle data.

- bpo-25691: Fixed crash on deleting ElementTree.Element attributes.

- bpo-25624: ZipFile now always writes a ZIP_STORED header for directory entries. Patch by Dingyuan Wang.

- bpo-25626: Change three zlib functions to accept sizes that fit in Py_ssize_t, but internally cap those sizes to UINT_MAX. This resolves a regression in 3.5 where GzipFile.read() failed to read chunks larger than 2 or 4 GiB. The change affects the zlib.Decompress.decompress() max_length parameter, the zlib.decompress() bufsize parameter, and the zlib.Decompress.flush() length parameter.

- bpo-25583: Avoid incorrect errors raised by os.makedirs(exist_ok=True) when the OS gives priority to errors such as EACCES over EEXIST.

- bpo-25593: Change semantics of EventLoop.stop() in asyncio.

- bpo-6973: When we know a subprocess.Popen process has died, do not allow the send_signal(), terminate(), or kill() methods to do anything as they could potentially signal a different process.

- bpo-23883: Added missing APIs to __all__ to match the documented APIs for the following modules: calendar, csv, enum, fileinput, ftplib, logging, optparse, tarfile, threading and wave. Also added a test.support.check__all__() helper. Patches by Jacek Kołodziej, Mauro S. M. Rodrigues and Joel Taddei.

- bpo-25590: In the Readline completer, only call getattr() once per attribute. Also complete names of attributes such as properties and slots which are listed by dir() but not yet created on an instance.

- bpo-25498: Fix a crash when garbage-collecting ctypes objects created by wrapping a memoryview. This was a regression made in 3.5a1. Based on patch by Eryksun.

- bpo-25584: Added “escape” to the __all__ list in the glob module.

- bpo-25584: Fixed recursive glob() with patterns starting with `**`.

- bpo-25446: Fix regression in smtplib’s AUTH LOGIN support.

- bpo-18010: Fix the pydoc web server’s module search function to handle exceptions from importing packages.

- bpo-25554: Got rid of circular references in regular expression parsing.

- bpo-18973: Command-line interface of the calendar module now uses argparse instead of optparse.

- bpo-25510: fileinput.FileInput.readline() now returns b’’ instead of ‘’ at the end if the FileInput was opened with binary mode. Patch by Ryosuke Ito.

- bpo-25503: Fixed inspect.getdoc() for inherited docstrings of properties. Original patch by John Mark Vandenberg.

- bpo-25515: Always use os.urandom as a source of randomness in uuid.uuid4.

- bpo-21827: Fixed textwrap.dedent() for the case when largest common whitespace is a substring of smallest leading whitespace. Based on patch by Robert Li.

- bpo-25447: The lru_cache() wrapper objects now can be copied and pickled (by returning the original object unchanged).

- bpo-25390: typing: Don’t crash on Union[str, Pattern].

- bpo-25441: asyncio: Raise error from drain() when socket is closed.

- bpo-25410: Cleaned up and fixed minor bugs in C implementation of OrderedDict.

- bpo-25411: Improved Unicode support in SMTPHandler through better use of the email package. Thanks to user simon04 for the patch.

- Move the imp module from a PendingDeprecationWarning to DeprecationWarning.

- bpo-25407: Remove mentions of the formatter module being removed in Python 3.6.

- bpo-25406: Fixed a bug in C implementation of OrderedDict.move_to_end() that caused segmentation fault or hang in iterating after moving several items to the start of ordered dict.

- bpo-25382: pickletools.dis() now outputs implicit memo index for the MEMOIZE opcode.

- bpo-25357: Add an optional newline parameter to binascii.b2a_base64(). base64.b64encode() uses it to avoid a memory copy.

- bpo-24164: Objects that need calling `__new__` with keyword arguments, can now be pickled using pickle protocols older than protocol version 4.

- bpo-25364: zipfile now works in threads disabled builds.

- bpo-25328: smtpd’s SMTPChannel now correctly raises a ValueError if both decode_data and enable_SMTPUTF8 are set to true.

- bpo-16099: RobotFileParser now supports Crawl-delay and Request-rate extensions. Patch by Nikolay Bogoychev.

- bpo-25316: distutils raises OSError instead of DistutilsPlatformError when MSVC is not installed.

- bpo-25380: Fixed protocol for the STACK_GLOBAL opcode in pickletools.opcodes.

- bpo-23972: Updates asyncio datagram create method allowing reuseport and reuseaddr socket options to be set prior to binding the socket. Mirroring the existing asyncio create_server method the reuseaddr option for datagram sockets defaults to True if the O/S is ‘posix’ (except if the platform is Cygwin). Patch by Chris Laws.

- bpo-25304: Add asyncio.run_coroutine_threadsafe(). This lets you submit a coroutine to a loop from another thread, returning a concurrent.futures.Future. By Vincent Michel.

- bpo-25232: Fix CGIRequestHandler to split the query from the URL at the first question mark (?) rather than the last. Patch from Xiang Zhang.

- bpo-24657: Prevent CGIRequestHandler from collapsing slashes in the query part of the URL as if it were a path. Patch from Xiang Zhang.

- bpo-25287: Don’t add crypt.METHOD_CRYPT to crypt.methods if it’s not supported. Check if it is supported, it may not be supported on OpenBSD for example.

- bpo-23600: Default implementation of tzinfo.fromutc() was returning wrong results in some cases.

- bpo-25203: Failed readline.set_completer_delims() no longer left the module in inconsistent state.

- bpo-25011: rlcompleter now omits private and special attribute names unless the prefix starts with underscores.

- bpo-25209: rlcompleter now can add a space or a colon after completed keyword.

- bpo-22241: timezone.utc name is now plain ‘UTC’, not ‘UTC-00:00’.

- bpo-23517: fromtimestamp() and utcfromtimestamp() methods of datetime.datetime now round microseconds to nearest with ties going to nearest even integer (ROUND_HALF_EVEN), as round(float), instead of rounding towards -Infinity (ROUND_FLOOR).

- bpo-23552: Timeit now warns when there is substantial (4x) variance between best and worst times. Patch from Serhiy Storchaka.

- bpo-24633: site-packages/README -> README.txt.

- bpo-24879: help() and pydoc can now list named tuple fields in the order they were defined rather than alphabetically. The ordering is determined by the _fields attribute if present.

- bpo-24874: Improve speed of itertools.cycle() and make its pickle more compact.

- Fix crash in itertools.cycle.__setstate__() when the first argument wasn’t a list.

- bpo-20059: urllib.parse raises ValueError on all invalid ports. Patch by Martin Panter.

- bpo-24360: Improve __repr__ of argparse.Namespace() for invalid identifiers. Patch by Matthias Bussonnier.

- bpo-23426: run_setup was broken in distutils. Patch from Alexander Belopolsky.

- bpo-13938: 2to3 converts StringTypes to a tuple. Patch from Mark Hammond.

- bpo-2091: open() accepted a ‘U’ mode string containing ‘+’, but ‘U’ can only be used with ‘r’. Patch from Jeff Balogh and John O’Connor.

- bpo-8585: improved tests for zipimporter2. Patch from Mark Lawrence.

- bpo-18622: unittest.mock.mock_open().reset_mock would recurse infinitely. Patch from Nicola Palumbo and Laurent De Buyst.

- bpo-24426: Fast searching optimization in regular expressions now works for patterns that starts with capturing groups. Fast searching optimization now can’t be disabled at compile time.

- bpo-23661: unittest.mock side_effects can now be exceptions again. This was a regression vs Python 3.4. Patch from Ignacio Rossi

- bpo-13248: Remove deprecated inspect.getmoduleinfo function.

- bpo-25578: Fix (another) memory leak in SSLSocket.getpeercer().

- bpo-25530: Disable the vulnerable SSLv3 protocol by default when creating ssl.SSLContext.

- bpo-25569: Fix memory leak in SSLSocket.getpeercert().

- bpo-25471: Sockets returned from accept() shouldn’t appear to be nonblocking.

- bpo-25319: When threading.Event is reinitialized, the underlying condition should use a regular lock rather than a recursive lock.

- Skip getaddrinfo if host is already resolved. Patch by A. Jesse Jiryu Davis.

- bpo-26050: Add asyncio.StreamReader.readuntil() method. Patch by Марк Коренберг.

- bpo-25924: Avoid unnecessary serialization of getaddrinfo(3) calls on OS X versions 10.5 or higher. Original patch by A. Jesse Jiryu Davis.

- bpo-26406: Avoid unnecessary serialization of getaddrinfo(3) calls on current versions of OpenBSD and NetBSD. Patch by A. Jesse Jiryu Davis.

- bpo-26848: Fix asyncio/subprocess.communicate() to handle empty input. Patch by Jack O’Connor.

- bpo-27040: Add loop.get_exception_handler method

- bpo-27041: asyncio: Add loop.create_future method

### IDLE

- bpo-20640: Add tests for idlelib.configHelpSourceEdit. Patch by Saimadhav Heblikar.

- In the ‘IDLE-console differences’ section of the IDLE doc, clarify how running with IDLE affects sys.modules and the standard streams.

- bpo-25507: fix incorrect change in IOBinding that prevented printing. Augment IOBinding htest to include all major IOBinding functions.

- bpo-25905: Revert unwanted conversion of ‘ to ’ RIGHT SINGLE QUOTATION MARK in README.txt and open this and NEWS.txt with ‘ascii’. Re-encode CREDITS.txt to utf-8 and open it with ‘utf-8’.

- bpo-15348: Stop the debugger engine (normally in a user process) before closing the debugger window (running in the IDLE process). This prevents the RuntimeErrors that were being caught and ignored.

- bpo-24455: Prevent IDLE from hanging when a) closing the shell while the debugger is active (15347); b) closing the debugger with the [X] button (15348); and c) activating the debugger when already active (24455). The patch by Mark Roseman does this by making two changes. 1. Suspend and resume the gui.interaction method with the tcl vwait mechanism intended for this purpose (instead of root.mainloop & .quit). 2. In gui.run, allow any existing interaction to terminate first.

- Change ‘The program’ to ‘Your program’ in an IDLE ‘kill program?’ message to make it clearer that the program referred to is the currently running user program, not IDLE itself.

- bpo-24750: Improve the appearance of the IDLE editor window status bar. Patch by Mark Roseman.

- bpo-25313: Change the handling of new built-in text color themes to better address the compatibility problem introduced by the addition of IDLE Dark. Consistently use the revised idleConf.CurrentTheme everywhere in idlelib.

- bpo-24782: Extension configuration is now a tab in the IDLE Preferences dialog rather than a separate dialog. The former tabs are now a sorted list. Patch by Mark Roseman.

- bpo-22726: Re-activate the config dialog help button with some content about the other buttons and the new IDLE Dark theme.

- bpo-24820: IDLE now has an ‘IDLE Dark’ built-in text color theme. It is more or less IDLE Classic inverted, with a cobalt blue background. Strings, comments, keywords, … are still green, red, orange, … . To use it with IDLEs released before November 2015, hit the ‘Save as New Custom Theme’ button and enter a new name, such as ‘Custom Dark’. The custom theme will work with any IDLE release, and can be modified.

- bpo-25224: README.txt is now an idlelib index for IDLE developers and curious users. The previous user content is now in the IDLE doc chapter. ‘IDLE’ now means ‘Integrated Development and Learning Environment’.

- bpo-24820: Users can now set breakpoint colors in Settings -> Custom Highlighting. Original patch by Mark Roseman.

- bpo-24972: Inactive selection background now matches active selection background, as configured by users, on all systems. Found items are now always highlighted on Windows. Initial patch by Mark Roseman.

- bpo-24570: Idle: make calltip and completion boxes appear on Macs affected by a tk regression. Initial patch by Mark Roseman.

- bpo-24988: Idle ScrolledList context menus (used in debugger) now work on Mac Aqua. Patch by Mark Roseman.

- bpo-24801: Make right-click for context menu work on Mac Aqua. Patch by Mark Roseman.

- bpo-25173: Associate tkinter messageboxes with a specific widget. For Mac OSX, make them a ‘sheet’. Patch by Mark Roseman.

- bpo-25198: Enhance the initial html viewer now used for Idle Help. Properly indent fixed-pitch text (patch by Mark Roseman). Give code snippet a very Sphinx-like light blueish-gray background. Re-use initial width and height set by users for shell and editor. When the Table of Contents (TOC) menu is used, put the section header at the top of the screen.

- bpo-25225: Condense and rewrite Idle doc section on text colors.

- bpo-21995: Explain some differences between IDLE and console Python.

- bpo-22820: Explain need for print when running file from Idle editor.

- bpo-25224: Doc: augment Idle feature list and no-subprocess section.

- bpo-25219: Update doc for Idle command line options. Some were missing and notes were not correct.

- bpo-24861: Most of idlelib is private and subject to change. Use idleib.idle.* to start Idle. See idlelib.__init__.__doc__.

- bpo-25199: Idle: add synchronization comments for future maintainers.

- bpo-16893: Replace help.txt with help.html for Idle doc display. The new idlelib/help.html is rstripped Doc/build/html/library/idle.html. It looks better than help.txt and will better document Idle as released. The tkinter html viewer that works for this file was written by Rose Roseman. The now unused EditorWindow.HelpDialog class and helt.txt file are deprecated.

- bpo-24199: Deprecate unused idlelib.idlever with possible removal in 3.6.

- bpo-24790: Remove extraneous code (which also create 2 & 3 conflicts).

### Documentation

- bpo-26736: Used HTTPS for external links in the documentation if possible.

- bpo-6953: Rework the Readline module documentation to group related functions together, and add more details such as what underlying Readline functions and variables are accessed.

- bpo-23606: Adds note to ctypes documentation regarding cdll.msvcrt.

- bpo-24952: Clarify the default size argument of stack_size() in the “threading” and “_thread” modules. Patch from Mattip.

- bpo-26014: Update 3.x packaging documentation: * “See also” links to the new docs are now provided in the legacy pages * links to setuptools documentation have been updated

### Tests

- bpo-21916: Added tests for the turtle module. Patch by ingrid, Gregory Loyse and Jelle Zijlstra.

- bpo-26295: When using “python3 -m test –testdir=TESTDIR”, regrtest doesn’t add “test.” prefix to test module names.

- bpo-26523: The multiprocessing thread pool (multiprocessing.dummy.Pool) was untested.

- bpo-26015: Added new tests for pickling iterators of mutable sequences.

- bpo-26325: Added test.support.check_no_resource_warning() to check that no ResourceWarning is emitted.

- bpo-25940: Changed test_ssl to use its internal local server more. This avoids relying on svn.python.org, which recently changed root certificate.

- bpo-25616: Tests for OrderedDict are extracted from test_collections into separate file test_ordered_dict.

- bpo-25449: Added tests for OrderedDict subclasses.

- bpo-25188: Add -P/–pgo to test.regrtest to suppress error output when running the test suite for the purposes of a PGO build. Initial patch by Alecsandru Patrascu.

- bpo-22806: Add `python -m test --list-tests` command to list tests.

- bpo-18174: `python -m test --huntrleaks ...` now also checks for leak of file descriptors. Patch written by Richard Oudkerk.

- bpo-25260: Fix `python -m test --coverage` on Windows. Remove the list of ignored directories.

- `PCbuild\rt.bat` now accepts an unlimited number of arguments to pass along to regrtest.py. Previously there was a limit of 9.

- bpo-26583: Skip test_timestamp_overflow in test_import if bytecode files cannot be written.

### Build

- bpo-21277: Don’t try to link _ctypes with a ffi_convenience library.

- bpo-26884: Fix linking extension modules for cross builds. Patch by Xavier de Gaye.

- bpo-26932: Fixed support of RTLD_* constants defined as enum values, not via macros (in particular on Android). Patch by Chi Hsuan Yen.

- bpo-22359: Disable the rules for running _freeze_importlib and pgen when cross-compiling. The output of these programs is normally saved with the source code anyway, and is still regenerated when doing a native build. Patch by Xavier de Gaye.

- bpo-21668: Link audioop, _datetime, _ctypes_test modules to libm, except on Mac OS X. Patch written by Chi Hsuan Yen.

- bpo-25702: A –with-lto configure option has been added that will enable link time optimizations at build time during a make profile-opt. Some compilers and toolchains are known to not produce stable code when using LTO, be sure to test things thoroughly before relying on it. It can provide a few % speed up over profile-opt alone.

- bpo-26624: Adds validation of ucrtbase[d].dll version with warning for old versions.

- bpo-17603: Avoid error about nonexistent fileblocks.o file by using a lower-level check for st_blocks in struct stat.

- bpo-26079: Fixing the build output folder for tix-8.4.3.6. Patch by Bjoern Thiel.

- bpo-26465: Update Windows builds to use OpenSSL 1.0.2g.

- bpo-25348: Added `--pgo` and `--pgo-job` arguments to `PCbuild\build.bat` for building with Profile-Guided Optimization. The old `PCbuild\build_pgo.bat` script is removed.

- bpo-25827: Add support for building with ICC to `configure`, including a new `--with-icc` flag.

- bpo-25696: Fix installation of Python on UNIX with make -j9.

- bpo-24986: It is now possible to build Python on Windows without errors when external libraries are not available.

- bpo-24421: Compile Modules/_math.c once, before building extensions. Previously it could fail to compile properly if the math and cmath builds were concurrent.

- bpo-26465: Update OS X 10.5+ 32-bit-only installer to build and link with OpenSSL 1.0.2g.

- bpo-26268: Update Windows builds to use OpenSSL 1.0.2f.

- bpo-25136: Support Apple Xcode 7’s new textual SDK stub libraries.

- bpo-24324: Do not enable unreachable code warnings when using gcc as the option does not work correctly in older versions of gcc and has been silently removed as of gcc-4.5.

### Windows

- bpo-27053: Updates make_zip.py to correctly generate library ZIP file.

- bpo-26268: Update the prepare_ssl.py script to handle OpenSSL releases that don’t include the contents of the include directory (that is, 1.0.2e and later).

- bpo-26071: bdist_wininst created binaries fail to start and find 32bit Python

- bpo-26073: Update the list of magic numbers in launcher

- bpo-26065: Excludes venv from library when generating embeddable distro.

- bpo-25022: Removed very outdated PC/example_nt/ directory.

### Tools/Demos

- bpo-26799: Fix python-gdb.py: don’t get C types once when the Python code is loaded, but get C types on demand. The C types can change if python-gdb.py is loaded before the Python executable. Patch written by Thomas Ilsche.

- bpo-26271: Fix the Freeze tool to properly use flags passed through configure. Patch by Daniel Shaulov.

- bpo-26489: Add dictionary unpacking support to Tools/parser/unparse.py. Patch by Guo Ci Teo.

- bpo-26316: Fix variable name typo in Argument Clinic.

- bpo-25440: Fix output of python-config –extension-suffix.

- bpo-25154: The pyvenv script has been deprecated in favour of `python3 -m venv`.

### C API

- bpo-26312: SystemError is now raised in all programming bugs with using PyArg_ParseTupleAndKeywords(). RuntimeError did raised before in some programming bugs.

- bpo-26198: ValueError is now raised instead of TypeError on buffer overflow in parsing “es#” and “et#” format units. SystemError is now raised instead of TypeError on programmatical error in parsing format string.

## Python 3.5.5 final

Release date: 2018-02-04

There were no new changes in version 3.5.5.

## Python 3.5.5 release candidate 1

Release date: 2018-01-23

### Security

- bpo-32551: The `sys.path[0]` initialization change for bpo-29139 caused a regression by revealing an inconsistency in how sys.path is initialized when executing `__main__` from a zipfile, directory, or other import location. This is considered a potential security issue, as it may lead to privileged processes unexpectedly loading code from user controlled directories in situations where that was not previously the case. The interpreter now consistently avoids ever adding the import location’s parent directory to `sys.path`, and ensures no other `sys.path` entries are inadvertently modified when inserting the import location named on the command line. (Originally reported as bpo-29723 against Python 3.6rc1, but it was missed at the time that the then upcoming Python 3.5.4 release would also be affected)

- bpo-30657: Fixed possible integer overflow in PyBytes_DecodeEscape, CVE-2017-1000158. Original patch by Jay Bosamiya; rebased to Python 3 by Miro Hrončok.

- bpo-30947: Upgrade libexpat embedded copy from version 2.2.1 to 2.2.3 to get security fixes.

### Core and Builtins

- bpo-31095: Fix potential crash during GC caused by `tp_dealloc` which doesn’t call `PyObject_GC_UnTrack()`.

### Library

- bpo-32072: Fixed issues with binary plists: Fixed saving bytearrays. Identical objects will be saved only once. Equal references will be load as identical objects. Added support for saving and loading recursive data structures.

- bpo-31170: expat: Update libexpat from 2.2.3 to 2.2.4. Fix copying of partial characters for UTF-8 input (libexpat bug 115): https://github.com/libexpat/libexpat/issues/115

## Python 3.5.4 final

Release date: 2017-08-07

### Library

- bpo-30119: ftplib.FTP.putline() now throws ValueError on commands that contains CR or LF. Patch by Dong-hee Na.

## Python 3.5.4 release candidate 1

Release date: 2017-07-23

### Security

- bpo-30730: Prevent environment variables injection in subprocess on Windows. Prevent passing other environment variables and command arguments.

- bpo-30694: Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes of multiple security vulnerabilities including: CVE-2017-9233 (External entity infinite loop DoS), CVE-2016-9063 (Integer overflow, re-fix), CVE-2016-0718 (Fix regression bugs from 2.2.0’s fix to CVE-2016-0718) and CVE-2012-0876 (Counter hash flooding with SipHash). Note: the CVE-2016-5300 (Use os-specific entropy sources like getrandom) doesn’t impact Python, since Python already gets entropy from the OS to set the expat secret using `XML_SetHashSalt()`.

- bpo-30500: Fix urllib.parse.splithost() to correctly parse fragments. For example, `splithost('//127.0.0.1#@evil.com/')` now correctly returns the `127.0.0.1` host, instead of treating `@evil.com` as the host in an authentication (`login@host`).

- bpo-29591: Update expat copy from 2.1.1 to 2.2.0 to get fixes of CVE-2016-0718 and CVE-2016-4472. See https://sourceforge.net/p/expat/bugs/537/ for more information.

### Core and Builtins

- bpo-30876: Relative import from unloaded package now reimports the package instead of failing with SystemError. Relative import from non-package now fails with ImportError rather than SystemError.

- bpo-30765: Avoid blocking in pthread_mutex_lock() when PyThread_acquire_lock() is asked not to block.

- bpo-27945: Fixed various segfaults with dict when input collections are mutated during searching, inserting or comparing. Based on patches by Duane Griffin and Tim Mitchell.

- bpo-25794: Fixed type.__setattr__() and type.__delattr__() for non-interned attribute names. Based on patch by Eryk Sun.

- bpo-29935: Fixed error messages in the index() method of tuple, list and deque when pass indices of wrong type.

- bpo-28876: `bool(range)` works even if `len(range)` raises `OverflowError`.

- bpo-29600: Fix wrapping coroutine return values in StopIteration.

- bpo-29537: Restore runtime compatibility with bytecode files generated by CPython 3.5.0 to 3.5.2, and adjust the eval loop to avoid the problems that could be caused by the malformed variant of the BUILD_MAP_UNPACK_WITH_CALL opcode that they may contain. Patch by Petr Viktorin, Serhiy Storchaka, and Nick Coghlan.

- bpo-28598: Support __rmod__ for subclasses of str being called before str.__mod__. Patch by Martijn Pieters.

- bpo-29602: Fix incorrect handling of signed zeros in complex constructor for complex subclasses and for inputs having a __complex__ method. Patch by Serhiy Storchaka.

- bpo-29347: Fixed possibly dereferencing undefined pointers when creating weakref objects.

- bpo-29438: Fixed use-after-free problem in key sharing dict.

- bpo-29319: Prevent RunMainFromImporter overwriting sys.path[0].

- bpo-29337: Fixed possible BytesWarning when compare the code objects. Warnings could be emitted at compile time.

- bpo-29478: If max_line_length=None is specified while using the Compat32 policy, it is no longer ignored. Patch by Mircea Cosbuc.

### Library

- bpo-29403: Fix `unittest.mock`’s autospec to not fail on method-bound builtin functions. Patch by Aaron Gallagher.

- bpo-30961: Fix decrementing a borrowed reference in tracemalloc.

- bpo-30886: Fix multiprocessing.Queue.join_thread(): it now waits until the thread completes, even if the thread was started by the same process which created the queue.

- bpo-29854: Fix segfault in readline when using readline’s history-size option. Patch by Nir Soffer.

- bpo-30807: signal.setitimer() may disable the timer when passed a tiny value. Tiny values (such as 1e-6) are valid non-zero values for setitimer(), which is specified as taking microsecond-resolution intervals. However, on some platform, our conversion routine could convert 1e-6 into a zero interval, therefore disabling the timer instead of (re-)scheduling it.

- bpo-30441: Fix bug when modifying os.environ while iterating over it

- bpo-30532: Fix email header value parser dropping folding white space in certain cases.

- bpo-29169: Update zlib to 1.2.11.

- bpo-30879: os.listdir() and os.scandir() now emit bytes names when called with bytes-like argument.

- bpo-30746: Prohibited the ‘=’ character in environment variable names in `os.putenv()` and `os.spawn*()`.

- bpo-29755: Fixed the lgettext() family of functions in the gettext module. They now always return bytes.

- bpo-30645: Fix path calculation in imp.load_package(), fixing it for cases when a package is only shipped with bytecodes. Patch by Alexandru Ardelean.

- bpo-23890: unittest.TestCase.assertRaises() now manually breaks a reference cycle to not keep objects alive longer than expected.

- bpo-30149: inspect.signature() now supports callables with variable-argument parameters wrapped with partialmethod. Patch by Dong-hee Na.

- bpo-29931: Fixed comparison check for ipaddress.ip_interface objects. Patch by Sanjay Sundaresan.

- bpo-24484: Avoid race condition in multiprocessing cleanup.

- bpo-28994: The traceback no longer displayed for SystemExit raised in a callback registered by atexit.

- bpo-30508: Don’t log exceptions if Task/Future “cancel()” method was called.

- bpo-28556: Updates to typing module: Add generic AsyncContextManager, add support for ContextManager on all versions. Original PRs by Jelle Zijlstra and Ivan Levkivskyi

- bpo-29870: Fix ssl sockets leaks when connection is aborted in asyncio/ssl implementation. Patch by Michaël Sghaïer.

- bpo-29743: Closing transport during handshake process leaks open socket. Patch by Nikolay Kim

- bpo-27585: Fix waiter cancellation in asyncio.Lock. Patch by Mathieu Sornay.

- bpo-30418: On Windows, subprocess.Popen.communicate() now also ignore EINVAL on stdin.write() if the child process is still running but closed the pipe.

- bpo-30378: Fix the problem that logging.handlers.SysLogHandler cannot handle IPv6 addresses.

- bpo-29960: Preserve generator state when _random.Random.setstate() raises an exception. Patch by Bryan Olson.

- bpo-30414: multiprocessing.Queue._feed background running thread do not break from main loop on exception.

- bpo-30003: Fix handling escape characters in HZ codec. Based on patch by Ma Lin.

- bpo-30301: Fix AttributeError when using SimpleQueue.empty() under spawn and forkserver start methods.

- bpo-30329: imaplib and poplib now catch the Windows socket WSAEINVAL error (code 10022) on shutdown(SHUT_RDWR): An invalid operation was attempted. This error occurs sometimes on SSL connections.

- bpo-30375: Warnings emitted when compile a regular expression now always point to the line in the user code. Previously they could point into inners of the re module if emitted from inside of groups or conditionals.

- bpo-30048: Fixed `Task.cancel()` can be ignored when the task is running coroutine and the coroutine returned without any more `await`.

- bpo-29990: Fix range checking in GB18030 decoder. Original patch by Ma Lin.

- bpo-26293: Change resulted because of zipfile breakage. (See also: bpo-29094)

- bpo-30243: Removed the __init__ methods of _json’s scanner and encoder. Misusing them could cause memory leaks or crashes. Now scanner and encoder objects are completely initialized in the __new__ methods.

- bpo-30185: Avoid KeyboardInterrupt tracebacks in forkserver helper process when Ctrl-C is received.

- bpo-28556: Various updates to typing module: add typing.NoReturn type, use WrapperDescriptorType, minor bug-fixes. Original PRs by Jim Fasarakis-Hilliard and Ivan Levkivskyi.

- bpo-30205: Fix getsockname() for unbound AF_UNIX sockets on Linux.

- bpo-30070: Fixed leaks and crashes in errors handling in the parser module.

- bpo-30061: Fixed crashes in IOBase methods __next__() and readlines() when readline() or __next__() respectively return non-sizeable object. Fixed possible other errors caused by not checking results of PyObject_Size(), PySequence_Size(), or PyMapping_Size().

- bpo-30068: _io._IOBase.readlines will check if it’s closed first when hint is present.

- bpo-29694: Fixed race condition in pathlib mkdir with flags parents=True. Patch by Armin Rigo.

- bpo-29692: Fixed arbitrary unchaining of RuntimeError exceptions in contextlib.contextmanager. Patch by Siddharth Velankar.

- bpo-29998: Pickling and copying ImportError now preserves name and path attributes.

- bpo-29942: Fix a crash in itertools.chain.from_iterable when encountering long runs of empty iterables.

- bpo-27863: Fixed multiple crashes in ElementTree caused by race conditions and wrong types.

- bpo-28699: Fixed a bug in pools in multiprocessing.pool that raising an exception at the very first of an iterable may swallow the exception or make the program hang. Patch by Davin Potts and Xiang Zhang.

- bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True) when the OS gives priority to errors such as EACCES over EEXIST.

- bpo-29861: Release references to tasks, their arguments and their results as soon as they are finished in multiprocessing.Pool.

- bpo-29884: faulthandler: Restore the old sigaltstack during teardown. Patch by Christophe Zeitouny.

- bpo-25455: Fixed crashes in repr of recursive buffered file-like objects.

- bpo-29800: Fix crashes in partial.__repr__ if the keys of partial.keywords are not strings. Patch by Michael Seifert.

- bpo-29742: get_extra_info() raises exception if get called on closed ssl transport. Patch by Nikolay Kim.

- bpo-8256: Fixed possible failing or crashing input() if attributes “encoding” or “errors” of sys.stdin or sys.stdout are not set or are not strings.

- bpo-28298: Fix a bug that prevented array ‘Q’, ‘L’ and ‘I’ from accepting big intables (objects that have __int__) as elements. Patch by Oren Milman.

- bpo-29615: SimpleXMLRPCDispatcher no longer chains KeyError (or any other exception) to exception(s) raised in the dispatched methods. Patch by Petr Motejlek.

- bpo-29704: asyncio.subprocess.SubprocessStreamProtocol no longer closes before all pipes are closed.

- bpo-29703: Fix asyncio to support instantiation of new event loops in child processes.

- bpo-29376: Fix assertion error in threading._DummyThread.is_alive().

- bpo-29110: Fix file object leak in aifc.open() when file is given as a filesystem path and is not in valid AIFF format. Patch by Anthony Zhang.

- bpo-28961: Fix unittest.mock._Call helper: don’t ignore the name parameter anymore. Patch written by Jiajun Huang.

- bpo-29532: Altering a kwarg dictionary passed to functools.partial() no longer affects a partial object after creation.

- bpo-28556: Various updates to typing module: typing.Counter, typing.ChainMap, improved ABC caching, etc. Original PRs by Jelle Zijlstra, Ivan Levkivskyi, Manuel Krebber, and Łukasz Langa.

- bpo-29100: Fix datetime.fromtimestamp() regression introduced in Python 3.6.0: check minimum and maximum years.

- bpo-29519: Fix weakref spewing exceptions during interpreter shutdown when used with a rare combination of multiprocessing and custom codecs.

- bpo-29416: Prevent infinite loop in pathlib.Path.mkdir

- bpo-29444: Fixed out-of-bounds buffer access in the group() method of the match object. Based on patch by WGH.

- bpo-29335: Fix subprocess.Popen.wait() when the child process has exited to a stopped instead of terminated state (ex: when under ptrace).

- bpo-29290: Fix a regression in argparse that help messages would wrap at non-breaking spaces.

- bpo-28735: Fixed the comparison of mock.MagickMock with mock.ANY.

- bpo-29011: Fix an important omission by adding Deque to the typing module.

- bpo-29219: Fixed infinite recursion in the repr of uninitialized ctypes.CDLL instances.

- bpo-28969: Fixed race condition in C implementation of functools.lru_cache. KeyError could be raised when cached function with full cache was simultaneously called from different threads with the same uncached arguments.

- bpo-29142: In urllib.request, suffixes in no_proxy environment variable with leading dots could match related hostnames again (e.g. .b.c matches a.b.c). Patch by Milan Oberkirch.

### Documentation

- bpo-30176: Add missing attribute related constants in curses documentation.

- bpo-26985: Add missing info of code object in inspect documentation.

- bpo-28929: Link the documentation to its source file on GitHub.

- bpo-25008: Document smtpd.py as effectively deprecated and add a pointer to aiosmtpd, a third-party asyncio-based replacement.

- bpo-26355: Add canonical header link on each page to corresponding major version of the documentation. Patch by Matthias Bussonnier.

- bpo-29349: Fix Python 2 syntax in code for building the documentation.

### Tests

- bpo-30822: Fix regrtest command line parser to allow passing -u extralargefile to run test_zipfile64.

- bpo-30383: regrtest: Enhance regrtest and backport features from the master branch. Add options: –coverage, –testdir, –list-tests (list test files, don’t run them), –list-cases (list test identifiers, don’t run them, bpo-30523), –matchfile (load a list of test filters from a text file, bpo-30540), –slowest (alias to –slow). Enhance output: add timestamp, test result, currently running tests, “Tests result: xxx” summary with total duration, etc. Fix reference leak hunting in regrtest, –huntrleaks: regrtest now warms up caches, create explicitly all internal singletons which are created on demand to prevent false positives when checking for reference leaks. (bpo-30675).

- bpo-30357: test_thread: setUp() now uses support.threading_setup() and support.threading_cleanup() to wait until threads complete to avoid random side effects on following tests. Initial patch written by Grzegorz Grzywacz.

- bpo-28087: Skip test_asyncore and test_eintr poll failures on macOS. Skip some tests of select.poll when running on macOS due to unresolved issues with the underlying system poll function on some macOS versions.

- bpo-30197: Enhanced functions swap_attr() and swap_item() in the test.support module. They now work when delete replaced attribute or item inside the with statement. The old value of the attribute or item (or None if it doesn’t exist) now will be assigned to the target of the “as” clause, if there is one.

- bpo-29571: to match the behaviour of the `re.LOCALE` flag, test_re.test_locale_flag now uses `locale.getpreferredencoding(False)` to determine the candidate encoding for the test regex (allowing it to correctly skip the test when the default locale encoding is a multi-byte encoding)

### Build

- bpo-29243: Prevent unnecessary rebuilding of Python during `make test`, `make install` and some other make targets when configured with `--enable-optimizations`.

- bpo-23404: Don’t regenerate generated files based on file modification time anymore: the action is now explicit. Replace `make touch` with `make regen-all`.

- bpo-29643: Fix `--enable-optimization` didn’t work.

### Windows

- bpo-30687: Locate msbuild.exe on Windows when building rather than vcvarsall.bat

- bpo-29392: Prevent crash when passing invalid arguments into msvcrt module.

### C API

- bpo-27867: Function PySlice_GetIndicesEx() is replaced with a macro if Py_LIMITED_API is set to the value between 0x03050400 and 0x03060000 (not including) or 0x03060100 or higher.

- bpo-29083: Fixed the declaration of some public API functions. PyArg_VaParse() and PyArg_VaParseTupleAndKeywords() were not available in limited API. PyArg_ValidateKeywordArguments(), PyArg_UnpackTuple() and Py_BuildValue() were not available in limited API of version < 3.3 when PY_SSIZE_T_CLEAN is defined.

## Python 3.5.3 final

Release date: 2017-01-17

There were no code changes between 3.5.3rc1 and 3.5.3 final.

## Python 3.5.3 release candidate 1

Release date: 2017-01-02

### Core and Builtins

- bpo-29073: bytearray formatting no longer truncates on first null byte.

- bpo-28932: Do not include <sys/random.h> if it does not exist.

- bpo-28147: Fix a memory leak in split-table dictionaries: setattr() must not convert combined table into split table.

- bpo-25677: Correct the positioning of the syntax error caret for indented blocks. Based on patch by Michael Layzell.

- bpo-29000: Fixed bytes formatting of octals with zero padding in alternate form.

- bpo-28512: Fixed setting the offset attribute of SyntaxError by PyErr_SyntaxLocationEx() and PyErr_SyntaxLocationObject().

- bpo-28991: functools.lru_cache() was susceptible to an obscure reentrancy bug caused by a monkey-patched len() function.

- bpo-28648: Fixed crash in Py_DecodeLocale() in debug build on Mac OS X when decode astral characters. Patch by Xiang Zhang.

- bpo-19398: Extra slash no longer added to sys.path components in case of empty compile-time PYTHONPATH components.

- bpo-28426: Fixed potential crash in PyUnicode_AsDecodedObject() in debug build.

- bpo-23782: Fixed possible memory leak in _PyTraceback_Add() and exception loss in PyTraceBack_Here().

- bpo-28379: Added sanity checks and tests for PyUnicode_CopyCharacters(). Patch by Xiang Zhang.

- bpo-28376: The type of long range iterator is now registered as Iterator. Patch by Oren Milman.

- bpo-28376: The constructor of range_iterator now checks that step is not 0. Patch by Oren Milman.

- bpo-26906: Resolving special methods of uninitialized type now causes implicit initialization of the type instead of a fail.

- bpo-18287: PyType_Ready() now checks that tp_name is not NULL. Original patch by Niklas Koep.

- bpo-24098: Fixed possible crash when AST is changed in process of compiling it.

- bpo-28350: String constants with null character no longer interned.

- bpo-26617: Fix crash when GC runs during weakref callbacks.

- bpo-27942: String constants now interned recursively in tuples and frozensets.

- bpo-21578: Fixed misleading error message when ImportError called with invalid keyword args.

- bpo-28203: Fix incorrect type in error message from `complex(1.0, {2:3})`. Patch by Soumya Sharma.

- bpo-27955: Fallback on reading /dev/urandom device when the getrandom() syscall fails with EPERM, for example when blocked by SECCOMP.

- bpo-28131: Fix a regression in zipimport’s compile_source(). zipimport should use the same optimization level as the interpreter.

- bpo-25221: Fix corrupted result from PyLong_FromLong(0) when Python is compiled with NSMALLPOSINTS = 0.

- bpo-25758: Prevents zipimport from unnecessarily encoding a filename (patch by Eryk Sun)

- bpo-28189: dictitems_contains no longer swallows compare errors. (Patch by Xiang Zhang)

- bpo-27812: Properly clear out a generator’s frame’s backreference to the generator to prevent crashes in frame.clear().

- bpo-27811: Fix a crash when a coroutine that has not been awaited is finalized with warnings-as-errors enabled.

- bpo-27587: Fix another issue found by PVS-Studio: Null pointer check after use of ‘def’ in _PyState_AddModule(). Initial patch by Christian Heimes.

- bpo-26020: set literal evaluation order did not match documented behaviour.

- bpo-27782: Multi-phase extension module import now correctly allows the `m_methods` field to be used to add module level functions to instances of non-module types returned from `Py_create_mod`. Patch by Xiang Zhang.

- bpo-27936: The round() function accepted a second None argument for some types but not for others. Fixed the inconsistency by accepting None for all numeric types.

- bpo-27487: Warn if a submodule argument to “python -m” or runpy.run_module() is found in sys.modules after parent packages are imported, but before the submodule is executed.

- bpo-27558: Fix a SystemError in the implementation of “raise” statement. In a brand new thread, raise a RuntimeError since there is no active exception to reraise. Patch written by Xiang Zhang.

- bpo-27419: Standard __import__() no longer look up “__import__” in globals or builtins for importing submodules or “from import”. Fixed handling an error of non-string package name.

- bpo-27083: Respect the PYTHONCASEOK environment variable under Windows.

- bpo-27514: Make having too many statically nested blocks a SyntaxError instead of SystemError.

- bpo-27473: Fixed possible integer overflow in bytes and bytearray concatenations. Patch by Xiang Zhang.

- bpo-27507: Add integer overflow check in bytearray.extend(). Patch by Xiang Zhang.

- bpo-27581: Don’t rely on wrapping for overflow check in PySequence_Tuple(). Patch by Xiang Zhang.

- bpo-27443: __length_hint__() of bytearray iterators no longer return a negative integer for a resized bytearray.

- bpo-27942: Fix memory leak in codeobject.c

### Library

- bpo-15812: inspect.getframeinfo() now correctly shows the first line of a context. Patch by Sam Breese.

- bpo-29094: Offsets in a ZIP file created with extern file object and modes “w” and “x” now are relative to the start of the file.

- bpo-13051: Fixed recursion errors in large or resized curses.textpad.Textbox. Based on patch by Tycho Andersen.

- bpo-29119: Fix weakrefs in the pure python version of collections.OrderedDict move_to_end() method. Contributed by Andra Bogildea.

- bpo-9770: curses.ascii predicates now work correctly with negative integers.

- bpo-28427: old keys should not remove new values from WeakValueDictionary when collecting from another thread.

- bpo-28923: Remove editor artifacts from Tix.py.

- bpo-28871: Fixed a crash when deallocate deep ElementTree.

- bpo-19542: Fix bugs in WeakValueDictionary.setdefault() and WeakValueDictionary.pop() when a GC collection happens in another thread.

- bpo-20191: Fixed a crash in resource.prlimit() when pass a sequence that doesn’t own its elements as limits.

- bpo-28779: multiprocessing.set_forkserver_preload() would crash the forkserver process if a preloaded module instantiated some multiprocessing objects such as locks.

- bpo-28847: dbm.dumb now supports reading read-only files and no longer writes the index file when it is not changed.

- bpo-25659: In ctypes, prevent a crash calling the from_buffer() and from_buffer_copy() methods on abstract classes like Array.

- bpo-28732: Fix crash in os.spawnv() with no elements in args

- bpo-28485: Always raise ValueError for negative compileall.compile_dir(workers=…) parameter, even when multithreading is unavailable.

- bpo-28387: Fixed possible crash in _io.TextIOWrapper deallocator when the garbage collector is invoked in other thread. Based on patch by Sebastian Cufre.

- bpo-27517: LZMA compressor and decompressor no longer raise exceptions if given empty data twice. Patch by Benjamin Fogle.

- bpo-28549: Fixed segfault in curses’s addch() with ncurses6.

- bpo-28449: tarfile.open() with mode “r” or “r:” now tries to open a tar file with compression before trying to open it without compression. Otherwise it had 50% chance failed with ignore_zeros=True.

- bpo-23262: The webbrowser module now supports Firefox 36+ and derived browsers. Based on patch by Oleg Broytman.

- bpo-27939: Fixed bugs in tkinter.ttk.LabeledScale and tkinter.Scale caused by representing the scale as float value internally in Tk. tkinter.IntVar now works if float value is set to underlying Tk variable.

- bpo-28255: calendar.TextCalendar().prmonth() no longer prints a space at the start of new line after printing a month’s calendar. Patch by Xiang Zhang.

- bpo-20491: The textwrap.TextWrapper class now honors non-breaking spaces. Based on patch by Kaarle Ritvanen.

- bpo-28353: os.fwalk() no longer fails on broken links.

- bpo-25464: Fixed HList.header_exists() in tkinter.tix module by addin a workaround to Tix library bug.

- bpo-28488: shutil.make_archive() no longer add entry “./” to ZIP archive.

- bpo-24452: Make webbrowser support Chrome on Mac OS X.

- bpo-20766: Fix references leaked by pdb in the handling of SIGINT handlers.

- bpo-26293: Fixed writing ZIP files that starts not from the start of the file. Offsets in ZIP file now are relative to the start of the archive in conforming to the specification.

- bpo-28321: Fixed writing non-BMP characters with binary format in plistlib.

- bpo-28322: Fixed possible crashes when unpickle itertools objects from incorrect pickle data. Based on patch by John Leitch.

- Fix possible integer overflows and crashes in the mmap module with unusual usage patterns.

- bpo-1703178: Fix the ability to pass the –link-objects option to the distutils build_ext command.

- bpo-28253: Fixed calendar functions for extreme months: 0001-01 and 9999-12. Methods itermonthdays() and itermonthdays2() are reimplemented so that they don’t call itermonthdates() which can cause datetime.date under/overflow.

- bpo-28275: Fixed possible use after free in the decompress() methods of the LZMADecompressor and BZ2Decompressor classes. Original patch by John Leitch.

- bpo-27897: Fixed possible crash in sqlite3.Connection.create_collation() if pass invalid string-like object as a name. Patch by Xiang Zhang.

- bpo-18893: Fix invalid exception handling in Lib/ctypes/macholib/dyld.py. Patch by Madison May.

- bpo-27611: Fixed support of default root window in the tkinter.tix module.

- bpo-27348: In the traceback module, restore the formatting of exception messages like “Exception: None”. This fixes a regression introduced in 3.5a2.

- bpo-25651: Allow falsy values to be used for msg parameter of subTest().

- bpo-27932: Prevent memory leak in win32_ver().

- Fix UnboundLocalError in socket._sendfile_use_sendfile.

- bpo-28075: Check for ERROR_ACCESS_DENIED in Windows implementation of os.stat(). Patch by Eryk Sun.

- bpo-25270: Prevent codecs.escape_encode() from raising SystemError when an empty bytestring is passed.

- bpo-28181: Get antigravity over HTTPS. Patch by Kaartic Sivaraam.

- bpo-25895: Enable WebSocket URL schemes in urllib.parse.urljoin. Patch by Gergely Imreh and Markus Holtermann.

- bpo-27599: Fixed buffer overrun in binascii.b2a_qp() and binascii.a2b_qp().

- bpo-19003: m email.generator now replaces only `\r` and/or `\n` line endings, per the RFC, instead of all unicode line endings.

- bpo-28019: itertools.count() no longer rounds non-integer step in range between 1.0 and 2.0 to 1.

- bpo-25969: Update the lib2to3 grammar to handle the unpacking generalizations added in 3.5.

- bpo-14977: mailcap now respects the order of the lines in the mailcap files (“first match”), as required by RFC 1542. Patch by Michael Lazar.

- bpo-24594: Validates persist parameter when opening MSI database

- bpo-17582: xml.etree.ElementTree nows preserves whitespaces in attributes (Patch by Duane Griffin. Reviewed and approved by Stefan Behnel.)

- bpo-28047: Fixed calculation of line length used for the base64 CTE in the new email policies.

- bpo-27445: Don’t pass str(_charset) to MIMEText.set_payload(). Patch by Claude Paroz.

- bpo-22450: urllib now includes an `Accept: */*` header among the default headers. This makes the results of REST API requests more consistent and predictable especially when proxy servers are involved.

- lib2to3.pgen3.driver.load_grammar() now creates a stable cache file between runs given the same Grammar.txt input regardless of the hash randomization setting.

- bpo-27570: Avoid zero-length memcpy() etc calls with null source pointers in the “ctypes” and “array” modules.

- bpo-22233: Break email header lines only on the RFC specified CR and LF characters, not on arbitrary unicode line breaks. This also fixes a bug in HTTP header parsing.

- bpo-27988: Fix email iter_attachments incorrect mutation of payload list.

- bpo-27691: Fix ssl module’s parsing of GEN_RID subject alternative name fields in X.509 certs.

- bpo-27850: Remove 3DES from ssl module’s default cipher list to counter measure sweet32 attack (CVE-2016-2183).

- bpo-27766: Add ChaCha20 Poly1305 to ssl module’s default cipher list. (Required OpenSSL 1.1.0 or LibreSSL).

- bpo-26470: Port ssl and hashlib module to OpenSSL 1.1.0.

- Remove support for passing a file descriptor to os.access. It never worked but previously didn’t raise.

- bpo-12885: Fix error when distutils encounters symlink.

- bpo-27881: Fixed possible bugs when setting sqlite3.Connection.isolation_level. Based on patch by Xiang Zhang.

- bpo-27861: Fixed a crash in sqlite3.Connection.cursor() when a factory creates not a cursor. Patch by Xiang Zhang.

- bpo-19884: Avoid spurious output on OS X with Gnu Readline.

- bpo-27706: Restore deterministic behavior of random.Random().seed() for string seeds using seeding version 1. Allows sequences of calls to random() to exactly match those obtained in Python 2. Patch by Nofar Schnider.

- bpo-10513: Fix a regression in Connection.commit(). Statements should not be reset after a commit.

- A new version of typing.py from https://github.com/python/typing: Collection (only for 3.6) (bpo-27598). Add FrozenSet to __all__ (upstream #261). Fix crash in _get_type_vars() (upstream #259). Remove the dict constraint in ForwardRef._eval_type (upstream #252).

- bpo-27539: Fix unnormalised `Fraction.__pow__` result in the case of negative exponent and negative base.

- bpo-21718: cursor.description is now available for queries using CTEs.

- bpo-2466: posixpath.ismount now correctly recognizes mount points which the user does not have permission to access.

- bpo-27773: Correct some memory management errors server_hostname in _ssl.wrap_socket().

- bpo-26750: unittest.mock.create_autospec() now works properly for subclasses of property() and other data descriptors.

- In the curses module, raise an error if window.getstr() or window.instr() is passed a negative value.

- bpo-27783: Fix possible usage of uninitialized memory in operator.methodcaller.

- bpo-27774: Fix possible Py_DECREF on unowned object in _sre.

- bpo-27760: Fix possible integer overflow in binascii.b2a_qp.

- bpo-27758: Fix possible integer overflow in the _csv module for large record lengths.

- bpo-27568: Prevent HTTPoxy attack (CVE-2016-1000110). Ignore the HTTP_PROXY variable when REQUEST_METHOD environment is set, which indicates that the script is in CGI mode.

- bpo-27656: Do not assume sched.h defines any SCHED_* constants.

- bpo-27130: In the “zlib” module, fix handling of large buffers (typically 4 GiB) when compressing and decompressing. Previously, inputs were limited to 4 GiB, and compression and decompression operations did not properly handle results of 4 GiB.

- bpo-27533: Release GIL in nt._isdir

- bpo-17711: Fixed unpickling by the persistent ID with protocol 0. Original patch by Alexandre Vassalotti.

- bpo-27522: Avoid an unintentional reference cycle in email.feedparser.

- bpo-26844: Fix error message for imp.find_module() to refer to ‘path’ instead of ‘name’. Patch by Lev Maximov.

- bpo-23804: Fix SSL zero-length recv() calls to not block and not raise an error about unclean EOF.

- bpo-27466: Change time format returned by http.cookie.time2netscape, confirming the netscape cookie format and making it consistent with documentation.

- bpo-26664: Fix activate.fish by removing mis-use of `$`.

- bpo-22115: Fixed tracing Tkinter variables: trace_vdelete() with wrong mode no longer break tracing, trace_vinfo() now always returns a list of pairs of strings, tracing in the “u” mode now works.

- Fix a scoping issue in importlib.util.LazyLoader which triggered an UnboundLocalError when lazy-loading a module that was already put into sys.modules.

- bpo-27079: Fixed curses.ascii functions isblank(), iscntrl() and ispunct().

- bpo-26754: Some functions (compile() etc) accepted a filename argument encoded as an iterable of integers. Now only strings and byte-like objects are accepted.

- bpo-27048: Prevents distutils failing on Windows when environment variables contain non-ASCII characters

- bpo-27330: Fixed possible leaks in the ctypes module.

- bpo-27238: Got rid of bare excepts in the turtle module. Original patch by Jelle Zijlstra.

- bpo-27122: When an exception is raised within the context being managed by a contextlib.ExitStack() and one of the exit stack generators catches and raises it in a chain, do not re-raise the original exception when exiting, let the new chained one through. This avoids the PEP 479 bug described in issue25782.

### Security

- bpo-27278: Fix os.urandom() implementation using getrandom() on Linux. Truncate size to INT_MAX and loop until we collected enough random bytes, instead of casting a directly Py_ssize_t to int.

### Library

- bpo-26386: Fixed ttk.TreeView selection operations with item id’s containing spaces.

### Security

- bpo-22636: Avoid shell injection problems with ctypes.util.find_library().

### Library

- bpo-16182: Fix various functions in the “readline” module to use the locale encoding, and fix get_begidx() and get_endidx() to return code point indexes.

- bpo-27392: Add loop.connect_accepted_socket(). Patch by Jim Fulton.

- bpo-27930: Improved behaviour of logging.handlers.QueueListener. Thanks to Paulo Andrade and Petr Viktorin for the analysis and patch.

- bpo-21201: Improves readability of multiprocessing error message. Thanks to Wojciech Walczak for patch.

- bpo-27456: asyncio: Set TCP_NODELAY by default.

- bpo-27906: Fix socket accept exhaustion during high TCP traffic. Patch by Kevin Conway.

- bpo-28174: Handle when SO_REUSEPORT isn’t properly supported. Patch by Seth Michael Larson.

- bpo-26654: Inspect functools.partial in asyncio.Handle.__repr__. Patch by iceboy.

- bpo-26909: Fix slow pipes IO in asyncio. Patch by INADA Naoki.

- bpo-28176: Fix callbacks race in asyncio.SelectorLoop.sock_connect.

- bpo-27759: Fix selectors incorrectly retain invalid file descriptors. Patch by Mark Williams.

- bpo-28368: Refuse monitoring processes if the child watcher has no loop attached. Patch by Vincent Michel.

- bpo-28369: Raise RuntimeError when transport’s FD is used with add_reader, add_writer, etc.

- bpo-28370: Speedup asyncio.StreamReader.readexactly. Patch by Коренберг Марк.

- bpo-28371: Deprecate passing asyncio.Handles to run_in_executor.

- bpo-28372: Fix asyncio to support formatting of non-python coroutines.

- bpo-28399: Remove UNIX socket from FS before binding. Patch by Коренберг Марк.

- bpo-27972: Prohibit Tasks to await on themselves.

- bpo-26923: Fix asyncio.Gather to refuse being cancelled once all children are done. Patch by Johannes Ebke.

- bpo-26796: Don’t configure the number of workers for default threadpool executor. Initial patch by Hans Lawrenz.

- bpo-28600: Optimize loop.call_soon().

- bpo-28613: Fix get_event_loop() return the current loop if called from coroutines/callbacks.

- bpo-28639: Fix inspect.isawaitable to always return bool Patch by Justin Mayfield.

- bpo-28652: Make loop methods reject socket kinds they do not support.

- bpo-28653: Fix a refleak in functools.lru_cache.

- bpo-28703: Fix asyncio.iscoroutinefunction to handle Mock objects.

- bpo-24142: Reading a corrupt config file left the parser in an invalid state. Original patch by Florian Höch.

- bpo-28990: Fix SSL hanging if connection is closed before handshake completed. (Patch by HoHo-Ho)

### IDLE

- bpo-15308: Add ‘interrupt execution’ (^C) to Shell menu. Patch by Roger Serwy, updated by Bayard Randel.

- bpo-27922: Stop IDLE tests from ‘flashing’ gui widgets on the screen.

- Add version to title of IDLE help window.

- bpo-25564: In section on IDLE – console differences, mention that using exec means that __builtins__ is defined for each statement.

- bpo-27714: text_textview and test_autocomplete now pass when re-run in the same process. This occurs when test_idle fails when run with the -w option but without -jn. Fix warning from test_config.

- bpo-25507: IDLE no longer runs buggy code because of its tkinter imports. Users must include the same imports required to run directly in Python.

- bpo-27452: add line counter and crc to IDLE configHandler test dump.

- bpo-27365: Allow non-ascii chars in IDLE NEWS.txt, for contributor names.

- bpo-27245: IDLE: Cleanly delete custom themes and key bindings. Previously, when IDLE was started from a console or by import, a cascade of warnings was emitted. Patch by Serhiy Storchaka.

### C API

- bpo-28808: PyUnicode_CompareWithASCIIString() now never raises exceptions.

- bpo-26754: PyUnicode_FSDecoder() accepted a filename argument encoded as an iterable of integers. Now only strings and bytes-like objects are accepted.

### Documentation

- bpo-28513: Documented command-line interface of zipfile.

### Tests

- bpo-28950: Disallow -j0 to be combined with -T/-l/-M in regrtest command line arguments.

- bpo-28666: Now test.support.rmtree is able to remove unwritable or unreadable directories.

- bpo-23839: Various caches now are cleared before running every test file.

- bpo-28409: regrtest: fix the parser of command line arguments.

- bpo-27787: Call gc.collect() before checking each test for “dangling threads”, since the dangling threads are weak references.

- bpo-27369: In test_pyexpat, avoid testing an error message detail that changed in Expat 2.2.0.

### Tools/Demos

- bpo-27952: Get Tools/scripts/fixcid.py working with Python 3 and the current “re” module, avoid invalid Python backslash escapes, and fix a bug parsing escaped C quote signs.

- bpo-27332: Fixed the type of the first argument of module-level functions generated by Argument Clinic. Patch by Petr Viktorin.

- bpo-27418: Fixed Tools/importbench/importbench.py.

### Windows

- bpo-28251: Improvements to help manuals on Windows.

- bpo-28110: launcher.msi has different product codes between 32-bit and 64-bit

- bpo-25144: Ensures TargetDir is set before continuing with custom install.

- bpo-27469: Adds a shell extension to the launcher so that drag and drop works correctly.

- bpo-27309: Enabled proper Windows styles in python[w].exe manifest.

### Build

- bpo-29080: Removes hard dependency on hg.exe from PCBuild/build.bat

- bpo-23903: Added missed names to PC/python3.def.

- bpo-10656: Fix out-of-tree building on AIX. Patch by Tristan Carel and Michael Haubenwallner.

- bpo-26359: Rename –with-optimiations to –enable-optimizations.

- bpo-28444: Fix missing extensions modules when cross compiling.

- bpo-28248: Update Windows build and OS X installers to use OpenSSL 1.0.2j.

- bpo-28258: Fixed build with Estonian locale (python-config and distclean targets in Makefile). Patch by Arfrever Frehtes Taifersar Arahesis.

- bpo-26661: setup.py now detects system libffi with multiarch wrapper.

- bpo-28066: Fix the logic that searches build directories for generated include files when building outside the source tree.

- bpo-15819: Remove redundant include search directory option for building outside the source tree.

- bpo-27566: Fix clean target in freeze makefile (patch by Lisa Roach)

- bpo-27705: Update message in validate_ucrtbase.py

- bpo-27983: Cause lack of llvm-profdata tool when using clang as required for PGO linking to be a configure time error rather than make time when –with-optimizations is enabled. Also improve our ability to find the llvm-profdata tool on MacOS and some Linuxes.

- bpo-26307: The profile-opt build now applies PGO to the built-in modules.

- bpo-26359: Add the –with-optimizations configure flag.

- bpo-27713: Suppress spurious build warnings when updating importlib’s bootstrap files. Patch by Xiang Zhang

- bpo-25825: Correct the references to Modules/python.exp and ld_so_aix, which are required on AIX. This updates references to an installation path that was changed in 3.2a4, and undoes changed references to the build tree that were made in 3.5.0a1.

- bpo-27453: CPP invocation in configure must use CPPFLAGS. Patch by Chi Hsuan Yen.

- bpo-27641: The configure script now inserts comments into the makefile to prevent the pgen and _freeze_importlib executables from being cross-compiled.

- bpo-26662: Set PYTHON_FOR_GEN in configure as the Python program to be used for file generation during the build.

- bpo-10910: Avoid C++ compilation errors on FreeBSD and OS X. Also update FreedBSD version checks for the original ctype UTF-8 workaround.

- bpo-28676: Prevent missing ‘getentropy’ declaration warning on macOS. Patch by Gareth Rees.

## Python 3.5.2 final

Release date: 2016-06-26

### Core and Builtins

- bpo-26930: Update Windows builds to use OpenSSL 1.0.2h.

### Tests

- bpo-26867: Ubuntu’s openssl OP_NO_SSLv3 is forced on by default; fix test.

### IDLE

- bpo-27365: Allow non-ascii in idlelib/NEWS.txt - minimal part for 3.5.2.

## Python 3.5.2 release candidate 1

Release date: 2016-06-12

### Core and Builtins

- bpo-27066: Fixed SystemError if a custom opener (for open()) returns a negative number without setting an exception.

- bpo-20041: Fixed TypeError when frame.f_trace is set to None. Patch by Xavier de Gaye.

- bpo-26168: Fixed possible refleaks in failing Py_BuildValue() with the “N” format unit.

- bpo-26991: Fix possible refleak when creating a function with annotations.

- bpo-27039: Fixed bytearray.remove() for values greater than 127. Patch by Joe Jevnik.

- bpo-23640: int.from_bytes() no longer bypasses constructors for subclasses.

- bpo-26811: gc.get_objects() no longer contains a broken tuple with NULL pointer.

- bpo-20120: Use RawConfigParser for .pypirc parsing, removing support for interpolation unintentionally added with move to Python 3. Behavior no longer does any interpolation in .pypirc files, matching behavior in Python 2.7 and Setuptools 19.0.

- bpo-26659: Make the builtin slice type support cycle collection.

- bpo-26718: super.__init__ no longer leaks memory if called multiple times. NOTE: A direct call of super.__init__ is not endorsed!

- bpo-25339: PYTHONIOENCODING now has priority over locale in setting the error handler for stdin and stdout.

- bpo-26494: Fixed crash on iterating exhausting iterators. Affected classes are generic sequence iterators, iterators of str, bytes, bytearray, list, tuple, set, frozenset, dict, OrderedDict, corresponding views and os.scandir() iterator.

- bpo-26581: If coding cookie is specified multiple times on a line in Python source code file, only the first one is taken to account.

- bpo-26464: Fix str.translate() when string is ASCII and first replacements removes character, but next replacement uses a non-ASCII character or a string longer than 1 character. Regression introduced in Python 3.5.0.

- bpo-22836: Ensure exception reports from PyErr_Display() and PyErr_WriteUnraisable() are sensible even when formatting them produces secondary errors. This affects the reports produced by sys.__excepthook__() and when __del__() raises an exception.

- bpo-26302: Correct behavior to reject comma as a legal character for cookie names.

- bpo-4806: Avoid masking the original TypeError exception when using star (`*`) unpacking in function calls. Based on patch by Hagen Fürstenau and Daniel Urban.

- bpo-27138: Fix the doc comment for FileFinder.find_spec().

- bpo-26154: Add a new private _PyThreadState_UncheckedGet() function to get the current Python thread state, but don’t issue a fatal error if it is NULL. This new function must be used instead of accessing directly the _PyThreadState_Current variable. The variable is no more exposed since Python 3.5.1 to hide the exact implementation of atomic C types, to avoid compiler issues.

- bpo-26194: Deque.insert() gave odd results for bounded deques that had reached their maximum size. Now an IndexError will be raised when attempting to insert into a full deque.

- bpo-25843: When compiling code, don’t merge constants if they are equal but have a different types. For example, `f1, f2 = lambda: 1, lambda: 1.0` is now correctly compiled to two different functions: `f1()` returns `1` (`int`) and `f2()` returns `1.0` (`int`), even if `1` and `1.0` are equal.

- bpo-22995: [UPDATE] Comment out the one of the pickleability tests in _PyObject_GetState() due to regressions observed in Cython-based projects.

- bpo-25961: Disallowed null characters in the type name.

- bpo-25973: Fix segfault when an invalid nonlocal statement binds a name starting with two underscores.

- bpo-22995: Instances of extension types with a state that aren’t subclasses of list or dict and haven’t implemented any pickle-related methods (__reduce__, __reduce_ex__, __getnewargs__, __getnewargs_ex__, or __getstate__), can no longer be pickled. Including memoryview.

- bpo-20440: Massive replacing unsafe attribute setting code with special macro Py_SETREF.

- bpo-25766: Special method __bytes__() now works in str subclasses.

- bpo-25421: __sizeof__ methods of builtin types now use dynamic basic size. This allows sys.getsize() to work correctly with their subclasses with __slots__ defined.

- bpo-25709: Fixed problem with in-place string concatenation and utf-8 cache.

- bpo-27147: Mention PEP 420 in the importlib docs.

- bpo-24097: Fixed crash in object.__reduce__() if slot name is freed inside __getattr__.

- bpo-24731: Fixed crash on converting objects with special methods __bytes__, __trunc__, and __float__ returning instances of subclasses of bytes, int, and float to subclasses of bytes, int, and float correspondingly.

- bpo-26478: Fix semantic bugs when using binary operators with dictionary views and tuples.

- bpo-26171: Fix possible integer overflow and heap corruption in zipimporter.get_data().

- bpo-25660: Fix TAB key behaviour in REPL with readline.

- bpo-25887: Raise a RuntimeError when a coroutine object is awaited more than once.

- bpo-27243: Update the __aiter__ protocol: instead of returning an awaitable that resolves to an asynchronous iterator, the asynchronous iterator should be returned directly. Doing the former will trigger a PendingDeprecationWarning.

### Security

- bpo-26556: Update expat to 2.1.1, fixes CVE-2015-1283.

- Fix TLS stripping vulnerability in smtplib, CVE-2016-0772. Reported by Team Oststrom

### Library

- bpo-21386: Implement missing IPv4Address.is_global property. It was documented since 07a5610bae9d. Initial patch by Roger Luethi.

- bpo-20900: distutils register command now decodes HTTP responses correctly. Initial patch by ingrid.

- A new version of typing.py provides several new classes and features: @overload outside stubs, Reversible, DefaultDict, Text, ContextManager, Type[], NewType(), TYPE_CHECKING, and numerous bug fixes (note that some of the new features are not yet implemented in mypy or other static analyzers). Also classes for PEP 492 (Awaitable, AsyncIterable, AsyncIterator) have been added (in fact they made it into 3.5.1 but were never mentioned).

- bpo-25738: Stop http.server.BaseHTTPRequestHandler.send_error() from sending a message body for 205 Reset Content. Also, don’t send Content header fields in responses that don’t have a body. Patch by Susumu Koshiba.

- bpo-21313: Fix the “platform” module to tolerate when sys.version contains truncated build information.

### Security

- bpo-26839: On Linux, `os.urandom()` now calls `getrandom()` with `GRND_NONBLOCK` to fall back on reading `/dev/urandom` if the urandom entropy pool is not initialized yet. Patch written by Colm Buckley.

### Library

- bpo-27164: In the zlib module, allow decompressing raw Deflate streams with a predefined zdict. Based on patch by Xiang Zhang.

- bpo-24291: Fix wsgiref.simple_server.WSGIRequestHandler to completely write data to the client. Previously it could do partial writes and truncate data. Also, wsgiref.handler.ServerHandler can now handle stdout doing partial writes, but this is deprecated.

- bpo-26809: Add `__all__` to `string`. Patch by Emanuel Barry.

- bpo-26373: subprocess.Popen.communicate now correctly ignores BrokenPipeError when the child process dies before .communicate() is called in more/all circumstances.

- bpo-21776: distutils.upload now correctly handles HTTPError. Initial patch by Claudiu Popa.

- bpo-27114: Fix SSLContext._load_windows_store_certs fails with PermissionError

- bpo-18383: Avoid creating duplicate filters when using filterwarnings and simplefilter. Based on patch by Alex Shkop.

- bpo-27057: Fix os.set_inheritable() on Android, ioctl() is blocked by SELinux and fails with EACCESS. The function now falls back to fcntl(). Patch written by Michał Bednarski.

- bpo-27014: Fix infinite recursion using typing.py. Thanks to Kalle Tuure!

- bpo-14132: Fix urllib.request redirect handling when the target only has a query string. Original fix by Ján Janech.

- bpo-17214: The “urllib.request” module now percent-encodes non-ASCII bytes found in redirect target URLs. Some servers send Location header fields with non-ASCII bytes, but “http.client” requires the request target to be ASCII-encodable, otherwise a UnicodeEncodeError is raised. Based on patch by Christian Heimes.

- bpo-26892: Honor debuglevel flag in urllib.request.HTTPHandler. Patch contributed by Chi Hsuan Yen.

- bpo-22274: In the subprocess module, allow stderr to be redirected to stdout even when stdout is not redirected. Patch by Akira Li.

- bpo-26807: mock_open ‘files’ no longer error on readline at end of file. Patch from Yolanda Robla.

- bpo-25745: Fixed leaking a userptr in curses panel destructor.

- bpo-26977: Removed unnecessary, and ignored, call to sum of squares helper in statistics.pvariance.

- bpo-26881: The modulefinder module now supports extended opcode arguments.

- bpo-23815: Fixed crashes related to directly created instances of types in _tkinter and curses.panel modules.

- bpo-17765: weakref.ref() no longer silently ignores keyword arguments. Patch by Georg Brandl.

- bpo-26873: xmlrpc now raises ResponseError on unsupported type tags instead of silently return incorrect result.

- bpo-26711: Fixed the comparison of plistlib.Data with other types.

- bpo-24114: Fix an uninitialized variable in `ctypes.util`. The bug only occurs on SunOS when the ctypes implementation searches for the `crle` program. Patch by Xiang Zhang. Tested on SunOS by Kees Bos.

- bpo-26864: In urllib.request, change the proxy bypass host checking against no_proxy to be case-insensitive, and to not match unrelated host names that happen to have a bypassed hostname as a suffix. Patch by Xiang Zhang.

- bpo-26634: recursive_repr() now sets __qualname__ of wrapper. Patch by Xiang Zhang.

- bpo-26804: urllib.request will prefer lower_case proxy environment variables over UPPER_CASE or Mixed_Case ones. Patch contributed by Hans-Peter Jansen.

- bpo-26837: assertSequenceEqual() now correctly outputs non-stringified differing items (like bytes in the -b mode). This affects assertListEqual() and assertTupleEqual().

- bpo-26041: Remove “will be removed in Python 3.7” from deprecation messages of platform.dist() and platform.linux_distribution(). Patch by Kumaripaba Miyurusara Athukorala.

- bpo-26822: itemgetter, attrgetter and methodcaller objects no longer silently ignore keyword arguments.

- bpo-26733: Disassembling a class now disassembles class and static methods. Patch by Xiang Zhang.

- bpo-26801: Fix error handling in `shutil.get_terminal_size()`, catch `AttributeError` instead of `NameError`. Patch written by Emanuel Barry.

- bpo-24838: tarfile’s ustar and gnu formats now correctly calculate name and link field limits for multibyte character encodings like utf-8.

### Security

- bpo-26657: Fix directory traversal vulnerability with http.server on Windows. This fixes a regression that was introduced in 3.3.4rc1 and 3.4.0rc1. Based on patch by Philipp Hagemeister.

### Library

- bpo-26717: Stop encoding Latin-1-ized WSGI paths with UTF-8. Patch by Anthony Sottile.

- bpo-26735: Fix `os.urandom()` on Solaris 11.3 and newer when reading more than 1,024 bytes: call `getrandom()` multiple times with a limit of 1024 bytes per call.

- bpo-16329: Add .webm to mimetypes.types_map. Patch by Giampaolo Rodola’.

- bpo-13952: Add .csv to mimetypes.types_map. Patch by Geoff Wilson.

- bpo-26709: Fixed Y2038 problem in loading binary PLists.

- bpo-23735: Handle terminal resizing with Readline 6.3+ by installing our own SIGWINCH handler. Patch by Eric Price.

- bpo-26586: In http.server, respond with “413 Request header fields too large” if there are too many header fields to parse, rather than killing the connection and raising an unhandled exception. Patch by Xiang Zhang.

- bpo-22854: Change BufferedReader.writable() and BufferedWriter.readable() to always return False.

- bpo-25195: Fix a regression in mock.MagicMock. _Call is a subclass of tuple (changeset 3603bae63c13 only works for classes) so we need to implement __ne__ ourselves. Patch by Andrew Plummer.

- bpo-26644: Raise ValueError rather than SystemError when a negative length is passed to SSLSocket.recv() or read().

- bpo-23804: Fix SSL recv(0) and read(0) methods to return zero bytes instead of up to 1024.

- bpo-26616: Fixed a bug in datetime.astimezone() method.

- bpo-21925: `warnings.formatwarning()` now catches exceptions on `linecache.getline(...)` to be able to log `ResourceWarning` emitted late during the Python shutdown process.

- bpo-24266: Ctrl+C during Readline history search now cancels the search mode when compiled with Readline 7.

- bpo-26560: Avoid potential ValueError in BaseHandler.start_response. Initial patch by Peter Inglesby.

### Security

- bpo-26313: ssl.py _load_windows_store_certs fails if windows cert store is empty. Patch by Baji.

### Library

- bpo-26569: Fix `pyclbr.readmodule()` and `pyclbr.readmodule_ex()` to support importing packages.

- bpo-26499: Account for remaining Content-Length in HTTPResponse.readline() and read1(). Based on patch by Silent Ghost. Also document that HTTPResponse now supports these methods.

- bpo-25320: Handle sockets in directories unittest discovery is scanning. Patch from Victor van den Elzen.

- bpo-16181: cookiejar.http2time() now returns None if year is higher than datetime.MAXYEAR.

- bpo-26513: Fixes platform module detection of Windows Server

- bpo-23718: Fixed parsing time in week 0 before Jan 1. Original patch by Tamás Bence Gedai.

- bpo-20589: Invoking Path.owner() and Path.group() on Windows now raise NotImplementedError instead of ImportError.

- bpo-26177: Fixed the keys() method for Canvas and Scrollbar widgets.

- bpo-15068: Got rid of excessive buffering in the fileinput module. The bufsize parameter is no longer used.

- bpo-2202: Fix UnboundLocalError in AbstractDigestAuthHandler.get_algorithm_impls. Initial patch by Mathieu Dupuy.

- bpo-25718: Fixed pickling and copying the accumulate() iterator with total is None.

- bpo-26475: Fixed debugging output for regular expressions with the (?x) flag.

- bpo-26457: Fixed the subnets() methods in IP network classes for the case when resulting prefix length is equal to maximal prefix length. Based on patch by Xiang Zhang.

- bpo-26385: Remove the file if the internal open() call in NamedTemporaryFile() fails. Patch by Silent Ghost.

- bpo-26402: Fix XML-RPC client to retry when the server shuts down a persistent connection. This was a regression related to the new http.client.RemoteDisconnected exception in 3.5.0a4.

- bpo-25913: Leading `<~` is optional now in base64.a85decode() with adobe=True. Patch by Swati Jaiswal.

- bpo-26186: Remove an invalid type check in importlib.util.LazyLoader.

- bpo-26367: importlib.__import__() raises SystemError like builtins.__import__() when `level` is specified but without an accompanying package specified.

- bpo-26309: In the “socketserver” module, shut down the request (closing the connected socket) when verify_request() returns false. Patch by Aviv Palivoda.

### Security

- bpo-25939: On Windows open the cert store readonly in ssl.enum_certificates.

### Library

- bpo-25995: os.walk() no longer uses FDs proportional to the tree depth.

- bpo-26117: The os.scandir() iterator now closes file descriptor not only when the iteration is finished, but when it was failed with error.

- bpo-25911: Restored support of bytes paths in os.walk() on Windows.

- bpo-26045: Add UTF-8 suggestion to error message when posting a non-Latin-1 string with http.client.

- bpo-12923: Reset FancyURLopener’s redirect counter even if there is an exception. Based on patches by Brian Brazil and Daniel Rocco.

- bpo-25945: Fixed a crash when unpickle the functools.partial object with wrong state. Fixed a leak in failed functools.partial constructor. “args” and “keywords” attributes of functools.partial have now always types tuple and dict correspondingly.

- bpo-26202: copy.deepcopy() now correctly copies range() objects with non-atomic attributes.

- bpo-23076: Path.glob() now raises a ValueError if it’s called with an invalid pattern. Patch by Thomas Nyberg.

- bpo-19883: Fixed possible integer overflows in zipimport.

- bpo-26227: On Windows, getnameinfo(), gethostbyaddr() and gethostbyname_ex() functions of the socket module now decode the hostname from the ANSI code page rather than UTF-8.

- bpo-26147: xmlrpc now works with strings not encodable with used non-UTF-8 encoding.

- bpo-25935: Garbage collector now breaks reference loops with OrderedDict.

- bpo-16620: Fixed AttributeError in msilib.Directory.glob().

- bpo-26013: Added compatibility with broken protocol 2 pickles created in old Python 3 versions (3.4.3 and lower).

- bpo-25850: Use cross-compilation by default for 64-bit Windows.

- bpo-17633: Improve zipimport’s support for namespace packages.

- bpo-24705: Fix sysconfig._parse_makefile not expanding ${} vars appearing before $() vars.

- bpo-22138: Fix mock.patch behavior when patching descriptors. Restore original values after patching. Patch contributed by Sean McCully.

- bpo-25672: In the ssl module, enable the SSL_MODE_RELEASE_BUFFERS mode option if it is safe to do so.

- bpo-26012: Don’t traverse into symlinks for `**` pattern in pathlib.Path.[r]glob().

- bpo-24120: Ignore PermissionError when traversing a tree with pathlib.Path.[r]glob(). Patch by Ulrich Petri.

- bpo-25447: fileinput now uses sys.stdin as-is if it does not have a buffer attribute (restores backward compatibility).

- bpo-25447: Copying the lru_cache() wrapper object now always works, independently from the type of the wrapped object (by returning the original object unchanged).

- bpo-24103: Fixed possible use after free in ElementTree.XMLPullParser.

- bpo-25860: os.fwalk() no longer skips remaining directories when error occurs. Original patch by Samson Lee.

- bpo-25914: Fixed and simplified OrderedDict.__sizeof__.

- bpo-25902: Fixed various refcount issues in ElementTree iteration.

- bpo-25717: Restore the previous behaviour of tolerating most fstat() errors when opening files. This was a regression in 3.5a1, and stopped anonymous temporary files from working in special cases.

- bpo-24903: Fix regression in number of arguments compileall accepts when ‘-d’ is specified. The check on the number of arguments has been dropped completely as it never worked correctly anyway.

- bpo-25764: In the subprocess module, preserve any exception caused by fork() failure when preexec_fn is used.

- bpo-6478: _strptime’s regexp cache now is reset after changing timezone with time.tzset().

- bpo-14285: When executing a package with the “python -m package” option, and package initialization fails, a proper traceback is now reported. The “runpy” module now lets exceptions from package initialization pass back to the caller, rather than raising ImportError.

- bpo-19771: Also in runpy and the “-m” option, omit the irrelevant message “… is a package and cannot be directly executed” if the package could not even be initialized (e.g. due to a bad `*.pyc` file).

- bpo-25177: Fixed problem with the mean of very small and very large numbers. As a side effect, statistics.mean and statistics.variance should be significantly faster.

- bpo-25718: Fixed copying object with state with boolean value is false.

- bpo-10131: Fixed deep copying of minidom documents. Based on patch by Marian Ganisin.

- bpo-25725: Fixed a reference leak in pickle.loads() when unpickling invalid data including tuple instructions.

- bpo-25663: In the Readline completer, avoid listing duplicate global names, and search the global namespace before searching builtins.

- bpo-25688: Fixed file leak in ElementTree.iterparse() raising an error.

- bpo-23914: Fixed SystemError raised by unpickler on broken pickle data.

- bpo-25691: Fixed crash on deleting ElementTree.Element attributes.

- bpo-25624: ZipFile now always writes a ZIP_STORED header for directory entries. Patch by Dingyuan Wang.

- Skip getaddrinfo if host is already resolved. Patch by A. Jesse Jiryu Davis.

- bpo-26050: Add asyncio.StreamReader.readuntil() method. Patch by Марк Коренберг.

- bpo-25924: Avoid unnecessary serialization of getaddrinfo(3) calls on OS X versions 10.5 or higher. Original patch by A. Jesse Jiryu Davis.

- bpo-26406: Avoid unnecessary serialization of getaddrinfo(3) calls on current versions of OpenBSD and NetBSD. Patch by A. Jesse Jiryu Davis.

- bpo-26848: Fix asyncio/subprocess.communicate() to handle empty input. Patch by Jack O’Connor.

- bpo-27040: Add loop.get_exception_handler method

- bpo-27041: asyncio: Add loop.create_future method

- bpo-27223: asyncio: Fix _read_ready and _write_ready to respect _conn_lost. Patch by Łukasz Langa.

- bpo-22970: asyncio: Fix inconsistency cancelling Condition.wait. Patch by David Coles.

### IDLE

- bpo-5124: Paste with text selected now replaces the selection on X11. This matches how paste works on Windows, Mac, most modern Linux apps, and ttk widgets. Original patch by Serhiy Storchaka.

- bpo-24759: Make clear in idlelib.idle_test.__init__ that the directory is a private implementation of test.test_idle and tool for maintainers.

- bpo-27196: Stop ‘ThemeChanged’ warnings when running IDLE tests. These persisted after other warnings were suppressed in #20567. Apply Serhiy Storchaka’s update_idletasks solution to four test files. Record this additional advice in idle_test/README.txt

- bpo-20567: Revise idle_test/README.txt with advice about avoiding tk warning messages from tests. Apply advice to several IDLE tests.

- bpo-27117: Make colorizer htest and turtledemo work with dark themes. Move code for configuring text widget colors to a new function.

- bpo-26673: When tk reports font size as 0, change to size 10. Such fonts on Linux prevented the configuration dialog from opening.

- bpo-21939: Add test for IDLE’s percolator. Original patch by Saimadhav Heblikar.

- bpo-21676: Add test for IDLE’s replace dialog. Original patch by Saimadhav Heblikar.

- bpo-18410: Add test for IDLE’s search dialog. Original patch by Westley Martínez.

- bpo-21703: Add test for IDLE’s undo delegator. Original patch by Saimadhav Heblikar .

- bpo-27044: Add ConfigDialog.remove_var_callbacks to stop memory leaks.

- bpo-23977: Add more asserts to test_delegator.

- bpo-20640: Add tests for idlelib.configHelpSourceEdit. Patch by Saimadhav Heblikar.

- In the ‘IDLE-console differences’ section of the IDLE doc, clarify how running with IDLE affects sys.modules and the standard streams.

- bpo-25507: fix incorrect change in IOBinding that prevented printing. Augment IOBinding htest to include all major IOBinding functions.

- bpo-25905: Revert unwanted conversion of ‘ to ’ RIGHT SINGLE QUOTATION MARK in README.txt and open this and NEWS.txt with ‘ascii’. Re-encode CREDITS.txt to utf-8 and open it with ‘utf-8’.

### Documentation

- bpo-19489: Moved the search box from the sidebar to the header and footer of each page. Patch by Ammar Askar.

- bpo-24136: Document the new PEP 448 unpacking syntax of 3.5.

- bpo-26736: Used HTTPS for external links in the documentation if possible.

- bpo-6953: Rework the Readline module documentation to group related functions together, and add more details such as what underlying Readline functions and variables are accessed.

- bpo-23606: Adds note to ctypes documentation regarding cdll.msvcrt.

- bpo-25500: Fix documentation to not claim that __import__ is searched for in the global scope.

- bpo-26014: Update 3.x packaging documentation: * “See also” links to the new docs are now provided in the legacy pages * links to setuptools documentation have been updated

### Tests

- bpo-21916: Added tests for the turtle module. Patch by ingrid, Gregory Loyse and Jelle Zijlstra.

- bpo-26523: The multiprocessing thread pool (multiprocessing.dummy.Pool) was untested.

- bpo-26015: Added new tests for pickling iterators of mutable sequences.

- bpo-26325: Added test.support.check_no_resource_warning() to check that no ResourceWarning is emitted.

- bpo-25940: Changed test_ssl to use self-signed.pythontest.net. This avoids relying on svn.python.org, which recently changed root certificate.

- bpo-25616: Tests for OrderedDict are extracted from test_collections into separate file test_ordered_dict.

- bpo-26583: Skip test_timestamp_overflow in test_import if bytecode files cannot be written.

### Build

- bpo-26884: Fix linking extension modules for cross builds. Patch by Xavier de Gaye.

- bpo-22359: Disable the rules for running _freeze_importlib and pgen when cross-compiling. The output of these programs is normally saved with the source code anyway, and is still regenerated when doing a native build. Patch by Xavier de Gaye.

- bpo-27229: Fix the cross-compiling pgen rule for in-tree builds. Patch by Xavier de Gaye.

- bpo-21668: Link audioop, _datetime, _ctypes_test modules to libm, except on Mac OS X. Patch written by Xavier de Gaye.

- bpo-25702: A –with-lto configure option has been added that will enable link time optimizations at build time during a make profile-opt. Some compilers and toolchains are known to not produce stable code when using LTO, be sure to test things thoroughly before relying on it. It can provide a few % speed up over profile-opt alone.

- bpo-26624: Adds validation of ucrtbase[d].dll version with warning for old versions.

- bpo-17603: Avoid error about nonexistent fileblocks.o file by using a lower-level check for st_blocks in struct stat.

- bpo-26079: Fixing the build output folder for tix-8.4.3.6. Patch by Bjoern Thiel.

- bpo-26465: Update Windows builds to use OpenSSL 1.0.2g.

- bpo-24421: Compile Modules/_math.c once, before building extensions. Previously it could fail to compile properly if the math and cmath builds were concurrent.

- bpo-25348: Added `--pgo` and `--pgo-job` arguments to `PCbuild\build.bat` for building with Profile-Guided Optimization. The old `PCbuild\build_pgo.bat` script is now deprecated, and simply calls `PCbuild\build.bat --pgo %*`.

- bpo-25827: Add support for building with ICC to `configure`, including a new `--with-icc` flag.

- bpo-25696: Fix installation of Python on UNIX with make -j9.

- bpo-26930: Update OS X 10.5+ 32-bit-only installer to build and link with OpenSSL 1.0.2h.

- bpo-26268: Update Windows builds to use OpenSSL 1.0.2f.

- bpo-25136: Support Apple Xcode 7’s new textual SDK stub libraries.

- bpo-24324: Do not enable unreachable code warnings when using gcc as the option does not work correctly in older versions of gcc and has been silently removed as of gcc-4.5.

### Windows

- bpo-27053: Updates make_zip.py to correctly generate library ZIP file.

- bpo-26268: Update the prepare_ssl.py script to handle OpenSSL releases that don’t include the contents of the include directory (that is, 1.0.2e and later).

- bpo-26071: bdist_wininst created binaries fail to start and find 32bit Python

- bpo-26073: Update the list of magic numbers in launcher

- bpo-26065: Excludes venv from library when generating embeddable distro.

### Tools/Demos

- bpo-26799: Fix python-gdb.py: don’t get C types once when the Python code is loaded, but get C types on demand. The C types can change if python-gdb.py is loaded before the Python executable. Patch written by Thomas Ilsche.

- bpo-26271: Fix the Freeze tool to properly use flags passed through configure. Patch by Daniel Shaulov.

- bpo-26489: Add dictionary unpacking support to Tools/parser/unparse.py. Patch by Guo Ci Teo.

- bpo-26316: Fix variable name typo in Argument Clinic.

### Windows

- bpo-17500: Remove unused and outdated icons. (See also: https://github.com/python/pythondotorg/issues/945)

## Python 3.5.1 final

Release date: 2015-12-06

### Core and Builtins

- bpo-25709: Fixed problem with in-place string concatenation and utf-8 cache.

### Windows

- bpo-25715: Python 3.5.1 installer shows wrong upgrade path and incorrect logic for launcher detection.

## Python 3.5.1 release candidate 1

Release date: 2015-11-22

### Core and Builtins

- bpo-25630: Fix a possible segfault during argument parsing in functions that accept filesystem paths.

- bpo-23564: Fixed a partially broken sanity check in the _posixsubprocess internals regarding how fds_to_pass were passed to the child. The bug had no actual impact as subprocess.py already avoided it.

- bpo-25388: Fixed tokenizer crash when processing undecodable source code with a null byte.

- bpo-25462: The hash of the key now is calculated only once in most operations in C implementation of OrderedDict.

- bpo-22995: Default implementation of __reduce__ and __reduce_ex__ now rejects builtin types with not defined __new__.

- bpo-25555: Fix parser and AST: fill lineno and col_offset of “arg” node when compiling AST from Python objects.

- bpo-24802: Avoid buffer overreads when int(), float(), compile(), exec() and eval() are passed bytes-like objects. These objects are not necessarily terminated by a null byte, but the functions assumed they were.

- bpo-24726: Fixed a crash and leaking NULL in repr() of OrderedDict that was mutated by direct calls of dict methods.

- bpo-25449: Iterating OrderedDict with keys with unstable hash now raises KeyError in C implementations as well as in Python implementation.

- bpo-25395: Fixed crash when highly nested OrderedDict structures were garbage collected.

- bpo-25274: sys.setrecursionlimit() now raises a RecursionError if the new recursion limit is too low depending at the current recursion depth. Modify also the “lower-water mark” formula to make it monotonic. This mark is used to decide when the overflowed flag of the thread state is reset.

- bpo-24402: Fix input() to prompt to the redirected stdout when sys.stdout.fileno() fails.

- bpo-24806: Prevent builtin types that are not allowed to be subclassed from being subclassed through multiple inheritance.

- bpo-24848: Fixed a number of bugs in UTF-7 decoding of misformed data.

- bpo-25280: Import trace messages emitted in verbose (-v) mode are no longer formatted twice.

- bpo-25003: On Solaris 11.3 or newer, os.urandom() now uses the getrandom() function instead of the getentropy() function. The getentropy() function is blocking to generate very good quality entropy, os.urandom() doesn’t need such high-quality entropy.

- bpo-25182: The stdprinter (used as sys.stderr before the io module is imported at startup) now uses the backslashreplace error handler.

- bpo-25131: Make the line number and column offset of set/dict literals and comprehensions correspond to the opening brace.

- bpo-25150: Hide the private _Py_atomic_xxx symbols from the public Python.h header to fix a compilation error with OpenMP. PyThreadState_GET() becomes an alias to PyThreadState_Get() to avoid ABI incompatibilities.

### Library

- bpo-25626: Change three zlib functions to accept sizes that fit in Py_ssize_t, but internally cap those sizes to UINT_MAX. This resolves a regression in 3.5 where GzipFile.read() failed to read chunks larger than 2 or 4 GiB. The change affects the zlib.Decompress.decompress() max_length parameter, the zlib.decompress() bufsize parameter, and the zlib.Decompress.flush() length parameter.

- bpo-25583: Avoid incorrect errors raised by os.makedirs(exist_ok=True) when the OS gives priority to errors such as EACCES over EEXIST.

- bpo-25593: Change semantics of EventLoop.stop() in asyncio.

- bpo-6973: When we know a subprocess.Popen process has died, do not allow the send_signal(), terminate(), or kill() methods to do anything as they could potentially signal a different process.

- bpo-25590: In the Readline completer, only call getattr() once per attribute.

- bpo-25498: Fix a crash when garbage-collecting ctypes objects created by wrapping a memoryview. This was a regression made in 3.5a1. Based on patch by Eryksun.

- bpo-25584: Added “escape” to the __all__ list in the glob module.

- bpo-25584: Fixed recursive glob() with patterns starting with `**`.

- bpo-25446: Fix regression in smtplib’s AUTH LOGIN support.

- bpo-18010: Fix the pydoc web server’s module search function to handle exceptions from importing packages.

- bpo-25554: Got rid of circular references in regular expression parsing.

- bpo-25510: fileinput.FileInput.readline() now returns b’’ instead of ‘’ at the end if the FileInput was opened with binary mode. Patch by Ryosuke Ito.

- bpo-25503: Fixed inspect.getdoc() for inherited docstrings of properties. Original patch by John Mark Vandenberg.

- bpo-25515: Always use os.urandom as a source of randomness in uuid.uuid4.

- bpo-21827: Fixed textwrap.dedent() for the case when largest common whitespace is a substring of smallest leading whitespace. Based on patch by Robert Li.

- bpo-25447: The lru_cache() wrapper objects now can be copied and pickled (by returning the original object unchanged).

- bpo-25390: typing: Don’t crash on Union[str, Pattern].

- bpo-25441: asyncio: Raise error from drain() when socket is closed.

- bpo-25410: Cleaned up and fixed minor bugs in C implementation of OrderedDict.

- bpo-25411: Improved Unicode support in SMTPHandler through better use of the email package. Thanks to user simon04 for the patch.

- bpo-25407: Remove mentions of the formatter module being removed in Python 3.6.

- bpo-25406: Fixed a bug in C implementation of OrderedDict.move_to_end() that caused segmentation fault or hang in iterating after moving several items to the start of ordered dict.

- bpo-25364: zipfile now works in threads disabled builds.

- bpo-25328: smtpd’s SMTPChannel now correctly raises a ValueError if both decode_data and enable_SMTPUTF8 are set to true.

- bpo-25316: distutils raises OSError instead of DistutilsPlatformError when MSVC is not installed.

- bpo-25380: Fixed protocol for the STACK_GLOBAL opcode in pickletools.opcodes.

- bpo-23972: Updates asyncio datagram create method allowing reuseport and reuseaddr socket options to be set prior to binding the socket. Mirroring the existing asyncio create_server method the reuseaddr option for datagram sockets defaults to True if the O/S is ‘posix’ (except if the platform is Cygwin). Patch by Chris Laws.

- bpo-25304: Add asyncio.run_coroutine_threadsafe(). This lets you submit a coroutine to a loop from another thread, returning a concurrent.futures.Future. By Vincent Michel.

- bpo-25232: Fix CGIRequestHandler to split the query from the URL at the first question mark (?) rather than the last. Patch from Xiang Zhang.

- bpo-24657: Prevent CGIRequestHandler from collapsing slashes in the query part of the URL as if it were a path. Patch from Xiang Zhang.

- bpo-24483: C implementation of functools.lru_cache() now calculates key’s hash only once.

- bpo-22958: Constructor and update method of weakref.WeakValueDictionary now accept the self and the dict keyword arguments.

- bpo-22609: Constructor of collections.UserDict now accepts the self keyword argument.

- bpo-25111: Fixed comparison of traceback.FrameSummary.

- bpo-25262: Added support for BINBYTES8 opcode in Python implementation of unpickler. Highest 32 bits of 64-bit size for BINUNICODE8 and BINBYTES8 opcodes no longer silently ignored on 32-bit platforms in C implementation.

- bpo-25034: Fix string.Formatter problem with auto-numbering and nested format_specs. Patch by Anthon van der Neut.

- bpo-25233: Rewrite the guts of asyncio.Queue and asyncio.Semaphore to be more understandable and correct.

- bpo-25203: Failed readline.set_completer_delims() no longer left the module in inconsistent state.

- bpo-23600: Default implementation of tzinfo.fromutc() was returning wrong results in some cases.

- bpo-23329: Allow the ssl module to be built with older versions of LibreSSL.

- Prevent overflow in _Unpickler_Read.

- bpo-25047: The XML encoding declaration written by Element Tree now respects the letter case given by the user. This restores the ability to write encoding names in uppercase like “UTF-8”, which worked in Python 2.

- bpo-25135: Make deque_clear() safer by emptying the deque before clearing. This helps avoid possible reentrancy issues.

- bpo-19143: platform module now reads Windows version from kernel32.dll to avoid compatibility shims.

- bpo-25092: Fix datetime.strftime() failure when errno was already set to EINVAL.

- bpo-23517: Fix rounding in fromtimestamp() and utcfromtimestamp() methods of datetime.datetime: microseconds are now rounded to nearest with ties going to nearest even integer (ROUND_HALF_EVEN), instead of being rounding towards minus infinity (ROUND_FLOOR). It’s important that these methods use the same rounding mode than datetime.timedelta to keep the property: (datetime(1970,1,1) + timedelta(seconds=t)) == datetime.utcfromtimestamp(t). It also the rounding mode used by round(float) for example.

- bpo-25155: Fix datetime.datetime.now() and datetime.datetime.utcnow() on Windows to support date after year 2038. It was a regression introduced in Python 3.5.0.

- bpo-25108: Omitted internal frames in traceback functions print_stack(), format_stack(), and extract_stack() called without arguments.

- bpo-25118: Fix a regression of Python 3.5.0 in os.waitpid() on Windows.

- bpo-24684: socket.socket.getaddrinfo() now calls PyUnicode_AsEncodedString() instead of calling the encode() method of the host, to handle correctly custom string with an encode() method which doesn’t return a byte string. The encoder of the IDNA codec is now called directly instead of calling the encode() method of the string.

- bpo-25060: Correctly compute stack usage of the BUILD_MAP opcode.

- bpo-24857: Comparing call_args to a long sequence now correctly returns a boolean result instead of raising an exception. Patch by A Kaptur.

- bpo-23144: Make sure that HTMLParser.feed() returns all the data, even when convert_charrefs is True.

- bpo-24982: shutil.make_archive() with the “zip” format now adds entries for directories (including empty directories) in ZIP file.

- bpo-25019: Fixed a crash caused by setting non-string key of expat parser. Based on patch by John Leitch.

- bpo-16180: Exit pdb if file has syntax error, instead of trapping user in an infinite loop. Patch by Xavier de Gaye.

- bpo-24891: Fix a race condition at Python startup if the file descriptor of stdin (0), stdout (1) or stderr (2) is closed while Python is creating sys.stdin, sys.stdout and sys.stderr objects. These attributes are now set to None if the creation of the object failed, instead of raising an OSError exception. Initial patch written by Marco Paolini.

- bpo-24992: Fix error handling and a race condition (related to garbage collection) in collections.OrderedDict constructor.

- bpo-24881: Fixed setting binary mode in Python implementation of FileIO on Windows and Cygwin. Patch from Akira Li.

- bpo-25578: Fix (another) memory leak in SSLSocket.getpeercer().

- bpo-25530: Disable the vulnerable SSLv3 protocol by default when creating ssl.SSLContext.

- bpo-25569: Fix memory leak in SSLSocket.getpeercert().

- bpo-25471: Sockets returned from accept() shouldn’t appear to be nonblocking.

- bpo-25319: When threading.Event is reinitialized, the underlying condition should use a regular lock rather than a recursive lock.

- bpo-21112: Fix regression in unittest.expectedFailure on subclasses. Patch from Berker Peksag.

- bpo-24764: cgi.FieldStorage.read_multi() now ignores the Content-Length header in part headers. Patch written by Peter Landry and reviewed by Pierre Quentel.

- bpo-24913: Fix overrun error in deque.index(). Found by John Leitch and Bryce Darling.

- bpo-24774: Fix docstring in http.server.test. Patch from Chiu-Hsiang Hsu.

- bpo-21159: Improve message in configparser.InterpolationMissingOptionError. Patch from Łukasz Langa.

- bpo-20362: Honour TestCase.longMessage correctly in assertRegex. Patch from Ilia Kurenkov.

- bpo-23572: Fixed functools.singledispatch on classes with falsy metaclasses. Patch by Ethan Furman.

- asyncio: ensure_future() now accepts awaitable objects.

### IDLE

- bpo-15348: Stop the debugger engine (normally in a user process) before closing the debugger window (running in the IDLE process). This prevents the RuntimeErrors that were being caught and ignored.

- bpo-24455: Prevent IDLE from hanging when a) closing the shell while the debugger is active (15347); b) closing the debugger with the [X] button (15348); and c) activating the debugger when already active (24455). The patch by Mark Roseman does this by making two changes. 1. Suspend and resume the gui.interaction method with the tcl vwait mechanism intended for this purpose (instead of root.mainloop & .quit). 2. In gui.run, allow any existing interaction to terminate first.

- Change ‘The program’ to ‘Your program’ in an IDLE ‘kill program?’ message to make it clearer that the program referred to is the currently running user program, not IDLE itself.

- bpo-24750: Improve the appearance of the IDLE editor window status bar. Patch by Mark Roseman.

- bpo-25313: Change the handling of new built-in text color themes to better address the compatibility problem introduced by the addition of IDLE Dark. Consistently use the revised idleConf.CurrentTheme everywhere in idlelib.

- bpo-24782: Extension configuration is now a tab in the IDLE Preferences dialog rather than a separate dialog. The former tabs are now a sorted list. Patch by Mark Roseman.

- bpo-22726: Re-activate the config dialog help button with some content about the other buttons and the new IDLE Dark theme.

- bpo-24820: IDLE now has an ‘IDLE Dark’ built-in text color theme. It is more or less IDLE Classic inverted, with a cobalt blue background. Strings, comments, keywords, … are still green, red, orange, … . To use it with IDLEs released before November 2015, hit the ‘Save as New Custom Theme’ button and enter a new name, such as ‘Custom Dark’. The custom theme will work with any IDLE release, and can be modified.

- bpo-25224: README.txt is now an idlelib index for IDLE developers and curious users. The previous user content is now in the IDLE doc chapter. ‘IDLE’ now means ‘Integrated Development and Learning Environment’.

- bpo-24820: Users can now set breakpoint colors in Settings -> Custom Highlighting. Original patch by Mark Roseman.

- bpo-24972: Inactive selection background now matches active selection background, as configured by users, on all systems. Found items are now always highlighted on Windows. Initial patch by Mark Roseman.

- bpo-24570: Idle: make calltip and completion boxes appear on Macs affected by a tk regression. Initial patch by Mark Roseman.

- bpo-24988: Idle ScrolledList context menus (used in debugger) now work on Mac Aqua. Patch by Mark Roseman.

- bpo-24801: Make right-click for context menu work on Mac Aqua. Patch by Mark Roseman.

- bpo-25173: Associate tkinter messageboxes with a specific widget. For Mac OSX, make them a ‘sheet’. Patch by Mark Roseman.

- bpo-25198: Enhance the initial html viewer now used for Idle Help. Properly indent fixed-pitch text (patch by Mark Roseman). Give code snippet a very Sphinx-like light blueish-gray background. Re-use initial width and height set by users for shell and editor. When the Table of Contents (TOC) menu is used, put the section header at the top of the screen.

- bpo-25225: Condense and rewrite Idle doc section on text colors.

- bpo-21995: Explain some differences between IDLE and console Python.

- bpo-22820: Explain need for print when running file from Idle editor.

- bpo-25224: Doc: augment Idle feature list and no-subprocess section.

- bpo-25219: Update doc for Idle command line options. Some were missing and notes were not correct.

- bpo-24861: Most of idlelib is private and subject to change. Use idleib.idle.* to start Idle. See idlelib.__init__.__doc__.

- bpo-25199: Idle: add synchronization comments for future maintainers.

- bpo-16893: Replace help.txt with help.html for Idle doc display. The new idlelib/help.html is rstripped Doc/build/html/library/idle.html. It looks better than help.txt and will better document Idle as released. The tkinter html viewer that works for this file was written by Mark Roseman. The now unused EditorWindow.HelpDialog class and helt.txt file are deprecated.

- bpo-24199: Deprecate unused idlelib.idlever with possible removal in 3.6.

- bpo-24790: Remove extraneous code (which also create 2 & 3 conflicts).

### Documentation

- bpo-22558: Add remaining doc links to source code for Python-coded modules. Patch by Yoni Lavi.

- bpo-12067: Rewrite Comparisons section in the Expressions chapter of the language reference. Some of the details of comparing mixed types were incorrect or ambiguous. NotImplemented is only relevant at a lower level than the Expressions chapter. Added details of comparing range() objects, and default behaviour and consistency suggestions for user-defined classes. Patch from Andy Maier.

- bpo-24952: Clarify the default size argument of stack_size() in the “threading” and “_thread” modules. Patch from Mattip.

- bpo-23725: Overhaul tempfile docs. Note deprecated status of mktemp. Patch from Zbigniew Jędrzejewski-Szmek.

- bpo-24808: Update the types of some PyTypeObject fields. Patch by Joseph Weston.

- bpo-22812: Fix unittest discovery examples. Patch from Pam McA’Nulty.

### Tests

- bpo-25449: Added tests for OrderedDict subclasses.

- bpo-25099: Make test_compileall not fail when an entry on sys.path cannot be written to (commonly seen in administrative installs on Windows).

- bpo-23919: Prevents assert dialogs appearing in the test suite.

- `PCbuild\rt.bat` now accepts an unlimited number of arguments to pass along to regrtest.py. Previously there was a limit of 9.

### Build

- bpo-24915: Add LLVM support for PGO builds and use the test suite to generate the profile data. Initial patch by Alecsandru Patrascu of Intel.

- bpo-24910: Windows MSIs now have unique display names.

- bpo-24986: It is now possible to build Python on Windows without errors when external libraries are not available.

### Windows

- bpo-25450: Updates shortcuts to start Python in installation directory.

- bpo-25164: Changes default all-users install directory to match per-user directory.

- bpo-25143: Improves installer error messages for unsupported platforms.

- bpo-25163: Display correct directory in installer when using non-default settings.

- bpo-25361: Disables use of SSE2 instructions in Windows 32-bit build

- bpo-25089: Adds logging to installer for case where launcher is not selected on upgrade.

- bpo-25165: Windows uninstallation should not remove launcher if other versions remain

- bpo-25112: py.exe launcher is missing icons

- bpo-25102: Windows installer does not precompile for -O or -OO.

- bpo-25081: Makes Back button in installer go back to upgrade page when upgrading.

- bpo-25091: Increases font size of the installer.

- bpo-25126: Clarifies that the non-web installer will download some components.

- bpo-25213: Restores requestedExecutionLevel to manifest to disable UAC virtualization.

- bpo-25022: Removed very outdated PC/example_nt/ directory.

### Tools/Demos

- bpo-25440: Fix output of python-config –extension-suffix.

## Python 3.5.0 final

Release date: 2015-09-13

### Build

- bpo-25071: Windows installer should not require TargetDir parameter when installing quietly.

## Python 3.5.0 release candidate 4

Release date: 2015-09-09

### Library

- bpo-25029: Fixes MemoryError in test_strptime.

### Build

- bpo-25027: Reverts partial-static build options and adds vcruntime140.dll to Windows installation.

## Python 3.5.0 release candidate 3

Release date: 2015-09-07

### Core and Builtins

- bpo-24305: Prevent import subsystem stack frames from being counted by the warnings.warn(stacklevel=) parameter.

- bpo-24912: Prevent __class__ assignment to immutable built-in objects.

- bpo-24975: Fix AST compilation for PEP 448 syntax.

### Library

- bpo-24917: time_strftime() buffer over-read.

- bpo-24748: To resolve a compatibility problem found with py2exe and pywin32, imp.load_dynamic() once again ignores previously loaded modules to support Python modules replacing themselves with extension modules. Patch by Petr Viktorin.

- bpo-24635: Fixed a bug in typing.py where isinstance([], typing.Iterable) would return True once, then False on subsequent calls.

- bpo-24989: Fixed buffer overread in BytesIO.readline() if a position is set beyond size. Based on patch by John Leitch.

- bpo-24913: Fix overrun error in deque.index(). Found by John Leitch and Bryce Darling.

## Python 3.5.0 release candidate 2

Release date: 2015-08-25

### Core and Builtins

- bpo-24769: Interpreter now starts properly when dynamic loading is disabled. Patch by Petr Viktorin.

- bpo-21167: NAN operations are now handled correctly when python is compiled with ICC even if -fp-model strict is not specified.

- bpo-24492: A “package” lacking a __name__ attribute when trying to perform a `from .. import ...` statement will trigger an ImportError instead of an AttributeError.

### Library

- bpo-24847: Removes vcruntime140.dll dependency from Tcl/Tk.

- bpo-24839: platform._syscmd_ver raises DeprecationWarning

- bpo-24867: Fix Task.get_stack() for ‘async def’ coroutines

## Python 3.5.0 release candidate 1

Release date: 2015-08-09

### Core and Builtins

- bpo-24667: Resize odict in all cases that the underlying dict resizes.

### Library

- bpo-24824: Signatures of codecs.encode() and codecs.decode() now are compatible with pydoc.

- bpo-24634: Importing uuid should not try to load libc on Windows

- bpo-24798: _msvccompiler.py doesn’t properly support manifests

- bpo-4395: Better testing and documentation of binary operators. Patch by Martin Panter.

- bpo-23973: Update typing.py from GitHub repo.

- bpo-23004: mock_open() now reads binary data correctly when the type of read_data is bytes. Initial patch by Aaron Hill.

- bpo-23888: Handle fractional time in cookie expiry. Patch by ssh.

- bpo-23652: Make it possible to compile the select module against the libc headers from the Linux Standard Base, which do not include some EPOLL macros. Patch by Matt Frank.

- bpo-22932: Fix timezones in email.utils.formatdate. Patch from Dmitry Shachnev.

- bpo-23779: imaplib raises TypeError if authenticator tries to abort. Patch from Craig Holmquist.

- bpo-23319: Fix ctypes.BigEndianStructure, swap correctly bytes. Patch written by Matthieu Gautier.

- bpo-23254: Document how to close the TCPServer listening socket. Patch from Martin Panter.

- bpo-19450: Update Windows and OS X installer builds to use SQLite 3.8.11.

- bpo-17527: Add PATCH to wsgiref.validator. Patch from Luca Sbardella.

- bpo-24791: Fix grammar regression for call syntax: ‘g(*a or b)’.

### IDLE

- bpo-23672: Allow Idle to edit and run files with astral chars in name. Patch by Mohd Sanad Zaki Rizvi.

- bpo-24745: Idle editor default font. Switch from Courier to platform-sensitive TkFixedFont. This should not affect current customized font selections. If there is a problem, edit $HOME/.idlerc/config-main.cfg and remove ‘fontxxx’ entries from [Editor Window]. Patch by Mark Roseman.

- bpo-21192: Idle editor. When a file is run, put its name in the restart bar. Do not print false prompts. Original patch by Adnan Umer.

- bpo-13884: Idle menus. Remove tearoff lines. Patch by Roger Serwy.

### Documentation

- bpo-24129: Clarify the reference documentation for name resolution. This includes removing the assumption that readers will be familiar with the name resolution scheme Python used prior to the introduction of lexical scoping for function namespaces. Patch by Ivan Levkivskyi.

- bpo-20769: Improve reload() docs. Patch by Dorian Pula.

- bpo-23589: Remove duplicate sentence from the FAQ. Patch by Yongzhi Pan.

- bpo-24729: Correct IO tutorial to match implementation regarding encoding parameter to open function.

### Tests

- bpo-24751: When running regrtest with the `-w` command line option, a test run is no longer marked as a failure if all tests succeed when re-run.

## Python 3.5.0 beta 4

Release date: 2015-07-26

### Core and Builtins

- bpo-23573: Restored optimization of bytes.rfind() and bytearray.rfind() for single-byte argument on Linux.

- bpo-24569: Make PEP 448 dictionary evaluation more consistent.

- bpo-24583: Fix crash when set is mutated while being updated.

- bpo-24407: Fix crash when dict is mutated while being updated.

- bpo-24619: New approach for tokenizing async/await. As a consequence, it is now possible to have one-line ‘async def foo(): await ..’ functions.

- bpo-24687: Plug refleak on SyntaxError in function parameters annotations.

- bpo-15944: memoryview: Allow arbitrary formats when casting to bytes. Patch by Martin Panter.

### Library

- bpo-23441: rcompleter now prints a tab character instead of displaying possible completions for an empty word. Initial patch by Martin Sekera.

- bpo-24683: Fixed crashes in _json functions called with arguments of inappropriate type.

- bpo-21697: shutil.copytree() now correctly handles symbolic links that point to directories. Patch by Eduardo Seabra and Thomas Kluyver.

- bpo-14373: Fixed segmentation fault when gc.collect() is called during constructing lru_cache (C implementation).

- bpo-24695: Fix a regression in traceback.print_exception(). If exc_traceback is None we shouldn’t print a traceback header like described in the documentation.

- bpo-24620: Random.setstate() now validates the value of state last element.

- bpo-22485: Fixed an issue that caused `inspect.getsource` to return incorrect results on nested functions.

- bpo-22153: Improve unittest docs. Patch from Martin Panter and evilzero.

- bpo-24580: Symbolic group references to open group in re patterns now are explicitly forbidden as well as numeric group references.

- bpo-24206: Fixed __eq__ and __ne__ methods of inspect classes.

- bpo-24631: Fixed regression in the timeit module with multiline setup.

- bpo-18622: unittest.mock.mock_open().reset_mock would recurse infinitely. Patch from Nicola Palumbo and Laurent De Buyst.

- bpo-23661: unittest.mock side_effects can now be exceptions again. This was a regression vs Python 3.4. Patch from Ignacio Rossi

- bpo-24608: chunk.Chunk.read() now always returns bytes, not str.

- bpo-18684: Fixed reading out of the buffer in the re module.

- bpo-24259: tarfile now raises a ReadError if an archive is truncated inside a data segment.

- bpo-15014: SMTP.auth() and SMTP.login() now support RFC 4954’s optional initial-response argument to the SMTP AUTH command.

- bpo-24669: Fix inspect.getsource() for ‘async def’ functions. Patch by Kai Groner.

- bpo-24688: ast.get_docstring() for ‘async def’ functions.

### Build

- bpo-24603: Update Windows builds and OS X 10.5 installer to use OpenSSL 1.0.2d.

## Python 3.5.0 beta 3

Release date: 2015-07-05

### Core and Builtins

- bpo-24467: Fixed possible buffer over-read in bytearray. The bytearray object now always allocates place for trailing null byte and it’s buffer now is always null-terminated.

- Upgrade to Unicode 8.0.0.

- bpo-24345: Add Py_tp_finalize slot for the stable ABI.

- bpo-24400: Introduce a distinct type for PEP 492 coroutines; add types.CoroutineType, inspect.getcoroutinestate, inspect.getcoroutinelocals; coroutines no longer use CO_GENERATOR flag; sys.set_coroutine_wrapper works only for ‘async def’ coroutines; inspect.iscoroutine no longer uses collections.abc.Coroutine, it’s intended to test for pure ‘async def’ coroutines only; add new opcode: GET_YIELD_FROM_ITER; fix generators wrapper used in types.coroutine to be instance of collections.abc.Generator; collections.abc.Awaitable and collections.abc.Coroutine can no longer be used to detect generator-based coroutines–use inspect.isawaitable instead.

- bpo-24450: Add gi_yieldfrom to generators and cr_await to coroutines. Contributed by Benno Leslie and Yury Selivanov.

- bpo-19235: Add new RecursionError exception. Patch by Georg Brandl.

### Library

- bpo-21750: mock_open.read_data can now be read from each instance, as it could in Python 3.3.

- bpo-24552: Fix use after free in an error case of the _pickle module.

- bpo-24514: tarfile now tolerates number fields consisting of only whitespace.

- bpo-19176: Fixed doctype() related bugs in C implementation of ElementTree. A deprecation warning no longer issued by XMLParser subclass with default doctype() method. Direct call of doctype() now issues a warning. Parser’s doctype() now is not called if target’s doctype() is called. Based on patch by Martin Panter.

- bpo-20387: Restore semantic round-trip correctness in tokenize/untokenize for tab-indented blocks.

- bpo-24456: Fixed possible buffer over-read in adpcm2lin() and lin2adpcm() functions of the audioop module.

- bpo-24336: The contextmanager decorator now works with functions with keyword arguments called “func” and “self”. Patch by Martin Panter.

- bpo-24522: Fix possible integer overflow in json accelerator module.

- bpo-24489: ensure a previously set C errno doesn’t disturb cmath.polar().

- bpo-24408: Fixed AttributeError in measure() and metrics() methods of tkinter.Font.

- bpo-14373: C implementation of functools.lru_cache() now can be used with methods.

- bpo-24347: Set KeyError if PyDict_GetItemWithError returns NULL.

- bpo-24348: Drop superfluous incref/decref.

- bpo-24359: Check for changed OrderedDict size during iteration.

- bpo-24368: Support keyword arguments in OrderedDict methods.

- bpo-24362: Simplify the C OrderedDict fast nodes resize logic.

- bpo-24377: Fix a ref leak in OrderedDict.__repr__.

- bpo-24369: Defend against key-changes during iteration.

### Tests

- bpo-24373: _testmultiphase and xxlimited now use tp_traverse and tp_finalize to avoid reference leaks encountered when combining tp_dealloc with PyType_FromSpec (see bpo-16690 for details)

### Documentation

- bpo-24458: Update documentation to cover multi-phase initialization for extension modules (PEP 489). Patch by Petr Viktorin.

- bpo-24351: Clarify what is meant by “identifier” in the context of string.Template instances.

### Build

- bpo-24432: Update Windows builds and OS X 10.5 installer to use OpenSSL 1.0.2c.

## Python 3.5.0 beta 2

Release date: 2015-05-31

### Core and Builtins

- bpo-24284: The startswith and endswith methods of the str class no longer return True when finding the empty string and the indexes are completely out of range.

- bpo-24115: Update uses of PyObject_IsTrue(), PyObject_Not(), PyObject_IsInstance(), PyObject_RichCompareBool() and _PyDict_Contains() to check for and handle errors correctly.

- bpo-24328: Fix importing one character extension modules.

- bpo-11205: In dictionary displays, evaluate the key before the value.

- bpo-24285: Fixed regression that prevented importing extension modules from inside packages. Patch by Petr Viktorin.

### Library

- bpo-23247: Fix a crash in the StreamWriter.reset() of CJK codecs.

- bpo-24270: Add math.isclose() and cmath.isclose() functions as per PEP 485. Contributed by Chris Barker and Tal Einat.

- bpo-5633: Fixed timeit when the statement is a string and the setup is not.

- bpo-24326: Fixed audioop.ratecv() with non-default weightB argument. Original patch by David Moore.

- bpo-16991: Add a C implementation of OrderedDict.

- bpo-23934: Fix inspect.signature to fail correctly for builtin types lacking signature information. Initial patch by James Powell.

## Python 3.5.0 beta 1

Release date: 2015-05-24

### Core and Builtins

- bpo-24276: Fixed optimization of property descriptor getter.

- bpo-24268: PEP 489: Multi-phase extension module initialization. Patch by Petr Viktorin.

- bpo-23955: Add pyvenv.cfg option to suppress registry/environment lookup for generating sys.path on Windows.

- bpo-24257: Fixed system error in the comparison of faked types.SimpleNamespace.

- bpo-22939: Fixed integer overflow in iterator object. Patch by Clement Rouault.

- bpo-23985: Fix a possible buffer overrun when deleting a slice from the front of a bytearray and then appending some other bytes data.

- bpo-24102: Fixed exception type checking in standard error handlers.

- bpo-15027: The UTF-32 encoder is now 3x to 7x faster.

- bpo-23290: Optimize set_merge() for cases where the target is empty. (Contributed by Serhiy Storchaka.)

- bpo-2292: PEP 448: Additional Unpacking Generalizations.

- bpo-24096: Make warnings.warn_explicit more robust against mutation of the warnings.filters list.

- bpo-23996: Avoid a crash when a delegated generator raises an unnormalized StopIteration exception. Patch by Stefan Behnel.

- bpo-23910: Optimize property() getter calls. Patch by Joe Jevnik.

- bpo-23911: Move path-based importlib bootstrap code to a separate frozen module.

- bpo-24192: Fix namespace package imports.

- bpo-24022: Fix tokenizer crash when processing undecodable source code.

- bpo-9951: Added a hex() method to bytes, bytearray, and memoryview.

- bpo-22906: PEP 479: Change StopIteration handling inside generators.

- bpo-24017: PEP 492: Coroutines with async and await syntax.

### Library

- bpo-14373: Added C implementation of functools.lru_cache(). Based on patches by Matt Joiner and Alexey Kachayev.

- bpo-24230: The tempfile module now accepts bytes for prefix, suffix and dir parameters and returns bytes in such situations (matching the os module APIs).

- bpo-22189: collections.UserString now supports __getnewargs__(), __rmod__(), casefold(), format_map(), isprintable(), and maketrans(). Patch by Joe Jevnik.

- bpo-24244: Prevents termination when an invalid format string is encountered on Windows in strftime.

- bpo-23973: PEP 484: Add the typing module.

- bpo-23086: The collections.abc.Sequence() abstract base class added start and stop parameters to the index() mixin. Patch by Devin Jeanpierre.

- bpo-20035: Replaced the `tkinter._fix` module used for setting up the Tcl/Tk environment on Windows with a private function in the `_tkinter` module that makes no permanent changes to the environment.

- bpo-24257: Fixed segmentation fault in sqlite3.Row constructor with faked cursor type.

- bpo-15836: assertRaises(), assertRaisesRegex(), assertWarns() and assertWarnsRegex() assertments now check the type of the first argument to prevent possible user error. Based on patch by Daniel Wagner-Hall.

- bpo-9858: Add missing method stubs to _io.RawIOBase. Patch by Laura Rupprecht.

- bpo-22955: attrgetter, itemgetter and methodcaller objects in the operator module now support pickling. Added readable and evaluable repr for these objects. Based on patch by Josh Rosenberg.

- bpo-22107: tempfile.gettempdir() and tempfile.mkdtemp() now try again when a directory with the chosen name already exists on Windows as well as on Unix. tempfile.mkstemp() now fails early if parent directory is not valid (not exists or is a file) on Windows.

- bpo-23780: Improved error message in os.path.join() with single argument.

- bpo-6598: Increased time precision and random number range in email.utils.make_msgid() to strengthen the uniqueness of the message ID.

- bpo-24091: Fixed various crashes in corner cases in C implementation of ElementTree.

- bpo-21931: msilib.FCICreate() now raises TypeError in the case of a bad argument instead of a ValueError with a bogus FCI error number. Patch by Jeffrey Armstrong.

- bpo-13866: quote_via argument added to urllib.parse.urlencode.

- bpo-20098: New mangle_from policy option for email, default True for compat32, but False for all other policies.

- bpo-24211: The email library now supports RFC 6532: it can generate headers using utf-8 instead of encoded words.

- bpo-16314: Added support for the LZMA compression in distutils.

- bpo-21804: poplib now supports RFC 6856 (UTF8).

- bpo-18682: Optimized pprint functions for builtin scalar types.

- bpo-22027: smtplib now supports RFC 6531 (SMTPUTF8).

- bpo-23488: Random generator objects now consume 2x less memory on 64-bit.

- bpo-1322: platform.dist() and platform.linux_distribution() functions are now deprecated. Initial patch by Vajrasky Kok.

- bpo-22486: Added the math.gcd() function. The fractions.gcd() function now is deprecated. Based on patch by Mark Dickinson.

- bpo-24064: Property() docstrings are now writeable. (Patch by Berker Peksag.)

- bpo-22681: Added support for the koi8_t encoding.

- bpo-22682: Added support for the kz1048 encoding.

- bpo-23796: peek and read1 methods of BufferedReader now raise ValueError if they called on a closed object. Patch by John Hergenroeder.

- bpo-21795: smtpd now supports the 8BITMIME extension whenever the new decode_data constructor argument is set to False.

- bpo-24155: optimize heapq.heapify() for better cache performance when heapifying large lists.

- bpo-21800: imaplib now supports RFC 5161 (enable), RFC 6855 (utf8/internationalized email) and automatically encodes non-ASCII usernames and passwords to UTF8.

- bpo-20274: When calling a _sqlite.Connection, it now complains if passed any keyword arguments. Previously it silently ignored them.

- bpo-20274: Remove ignored and erroneous “kwargs” parameters from three METH_VARARGS methods on _sqlite.Connection.

- bpo-24134: assertRaises(), assertRaisesRegex(), assertWarns() and assertWarnsRegex() checks now emits a deprecation warning when callable is None or keyword arguments except msg is passed in the context manager mode.

- bpo-24018: Add a collections.abc.Generator abstract base class. Contributed by Stefan Behnel.

- bpo-23880: Tkinter’s getint() and getdouble() now support Tcl_Obj. Tkinter’s getdouble() now supports any numbers (in particular int).

- bpo-22619: Added negative limit support in the traceback module. Based on patch by Dmitry Kazakov.

- bpo-24094: Fix possible crash in json.encode with poorly behaved dict subclasses.

- bpo-9246: On POSIX, os.getcwd() now supports paths longer than 1025 bytes. Patch written by William Orr.

- bpo-17445: add difflib.diff_bytes() to support comparison of byte strings (fixes a regression from Python 2).

- bpo-23917: Fall back to sequential compilation when ProcessPoolExecutor doesn’t exist. Patch by Claudiu Popa.

- bpo-23008: Fixed resolving attributes with boolean value is False in pydoc.

- Fix asyncio issue 235: LifoQueue and PriorityQueue’s put didn’t increment unfinished tasks (this bug was introduced when JoinableQueue was merged with Queue).

- bpo-23908: os functions now reject paths with embedded null character on Windows instead of silently truncating them.

- bpo-23728: binascii.crc_hqx() could return an integer outside of the range 0-0xffff for empty data.

- bpo-23887: urllib.error.HTTPError now has a proper repr() representation. Patch by Berker Peksag.

- asyncio: New event loop APIs: set_task_factory() and get_task_factory().

- asyncio: async() function is deprecated in favour of ensure_future().

- bpo-24178: asyncio.Lock, Condition, Semaphore, and BoundedSemaphore support new ‘async with’ syntax. Contributed by Yury Selivanov.

- bpo-24179: Support ‘async for’ for asyncio.StreamReader. Contributed by Yury Selivanov.

- bpo-24184: Add AsyncIterator and AsyncIterable ABCs to collections.abc. Contributed by Yury Selivanov.

- bpo-22547: Implement informative __repr__ for inspect.BoundArguments. Contributed by Yury Selivanov.

- bpo-24190: Implement inspect.BoundArgument.apply_defaults() method. Contributed by Yury Selivanov.

- bpo-20691: Add ‘follow_wrapped’ argument to inspect.Signature.from_callable() and inspect.signature(). Contributed by Yury Selivanov.

- bpo-24248: Deprecate inspect.Signature.from_function() and inspect.Signature.from_builtin().

- bpo-23898: Fix inspect.classify_class_attrs() to support attributes with overloaded __eq__ and __bool__. Patch by Mike Bayer.

- bpo-24298: Fix inspect.signature() to correctly unwrap wrappers around bound methods.

### IDLE

- bpo-23184: remove unused names and imports in idlelib. Initial patch by Al Sweigart.

### Tests

- bpo-21520: test_zipfile no longer fails if the word ‘bad’ appears anywhere in the name of the current directory.

- bpo-9517: Move script_helper into the support package. Patch by Christie Wilson.

### Documentation

- bpo-22155: Add File Handlers subsection with createfilehandler to tkinter doc. Remove obsolete example from FAQ. Patch by Martin Panter.

- bpo-24029: Document the name binding behavior for submodule imports.

- bpo-24077: Fix typo in man page for -I command option: -s, not -S

### Tools/Demos

- bpo-24000: Improved Argument Clinic’s mapping of converters to legacy “format units”. Updated the documentation to match.

- bpo-24001: Argument Clinic converters now use accept={type} instead of types={‘type’} to specify the types the converter accepts.

- bpo-23330: h2py now supports arbitrary filenames in #include.

- bpo-24031: make patchcheck now supports git checkouts, too.

## Python 3.5.0 alpha 4

Release date: 2015-04-19

### Core and Builtins

- bpo-22980: Under Linux, GNU/KFreeBSD and the Hurd, C extensions now include the architecture triplet in the extension name, to make it easy to test builds for different ABIs in the same working tree. Under OS X, the extension name now includes PEP 3149-style information.

- bpo-22631: Added Linux-specific socket constant CAN_RAW_FD_FRAMES. Patch courtesy of Joe Jevnik.

- bpo-23731: Implement PEP 488: removal of .pyo files.

- bpo-23726: Don’t enable GC for user subclasses of non-GC types that don’t add any new fields. Patch by Eugene Toder.

- bpo-23309: Avoid a deadlock at shutdown if a daemon thread is aborted while it is holding a lock to a buffered I/O object, and the main thread tries to use the same I/O object (typically stdout or stderr). A fatal error is emitted instead.

- bpo-22977: Fixed formatting Windows error messages on Wine. Patch by Martin Panter.

- bpo-23466: %c, %o, %x, and %X in bytes formatting now raise TypeError on non-integer input.

- bpo-24044: Fix possible null pointer dereference in list.sort in out of memory conditions.

- bpo-21354: PyCFunction_New function is exposed by python DLL again.

### Library

- bpo-23840: tokenize.open() now closes the temporary binary file on error to fix a resource warning.

- bpo-16914: new debuglevel 2 in smtplib adds timestamps to debug output.

- bpo-7159: urllib.request now supports sending auth credentials automatically after the first 401. This enhancement is a superset of the enhancement from bpo-19494 and supersedes that change.

- bpo-23703: Fix a regression in urljoin() introduced in 901e4e52b20a. Patch by Demian Brecht.

- bpo-4254: Adds _curses.update_lines_cols(). Patch by Arnon Yaari

- bpo-19933: Provide default argument for ndigits in round. Patch by Vajrasky Kok.

- bpo-23193: Add a numeric_owner parameter to tarfile.TarFile.extract and tarfile.TarFile.extractall. Patch by Michael Vogt and Eric Smith.

- bpo-23342: Add a subprocess.run() function than returns a CalledProcess instance for a more consistent API than the existing call* functions.

- bpo-21217: inspect.getsourcelines() now tries to compute the start and end lines from the code object, fixing an issue when a lambda function is used as decorator argument. Patch by Thomas Ballinger and Allison Kaptur.

- bpo-24521: Fix possible integer overflows in the pickle module.

- bpo-22931: Allow ‘[’ and ‘]’ in cookie values.

- The keywords attribute of functools.partial is now always a dictionary.

- bpo-23811: Add missing newline to the PyCompileError error message. Patch by Alex Shkop.

- bpo-21116: Avoid blowing memory when allocating a multiprocessing shared array that’s larger than 50% of the available RAM. Patch by Médéric Boquien.

- bpo-22982: Improve BOM handling when seeking to multiple positions of a writable text file.

- bpo-23464: Removed deprecated asyncio JoinableQueue.

- bpo-23529: Limit the size of decompressed data when reading from GzipFile, BZ2File or LZMAFile. This defeats denial of service attacks using compressed bombs (i.e. compressed payloads which decompress to a huge size). Patch by Martin Panter and Nikolaus Rath.

- bpo-21859: Added Python implementation of io.FileIO.

- bpo-23865: close() methods in multiple modules now are idempotent and more robust at shutdown. If they need to release multiple resources, all are released even if errors occur.

- bpo-23400: Raise same exception on both Python 2 and 3 if sem_open is not available. Patch by Davin Potts.

- bpo-10838: The subprocess now module includes SubprocessError and TimeoutError in its list of exported names for the users wild enough to use `from subprocess import *`.

- bpo-23411: Added DefragResult, ParseResult, SplitResult, DefragResultBytes, ParseResultBytes, and SplitResultBytes to urllib.parse.__all__. Patch by Martin Panter.

- bpo-23881: urllib.request.ftpwrapper constructor now closes the socket if the FTP connection failed to fix a ResourceWarning.

- bpo-23853: `socket.socket.sendall()` does no more reset the socket timeout each time data is sent successfully. The socket timeout is now the maximum total duration to send all data.

- bpo-22721: An order of multiline pprint output of set or dict containing orderable and non-orderable elements no longer depends on iteration order of set or dict.

- bpo-15133: _tkinter.tkapp.getboolean() now supports Tcl_Obj and always returns bool. tkinter.BooleanVar now validates input values (accepted bool, int, str, and Tcl_Obj). tkinter.BooleanVar.get() now always returns bool.

- bpo-10590: xml.sax.parseString() now supports string argument.

- bpo-23338: Fixed formatting ctypes error messages on Cygwin. Patch by Makoto Kato.

- bpo-15582: inspect.getdoc() now follows inheritance chains.

- bpo-2175: SAX parsers now support a character stream of InputSource object.

- bpo-16840: Tkinter now supports 64-bit integers added in Tcl 8.4 and arbitrary precision integers added in Tcl 8.5.

- bpo-23834: Fix socket.sendto(), use the C Py_ssize_t type to store the result of sendto() instead of the C int type.

- bpo-23618: `socket.socket.connect()` now waits until the connection completes instead of raising `InterruptedError` if the connection is interrupted by signals, signal handlers don’t raise an exception and the socket is blocking or has a timeout. `socket.socket.connect()` still raise `InterruptedError` for non-blocking sockets.

- bpo-21526: Tkinter now supports new boolean type in Tcl 8.5.

- bpo-23836: Fix the faulthandler module to handle reentrant calls to its signal handlers.

- bpo-23838: linecache now clears the cache and returns an empty result on MemoryError.

- bpo-10395: Added os.path.commonpath(). Implemented in posixpath and ntpath. Based on patch by Rafik Draoui.

- bpo-23611: Serializing more “lookupable” objects (such as unbound methods or nested classes) now are supported with pickle protocols < 4.

- bpo-13583: sqlite3.Row now supports slice indexing.

- bpo-18473: Fixed 2to3 and 3to2 compatible pickle mappings. Fixed ambiguous reverse mappings. Added many new mappings. Import mapping is no longer applied to modules already mapped with full name mapping.

- bpo-23485: select.select() is now retried automatically with the recomputed timeout when interrupted by a signal, except if the signal handler raises an exception. This change is part of the PEP 475.

- bpo-23752: When built from an existing file descriptor, io.FileIO() now only calls fstat() once. Before fstat() was called twice, which was not necessary.

- bpo-23704: collections.deque() objects now support __add__, __mul__, and __imul__().

- bpo-23171: csv.Writer.writerow() now supports arbitrary iterables.

- bpo-23745: The new email header parser now handles duplicate MIME parameter names without error, similar to how get_param behaves.

- bpo-22117: Fix os.utime(), it now rounds the timestamp towards minus infinity (-inf) instead of rounding towards zero.

- bpo-23310: Fix MagicMock’s initializer to work with __methods__, just like configure_mock(). Patch by Kasia Jachim.

### Build

- bpo-23817: FreeBSD now uses “1.0” in the SOVERSION as other operating systems, instead of just “1”.

- bpo-23501: Argument Clinic now generates code into separate files by default.

### Tests

- bpo-23799: Added test.support.start_threads() for running and cleaning up multiple threads.

- bpo-22390: test.regrtest now emits a warning if temporary files or directories are left after running a test.

### Tools/Demos

- bpo-18128: pygettext now uses standard +NNNN format in the POT-Creation-Date header.

- bpo-23935: Argument Clinic’s understanding of format units accepting bytes, bytearrays, and buffers is now consistent with both the documentation and the implementation.

- bpo-23944: Argument Clinic now wraps long impl prototypes at column 78.

- bpo-20586: Argument Clinic now ensures that functions without docstrings have signatures.

- bpo-23492: Argument Clinic now generates argument parsing code with PyArg_Parse instead of PyArg_ParseTuple if possible.

- bpo-23500: Argument Clinic is now smarter about generating the “#ifndef” (empty) definition of the methoddef macro: it’s only generated once, even if Argument Clinic processes the same symbol multiple times, and it’s emitted at the end of all processing rather than immediately after the first use.

### C API

- bpo-23998: PyImport_ReInitLock() now checks for lock allocation error

## Python 3.5.0 alpha 3

Release date: 2015-03-28

### Core and Builtins

- bpo-23573: Increased performance of string search operations (str.find, str.index, str.count, the in operator, str.split, str.partition) with arguments of different kinds (UCS1, UCS2, UCS4).

- bpo-23753: Python doesn’t support anymore platforms without stat() or fstat(), these functions are always required.

- bpo-23681: The -b option now affects comparisons of bytes with int.

- bpo-23632: Memoryviews now allow tuple indexing (including for multi-dimensional memoryviews).

- bpo-23192: Fixed generator lambdas. Patch by Bruno Cauet.

- bpo-23629: Fix the default __sizeof__ implementation for variable-sized objects.

### Library

- bpo-14260: The groupindex attribute of regular expression pattern object now is non-modifiable mapping.

- bpo-23792: Ignore KeyboardInterrupt when the pydoc pager is active. This mimics the behavior of the standard unix pagers, and prevents pipepager from shutting down while the pager itself is still running.

- bpo-23775: pprint() of OrderedDict now outputs the same representation as repr().

- bpo-23765: Removed IsBadStringPtr calls in ctypes

- bpo-22364: Improved some re error messages using regex for hints.

- bpo-23742: ntpath.expandvars() no longer loses unbalanced single quotes.

- bpo-21717: The zipfile.ZipFile.open function now supports ‘x’ (exclusive creation) mode.

- bpo-21802: The reader in BufferedRWPair now is closed even when closing writer failed in BufferedRWPair.close().

- bpo-23622: Unknown escapes in regular expressions that consist of `'\'` and ASCII letter now raise a deprecation warning and will be forbidden in Python 3.6.

- bpo-23671: string.Template now allows specifying the “self” parameter as a keyword argument. string.Formatter now allows specifying the “self” and the “format_string” parameters as keyword arguments.

- bpo-23502: The pprint module now supports mapping proxies.

- bpo-17530: pprint now wraps long bytes objects and bytearrays.

- bpo-22687: Fixed some corner cases in breaking words in tetxtwrap. Got rid of quadratic complexity in breaking long words.

- bpo-4727: The copy module now uses pickle protocol 4 (PEP 3154) and supports copying of instances of classes whose __new__ method takes keyword-only arguments.

- bpo-23491: Added a zipapp module to support creating executable zip file archives of Python code. Registered “.pyz” and “.pyzw” extensions on Windows for these archives (PEP 441).

- bpo-23657: Avoid explicit checks for str in zipapp, adding support for pathlib.Path objects as arguments.

- bpo-23688: Added support of arbitrary bytes-like objects and avoided unnecessary copying of memoryview in gzip.GzipFile.write(). Original patch by Wolfgang Maier.

- bpo-23252: Added support for writing ZIP files to unseekable streams.

- bpo-23647: Increase imaplib’s MAXLINE to accommodate modern mailbox sizes.

- bpo-23539: If body is None, http.client.HTTPConnection.request now sets Content-Length to 0 for PUT, POST, and PATCH headers to avoid 411 errors from some web servers.

- bpo-22351: The nntplib.NNTP constructor no longer leaves the connection and socket open until the garbage collector cleans them up. Patch by Martin Panter.

- bpo-23704: collections.deque() objects now support methods for index(), insert(), and copy(). This allows deques to be registered as a MutableSequence and it improves their substitutability for lists.

- bpo-23715: `signal.sigwaitinfo()` and `signal.sigtimedwait()` are now retried when interrupted by a signal not in the sigset parameter, if the signal handler does not raise an exception. signal.sigtimedwait() recomputes the timeout with a monotonic clock when it is retried.

- bpo-23001: Few functions in modules mmap, ossaudiodev, socket, ssl, and codecs, that accepted only read-only bytes-like object now accept writable bytes-like object too.

- bpo-23646: If time.sleep() is interrupted by a signal, the sleep is now retried with the recomputed delay, except if the signal handler raises an exception (PEP 475).

- bpo-23136: _strptime now uniformly handles all days in week 0, including Dec 30 of previous year. Based on patch by Jim Carroll.

- bpo-23700: Iterator of NamedTemporaryFile now keeps a reference to NamedTemporaryFile instance. Patch by Bohuslav Kabrda.

- bpo-22903: The fake test case created by unittest.loader when it fails importing a test module is now picklable.

- bpo-22181: On Linux, os.urandom() now uses the new getrandom() syscall if available, syscall introduced in the Linux kernel 3.17. It is more reliable and more secure, because it avoids the need of a file descriptor and waits until the kernel has enough entropy.

- bpo-2211: Updated the implementation of the http.cookies.Morsel class. Setting attributes key, value and coded_value directly now is deprecated. update() and setdefault() now transform and check keys. Comparing for equality now takes into account attributes key, value and coded_value. copy() now returns a Morsel, not a dict. repr() now contains all attributes. Optimized checking keys and quoting values. Added new tests. Original patch by Demian Brecht.

- bpo-18983: Allow selection of output units in timeit. Patch by Julian Gindi.

- bpo-23631: Fix traceback.format_list when a traceback has been mutated.

- bpo-23568: Add rdivmod support to MagicMock() objects. Patch by Håkan Lövdahl.

- bpo-2052: Add charset parameter to HtmlDiff.make_file().

- bpo-23668: Support os.truncate and os.ftruncate on Windows.

- bpo-23138: Fixed parsing cookies with absent keys or values in cookiejar. Patch by Demian Brecht.

- bpo-23051: multiprocessing.Pool methods imap() and imap_unordered() now handle exceptions raised by an iterator. Patch by Alon Diamant and Davin Potts.

- bpo-23581: Add matmul support to MagicMock. Patch by Håkan Lövdahl.

- bpo-23566: enable(), register(), dump_traceback() and dump_traceback_later() functions of faulthandler now accept file descriptors. Patch by Wei Wu.

- bpo-22928: Disabled HTTP header injections in http.client. Original patch by Demian Brecht.

- bpo-23615: Modules bz2, tarfile and tokenize now can be reloaded with imp.reload(). Patch by Thomas Kluyver.

- bpo-23605: os.walk() now calls os.scandir() instead of os.listdir(). The usage of os.scandir() reduces the number of calls to os.stat(). Initial patch written by Ben Hoyt.

### Build

- bpo-23585: make patchcheck will ensure the interpreter is built.

### Tests

- bpo-23583: Added tests for standard IO streams in IDLE.

- bpo-22289: Prevent test_urllib2net failures due to ftp connection timeout.

### Tools/Demos

- bpo-22826: The result of open() in Tools/freeze/bkfile.py is now better compatible with regular files (in particular it now supports the context management protocol).

## Python 3.5.0 alpha 2

Release date: 2015-03-09

### Core and Builtins

- bpo-23571: PyObject_Call() and PyCFunction_Call() now raise a SystemError if a function returns a result and raises an exception. The SystemError is chained to the previous exception.

### Library

- bpo-22524: New os.scandir() function, part of the PEP 471: “os.scandir() function – a better and faster directory iterator”. Patch written by Ben Hoyt.

- bpo-23103: Reduced the memory consumption of IPv4Address and IPv6Address.

- bpo-21793: BaseHTTPRequestHandler again logs response code as numeric, not as stringified enum. Patch by Demian Brecht.

- bpo-23476: In the ssl module, enable OpenSSL’s X509_V_FLAG_TRUSTED_FIRST flag on certificate stores when it is available.

- bpo-23576: Avoid stalling in SSL reads when EOF has been reached in the SSL layer but the underlying connection hasn’t been closed.

- bpo-23504: Added an __all__ to the types module.

- bpo-23563: Optimized utility functions in urllib.parse.

- bpo-7830: Flatten nested functools.partial.

- bpo-20204: Added the __module__ attribute to _tkinter classes.

- bpo-19980: Improved help() for non-recognized strings. help(‘’) now shows the help on str. help(‘help’) now shows the help on help(). Original patch by Mark Lawrence.

- bpo-23521: Corrected pure python implementation of timedelta division. Eliminated OverflowError from `timedelta * float` for some floats; Corrected rounding in timedelta true division.

- bpo-21619: Popen objects no longer leave a zombie after exit in the with statement if the pipe was broken. Patch by Martin Panter.

- bpo-22936: Make it possible to show local variables in tracebacks for both the traceback module and unittest.

- bpo-15955: Add an option to limit the output size in bz2.decompress(). Patch by Nikolaus Rath.

- bpo-6639: Module-level turtle functions no longer raise TclError after closing the window.

- bpo-814253: Group references and conditional group references now work in lookbehind assertions in regular expressions. (See also: bpo-9179)

- bpo-23215: Multibyte codecs with custom error handlers that ignores errors consumed too much memory and raised SystemError or MemoryError. Original patch by Aleksi Torhamo.

- bpo-5700: io.FileIO() called flush() after closing the file. flush() was not called in close() if closefd=False.

- bpo-23374: Fixed pydoc failure with non-ASCII files when stdout encoding differs from file system encoding (e.g. on Mac OS).

- bpo-23481: Remove RC4 from the SSL module’s default cipher list.

- bpo-21548: Fix pydoc.synopsis() and pydoc.apropos() on modules with empty docstrings.

- bpo-22885: Fixed arbitrary code execution vulnerability in the dbm.dumb module. Original patch by Claudiu Popa.

- bpo-23239: ssl.match_hostname() now supports matching of IP addresses.

- bpo-23146: Fix mishandling of absolute Windows paths with forward slashes in pathlib.

- bpo-23096: Pickle representation of floats with protocol 0 now is the same for both Python and C implementations.

- bpo-19105: pprint now more efficiently uses free space at the right.

- bpo-14910: Add allow_abbrev parameter to argparse.ArgumentParser. Patch by Jonathan Paugh, Steven Bethard, paul j3 and Daniel Eriksson.

- bpo-21717: tarfile.open() now supports ‘x’ (exclusive creation) mode.

- bpo-23344: marshal.dumps() is now 20-25% faster on average.

- bpo-20416: marshal.dumps() with protocols 3 and 4 is now 40-50% faster on average.

- bpo-23421: Fixed compression in tarfile CLI. Patch by wdv4758h.

- bpo-23367: Fix possible overflows in the unicodedata module.

- bpo-23361: Fix possible overflow in Windows subprocess creation code.

- logging.handlers.QueueListener now takes a respect_handler_level keyword argument which, if set to True, will pass messages to handlers taking handler levels into account.

- bpo-19705: turtledemo now has a visual sorting algorithm demo. Original patch from Jason Yeo.

- bpo-23801: Fix issue where cgi.FieldStorage did not always ignore the entire preamble to a multipart body.

### Build

- bpo-23445: pydebug builds now use “gcc -Og” where possible, to make the resulting executable faster.

- bpo-23686: Update OS X 10.5 installer build to use OpenSSL 1.0.2a.

### C API

- bpo-20204: Deprecation warning is now raised for builtin types without the __module__ attribute.

### Windows

- bpo-23465: Implement PEP 486 - Make the Python Launcher aware of virtual environments. Patch by Paul Moore.

- bpo-23437: Make user scripts directory versioned on Windows. Patch by Paul Moore.

## Python 3.5.0 alpha 1

Release date: 2015-02-08

### Core and Builtins

- bpo-23285: PEP 475 - EINTR handling.

- bpo-22735: Fix many edge cases (including crashes) involving custom mro() implementations.

- bpo-22896: Avoid using PyObject_AsCharBuffer(), PyObject_AsReadBuffer() and PyObject_AsWriteBuffer().

- bpo-21295: Revert some changes (bpo-16795) to AST line numbers and column offsets that constituted a regression.

- bpo-22986: Allow changing an object’s __class__ between a dynamic type and static type in some cases.

- bpo-15859: PyUnicode_EncodeFSDefault(), PyUnicode_EncodeMBCS() and PyUnicode_EncodeCodePage() now raise an exception if the object is not a Unicode object. For PyUnicode_EncodeFSDefault(), it was already the case on platforms other than Windows. Patch written by Campbell Barton.

- bpo-21408: The default __ne__() now returns NotImplemented if __eq__() returned NotImplemented. Original patch by Martin Panter.

- bpo-23321: Fixed a crash in str.decode() when error handler returned replacement string longer than malformed input data.

- bpo-22286: The “backslashreplace” error handlers now works with decoding and translating.

- bpo-23253: Delay-load ShellExecute[AW] in os.startfile for reduced startup overhead on Windows.

- bpo-22038: pyatomic.h now uses stdatomic.h or GCC built-in functions for atomic memory access if available. Patch written by Vitor de Lima and Gustavo Temple.

- bpo-20284: %-interpolation (aka printf) formatting added for bytes and bytearray.

- bpo-23048: Fix jumping out of an infinite while loop in the pdb.

- bpo-20335: bytes constructor now raises TypeError when encoding or errors is specified with non-string argument. Based on patch by Renaud Blanch.

- bpo-22834: If the current working directory ends up being set to a non-existent directory then import will no longer raise FileNotFoundError.

- bpo-22869: Move the interpreter startup & shutdown code to a new dedicated pylifecycle.c module

- bpo-22847: Improve method cache efficiency.

- bpo-22335: Fix crash when trying to enlarge a bytearray to 0x7fffffff bytes on a 32-bit platform.

- bpo-22653: Fix an assertion failure in debug mode when doing a reentrant dict insertion in debug mode.

- bpo-22643: Fix integer overflow in Unicode case operations (upper, lower, title, swapcase, casefold).

- bpo-17636: Circular imports involving relative imports are now supported.

- bpo-22604: Fix assertion error in debug mode when dividing a complex number by (nan+0j).

- bpo-21052: Do not raise ImportWarning when sys.path_hooks or sys.meta_path are set to None.

- bpo-16518: Use ‘bytes-like object required’ in error messages that previously used the far more cryptic “‘x’ does not support the buffer protocol.

- bpo-22470: Fixed integer overflow issues in “backslashreplace”, “xmlcharrefreplace”, and “surrogatepass” error handlers.

- bpo-22540: speed up `PyObject_IsInstance` and `PyObject_IsSubclass` in the common case that the second argument has metaclass `type`.

- bpo-18711: Add a new `PyErr_FormatV` function, similar to `PyErr_Format` but accepting a `va_list` argument.

- bpo-22520: Fix overflow checking when generating the repr of a unicode object.

- bpo-22519: Fix overflow checking in PyBytes_Repr.

- bpo-22518: Fix integer overflow issues in latin-1 encoding.

- bpo-16324: _charset parameter of MIMEText now also accepts email.charset.Charset instances. Initial patch by Claude Paroz.

- bpo-1764286: Fix inspect.getsource() to support decorated functions. Patch by Claudiu Popa.

- bpo-18554: os.__all__ includes posix functions.

- bpo-21391: Use os.path.abspath in the shutil module.

- bpo-11471: avoid generating a JUMP_FORWARD instruction at the end of an if-block if there is no else-clause. Original patch by Eugene Toder.

- bpo-22215: Now ValueError is raised instead of TypeError when str or bytes argument contains not permitted null character or byte.

- bpo-22258: Fix the internal function set_inheritable() on Illumos. This platform exposes the function `ioctl(FIOCLEX)`, but calling it fails with errno is ENOTTY: “Inappropriate ioctl for device”. set_inheritable() now falls back to the slower `fcntl()` (`F_GETFD` and then `F_SETFD`).

- bpo-21389: Displaying the __qualname__ of the underlying function in the repr of a bound method.

- bpo-22206: Using pthread, PyThread_create_key() now sets errno to ENOMEM and returns -1 (error) on integer overflow.

- bpo-20184: Argument Clinic based signature introspection added for 30 of the builtin functions.

- bpo-22116: C functions and methods (of the ‘builtin_function_or_method’ type) can now be weakref’ed. Patch by Wei Wu.

- bpo-22077: Improve index error messages for bytearrays, bytes, lists, and tuples by adding ‘or slices’. Added ‘, not <typename>’ for bytearrays. Original patch by Claudiu Popa.

- bpo-20179: Apply Argument Clinic to bytes and bytearray. Patch by Tal Einat.

- bpo-22082: Clear interned strings in slotdefs.

- Upgrade Unicode database to Unicode 7.0.0.

- bpo-21897: Fix a crash with the f_locals attribute with closure variables when frame.clear() has been called.

- bpo-21205: Add a new `__qualname__` attribute to generator, the qualified name, and use it in the representation of a generator (`repr(gen)`). The default name of the generator (`__name__` attribute) is now get from the function instead of the code. Use `gen.gi_code.co_name` to get the name of the code.

- bpo-21669: With the aid of heuristics in SyntaxError.__init__, the parser now attempts to generate more meaningful (or at least more search engine friendly) error messages when “exec” and “print” are used as statements.

- bpo-21642: In the conditional if-else expression, allow an integer written with no space between itself and the `else` keyword (e.g. `True if 42else False`) to be valid syntax.

- bpo-21523: Fix over-pessimistic computation of the stack effect of some opcodes in the compiler. This also fixes a quadratic compilation time issue noticeable when compiling code with a large number of “and” and “or” operators.

- bpo-21418: Fix a crash in the builtin function super() when called without argument and without current frame (ex: embedded Python).

- bpo-21425: Fix flushing of standard streams in the interactive interpreter.

- bpo-21435: In rare cases, when running finalizers on objects in cyclic trash a bad pointer dereference could occur due to a subtle flaw in internal iteration logic.

- bpo-21377: PyBytes_Concat() now tries to concatenate in-place when the first argument has a reference count of 1. Patch by Nikolaus Rath.

- bpo-20355: -W command line options now have higher priority than the PYTHONWARNINGS environment variable. Patch by Arfrever.

- bpo-21274: Define PATH_MAX for GNU/Hurd in Python/pythonrun.c.

- bpo-20904: Support setting FPU precision on m68k.

- bpo-21209: Fix sending tuples to custom generator objects with the yield from syntax.

- bpo-21193: pow(a, b, c) now raises ValueError rather than TypeError when b is negative. Patch by Josh Rosenberg.

- bpo-21176: PEP 465: Add the ‘@’ operator for matrix multiplication.

- bpo-21134: Fix segfault when str is called on an uninitialized UnicodeEncodeError, UnicodeDecodeError, or UnicodeTranslateError object.

- bpo-19537: Fix PyUnicode_DATA() alignment under m68k. Patch by Andreas Schwab.

- bpo-20929: Add a type cast to avoid shifting a negative number.

- bpo-20731: Properly position in source code files even if they are opened in text mode. Patch by Serhiy Storchaka.

- bpo-20637: Key-sharing now also works for instance dictionaries of subclasses. Patch by Peter Ingebretson.

- bpo-8297: Attributes missing from modules now include the module name in the error text. Original patch by ysj.ray.

- bpo-19995: %c, %o, %x, and %X now raise TypeError on non-integer input.

- bpo-19655: The ASDL parser - used by the build process to generate code for managing the Python AST in C - was rewritten. The new parser is self contained and does not require to carry long the spark.py parser-generator library; spark.py was removed from the source base.

- bpo-12546: Allow `\x00` to be used as a fill character when using str, int, float, and complex __format__ methods.

- bpo-20480: Add ipaddress.reverse_pointer. Patch by Leon Weber.

- bpo-13598: Modify string.Formatter to support auto-numbering of replacement fields. It now matches the behavior of str.format() in this regard. Patches by Phil Elson and Ramchandra Apte.

- bpo-8931: Make alternate formatting (‘#’) for type ‘c’ raise an exception. In versions prior to 3.5, ‘#’ with ‘c’ had no effect. Now specifying it is an error. Patch by Torsten Landschoff.

- bpo-23165: Perform overflow checks before allocating memory in the _Py_char2wchar function.

### Library

- bpo-23399: pyvenv creates relative symlinks where possible.

- bpo-20289: cgi.FieldStorage() now supports the context management protocol.

- bpo-13128: Print response headers for CONNECT requests when debuglevel > 0. Patch by Demian Brecht.

- bpo-15381: Optimized io.BytesIO to make less allocations and copyings.

- bpo-22818: Splitting on a pattern that could match an empty string now raises a warning. Patterns that can only match empty strings are now rejected.

- bpo-23099: Closing io.BytesIO with exported buffer is rejected now to prevent corrupting exported buffer.

- bpo-23326: Removed __ne__ implementations. Since fixing default __ne__ implementation in bpo-21408 they are redundant.

- bpo-23363: Fix possible overflow in itertools.permutations.

- bpo-23364: Fix possible overflow in itertools.product.

- bpo-23366: Fixed possible integer overflow in itertools.combinations.

- bpo-23369: Fixed possible integer overflow in _json.encode_basestring_ascii.

- bpo-23353: Fix the exception handling of generators in PyEval_EvalFrameEx(). At entry, save or swap the exception state even if PyEval_EvalFrameEx() is called with throwflag=0. At exit, the exception state is now always restored or swapped, not only if why is WHY_YIELD or WHY_RETURN. Patch co-written with Antoine Pitrou.

- bpo-14099: Restored support of writing ZIP files to tellable but non-seekable streams.

- bpo-14099: Writing to ZipFile and reading multiple ZipExtFiles is threadsafe now.

- bpo-19361: JSON decoder now raises JSONDecodeError instead of ValueError.

- bpo-18518: timeit now rejects statements which can’t be compiled outside a function or a loop (e.g. “return” or “break”).

- bpo-23094: Fixed readline with frames in Python implementation of pickle.

- bpo-23268: Fixed bugs in the comparison of ipaddress classes.

- bpo-21408: Removed incorrect implementations of __ne__() which didn’t returned NotImplemented if __eq__() returned NotImplemented. The default __ne__() now works correctly.

- bpo-19996: `email.feedparser.FeedParser` now handles (malformed) headers with no key rather than assuming the body has started.

- bpo-20188: Support Application-Layer Protocol Negotiation (ALPN) in the ssl module.

- bpo-23133: Pickling of ipaddress objects now produces more compact and portable representation.

- bpo-23248: Update ssl error codes from latest OpenSSL git master.

- bpo-23266: Much faster implementation of ipaddress.collapse_addresses() when there are many non-consecutive addresses.

- bpo-23098: 64-bit dev_t is now supported in the os module.

- bpo-21817: When an exception is raised in a task submitted to a ProcessPoolExecutor, the remote traceback is now displayed in the parent process. Patch by Claudiu Popa.

- bpo-15955: Add an option to limit output size when decompressing LZMA data. Patch by Nikolaus Rath and Martin Panter.

- bpo-23250: In the http.cookies module, capitalize “HttpOnly” and “Secure” as they are written in the standard.

- bpo-23063: In the distutils’ check command, fix parsing of reST with code or code-block directives.

- bpo-23209: selectors.BaseSelector.get_key() now raises a RuntimeError if the selector is closed. And selectors.BaseSelector.close() now clears its internal reference to the selector mapping to break a reference cycle. Initial patch written by Martin Richard. (See also: bpo-23225)

- bpo-17911: Provide a way to seed the linecache for a PEP-302 module without actually loading the code.

- bpo-17911: Provide a new object API for traceback, including the ability to not lookup lines at all until the traceback is actually rendered, without any trace of the original objects being kept alive.

- bpo-19777: Provide a home() classmethod on Path objects. Contributed by Victor Salgado and Mayank Tripathi.

- bpo-23206: Make `json.dumps(..., ensure_ascii=False)` as fast as the default case of `ensure_ascii=True`. Patch by Naoki Inada.

- bpo-23185: Add math.inf and math.nan constants.

- bpo-23186: Add ssl.SSLObject.shared_ciphers() and ssl.SSLSocket.shared_ciphers() to fetch the client’s list ciphers sent at handshake.

- bpo-23143: Remove compatibility with OpenSSLs older than 0.9.8.

- bpo-23132: Improve performance and introspection support of comparison methods created by functool.total_ordering.

- bpo-19776: Add an expanduser() method on Path objects.

- bpo-23112: Fix SimpleHTTPServer to correctly carry the query string and fragment when it redirects to add a trailing slash.

- bpo-21793: Added http.HTTPStatus enums (i.e. HTTPStatus.OK, HTTPStatus.NOT_FOUND). Patch by Demian Brecht.

- bpo-23093: In the io, module allow more operations to work on detached streams.

- bpo-23111: In the ftplib, make ssl.PROTOCOL_SSLv23 the default protocol version.

- bpo-22585: On OpenBSD 5.6 and newer, os.urandom() now calls getentropy(), instead of reading /dev/urandom, to get pseudo-random bytes.

- bpo-19104: pprint now produces evaluable output for wrapped strings.

- bpo-23071: Added missing names to codecs.__all__. Patch by Martin Panter.

- bpo-22783: Pickling now uses the NEWOBJ opcode instead of the NEWOBJ_EX opcode if possible.

- bpo-15513: Added a __sizeof__ implementation for pickle classes.

- bpo-19858: pickletools.optimize() now aware of the MEMOIZE opcode, can produce more compact result and no longer produces invalid output if input data contains MEMOIZE opcodes together with PUT or BINPUT opcodes.

- bpo-22095: Fixed HTTPConnection.set_tunnel with default port. The port value in the host header was set to “None”. Patch by Demian Brecht.

- bpo-23016: A warning no longer produces an AttributeError when the program is run with pythonw.exe.

- bpo-21775: shutil.copytree(): fix crash when copying to VFAT. An exception handler assumed that OSError objects always have a ‘winerror’ attribute. That is not the case, so the exception handler itself raised AttributeError when run on Linux (and, presumably, any other non-Windows OS). Patch by Greg Ward.

- bpo-1218234: Fix inspect.getsource() to load updated source of reloaded module. Initial patch by Berker Peksag.

- bpo-21740: Support wrapped callables in doctest. Patch by Claudiu Popa.

- bpo-23009: Make sure selectors.EpollSelector.select() works when no FD is registered.

- bpo-22959: In the constructor of http.client.HTTPSConnection, prefer the context’s check_hostname attribute over the check_hostname parameter.

- bpo-22696: Add function `sys.is_finalizing()` to know about interpreter shutdown.

- bpo-16043: Add a default limit for the amount of data xmlrpclib.gzip_decode will return. This resolves CVE-2013-1753.

- bpo-14099: ZipFile.open() no longer reopen the underlying file. Objects returned by ZipFile.open() can now operate independently of the ZipFile even if the ZipFile was created by passing in a file-like object as the first argument to the constructor.

- bpo-22966: Fix __pycache__ pyc file name clobber when pyc_compile is asked to compile a source file containing multiple dots in the source file name.

- bpo-21971: Update turtledemo doc and add module to the index.

- bpo-21032: Fixed socket leak if HTTPConnection.getresponse() fails. Original patch by Martin Panter.

- bpo-22407: Deprecated the use of re.LOCALE flag with str patterns or re.ASCII. It was newer worked.

- bpo-22902: The “ip” command is now used on Linux to determine MAC address in uuid.getnode(). Pach by Bruno Cauet.

- bpo-22960: Add a context argument to xmlrpclib.ServerProxy constructor.

- bpo-22389: Add contextlib.redirect_stderr().

- bpo-21356: Make ssl.RAND_egd() optional to support LibreSSL. The availability of the function is checked during the compilation. Patch written by Bernard Spil.

- bpo-22915: SAX parser now supports files opened with file descriptor or bytes path.

- bpo-22609: Constructors and update methods of mapping classes in the collections module now accept the self keyword argument.

- bpo-22940: Add readline.append_history_file.

- bpo-19676: Added the “namereplace” error handler.

- bpo-22788: Add context parameter to logging.handlers.HTTPHandler.

- bpo-22921: Allow SSLContext to take the hostname parameter even if OpenSSL doesn’t support SNI.

- bpo-22894: TestCase.subTest() would cause the test suite to be stopped when in failfast mode, even in the absence of failures.

- bpo-22796: HTTP cookie parsing is now stricter, in order to protect against potential injection attacks.

- bpo-22370: Windows detection in pathlib is now more robust.

- bpo-22841: Reject coroutines in asyncio add_signal_handler(). Patch by Ludovic.Gasc.

- bpo-19494: Added urllib.request.HTTPBasicPriorAuthHandler. Patch by Matej Cepl.

- bpo-22578: Added attributes to the re.error class.

- bpo-22849: Fix possible double free in the io.TextIOWrapper constructor.

- bpo-12728: Different Unicode characters having the same uppercase but different lowercase are now matched in case-insensitive regular expressions.

- bpo-22821: Fixed fcntl() with integer argument on 64-bit big-endian platforms.

- bpo-21650: Add an `--sort-keys` option to json.tool CLI.

- bpo-22824: Updated reprlib output format for sets to use set literals. Patch contributed by Berker Peksag.

- bpo-22824: Updated reprlib output format for arrays to display empty arrays without an unnecessary empty list. Suggested by Serhiy Storchaka.

- bpo-22406: Fixed the uu_codec codec incorrectly ported to 3.x. Based on patch by Martin Panter.

- bpo-17293: uuid.getnode() now determines MAC address on AIX using netstat. Based on patch by Aivars Kalvāns.

- bpo-22769: Fixed ttk.Treeview.tag_has() when called without arguments.

- bpo-22417: Verify certificates by default in httplib (PEP 476).

- bpo-22775: Fixed unpickling of http.cookies.SimpleCookie with protocol 2 and above. Patch by Tim Graham.

- bpo-22776: Brought excluded code into the scope of a try block in SysLogHandler.emit().

- bpo-22665: Add missing get_terminal_size and SameFileError to shutil.__all__.

- bpo-6623: Remove deprecated Netrc class in the ftplib module. Patch by Matt Chaput.

- bpo-17381: Fixed handling of case-insensitive ranges in regular expressions.

- bpo-22410: Module level functions in the re module now cache compiled locale-dependent regular expressions taking into account the locale.

- bpo-22759: Query methods on pathlib.Path() (exists(), is_dir(), etc.) now return False when the underlying stat call raises NotADirectoryError.

- bpo-8876: distutils now falls back to copying files when hard linking doesn’t work. This allows use with special filesystems such as VirtualBox shared folders.

- bpo-22217: Implemented reprs of classes in the zipfile module.

- bpo-22457: Honour load_tests in the start_dir of discovery.

- bpo-18216: gettext now raises an error when a .mo file has an unsupported major version number. Patch by Aaron Hill.

- bpo-13918: Provide a locale.delocalize() function which can remove locale-specific number formatting from a string representing a number, without then converting it to a specific type. Patch by Cédric Krier.

- bpo-22676: Make the pickling of global objects which don’t have a __module__ attribute less slow.

- bpo-18853: Fixed ResourceWarning in shlex.__nain__.

- bpo-9351: Defaults set with set_defaults on an argparse subparser are no longer ignored when also set on the parent parser.

- bpo-7559: unittest test loading ImportErrors are reported as import errors with their import exception rather than as attribute errors after the import has already failed.

- bpo-19746: Make it possible to examine the errors from unittest discovery without executing the test suite. The new `errors` attribute on TestLoader exposes these non-fatal errors encountered during discovery.

- bpo-21991: Make email.headerregistry’s header ‘params’ attributes be read-only (MappingProxyType). Previously the dictionary was modifiable but a new one was created on each access of the attribute.

- bpo-22638: SSLv3 is now disabled throughout the standard library. It can still be enabled by instantiating a SSLContext manually.

- bpo-22641: In asyncio, the default SSL context for client connections is now created using ssl.create_default_context(), for stronger security.

- bpo-17401: Include closefd in io.FileIO repr.

- bpo-21338: Add silent mode for compileall. quiet parameters of compile_{dir, file, path} functions now have a multilevel value. Also, -q option of the CLI now have a multilevel value. Patch by Thomas Kluyver.

- bpo-20152: Convert the array and cmath modules to Argument Clinic.

- bpo-18643: Add socket.socketpair() on Windows.

- bpo-22435: Fix a file descriptor leak when socketserver bind fails.

- bpo-13096: Fixed segfault in CTypes POINTER handling of large values.

- bpo-11694: Raise ConversionError in xdrlib as documented. Patch by Filip Gruszczyński and Claudiu Popa.

- bpo-19380: Optimized parsing of regular expressions.

- bpo-1519638: Now unmatched groups are replaced with empty strings in re.sub() and re.subn().

- bpo-18615: sndhdr.what/whathdr now return a namedtuple.

- bpo-22462: Fix pyexpat’s creation of a dummy frame to make it appear in exception tracebacks.

- bpo-21965: Add support for in-memory SSL to the ssl module. Patch by Geert Jansen.

- bpo-21173: Fix len() on a WeakKeyDictionary when .clear() was called with an iterator alive.

- bpo-11866: Eliminated race condition in the computation of names for new threads.

- bpo-21905: Avoid RuntimeError in pickle.whichmodule() when sys.modules is mutated while iterating. Patch by Olivier Grisel.

- bpo-11271: concurrent.futures.Executor.map() now takes a chunksize argument to allow batching of tasks in child processes and improve performance of ProcessPoolExecutor. Patch by Dan O’Reilly.

- bpo-21883: os.path.join() and os.path.relpath() now raise a TypeError with more helpful error message for unsupported or mismatched types of arguments.

- bpo-22219: The zipfile module CLI now adds entries for directories (including empty directories) in ZIP file.

- bpo-22449: In the ssl.SSLContext.load_default_certs, consult the environmental variables SSL_CERT_DIR and SSL_CERT_FILE on Windows.

- bpo-22508: The email.__version__ variable has been removed; the email code is no longer shipped separately from the stdlib, and __version__ hasn’t been updated in several releases.

- bpo-20076: Added non derived UTF-8 aliases to locale aliases table.

- bpo-20079: Added locales supported in glibc 2.18 to locale alias table.

- bpo-20218: Added convenience methods read_text/write_text and read_bytes/ write_bytes to pathlib.Path objects.

- bpo-22396: On 32-bit AIX platform, don’t expose os.posix_fadvise() nor os.posix_fallocate() because their prototypes in system headers are wrong.

- bpo-22517: When an io.BufferedRWPair object is deallocated, clear its weakrefs.

- bpo-22437: Number of capturing groups in regular expression is no longer limited by 100.

- bpo-17442: InteractiveInterpreter now displays the full chained traceback in its showtraceback method, to match the built in interactive interpreter.

- bpo-23392: Added tests for marshal C API that works with FILE*.

- bpo-10510: distutils register and upload methods now use HTML standards compliant CRLF line endings.

- bpo-9850: Fixed macpath.join() for empty first component. Patch by Oleg Oshmyan.

- bpo-5309: distutils’ build and build_ext commands now accept a `-j` option to enable parallel building of extension modules.

- bpo-22448: Improve canceled timer handles cleanup to prevent unbound memory usage. Patch by Joshua Moore-Oliva.

- bpo-22427: TemporaryDirectory no longer attempts to clean up twice when used in the with statement in generator.

- bpo-22362: Forbidden ambiguous octal escapes out of range 0-0o377 in regular expressions.

- bpo-20912: Now directories added to ZIP file have correct Unix and MS-DOS directory attributes.

- bpo-21866: ZipFile.close() no longer writes ZIP64 central directory records if allowZip64 is false.

- bpo-22278: Fix urljoin problem with relative urls, a regression observed after changes to issue22118 were submitted.

- bpo-22415: Fixed debugging output of the GROUPREF_EXISTS opcode in the re module. Removed trailing spaces in debugging output.

- bpo-22423: Unhandled exception in thread no longer causes unhandled AttributeError when sys.stderr is None.

- bpo-21332: Ensure that `bufsize=1` in subprocess.Popen() selects line buffering, rather than block buffering. Patch by Akira Li.

- bpo-21091: Fix API bug: email.message.EmailMessage.is_attachment is now a method.

- bpo-21079: Fix email.message.EmailMessage.is_attachment to return the correct result when the header has parameters as well as a value.

- bpo-22247: Add NNTPError to nntplib.__all__.

- bpo-22366: urllib.request.urlopen will accept a context object (SSLContext) as an argument which will then be used for HTTPS connection. Patch by Alex Gaynor.

- bpo-4180: The warnings registries are now reset when the filters are modified.

- bpo-22419: Limit the length of incoming HTTP request in wsgiref server to 65536 bytes and send a 414 error code for higher lengths. Patch contributed by Devin Cook.

- Lax cookie parsing in http.cookies could be a security issue when combined with non-standard cookie handling in some Web browsers. Reported by Sergey Bobrov.

- bpo-20537: logging methods now accept an exception instance as well as a Boolean value or exception tuple. Thanks to Yury Selivanov for the patch.

- bpo-22384: An exception in Tkinter callback no longer crashes the program when it is run with pythonw.exe.

- bpo-22168: Prevent turtle AttributeError with non-default Canvas on OS X.

- bpo-21147: sqlite3 now raises an exception if the request contains a null character instead of truncating it. Based on patch by Victor Stinner.

- bpo-13968: The glob module now supports recursive search in subdirectories using the `**` pattern.

- bpo-21951: Fixed a crash in Tkinter on AIX when called Tcl command with empty string or tuple argument.

- bpo-21951: Tkinter now most likely raises MemoryError instead of crash if the memory allocation fails.

- bpo-22338: Fix a crash in the json module on memory allocation failure.

- bpo-12410: imaplib.IMAP4 now supports the context management protocol. Original patch by Tarek Ziadé.

- bpo-21270: We now override tuple methods in mock.call objects so that they can be used as normal call attributes.

- bpo-16662: load_tests() is now unconditionally run when it is present in a package’s __init__.py. TestLoader.loadTestsFromModule() still accepts use_load_tests, but it is deprecated and ignored. A new keyword-only attribute `pattern` is added and documented. Patch given by Robert Collins, tweaked by Barry Warsaw.

- bpo-22226: First letter no longer is stripped from the “status” key in the result of Treeview.heading().

- bpo-19524: Fixed resource leak in the HTTP connection when an invalid response is received. Patch by Martin Panter.

- bpo-20421: Add a .version() method to SSL sockets exposing the actual protocol version in use.

- bpo-19546: configparser exceptions no longer expose implementation details. Chained KeyErrors are removed, which leads to cleaner tracebacks. Patch by Claudiu Popa.

- bpo-22051: turtledemo no longer reloads examples to re-run them. Initialization of variables and gui setup should be done in main(), which is called each time a demo is run, but not on import.

- bpo-21933: Turtledemo users can change the code font size with a menu selection or control(command) ‘-’ or ‘+’ or control-mousewheel. Original patch by Lita Cho.

- bpo-21597: The separator between the turtledemo text pane and the drawing canvas can now be grabbed and dragged with a mouse. The code text pane can be widened to easily view or copy the full width of the text. The canvas can be widened on small screens. Original patches by Jan Kanis and Lita Cho.

- bpo-18132: Turtledemo buttons no longer disappear when the window is shrunk. Original patches by Jan Kanis and Lita Cho.

- bpo-22043: time.monotonic() is now always available. `threading.Lock.acquire()`, `threading.RLock.acquire()` and socket operations now use a monotonic clock, instead of the system clock, when a timeout is used.

- bpo-21527: Add a default number of workers to ThreadPoolExecutor equal to 5 times the number of CPUs. Patch by Claudiu Popa.

- bpo-22216: smtplib now resets its state more completely after a quit. The most obvious consequence of the previous behavior was a STARTTLS failure during a connect/starttls/quit/connect/starttls sequence.

- bpo-22098: ctypes’ BigEndianStructure and LittleEndianStructure now define an empty __slots__ so that subclasses don’t always get an instance dict. Patch by Claudiu Popa.

- bpo-22185: Fix an occasional RuntimeError in threading.Condition.wait() caused by mutation of the waiters queue without holding the lock. Patch by Doug Zongker.

- bpo-22287: On UNIX, _PyTime_gettimeofday() now uses clock_gettime(CLOCK_REALTIME) if available. As a side effect, Python now depends on the librt library on Solaris and on Linux (only with glibc older than 2.17).

- bpo-22182: Use e.args to unpack exceptions correctly in distutils.file_util.move_file. Patch by Claudiu Popa.

- The webbrowser module now uses subprocess’s start_new_session=True rather than a potentially risky preexec_fn=os.setsid call.

- bpo-22042: signal.set_wakeup_fd(fd) now raises an exception if the file descriptor is in blocking mode.

- bpo-16808: inspect.stack() now returns a named tuple instead of a tuple. Patch by Daniel Shahaf.

- bpo-22236: Fixed Tkinter images copying operations in NoDefaultRoot mode.

- bpo-2527: Add a globals argument to timeit functions, in order to override the globals namespace in which the timed code is executed. Patch by Ben Roberts.

- bpo-22118: Switch urllib.parse to use RFC 3986 semantics for the resolution of relative URLs, rather than RFCs 1808 and 2396. Patch by Demian Brecht.

- bpo-21549: Added the “members” parameter to TarFile.list().

- bpo-19628: Allow compileall recursion depth to be specified with a -r option.

- bpo-15696: Add a __sizeof__ implementation for mmap objects on Windows.

- bpo-22068: Avoided reference loops with Variables and Fonts in Tkinter.

- bpo-22165: SimpleHTTPRequestHandler now supports undecodable file names.

- bpo-15381: Optimized line reading in io.BytesIO.

- bpo-8797: Raise HTTPError on failed Basic Authentication immediately. Initial patch by Sam Bull.

- bpo-20729: Restored the use of lazy iterkeys()/itervalues()/iteritems() in the mailbox module.

- bpo-21448: Changed FeedParser feed() to avoid O(N**2) behavior when parsing long line. Original patch by Raymond Hettinger.

- bpo-22184: The functools LRU Cache decorator factory now gives an earlier and clearer error message when the user forgets the required parameters.

- bpo-17923: glob() patterns ending with a slash no longer match non-dirs on AIX. Based on patch by Delhallt.

- bpo-21725: Added support for RFC 6531 (SMTPUTF8) in smtpd.

- bpo-22176: Update the ctypes module’s libffi to v3.1. This release adds support for the Linux AArch64 and POWERPC ELF ABIv2 little endian architectures.

- bpo-5411: Added support for the “xztar” format in the shutil module.

- bpo-21121: Don’t force 3rd party C extensions to be built with -Werror=declaration-after-statement.

- bpo-21975: Fixed crash when using uninitialized sqlite3.Row (in particular when unpickling pickled sqlite3.Row). sqlite3.Row is now initialized in the __new__() method.

- bpo-20170: Convert posixmodule to use Argument Clinic.

- bpo-21539: Add an exists_ok argument to `Pathlib.mkdir()` to mimic `mkdir -p` and `os.makedirs()` functionality. When true, ignore FileExistsErrors. Patch by Berker Peksag.

- bpo-22127: Bypass IDNA for pure-ASCII host names in the socket module (in particular for numeric IPs).

- bpo-21047: set the default value for the convert_charrefs argument of HTMLParser to True. Patch by Berker Peksag.

- Add an __all__ to html.entities.

- bpo-15114: the strict mode and argument of HTMLParser, HTMLParser.error, and the HTMLParserError exception have been removed.

- bpo-22085: Dropped support of Tk 8.3 in Tkinter.

- bpo-21580: Now Tkinter correctly handles bytes arguments passed to Tk. In particular this allows initializing images from binary data.

- bpo-22003: When initialized from a bytes object, io.BytesIO() now defers making a copy until it is mutated, improving performance and memory use on some use cases. Patch by David Wilson.

- bpo-22018: On Windows, signal.set_wakeup_fd() now also supports sockets. A side effect is that Python depends to the WinSock library.

- bpo-22054: Add os.get_blocking() and os.set_blocking() functions to get and set the blocking mode of a file descriptor (False if the O_NONBLOCK flag is set, True otherwise). These functions are not available on Windows.

- bpo-17172: Make turtledemo start as active on OS X even when run with subprocess. Patch by Lita Cho.

- bpo-21704: Fix build error for _multiprocessing when semaphores are not available. Patch by Arfrever Frehtes Taifersar Arahesis.

- bpo-20173: Convert sha1, sha256, sha512 and md5 to ArgumentClinic. Patch by Vajrasky Kok.

- Fix repr(_socket.socket) on Windows 64-bit: don’t fail with OverflowError on closed socket. repr(socket.socket) already works fine.

- bpo-22033: Reprs of most Python implemented classes now contain actual class name instead of hardcoded one.

- bpo-21947: The dis module can now disassemble generator-iterator objects based on their gi_code attribute. Patch by Clement Rouault.

- bpo-16133: The asynchat.async_chat.handle_read() method now ignores BlockingIOError exceptions.

- bpo-22044: Fixed premature DECREF in call_tzinfo_method. Patch by Tom Flanagan.

- bpo-19884: readline: Disable the meta modifier key if stdout is not a terminal to not write the ANSI sequence `"\033[1034h"` into stdout. This sequence is used on some terminal (ex: TERM=xterm-256color”) to enable support of 8 bit characters.

- bpo-4350: Removed a number of out-of-dated and non-working for a long time Tkinter methods.

- bpo-6167: Scrollbar.activate() now returns the name of active element if the argument is not specified. Scrollbar.set() now always accepts only 2 arguments.

- bpo-15275: Clean up and speed up the ntpath module.

- bpo-21888: plistlib’s load() and loads() now work if the fmt parameter is specified.

- bpo-22032: __qualname__ instead of __name__ is now always used to format fully qualified class names of Python implemented classes.

- bpo-22031: Reprs now always use hexadecimal format with the “0x” prefix when contain an id in form ” at 0x…”.

- bpo-22018: signal.set_wakeup_fd() now raises an OSError instead of a ValueError on `fstat()` failure.

- bpo-21044: tarfile.open() now handles fileobj with an integer ‘name’ attribute. Based on patch by Antoine Pietri.

- bpo-21966: Respect -q command-line option when code module is ran.

- bpo-19076: Don’t pass the redundant ‘file’ argument to self.error().

- bpo-16382: Improve exception message of warnings.warn() for bad category. Initial patch by Phil Elson.

- bpo-21932: os.read() now uses a `Py_ssize_t()` type instead of `int` for the size to support reading more than 2 GB at once. On Windows, the size is truncated to INT_MAX. As any call to os.read(), the OS may read less bytes than the number of requested bytes.

- bpo-21942: Fixed source file viewing in pydoc’s server mode on Windows.

- bpo-11259: asynchat.async_chat().set_terminator() now raises a ValueError if the number of received bytes is negative.

- bpo-12523: asynchat.async_chat.push() now raises a TypeError if it doesn’t get a bytes string

- bpo-21707: Add missing kwonlyargcount argument to ModuleFinder.replace_paths_in_code().

- bpo-20639: calling Path.with_suffix(‘’) allows removing the suffix again. Patch by July Tikhonov.

- bpo-21714: Disallow the construction of invalid paths using Path.with_name(). Original patch by Antony Lee.

- bpo-15014: Added ‘auth’ method to smtplib to make implementing auth mechanisms simpler, and used it internally in the login method.

- bpo-21151: Fixed a segfault in the winreg module when `None` is passed as a `REG_BINARY` value to SetValueEx. Patch by John Ehresman.

- bpo-21090: io.FileIO.readall() does not ignore I/O errors anymore. Before, it ignored I/O errors if at least the first C call read() succeed.

- bpo-5800: headers parameter of wsgiref.headers.Headers is now optional. Initial patch by Pablo Torres Navarrete and SilentGhost.

- bpo-21781: ssl.RAND_add() now supports strings longer than 2 GB.

- bpo-21679: Prevent extraneous fstat() calls during open(). Patch by Bohuslav Kabrda.

- bpo-21863: cProfile now displays the module name of C extension functions, in addition to their own name.

- bpo-11453: asyncore: emit a ResourceWarning when an unclosed file_wrapper object is destroyed. The destructor now closes the file if needed. The close() method can now be called twice: the second call does nothing.

- bpo-21858: Better handling of Python exceptions in the sqlite3 module.

- bpo-21476: Make sure the email.parser.BytesParser TextIOWrapper is discarded after parsing, so the input file isn’t unexpectedly closed.

- bpo-20295: imghdr now recognizes OpenEXR format images.

- bpo-21729: Used the “with” statement in the dbm.dumb module to ensure files closing. Patch by Claudiu Popa.

- bpo-21491: socketserver: Fix a race condition in child processes reaping.

- bpo-21719: Added the `st_file_attributes` field to os.stat_result on Windows.

- bpo-21832: Require named tuple inputs to be exact strings.

- bpo-21722: The distutils “upload” command now exits with a non-zero return code when uploading fails. Patch by Martin Dengler.

- bpo-21723: asyncio.Queue: support any type of number (ex: float) for the maximum size. Patch written by Vajrasky Kok.

- bpo-21711: support for “site-python” directories has now been removed from the site module (it was deprecated in 3.4).

- bpo-17552: new socket.sendfile() method allowing a file to be sent over a socket by using high-performance os.sendfile() on UNIX. Patch by Giampaolo Rodola’.

- bpo-18039: dbm.dump.open() now always creates a new database when the flag has the value ‘n’. Patch by Claudiu Popa.

- bpo-21326: Add a new is_closed() method to asyncio.BaseEventLoop. run_forever() and run_until_complete() methods of asyncio.BaseEventLoop now raise an exception if the event loop was closed.

- bpo-21766: Prevent a security hole in CGIHTTPServer by URL unquoting paths before checking for a CGI script at that path.

- bpo-21310: Fixed possible resource leak in failed open().

- bpo-21256: Printout of keyword args should be in deterministic order in a mock function call. This will help to write better doctests.

- bpo-21677: Fixed chaining nonnormalized exceptions in io close() methods.

- bpo-11709: Fix the pydoc.help function to not fail when sys.stdin is not a valid file.

- bpo-21515: tempfile.TemporaryFile now uses os.O_TMPFILE flag is available.

- bpo-13223: Fix pydoc.writedoc so that the HTML documentation for methods that use ‘self’ in the example code is generated correctly.

- bpo-21463: In urllib.request, fix pruning of the FTP cache.

- bpo-21618: The subprocess module could fail to close open fds that were inherited by the calling process and already higher than POSIX resource limits would otherwise allow. On systems with a functioning /proc/self/fd or /dev/fd interface the max is now ignored and all fds are closed.

- bpo-20383: Introduce importlib.util.module_from_spec() as the preferred way to create a new module.

- bpo-21552: Fixed possible integer overflow of too long string lengths in the tkinter module on 64-bit platforms.

- bpo-14315: The zipfile module now ignores extra fields in the central directory that are too short to be parsed instead of letting a struct.unpack error bubble up as this “bad data” appears in many real world zip files in the wild and is ignored by other zip tools.

- bpo-13742: Added “key” and “reverse” parameters to heapq.merge(). (First draft of patch contributed by Simon Sapin.)

- bpo-21402: tkinter.ttk now works when default root window is not set.

- bpo-3015: _tkinter.create() now creates tkapp object with wantobject=1 by default.

- bpo-10203: sqlite3.Row now truly supports sequence protocol. In particular it supports reverse() and negative indices. Original patch by Claudiu Popa.

- bpo-18807: If copying (no symlinks) specified for a venv, then the python interpreter aliases (python, python3) are now created by copying rather than symlinking.

- bpo-20197: Added support for the WebP image type in the imghdr module. Patch by Fabrice Aneche and Claudiu Popa.

- bpo-21513: Speedup some properties of IP addresses (IPv4Address, IPv6Address) such as .is_private or .is_multicast.

- bpo-21137: Improve the repr for threading.Lock() and its variants by showing the “locked” or “unlocked” status. Patch by Berker Peksag.

- bpo-21538: The plistlib module now supports loading of binary plist files when reference or offset size is not a power of two.

- bpo-21455: Add a default backlog to socket.listen().

- bpo-21525: Most Tkinter methods which accepted tuples now accept lists too.

- bpo-22166: With the assistance of a new internal _codecs._forget_codec helping function, test_codecs now clears the encoding caches to avoid the appearance of a reference leak

- bpo-22236: Tkinter tests now don’t reuse default root window. New root window is created for every test class.

- bpo-10744: Fix PEP 3118 format strings on ctypes objects with a nontrivial shape.

- bpo-20826: Optimize ipaddress.collapse_addresses().

- bpo-21487: Optimize ipaddress.summarize_address_range() and ipaddress.{IPv4Network,IPv6Network}.subnets().

- bpo-21486: Optimize parsing of netmasks in ipaddress.IPv4Network and ipaddress.IPv6Network.

- bpo-13916: Disallowed the surrogatepass error handler for non UTF-* encodings.

- bpo-20998: Fixed re.fullmatch() of repeated single character pattern with ignore case. Original patch by Matthew Barnett.

- bpo-21075: fileinput.FileInput now reads bytes from standard stream if binary mode is specified. Patch by Sam Kimbrel.

- bpo-19775: Add a samefile() method to pathlib Path objects. Initial patch by Vajrasky Kok.

- bpo-21226: Set up modules properly in PyImport_ExecCodeModuleObject (and friends).

- bpo-21398: Fix a unicode error in the pydoc pager when the documentation contains characters not encodable to the stdout encoding.

- bpo-16531: ipaddress.IPv4Network and ipaddress.IPv6Network now accept an (address, netmask) tuple argument, so as to easily construct network objects from existing addresses.

- bpo-21156: importlib.abc.InspectLoader.source_to_code() is now a staticmethod.

- bpo-21424: Simplified and optimized heaqp.nlargest() and nmsmallest() to make fewer tuple comparisons.

- bpo-21396: Fix TextIOWrapper(…, write_through=True) to not force a flush() on the underlying binary stream. Patch by akira.

- bpo-18314: Unlink now removes junctions on Windows. Patch by Kim Gräsman

- bpo-21088: Bugfix for curses.window.addch() regression in 3.4.0. In porting to Argument Clinic, the first two arguments were reversed.

- bpo-21407: _decimal: The module now supports function signatures.

- bpo-10650: Remove the non-standard ‘watchexp’ parameter from the Decimal.quantize() method in the Python version. It had never been present in the C version.

- bpo-21469: Reduced the risk of false positives in robotparser by checking to make sure that robots.txt has been read or does not exist prior to returning True in can_fetch().

- bpo-19414: Have the OrderedDict mark deleted links as unusable. This gives an early failure if the link is deleted during iteration.

- bpo-21421: Add __slots__ to the MappingViews ABC. Patch by Josh Rosenberg.

- bpo-21101: Eliminate double hashing in the C speed-up code for collections.Counter().

- bpo-21321: itertools.islice() now releases the reference to the source iterator when the slice is exhausted. Patch by Anton Afanasyev.

- bpo-21057: TextIOWrapper now allows the underlying binary stream’s read() or read1() method to return an arbitrary bytes-like object (such as a memoryview). Patch by Nikolaus Rath.

- bpo-20951: SSLSocket.send() now raises either SSLWantReadError or SSLWantWriteError on a non-blocking socket if the operation would block. Previously, it would return 0. Patch by Nikolaus Rath.

- bpo-13248: removed previously deprecated asyncore.dispatcher __getattr__ cheap inheritance hack.

- bpo-9815: assertRaises now tries to clear references to local variables in the exception’s traceback.

- bpo-19940: ssl.cert_time_to_seconds() now interprets the given time string in the UTC timezone (as specified in RFC 5280), not the local timezone.

- bpo-13204: Calling sys.flags.__new__ would crash the interpreter, now it raises a TypeError.

- bpo-19385: Make operations on a closed dbm.dumb database always raise the same exception.

- bpo-21207: Detect when the os.urandom cached fd has been closed or replaced, and open it anew.

- bpo-21291: subprocess’s Popen.wait() is now thread safe so that multiple threads may be calling wait() or poll() on a Popen instance at the same time without losing the Popen.returncode value.

- bpo-21127: Path objects can now be instantiated from str subclass instances (such as `numpy.str_`).

- bpo-15002: urllib.response object to use _TemporaryFileWrapper (and _TemporaryFileCloser) facility. Provides a better way to handle file descriptor close. Patch contributed by Christian Theune.

- bpo-12220: mindom now raises a custom ValueError indicating it doesn’t support spaces in URIs instead of letting a ‘split’ ValueError bubble up.

- bpo-21068: The ssl.PROTOCOL* constants are now enum members.

- bpo-21276: posixmodule: Don’t define USE_XATTRS on KFreeBSD and the Hurd.

- bpo-21262: New method assert_not_called for Mock. It raises AssertionError if the mock has been called.

- bpo-21238: New keyword argument `unsafe` to Mock. It raises `AttributeError` incase of an attribute startswith assert or assret.

- bpo-20896: ssl.get_server_certificate() now uses PROTOCOL_SSLv23, not PROTOCOL_SSLv3, for maximum compatibility.

- bpo-21239: patch.stopall() didn’t work deterministically when the same name was patched more than once.

- bpo-21203: Updated fileConfig and dictConfig to remove inconsistencies. Thanks to Jure Koren for the patch.

- bpo-21222: Passing name keyword argument to mock.create_autospec now works.

- bpo-21197: Add lib64 -> lib symlink in venvs on 64-bit non-OS X POSIX.

- bpo-17498: Some SMTP servers disconnect after certain errors, violating strict RFC conformance. Instead of losing the error code when we issue the subsequent RSET, smtplib now returns the error code and defers raising the SMTPServerDisconnected error until the next command is issued.

- bpo-17826: setting an iterable side_effect on a mock function created by create_autospec now works. Patch by Kushal Das.

- bpo-7776: Fix `Host:` header and reconnection when using http.client.HTTPConnection.set_tunnel(). Patch by Nikolaus Rath.

- bpo-20968: unittest.mock.MagicMock now supports division. Patch by Johannes Baiter.

- bpo-21529: Fix arbitrary memory access in JSONDecoder.raw_decode with a negative second parameter. Bug reported by Guido Vranken. (See also: CVE-2014-4616)

- bpo-21169: getpass now handles non-ascii characters that the input stream encoding cannot encode by re-encoding using the replace error handler.

- bpo-21171: Fixed undocumented filter API of the rot13 codec. Patch by Berker Peksag.

- bpo-20539: Improved math.factorial error message for large positive inputs and changed exception type (OverflowError -> ValueError) for large negative inputs.

- bpo-21172: isinstance check relaxed from dict to collections.Mapping.

- bpo-21155: asyncio.EventLoop.create_unix_server() now raises a ValueError if path and sock are specified at the same time.

- bpo-21136: Avoid unnecessary normalization of Fractions resulting from power and other operations. Patch by Raymond Hettinger.

- bpo-17621: Introduce importlib.util.LazyLoader.

- bpo-21076: signal module constants were turned into enums. Patch by Giampaolo Rodola’.

- bpo-20636: Improved the repr of Tkinter widgets.

- bpo-19505: The items, keys, and values views of OrderedDict now support reverse iteration using reversed().

- bpo-21149: Improved thread-safety in logging cleanup during interpreter shutdown. Thanks to Devin Jeanpierre for the patch.

- bpo-21058: Fix a leak of file descriptor in `tempfile.NamedTemporaryFile()`, close the file descriptor if `io.open()` fails

- bpo-21200: Return None from pkgutil.get_loader() when __spec__ is missing.

- bpo-21013: Enhance ssl.create_default_context() when used for server side sockets to provide better security by default.

- bpo-20145: `assertRaisesRegex` and `assertWarnsRegex` now raise a TypeError if the second argument is not a string or compiled regex.

- bpo-20633: Replace relative import by absolute import.

- bpo-20980: Stop wrapping exception when using ThreadPool.

- bpo-21082: In os.makedirs, do not set the process-wide umask. Note this changes behavior of makedirs when exist_ok=True.

- bpo-20990: Fix issues found by pyflakes for multiprocessing.

- bpo-21015: SSL contexts will now automatically select an elliptic curve for ECDH key exchange on OpenSSL 1.0.2 and later, and otherwise default to “prime256v1”.

- bpo-21000: Improve the command-line interface of json.tool.

- bpo-20995: Enhance default ciphers used by the ssl module to enable better security and prioritize perfect forward secrecy.

- bpo-20884: Don’t assume that __file__ is defined on importlib.__init__.

- bpo-21499: Ignore __builtins__ in several test_importlib.test_api tests.

- bpo-20627: xmlrpc.client.ServerProxy is now a context manager.

- bpo-19165: The formatter module now raises DeprecationWarning instead of PendingDeprecationWarning.

- bpo-13936: Remove the ability of datetime.time instances to be considered false in boolean contexts.

- bpo-18931: selectors module now supports /dev/poll on Solaris. Patch by Giampaolo Rodola’.

- bpo-19977: When the `LC_TYPE` locale is the POSIX locale (`C` locale), `sys.stdin` and `sys.stdout` are now using the `surrogateescape` error handler, instead of the `strict` error handler.

- bpo-20574: Implement incremental decoder for cp65001 code (Windows code page 65001, Microsoft UTF-8).

- bpo-20879: Delay the initialization of encoding and decoding tables for base32, ascii85 and base85 codecs in the base64 module, and delay the initialization of the unquote_to_bytes() table of the urllib.parse module, to not waste memory if these modules are not used.

- bpo-19157: Include the broadcast address in the usuable hosts for IPv6 in ipaddress.

- bpo-11599: When an external command (e.g. compiler) fails, distutils now prints out the whole command line (instead of just the command name) if the environment variable DISTUTILS_DEBUG is set.

- bpo-4931: distutils should not produce unhelpful “error: None” messages anymore. distutils.util.grok_environment_error is kept but doc-deprecated.

- bpo-20875: Prevent possible gzip “‘read’ is not defined” NameError. Patch by Claudiu Popa.

- bpo-11558: `email.message.Message.attach` now returns a more useful error message if `attach` is called on a message for which `is_multipart` is False.

- bpo-20283: RE pattern methods now accept the string keyword parameters as documented. The pattern and source keyword parameters are left as deprecated aliases.

- bpo-20778: Fix modulefinder to work with bytecode-only modules.

- bpo-20791: copy.copy() now doesn’t make a copy when the input is a bytes object. Initial patch by Peter Otten.

- bpo-19748: On AIX, time.mktime() now raises an OverflowError for year outsize range [1902; 2037].

- bpo-19573: inspect.signature: Use enum for parameter kind constants.

- bpo-20726: inspect.signature: Make Signature and Parameter picklable.

- bpo-17373: Add inspect.Signature.from_callable method.

- bpo-20378: Improve repr of inspect.Signature and inspect.Parameter.

- bpo-20816: Fix inspect.getcallargs() to raise correct TypeError for missing keyword-only arguments. Patch by Jeremiah Lowin.

- bpo-20817: Fix inspect.getcallargs() to fail correctly if more than 3 arguments are missing. Patch by Jeremiah Lowin.

- bpo-6676: Ensure a meaningful exception is raised when attempting to parse more than one XML document per pyexpat xmlparser instance. (Original patches by Hirokazu Yamamoto and Amaury Forgeot d’Arc, with suggested wording by David Gutteridge)

- bpo-21117: Fix inspect.signature to better support functools.partial. Due to the specifics of functools.partial implementation, positional-or-keyword arguments passed as keyword arguments become keyword-only.

- bpo-20334: inspect.Signature and inspect.Parameter are now hashable. Thanks to Antony Lee for bug reports and suggestions.

- bpo-15916: doctest.DocTestSuite returns an empty unittest.TestSuite instead of raising ValueError if it finds no tests

- bpo-21209: Fix asyncio.tasks.CoroWrapper to workaround a bug in yield-from implementation in CPythons prior to 3.4.1.

- asyncio: Add gi_{frame,running,code} properties to CoroWrapper (upstream bpo-163).

- bpo-21311: Avoid exception in _osx_support with non-standard compiler configurations. Patch by John Szakmeister.

- bpo-11571: Ensure that the turtle window becomes the topmost window when launched on OS X.

- bpo-21801: Validate that __signature__ is None or an instance of Signature.

- bpo-21923: Prevent AttributeError in distutils.sysconfig.customize_compiler due to possible uninitialized _config_vars.

- bpo-21323: Fix http.server to again handle scripts in CGI subdirectories, broken by the fix for security bpo-19435. Patch by Zach Byrne.

- bpo-22733: Fix ffi_prep_args not zero-extending argument values correctly on 64-bit Windows.

- bpo-23302: Default to TCP_NODELAY=1 upon establishing an HTTPConnection. Removed use of hard-coded MSS as it’s an optimization that’s no longer needed with Nagle disabled.

### IDLE

- bpo-20577: Configuration of the max line length for the FormatParagraph extension has been moved from the General tab of the Idle preferences dialog to the FormatParagraph tab of the Config Extensions dialog. Patch by Tal Einat.

- bpo-16893: Update Idle doc chapter to match current Idle and add new information.

- bpo-3068: Add Idle extension configuration dialog to Options menu. Changes are written to HOME/.idlerc/config-extensions.cfg. Original patch by Tal Einat.

- bpo-16233: A module browser (File : Class Browser, Alt+C) requires an editor window with a filename. When Class Browser is requested otherwise, from a shell, output window, or ‘Untitled’ editor, Idle no longer displays an error box. It now pops up an Open Module box (Alt+M). If a valid name is entered and a module is opened, a corresponding browser is also opened.

- bpo-4832: Save As to type Python files automatically adds .py to the name you enter (even if your system does not display it). Some systems automatically add .txt when type is Text files.

- bpo-21986: Code objects are not normally pickled by the pickle module. To match this, they are no longer pickled when running under Idle.

- bpo-17390: Adjust Editor window title; remove ‘Python’, move version to end.

- bpo-14105: Idle debugger breakpoints no longer disappear when inserting or deleting lines.

- bpo-17172: Turtledemo can now be run from Idle. Currently, the entry is on the Help menu, but it may move to Run. Patch by Ramchandra Apt and Lita Cho.

- bpo-21765: Add support for non-ascii identifiers to HyperParser.

- bpo-21940: Add unittest for WidgetRedirector. Initial patch by Saimadhav Heblikar.

- bpo-18592: Add unittest for SearchDialogBase. Patch by Phil Webster.

- bpo-21694: Add unittest for ParenMatch. Patch by Saimadhav Heblikar.

- bpo-21686: add unittest for HyperParser. Original patch by Saimadhav Heblikar.

- bpo-12387: Add missing upper(lower)case versions of default Windows key bindings for Idle so Caps Lock does not disable them. Patch by Roger Serwy.

- bpo-21695: Closing a Find-in-files output window while the search is still in progress no longer closes Idle.

- bpo-18910: Add unittest for textView. Patch by Phil Webster.

- bpo-18292: Add unittest for AutoExpand. Patch by Saihadhav Heblikar.

- bpo-18409: Add unittest for AutoComplete. Patch by Phil Webster.

- bpo-21477: htest.py - Improve framework, complete set of tests. Patches by Saimadhav Heblikar

- bpo-18104: Add idlelib/idle_test/htest.py with a few sample tests to begin consolidating and improving human-validated tests of Idle. Change other files as needed to work with htest. Running the module as __main__ runs all tests.

- bpo-21139: Change default paragraph width to 72, the PEP 8 recommendation.

- bpo-21284: Paragraph reformat test passes after user changes reformat width.

- bpo-17654: Ensure IDLE menus are customized properly on OS X for non-framework builds and for all variants of Tk.

- bpo-23180: Rename IDLE “Windows” menu item to “Window”. Patch by Al Sweigart.

### Build

- bpo-15506: Use standard PKG_PROG_PKG_CONFIG autoconf macro in the configure script.

- bpo-22935: Allow the ssl module to be compiled if openssl doesn’t support SSL 3.

- bpo-22592: Drop support of the Borland C compiler to build Python. The distutils module still supports it to build extensions.

- bpo-22591: Drop support of MS-DOS, especially of the DJGPP compiler (MS-DOS port of GCC).

- bpo-16537: Check whether self.extensions is empty in setup.py. Patch by Jonathan Hosmer.

- bpo-22359: Remove incorrect uses of recursive make. Patch by Jonas Wagner.

- bpo-21958: Define HAVE_ROUND when building with Visual Studio 2013 and above. Patch by Zachary Turner.

- bpo-18093: the programs that embed the CPython runtime are now in a separate “Programs” directory, rather than being kept in the Modules directory.

- bpo-15759: “make suspicious”, “make linkcheck” and “make doctest” in Doc/ now display special message when and only when there are failures.

- bpo-21141: The Windows build process no longer attempts to find Perl, instead relying on OpenSSL source being configured and ready to build. The `PCbuild\build_ssl.py` script has been re-written and re-named to `PCbuild\prepare_ssl.py`, and takes care of configuring OpenSSL source for both 32 and 64 bit platforms. OpenSSL sources obtained from svn.python.org will always be pre-configured and ready to build.

- bpo-21037: Add a build option to enable AddressSanitizer support.

- bpo-19962: The Windows build process now creates “python.bat” in the root of the source tree, which passes all arguments through to the most recently built interpreter.

- bpo-21285: Refactor and fix curses configure check to always search in a ncursesw directory.

- bpo-15234: For BerkeleyDB and Sqlite, only add the found library and include directories if they aren’t already being searched. This avoids an explicit runtime library dependency.

- bpo-17861: Tools/scripts/generate_opcode_h.py automatically regenerates Include/opcode.h from Lib/opcode.py if the latter gets any change.

- bpo-20644: OS X installer build support for documentation build changes in 3.4.1: assume externally supplied sphinx-build is available in /usr/bin.

- bpo-20022: Eliminate use of deprecated bundlebuilder in OS X builds.

- bpo-15968: Incorporated Tcl, Tk, and Tix builds into the Windows build solution.

- bpo-17095: Fix Modules/Setup shared support.

- bpo-21811: Anticipated fixes to support OS X versions > 10.9.

- bpo-21166: Prevent possible segfaults and other random failures of python –generate-posix-vars in pybuilddir.txt build target.

- bpo-18096: Fix library order returned by python-config.

- bpo-17219: Add library build dir for Python extension cross-builds.

- bpo-22919: Windows build updated to support VC 14.0 (Visual Studio 2015), which will be used for the official release.

- bpo-21236: Build _msi.pyd with cabinet.lib instead of fci.lib

- bpo-17128: Use private version of OpenSSL for OS X 10.5+ installer.

### C API

- bpo-14203: Remove obsolete support for view==NULL in PyBuffer_FillInfo(), bytearray_getbuffer(), bytesiobuf_getbuffer() and array_buffer_getbuf(). All functions now raise BufferError in that case.

- bpo-22445: PyBuffer_IsContiguous() now implements precise contiguity tests, compatible with NumPy’s NPY_RELAXED_STRIDES_CHECKING compilation flag. Previously the function reported false negatives for corner cases.

- bpo-22079: PyType_Ready() now checks that statically allocated type has no dynamically allocated bases.

- bpo-22453: Removed non-documented macro PyObject_REPR().

- bpo-18395: Rename `_Py_char2wchar()` to `Py_DecodeLocale()`, rename `_Py_wchar2char()` to `Py_EncodeLocale()`, and document these functions.

- bpo-21233: Add new C functions: PyMem_RawCalloc(), PyMem_Calloc(), PyObject_Calloc(), _PyObject_GC_Calloc(). bytes(int) is now using `calloc()` instead of `malloc()` for large objects which is faster and use less memory.

- bpo-20942: PyImport_ImportFrozenModuleObject() no longer sets __file__ to match what importlib does; this affects _frozen_importlib as well as any module loaded using imp.init_frozen().

### Documentation

- bpo-19548: Update the codecs module documentation to better cover the distinction between text encodings and other codecs, together with other clarifications. Patch by Martin Panter.

- bpo-22394: Doc/Makefile now supports `make venv PYTHON=../python` to create a venv for generating the documentation, e.g., `make html PYTHON=venv/bin/python3`.

- bpo-21514: The documentation of the json module now refers to new JSON RFC 7159 instead of obsoleted RFC 4627.

- bpo-21777: The binary sequence methods on bytes and bytearray are now documented explicitly, rather than assuming users will be able to derive the expected behaviour from the behaviour of the corresponding str methods.

- bpo-6916: undocument deprecated asynchat.fifo class.

- bpo-17386: Expanded functionality of the `Doc/make.bat` script to make it much more comparable to `Doc/Makefile`.

- bpo-21312: Update the thread_foobar.h template file to include newer threading APIs. Patch by Jack McCracken.

- bpo-21043: Remove the recommendation for specific CA organizations and to mention the ability to load the OS certificates.

- bpo-20765: Add missing documentation for PurePath.with_name() and PurePath.with_suffix().

- bpo-19407: New package installation and distribution guides based on the Python Packaging Authority tools. Existing guides have been retained as legacy links from the distutils docs, as they still contain some required reference material for tool developers that isn’t recorded anywhere else.

- bpo-19697: Document cases where __main__.__spec__ is None.

### Tests

- bpo-18982: Add tests for CLI of the calendar module.

- bpo-19548: Added some additional checks to test_codecs to ensure that statements in the updated documentation remain accurate. Patch by Martin Panter.

- bpo-22838: All test_re tests now work with unittest test discovery.

- bpo-22173: Update lib2to3 tests to use unittest test discovery.

- bpo-16000: Convert test_curses to use unittest.

- bpo-21456: Skip two tests in test_urllib2net.py if _ssl module not present. Patch by Remi Pointel.

- bpo-20746: Fix test_pdb to run in refleak mode (-R). Patch by Xavier de Gaye.

- bpo-22060: test_ctypes has been somewhat cleaned up and simplified; it now uses unittest test discovery to find its tests.

- bpo-22104: regrtest.py no longer holds a reference to the suite of tests loaded from test modules that don’t define test_main().

- bpo-22111: Assorted cleanups in test_imaplib. Patch by Milan Oberkirch.

- bpo-22002: Added `load_package_tests` function to test.support and used it to implement/augment test discovery in test_asyncio, test_email, test_importlib, test_json, and test_tools.

- bpo-21976: Fix test_ssl to accept LibreSSL version strings. Thanks to William Orr.

- bpo-21918: Converted test_tools from a module to a package containing separate test files for each tested script.

- bpo-9554: Use modern unittest features in test_argparse. Initial patch by Denver Coneybeare and Radu Voicilas.

- bpo-20155: Changed HTTP method names in failing tests in test_httpservers so that packet filtering software (specifically Windows Base Filtering Engine) does not interfere with the transaction semantics expected by the tests.

- bpo-19493: Refactored the ctypes test package to skip tests explicitly rather than silently.

- bpo-18492: All resources are now allowed when tests are not run by regrtest.py.

- bpo-21634: Fix pystone micro-benchmark: use floor division instead of true division to benchmark integers instead of floating point numbers. Set pystone version to 1.2. Patch written by Lennart Regebro.

- bpo-21605: Added tests for Tkinter images.

- bpo-21493: Added test for ntpath.expanduser(). Original patch by Claudiu Popa.

- bpo-19925: Added tests for the spwd module. Original patch by Vajrasky Kok.

- bpo-21522: Added Tkinter tests for Listbox.itemconfigure(), PanedWindow.paneconfigure(), and Menu.entryconfigure().

- bpo-17756: Fix test_code test when run from the installed location.

- bpo-17752: Fix distutils tests when run from the installed location.

- bpo-18604: Consolidated checks for GUI availability. All platforms now at least check whether Tk can be instantiated when the GUI resource is requested.

- bpo-21275: Fix a socket test on KFreeBSD.

- bpo-21223: Pass test_site/test_startup_imports when some of the extensions are built as builtins.

- bpo-20635: Added tests for Tk geometry managers.

- Add test case for freeze.

- bpo-20743: Fix a reference leak in test_tcl.

- bpo-21097: Move test_namespace_pkgs into test_importlib.

- bpo-21503: Use test_both() consistently in test_importlib.

- bpo-20939: Avoid various network test failures due to new redirect of http://www.python.org/ to https://www.python.org: use http://www.example.com instead.

- bpo-20668: asyncio tests no longer rely on tests.txt file. (Patch by Vajrasky Kok)

- bpo-21093: Prevent failures of ctypes test_macholib on OS X if a copy of libz exists in $HOME/lib or /usr/local/lib.

- bpo-22770: Prevent some Tk segfaults on OS X when running gui tests.

- bpo-23211: Workaround test_logging failure on some OS X 10.6 systems.

- bpo-23345: Prevent test_ssl failures with large OpenSSL patch level values (like 0.9.8zc).

### Tools/Demos

- bpo-22314: pydoc now works when the LINES environment variable is set.

- bpo-22615: Argument Clinic now supports the “type” argument for the int converter. This permits using the int converter with enums and typedefs.

- bpo-20076: The makelocalealias.py script no longer ignores UTF-8 mapping.

- bpo-20079: The makelocalealias.py script now can parse the SUPPORTED file from glibc sources and supports command line options for source paths.

- bpo-22201: Command-line interface of the zipfile module now correctly extracts ZIP files with directory entries. Patch by Ryan Wilson.

- bpo-22120: For functions using an unsigned integer return converter, Argument Clinic now generates a cast to that type for the comparison to -1 in the generated code. (This suppresses a compilation warning.)

- bpo-18974: Tools/scripts/diff.py now uses argparse instead of optparse.

- bpo-21906: Make Tools/scripts/md5sum.py work in Python 3. Patch by Zachary Ware.

- bpo-21629: Fix Argument Clinic’s “–converters” feature.

- Add support for `yield from` to 2to3.

- Add support for the PEP 465 matrix multiplication operator to 2to3.

- bpo-16047: Fix module exception list and __file__ handling in freeze. Patch by Meador Inge.

- bpo-11824: Consider ABI tags in freeze. Patch by Meador Inge.

- bpo-20535: PYTHONWARNING no longer affects the run_tests.py script. Patch by Arfrever Frehtes Taifersar Arahesis.

### Windows

- bpo-23260: Update Windows installer

- The bundled version of Tcl/Tk has been updated to 8.6.3. The most visible result of this change is the addition of new native file dialogs when running on Windows Vista or newer. See Tcl/Tk’s TIP 432 for more information. Also, this version of Tcl/Tk includes support for Windows 10.

- bpo-17896: The Windows build scripts now expect external library sources to be in `PCbuild\..\externals` rather than `PCbuild\..\..`.

- bpo-17717: The Windows build scripts now use a copy of NASM pulled from svn.python.org to build OpenSSL.

- bpo-21907: Improved the batch scripts provided for building Python.

- bpo-22644: The bundled version of OpenSSL has been updated to 1.0.1j.

- bpo-10747: Use versioned labels in the Windows start menu. Patch by Olive Kilburn.

- bpo-22980: .pyd files with a version and platform tag (for example, “.cp35-win32.pyd”) will now be loaded in preference to those without tags.

(For information about older versions, consult the HISTORY file.)