
****************************
  What's New In Python 3.13
****************************

:Editors: Adam Turner and Thomas Wouters

.. Rules for maintenance:

   * Anyone can add text to this document.  Do not spend very much time
   on the wording of your changes, because your text will probably
   get rewritten to some degree.

   * The maintainer will go through Misc/NEWS periodically and add
   changes; it's therefore more important to add your changes to
   Misc/NEWS than to this file.

   * This is not a complete list of every single change; completeness
   is the purpose of Misc/NEWS.  Some changes I consider too small
   or esoteric to include.  If such a change is added to the text,
   I'll just remove it.  (This is another reason you shouldn't spend
   too much time on writing your addition.)

   * If you want to draw your new text to the attention of the
   maintainer, add 'XXX' to the beginning of the paragraph or
   section.

   * It's OK to just add a fragmentary note about a change.  For
   example: "XXX Describe the transmogrify() function added to the
   socket module."  The maintainer will research the change and
   write the necessary text.

   * You can comment out your additions if you like, but it's not
   necessary (especially when a final release is some months away).

   * Credit the author of a patch or bugfix.   Just the name is
   sufficient; the e-mail address isn't necessary.

   * It's helpful to add the issue number as a comment:

   XXX Describe the transmogrify() function added to the socket
   module.
   (Contributed by P.Y. Developer in :gh:`12345`.)

   This saves the maintainer the effort of going through the VCS log
   when researching a change.

This article explains the new features in Python 3.13, compared to 3.12.
Python 3.13 was released on October 7, 2024.
For full details, see the :ref:`changelog <changelog>`.

.. seealso::

   :pep:`719` -- Python 3.13 Release Schedule


Summary -- Release Highlights
=============================

.. This section singles out the most important changes in Python 3.13.
   Brevity is key.

Python 3.13 is a stable release of the Python programming
language, with a mix of changes to the language, the implementation
and the standard library.
The biggest changes include a new `interactive interpreter
<whatsnew313-better-interactive-interpreter_>`_,
experimental support for running in a `free-threaded mode
<whatsnew313-free-threaded-cpython_>`_ (:pep:`703`),
and a `Just-In-Time compiler <whatsnew313-jit-compiler_>`_ (:pep:`744`).

Error messages continue to improve, with tracebacks now highlighted in color
by default. The :func:`locals` builtin now has :ref:`defined semantics
<whatsnew313-locals-semantics>` for changing the returned mapping,
and type parameters now support default values.

The library changes contain removal of deprecated APIs and modules,
as well as the usual improvements in user-friendliness and correctness.
Several legacy standard library modules have now `been removed
<whatsnew313-pep594_>`_ following their deprecation in Python 3.11 (:pep:`594`).

This article doesn't attempt to provide a complete specification
of all new features, but instead gives a convenient overview.
For full details refer to the documentation,
such as the :ref:`Library Reference <library-index>`
and :ref:`Language Reference <reference-index>`.
To understand the complete implementation and design rationale for a change,
refer to the PEP for a particular new feature;
but note that PEPs usually are not kept up-to-date
once a feature has been fully implemented.
See `Porting to Python 3.13`_ for guidance on upgrading from
earlier versions of Python.

--------------

.. PEP-sized items next.

Interpreter improvements:

* A greatly improved :ref:`interactive interpreter
  <whatsnew313-better-interactive-interpreter>` and
  :ref:`improved error messages <whatsnew313-improved-error-messages>`.
* :pep:`667`: The :func:`locals` builtin now has
  :ref:`defined semantics <whatsnew313-locals-semantics>` when mutating the
  returned mapping. Python debuggers and similar tools may now more reliably
  update local variables in optimized scopes even during concurrent code
  execution.
* :pep:`703`: CPython 3.13 has experimental support for running with the
  :term:`global interpreter lock` disabled. See :ref:`Free-threaded CPython
  <whatsnew313-free-threaded-cpython>` for more details.
* :pep:`744`: A basic :ref:`JIT compiler <whatsnew313-jit-compiler>` was added.
  It is currently disabled by default (though we may turn it on later).
  Performance improvements are modest -- we expect to improve this
  over the next few releases.
* Color support in the new :ref:`interactive interpreter
  <whatsnew313-better-interactive-interpreter>`,
  as well as in :ref:`tracebacks <whatsnew313-improved-error-messages>`
  and :ref:`doctest <whatsnew313-doctest>` output.
  This can be disabled through the :envvar:`PYTHON_COLORS` and |NO_COLOR|_
  environment variables.

Python data model improvements:

* :attr:`~type.__static_attributes__` stores the names of attributes accessed
  through ``self.X`` in any function in a class body.
* :attr:`~type.__firstlineno__` records the first line number of a class
  definition.

Significant improvements in the standard library:

* Add a new :exc:`PythonFinalizationError` exception, raised when an operation
  is blocked during :term:`finalization <interpreter shutdown>`.
* The :mod:`argparse` module now supports deprecating command-line options,
  positional arguments, and subcommands.
* The new functions :func:`base64.z85encode` and :func:`base64.z85decode`
  support encoding and decoding `Z85 data`_.
* The :mod:`copy` module now has a :func:`copy.replace` function,
  with support for many builtin types and any class defining
  the :func:`~object.__replace__` method.
* The new :mod:`dbm.sqlite3` module is now the default :mod:`dbm` backend.
* The :mod:`os` module has a :ref:`suite of new functions <os-timerfd>`
  for working with Linux's timer notification file descriptors.
* The :mod:`random` module now has a :ref:`command-line interface <random-cli>`.

Security improvements:

* :func:`ssl.create_default_context` sets :data:`ssl.VERIFY_X509_PARTIAL_CHAIN`
  and :data:`ssl.VERIFY_X509_STRICT` as default flags.

C API improvements:

* The :c:data:`Py_mod_gil` slot is now used to indicate that
  an extension module supports running with the :term:`GIL` disabled.
* The :doc:`PyTime C API </c-api/time>` has been added,
  providing access to system clocks.
* :c:type:`PyMutex` is a new lightweight mutex that occupies a single byte.
* There is a new :ref:`suite of functions <c-api-monitoring>`
  for generating :pep:`669` monitoring events in the C API.

New typing features:

* :pep:`696`: Type parameters (:data:`typing.TypeVar`, :data:`typing.ParamSpec`,
  and :data:`typing.TypeVarTuple`) now support defaults.
* :pep:`702`: The new :func:`warnings.deprecated` decorator adds support
  for marking deprecations in the type system and at runtime.
* :pep:`705`: :data:`typing.ReadOnly` can be used to mark an item of a
  :class:`typing.TypedDict` as read-only for type checkers.
* :pep:`742`: :data:`typing.TypeIs` provides more intuitive
  type narrowing behavior, as an alternative to :data:`typing.TypeGuard`.

Platform support:

* :pep:`730`: Apple's iOS is now an :ref:`officially supported platform
  <whatsnew313-platform-support>`, at :pep:`tier 3 <11#tier-3>`.
* :pep:`738`: Android is now an :ref:`officially supported platform
  <whatsnew313-platform-support>`, at :pep:`tier 3 <11#tier-3>`.
* ``wasm32-wasi`` is now supported as a :pep:`tier 2 <11#tier-2>` platform.
* ``wasm32-emscripten`` is no longer an officially supported platform.

Important removals:

* :ref:`PEP 594 <whatsnew313-pep594>`: The remaining 19 "dead batteries"
  (legacy stdlib modules) have been removed from the standard library:
  :mod:`!aifc`, :mod:`!audioop`, :mod:`!cgi`, :mod:`!cgitb`, :mod:`!chunk`,
  :mod:`!crypt`, :mod:`!imghdr`, :mod:`!mailcap`, :mod:`!msilib`, :mod:`!nis`,
  :mod:`!nntplib`, :mod:`!ossaudiodev`, :mod:`!pipes`, :mod:`!sndhdr`,
  :mod:`!spwd`, :mod:`!sunau`, :mod:`!telnetlib`, :mod:`!uu` and :mod:`!xdrlib`.
* Remove the :program:`2to3` tool and :mod:`!lib2to3` module
  (deprecated in Python 3.11).
* Remove the :mod:`!tkinter.tix` module (deprecated in Python 3.6).
* Remove the :func:`!locale.resetlocale` function.
* Remove the :mod:`!typing.io` and :mod:`!typing.re` namespaces.
* Remove chained :class:`classmethod` descriptors.

Release schedule changes:

:pep:`602` ("Annual Release Cycle for Python") has been updated
to extend the full support ('bugfix') period for new releases to two years.
This updated policy means that:

* Python 3.9--3.12 have one and a half years of full support,
  followed by three and a half years of security fixes.
* Python 3.13 and later have two years of full support,
  followed by three years of security fixes.


New Features
============


.. _whatsnew313-better-interactive-interpreter:

A better interactive interpreter
--------------------------------

Python now uses a new :term:`interactive` shell by default, based on code
from the `PyPy project`_.
When the user starts the :term:`REPL` from an interactive terminal,
the following new features are now supported:

* Multiline editing with history preservation.
* Direct support for REPL-specific commands like :kbd:`help`, :kbd:`exit`,
  and :kbd:`quit`, without the need to call them as functions.
* Prompts and tracebacks with :ref:`color enabled by default
  <using-on-controlling-color>`.
* Interactive help browsing using :kbd:`F1` with a separate command
  history.
* History browsing using :kbd:`F2` that skips output as well as the
  :term:`>>>` and :term:`...` prompts.
* "Paste mode" with :kbd:`F3` that makes pasting larger blocks of code
  easier (press :kbd:`F3` again to return to the regular prompt).

To disable the new interactive shell,
set the :envvar:`PYTHON_BASIC_REPL` environment variable.
For more on interactive mode, see :ref:`tut-interac`.

(Contributed by Pablo Galindo Salgado, Łukasz Langa, and
Lysandros Nikolaou in :gh:`111201` based on code from the PyPy project.
Windows support contributed by Dino Viehland and Anthony Shaw.)

.. _`PyPy project`: https://pypy.org/


.. _whatsnew313-improved-error-messages:

Improved error messages
-----------------------

* The interpreter now uses color by default when displaying tracebacks in the
  terminal. This feature :ref:`can be controlled <using-on-controlling-color>`
  via the new :envvar:`PYTHON_COLORS` environment variable as well as
  the canonical |NO_COLOR|_ and |FORCE_COLOR|_ environment variables.
  (Contributed by Pablo Galindo Salgado in :gh:`112730`.)

* A common mistake is to write a script with the same name as a
  standard library module. When this results in errors, we now
  display a more helpful error message:

  .. code-block:: pytb

     $ python random.py
     Traceback (most recent call last):
       File "/home/me/random.py", line 1, in <module>
         import random
       File "/home/me/random.py", line 3, in <module>
         print(random.randint(5))
               ^^^^^^^^^^^^^^
     AttributeError: module 'random' has no attribute 'randint' (consider renaming '/home/me/random.py' since it has the same name as the standard library module named 'random' and prevents importing that standard library module)

  Similarly, if a script has the same name as a third-party
  module that it attempts to import and this results in errors,
  we also display a more helpful error message:

  .. code-block:: pytb

     $ python numpy.py
     Traceback (most recent call last):
       File "/home/me/numpy.py", line 1, in <module>
         import numpy as np
       File "/home/me/numpy.py", line 3, in <module>
         np.array([1, 2, 3])
         ^^^^^^^^
     AttributeError: module 'numpy' has no attribute 'array' (consider renaming '/home/me/numpy.py' if it has the same name as a library you intended to import)

  (Contributed by Shantanu Jain in :gh:`95754`.)

* The error message now tries to suggest the correct keyword argument
  when an incorrect keyword argument is passed to a function.

  .. code-block:: pycon

     >>> "Better error messages!".split(max_split=1)
     Traceback (most recent call last):
       File "<python-input-0>", line 1, in <module>
         "Better error messages!".split(max_split=1)
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
     TypeError: split() got an unexpected keyword argument 'max_split'. Did you mean 'maxsplit'?

  (Contributed by Pablo Galindo Salgado and Shantanu Jain in :gh:`107944`.)


.. _whatsnew313-free-threaded-cpython:

Free-threaded CPython
---------------------

CPython now has experimental support for running in a free-threaded mode,
with the :term:`global interpreter lock` (GIL) disabled.
This is an experimental feature and therefore is not enabled by default.
The free-threaded mode requires a different executable,
usually called ``python3.13t`` or ``python3.13t.exe``.
Pre-built binaries marked as *free-threaded* can be installed as part of
the official :ref:`Windows <install-freethreaded-windows>`
and :ref:`macOS <install-freethreaded-macos>` installers,
or CPython can be built from source with the :option:`--disable-gil` option.

Free-threaded execution allows for full utilization of the available
processing power by running threads in parallel on available CPU cores.
While not all software will benefit from this automatically, programs
designed with threading in mind will run faster on multi-core hardware.
**The free-threaded mode is experimental** and work is ongoing to improve it:
expect some bugs and a substantial single-threaded performance hit.
Free-threaded builds of CPython support optionally running with the GIL
enabled at runtime using the environment variable :envvar:`PYTHON_GIL` or
the command-line option :option:`-X gil=1`.

To check if the current interpreter supports free-threading, :option:`python -VV <-V>`
and :data:`sys.version` contain "experimental free-threading build".
The new :func:`!sys._is_gil_enabled` function can be used to check whether
the GIL is actually disabled in the running process.

C-API extension modules need to be built specifically for the free-threaded
build. Extensions that support running with the :term:`GIL` disabled should
use the :c:data:`Py_mod_gil` slot. Extensions using single-phase init should
use :c:func:`PyUnstable_Module_SetGIL` to indicate whether they support
running with the GIL disabled. Importing C extensions that don't use these
mechanisms will cause the GIL to be enabled, unless the GIL was explicitly
disabled with the :envvar:`PYTHON_GIL` environment variable or the
:option:`-X gil=0` option.
pip 24.1 or newer is required to install packages with C extensions in the
free-threaded build.

This work was made possible thanks to many individuals and
organizations, including the large community of contributors to Python
and third-party projects to test and enable free-threading support.
Notable contributors include:
Sam Gross, Ken Jin, Donghee Na, Itamar Oren, Matt Page, Brett Simmers,
Dino Viehland, Carl Meyer, Nathan Goldbaum, Ralf Gommers,
Lysandros Nikolaou, and many others.
Many of these contributors are employed by Meta, which has
provided significant engineering resources to support this project.

.. seealso::

   :pep:`703` "Making the Global Interpreter Lock Optional in CPython"
   contains rationale and information surrounding this work.

   `Porting Extension Modules to Support Free-Threading
   <https://py-free-threading.github.io/porting/>`_: A community-maintained
   porting guide for extension authors.


.. _whatsnew313-jit-compiler:

An experimental just-in-time (JIT) compiler
-------------------------------------------

When CPython is configured and built using
the :option:`!--enable-experimental-jit` option,
a just-in-time (JIT) compiler is added which may speed up some Python programs.
On Windows, use ``PCbuild/build.bat --experimental-jit`` to enable the JIT
or ``--experimental-jit-interpreter`` to enable the Tier 2 interpreter.
Build requirements and further supporting information `are contained at`__
:file:`Tools/jit/README.md`.

__ https://github.com/python/cpython/blob/main/Tools/jit/README.md

The :option:`!--enable-experimental-jit` option takes these (optional) values,
defaulting to ``yes`` if :option:`!--enable-experimental-jit` is present
without the optional value.

* ``no``: Disable the entire Tier 2 and JIT pipeline.
* ``yes``: Enable the JIT.
  To disable the JIT at runtime, pass the environment variable ``PYTHON_JIT=0``.
* ``yes-off``: Build the JIT but disable it by default.
  To enable the JIT at runtime, pass the environment variable ``PYTHON_JIT=1``.
* ``interpreter``: Enable the Tier 2 interpreter but disable the JIT.
  The interpreter can be disabled by running with ``PYTHON_JIT=0``.

The internal architecture is roughly as follows:

* We start with specialized *Tier 1 bytecode*.
  See :ref:`What's new in 3.11 <whatsnew311-pep659>` for details.
* When the Tier 1 bytecode gets hot enough, it gets translated
  to a new purely internal intermediate representation (IR),
  called the *Tier 2 IR*, and sometimes referred to as micro-ops ("uops").
* The Tier 2 IR uses the same stack-based virtual machine as Tier 1,
  but the instruction format is better suited to translation to machine code.
* We have several optimization passes for Tier 2 IR, which are applied
  before it is interpreted or translated to machine code.
* There is a Tier 2 interpreter, but it is mostly intended for debugging
  the earlier stages of the optimization pipeline.
  The Tier 2 interpreter can be enabled by configuring Python
  with ``--enable-experimental-jit=interpreter``.
* When the JIT is enabled, the optimized
  Tier 2 IR is translated to machine code, which is then executed.
* The machine code translation process uses a technique called
  *copy-and-patch*. It has no runtime dependencies, but there is a new
  build-time dependency on LLVM.

.. seealso:: :pep:`744`

(JIT by Brandt Bucher, inspired by a paper by Haoran Xu and Fredrik Kjolstad.
Tier 2 IR by Mark Shannon and Guido van Rossum.
Tier 2 optimizer by Ken Jin.)


.. _whatsnew313-locals-semantics:

Defined mutation semantics for :py:func:`locals`
------------------------------------------------

Historically, the expected result of mutating the return value of
:func:`locals` has been left to individual Python implementations to define.
Starting from Python 3.13, :pep:`667` standardises
the historical behavior of CPython for most code execution scopes,
but changes :term:`optimized scopes <optimized scope>`
(functions, generators, coroutines, comprehensions, and generator expressions)
to explicitly return independent snapshots of the currently assigned local
variables, including locally referenced nonlocal variables captured in closures.

This change to the semantics of :func:`locals` in optimized scopes also
affects the default behavior of code execution functions that implicitly
target :func:`!locals` if no explicit namespace is provided
(such as :func:`exec` and :func:`eval`).
In previous versions, whether or not changes could be accessed by calling
:func:`!locals` after calling the code execution function was
implementation-dependent. In CPython specifically, such code would typically
appear to work as desired, but could sometimes fail in optimized scopes based
on other code (including debuggers and code execution tracing tools)
potentially resetting the shared snapshot in that scope.
Now, the code will always run against an independent snapshot of
the local variables in optimized scopes, and hence the changes will never
be visible in subsequent calls to :func:`!locals`.
To access the changes made in these cases, an explicit namespace reference
must now be passed to the relevant function.
Alternatively, it may make sense to update affected code to use a higher level
code execution API that returns the resulting code execution namespace
(e.g. :func:`runpy.run_path` when executing Python files from disk).

To ensure debuggers and similar tools can reliably update local variables in
scopes affected by this change, :attr:`FrameType.f_locals <frame.f_locals>` now
returns a write-through proxy to the frame's local and locally referenced
nonlocal variables in these scopes, rather than returning an inconsistently
updated shared ``dict`` instance with undefined runtime semantics.

See :pep:`667` for more details, including related C API changes
and deprecations. Porting notes are also provided below for the affected
:ref:`Python APIs <pep667-porting-notes-py>` and :ref:`C APIs
<pep667-porting-notes-c>`.

(PEP and implementation contributed by Mark Shannon and Tian Gao in
:gh:`74929`. Documentation updates provided by Guido van Rossum and
Alyssa Coghlan.)


.. _whatsnew313-platform-support:

Support for mobile platforms
----------------------------

:pep:`730`: iOS is now a :pep:`11` supported platform, with the
``arm64-apple-ios`` and ``arm64-apple-ios-simulator`` targets at tier 3
(iPhone and iPad devices released after 2013 and the Xcode iOS simulator
running on Apple silicon hardware, respectively).
``x86_64-apple-ios-simulator``
(the Xcode iOS simulator running on older ``x86_64`` hardware)
is not a tier 3 supported platform, but will have best-effort support.
(PEP written and implementation contributed by Russell Keith-Magee in
:gh:`114099`.)

:pep:`738`: Android is now a :pep:`11` supported platform, with the
``aarch64-linux-android`` and ``x86_64-linux-android`` targets at tier 3.
The 32-bit targets ``arm-linux-androideabi`` and ``i686-linux-android``
are not tier 3 supported platforms, but will have best-effort support.
(PEP written and implementation contributed by Malcolm Smith in
:gh:`116622`.)

.. seealso:: :pep:`730`, :pep:`738`


Other Language Changes
======================

* The compiler now strips common leading whitespace
  from every line in a docstring.
  This reduces the size of the :term:`bytecode cache <bytecode>`
  (such as ``.pyc`` files), with reductions in file size of around 5%,
  for example in :mod:`!sqlalchemy.orm.session` from SQLAlchemy 2.0.
  This change affects tools that use docstrings, such as :mod:`doctest`.

  .. doctest::

     >>> def spam():
     ...     """
     ...         This is a docstring with
     ...           leading whitespace.
     ...
     ...         It even has multiple paragraphs!
     ...     """
     ...
     >>> spam.__doc__
     '\nThis is a docstring with\n  leading whitespace.\n\nIt even has multiple paragraphs!\n'

  (Contributed by Inada Naoki in :gh:`81283`.)

* :ref:`Annotation scopes <annotation-scopes>` within class scopes
  can now contain lambdas and comprehensions.
  Comprehensions that are located within class scopes
  are not inlined into their parent scope.

  .. code-block:: python

     class C[T]:
         type Alias = lambda: T

  (Contributed by Jelle Zijlstra in :gh:`109118` and :gh:`118160`.)

* :ref:`Future statements <future>` are no longer triggered by
  relative imports of the :mod:`__future__` module,
  meaning that statements of the form ``from .__future__ import ...``
  are now simply standard relative imports, with no special features activated.
  (Contributed by Jeremiah Gabriel Pascual in :gh:`118216`.)

* :keyword:`global` declarations are now permitted in :keyword:`except` blocks
  when that global is used in the :keyword:`else` block.
  Previously this raised an erroneous :exc:`SyntaxError`.
  (Contributed by Irit Katriel in :gh:`111123`.)

* Add :envvar:`PYTHON_FROZEN_MODULES`, a new environment variable that
  determines whether frozen modules are ignored by the import machinery,
  equivalent to the :option:`-X frozen_modules <-X>` command-line option.
  (Contributed by Yilei Yang in :gh:`111374`.)

* Add :ref:`support for the perf profiler <perf_profiling>` working
  without `frame pointers <https://en.wikipedia.org/wiki/Call_stack>`_ through
  the new environment variable :envvar:`PYTHON_PERF_JIT_SUPPORT`
  and command-line option :option:`-X perf_jit <-X>`.
  (Contributed by Pablo Galindo in :gh:`118518`.)

* The location of a :file:`.python_history` file can be changed via the
  new :envvar:`PYTHON_HISTORY` environment variable.
  (Contributed by Levi Sabah, Zackery Spytz and Hugo van Kemenade
  in :gh:`73965`.)

* Classes have a new :attr:`~type.__static_attributes__` attribute.
  This is populated by the compiler with a tuple of the class's attribute names
  which are assigned through ``self.<name>`` from any function in its body.
  (Contributed by Irit Katriel in :gh:`115775`.)

* The compiler now creates a :attr:`!__firstlineno__` attribute on classes
  with the line number of the first line of the class definition.
  (Contributed by Serhiy Storchaka in :gh:`118465`.)

* The :func:`exec` and :func:`eval` builtins now accept
  the *globals* and *locals* arguments as keywords.
  (Contributed by Raphael Gaschignard in :gh:`105879`)

* The :func:`compile` builtin now accepts a new flag,
  ``ast.PyCF_OPTIMIZED_AST``, which is similar to ``ast.PyCF_ONLY_AST``
  except that the returned AST is optimized according to
  the value of the *optimize* argument.
  (Contributed by Irit Katriel in :gh:`108113`).

* Add a :attr:`~property.__name__` attribute on :class:`property` objects.
  (Contributed by Eugene Toder in :gh:`101860`.)

* Add :exc:`PythonFinalizationError`, a new exception derived from
  :exc:`RuntimeError` and used to signal when operations are blocked
  during :term:`finalization <interpreter shutdown>`.
  The following callables now raise :exc:`!PythonFinalizationError`,
  instead of :exc:`RuntimeError`:

  * :func:`_thread.start_new_thread`
  * :func:`os.fork`
  * :func:`os.forkpty`
  * :class:`subprocess.Popen`

  (Contributed by Victor Stinner in :gh:`114570`.)

* Allow the *count* argument of :meth:`str.replace` to be a keyword.
  (Contributed by Hugo van Kemenade in :gh:`106487`.)

* Many functions now emit a warning if a boolean value is passed as
  a file descriptor argument.
  This can help catch some errors earlier.
  (Contributed by Serhiy Storchaka in :gh:`82626`.)

* Added :attr:`!name` and :attr:`!mode` attributes
  for compressed and archived file-like objects in
  the :mod:`bz2`, :mod:`lzma`, :mod:`tarfile`, and :mod:`zipfile` modules.
  (Contributed by Serhiy Storchaka in :gh:`115961`.)


New Modules
===========

* :mod:`dbm.sqlite3`: An SQLite backend for :mod:`dbm`.
  (Contributed by Raymond Hettinger and Erlend E. Aasland in :gh:`100414`.)


Improved Modules
================


argparse
--------

* Add the *deprecated* parameter to the
  :meth:`~argparse.ArgumentParser.add_argument`
  and :meth:`!add_parser` methods, to enable deprecating
  command-line options, positional arguments, and subcommands.
  (Contributed by Serhiy Storchaka in :gh:`83648`.)


array
-----

* Add the ``'w'`` type code (``Py_UCS4``) for Unicode characters.
  It should be used instead of the deprecated ``'u'`` type code.
  (Contributed by Inada Naoki in :gh:`80480`.)

* Register :class:`array.array` as a :class:`~collections.abc.MutableSequence`
  by implementing the :meth:`~array.array.clear` method.
  (Contributed by Mike Zimin in :gh:`114894`.)


ast
---

* The constructors of node types in the :mod:`ast` module are now
  stricter in the arguments they accept,
  with more intuitive behavior when arguments are omitted.

  If an optional field on an AST node is not included as an argument when
  constructing an instance, the field will now be set to ``None``. Similarly,
  if a list field is omitted, that field will now be set to an empty list,
  and if an :class:`!expr_context` field is omitted, it defaults to
  :class:`Load() <ast.Load>`.
  (Previously, in all cases, the attribute would be missing on the newly
  constructed AST node instance.)

  In all other cases, where a required argument is omitted,
  the node constructor will emit a :exc:`DeprecationWarning`.
  This will raise an exception in Python 3.15.
  Similarly, passing a keyword argument to the constructor
  that does not map to a field on the AST node is now deprecated,
  and will raise an exception in Python 3.15.

  These changes do not apply to user-defined subclasses of :class:`ast.AST`
  unless the class opts in to the new behavior
  by defining the :attr:`.AST._field_types` mapping.

  (Contributed by Jelle Zijlstra in :gh:`105858`, :gh:`117486`, and :gh:`118851`.)

* :func:`ast.parse` now accepts an optional argument *optimize*
  which is passed on to :func:`compile`.
  This makes it possible to obtain an optimized AST.
  (Contributed by Irit Katriel in :gh:`108113`.)


asyncio
-------

* :func:`asyncio.as_completed` now returns an object that is both an
  :term:`asynchronous iterator` and a plain :term:`iterator`
  of :term:`awaitables <awaitable>`.
  The awaitables yielded by asynchronous iteration include original task
  or future objects that were passed in,
  making it easier to associate results with the tasks being completed.
  (Contributed by Justin Arthur in :gh:`77714`.)

* :meth:`asyncio.loop.create_unix_server` will now automatically remove
  the Unix socket when the server is closed.
  (Contributed by Pierre Ossman in :gh:`111246`.)

* :meth:`.DatagramTransport.sendto` will now send zero-length
  datagrams if called with an empty bytes object.
  The transport flow control also now accounts for the datagram header
  when calculating the buffer size.
  (Contributed by Jamie Phan in :gh:`115199`.)

* Add :meth:`Queue.shutdown <asyncio.Queue.shutdown>`
  and :exc:`~asyncio.QueueShutDown` to manage queue termination.
  (Contributed by Laurie Opperman and Yves Duprat in :gh:`104228`.)

* Add the :meth:`.Server.close_clients` and :meth:`.Server.abort_clients`
  methods, which more forcefully close an asyncio server.
  (Contributed by Pierre Ossman in :gh:`113538`.)

* Accept a tuple of separators in :meth:`.StreamReader.readuntil`,
  stopping when any one of them is encountered.
  (Contributed by Bruce Merry in :gh:`81322`.)

* Improve the behavior of :class:`~asyncio.TaskGroup` when
  an external cancellation collides with an internal cancellation.
  For example, when two task groups are nested
  and both experience an exception in a child task simultaneously,
  it was possible that the outer task group would hang,
  because its internal cancellation was swallowed by the inner task group.

  In the case where a task group is cancelled externally
  and also must raise an :exc:`ExceptionGroup`,
  it will now call the parent task's :meth:`~asyncio.Task.cancel` method.
  This ensures that a :exc:`~asyncio.CancelledError` will be raised
  at the next :keyword:`await`, so the cancellation is not lost.

  An added benefit of these changes is that task groups now preserve
  the cancellation count (:meth:`~asyncio.Task.cancelling`).

  In order to handle some corner cases, :meth:`~asyncio.Task.uncancel` may now
  reset the undocumented ``_must_cancel`` flag
  when the cancellation count reaches zero.

  (Inspired by an issue reported by Arthur Tacca in :gh:`116720`.)

* When :meth:`.TaskGroup.create_task` is called on an inactive
  :class:`~asyncio.TaskGroup`, the given coroutine will be closed (which
  prevents a :exc:`RuntimeWarning` about the given coroutine being
  never awaited).
  (Contributed by Arthur Tacca and Jason Zhang in :gh:`115957`.)

* The function and methods named ``create_task`` have received a new
  ``**kwargs`` argument that is passed through to the task constructor.
  This change was accidentally added in 3.13.3,
  and broke the API contract for custom task factories.
  Several third-party task factories implemented workarounds for this.
  In 3.13.4 and later releases the old factory contract is honored
  once again (until 3.14).
  To keep the workarounds working, the extra ``**kwargs`` argument still
  allows passing additional keyword arguments to :class:`~asyncio.Task`
  and to custom task factories.

  This affects the following function and methods:
  :meth:`asyncio.create_task`,
  :meth:`asyncio.loop.create_task`,
  :meth:`asyncio.TaskGroup.create_task`.
  (Contributed by Thomas Grainger in :gh:`128307`.)

base64
------

* Add :func:`~base64.z85encode` and :func:`~base64.z85decode` functions
  for encoding :class:`bytes` as `Z85 data`_
  and decoding Z85-encoded data to :class:`!bytes`.
  (Contributed by Matan Perelman in :gh:`75299`.)

  .. _Z85 data: https://rfc.zeromq.org/spec/32/


compileall
----------

* The default number of worker threads and processes is now selected using
  :func:`os.process_cpu_count` instead of :func:`os.cpu_count`.
  (Contributed by Victor Stinner in :gh:`109649`.)


concurrent.futures
------------------

* The default number of worker threads and processes is now selected using
  :func:`os.process_cpu_count` instead of :func:`os.cpu_count`.
  (Contributed by Victor Stinner in :gh:`109649`.)


configparser
------------

* :class:`~configparser.ConfigParser` now has support for unnamed sections,
  which allows for top-level key-value pairs.
  This can be enabled with the new *allow_unnamed_section* parameter.
  (Contributed by Pedro Sousa Lacerda in :gh:`66449`.)


copy
----

* The new :func:`~copy.replace` function and the :meth:`replace protocol
  <object.__replace__>` make creating modified copies of objects much simpler.
  This is especially useful when working with immutable objects.
  The following types support the :func:`~copy.replace` function
  and implement the replace protocol:

  * :func:`collections.namedtuple`
  * :class:`dataclasses.dataclass`
  * :class:`datetime.datetime`, :class:`datetime.date`, :class:`datetime.time`
  * :class:`inspect.Signature`, :class:`inspect.Parameter`
  * :class:`types.SimpleNamespace`
  * :ref:`code objects <code-objects>`

  Any user-defined class can also support :func:`copy.replace` by defining
  the :meth:`~object.__replace__` method.
  (Contributed by Serhiy Storchaka in :gh:`108751`.)


ctypes
------

* As a consequence of necessary internal refactoring, initialization of
  internal metaclasses now happens in ``__init__`` rather
  than in ``__new__``. This affects projects that subclass these internal
  metaclasses to provide custom initialization.
  Generally:

  - Custom logic that was done in ``__new__`` after calling ``super().__new__``
    should be moved to ``__init__``.
  - To create a class, call the metaclass, not only the metaclass's
    ``__new__`` method.

  See :gh:`124520` for discussion and links to changes in some affected
  projects.

* :class:`ctypes.Structure` objects have a new :attr:`~ctypes.Structure._align_`
  attribute which allows the alignment of the structure being packed to/from
  memory to be specified explicitly.
  (Contributed by Matt Sanderson in :gh:`112433`)

dbm
---

* Add :mod:`dbm.sqlite3`, a new module which implements an SQLite backend,
  and make it the default :mod:`!dbm` backend.
  (Contributed by Raymond Hettinger and Erlend E. Aasland in :gh:`100414`.)

* Allow removing all items from the database through
  the new :meth:`!clear` methods of the GDBM and NDBM database objects.
  (Contributed by Donghee Na in :gh:`107122`.)


dis
---

* Change the output of :mod:`dis` module functions to show logical
  labels for jump targets and exception handlers, rather than offsets.
  The offsets can be added with the new
  :option:`-O <dis --show-offsets>` command-line option
  or the *show_offsets* argument.
  (Contributed by Irit Katriel in :gh:`112137`.)

* :meth:`~dis.get_instructions` no longer represents cache entries
  as separate instructions.
  Instead, it returns them as part of the :class:`~dis.Instruction`,
  in the new *cache_info* field.
  The *show_caches* argument to :meth:`~dis.get_instructions` is deprecated
  and no longer has any effect.
  (Contributed by Irit Katriel in :gh:`112962`.)


.. _whatsnew313-doctest:

doctest
-------

* :mod:`doctest` output is now colored by default.
  This can be controlled via the new :envvar:`PYTHON_COLORS` environment
  variable as well as the canonical |NO_COLOR|_
  and |FORCE_COLOR|_ environment variables.
  See also :ref:`using-on-controlling-color`.
  (Contributed by Hugo van Kemenade in :gh:`117225`.)

* The :meth:`.DocTestRunner.run` method now counts the number of skipped tests.
  Add the :attr:`.DocTestRunner.skips` and :attr:`.TestResults.skipped` attributes.
  (Contributed by Victor Stinner in :gh:`108794`.)


email
-----

* Headers with embedded newlines are now quoted on output.
  The :mod:`~email.generator` will now refuse to serialize (write) headers
  that are improperly folded or delimited, such that they would be parsed as
  multiple headers or joined with adjacent data.
  If you need to turn this safety feature off,
  set :attr:`~email.policy.Policy.verify_generated_headers`.
  (Contributed by Bas Bloemsaat and Petr Viktorin in :gh:`121650`.)

* :func:`~email.utils.getaddresses` and :func:`~email.utils.parseaddr` now
  return ``('', '')`` pairs in more situations where invalid email addresses
  are encountered instead of potentially inaccurate values.
  The two functions have a new optional *strict* parameter (default ``True``).
  To get the old behavior (accepting malformed input), use ``strict=False``.
  ``getattr(email.utils, 'supports_strict_parsing', False)`` can be used
  to check if the *strict* parameter is available.
  (Contributed by Thomas Dwyer and Victor Stinner for :gh:`102988` to improve
  the :cve:`2023-27043` fix.)


enum
----

* :class:`~enum.EnumDict` has been made public to better support subclassing
  :class:`~enum.EnumType`.


fractions
---------

* :class:`~fractions.Fraction` objects now support the standard
  :ref:`format specification mini-language <formatspec>` rules
  for fill, alignment, sign handling, minimum width, and grouping.
  (Contributed by Mark Dickinson in :gh:`111320`.)


glob
----

* Add :func:`~glob.translate`, a function to convert a path specification
  with shell-style wildcards to a regular expression.
  (Contributed by Barney Gale in :gh:`72904`.)


importlib
---------

* The following functions in :mod:`importlib.resources` now allow accessing
  a directory (or tree) of resources, using multiple positional arguments
  (the *encoding* and *errors* arguments in the text-reading functions
  are now keyword-only):

  * :func:`~importlib.resources.is_resource`
  * :func:`~importlib.resources.open_binary`
  * :func:`~importlib.resources.open_text`
  * :func:`~importlib.resources.path`
  * :func:`~importlib.resources.read_binary`
  * :func:`~importlib.resources.read_text`

  These functions are no longer deprecated and are not scheduled for removal.
  (Contributed by Petr Viktorin in :gh:`116608`.)

* :func:`~importlib.resources.contents` remains deprecated in favor of
  the fully-featured :class:`~importlib.resources.abc.Traversable` API.
  However, there is now no plan to remove it.
  (Contributed by Petr Viktorin in :gh:`116608`.)


io
--

* The :class:`~io.IOBase` finalizer now logs any errors raised by
  the :meth:`~io.IOBase.close` method with :data:`sys.unraisablehook`.
  Previously, errors were ignored silently by default,
  and only logged in :ref:`Python Development Mode <devmode>`
  or when using a :ref:`Python debug build <debug-build>`.
  (Contributed by Victor Stinner in :gh:`62948`.)


ipaddress
---------

* Add the :attr:`.IPv4Address.ipv6_mapped` property,
  which returns the IPv4-mapped IPv6 address.
  (Contributed by Charles Machalow in :gh:`109466`.)

* Fix ``is_global`` and ``is_private`` behavior in
  :class:`~ipaddress.IPv4Address`, :class:`~ipaddress.IPv6Address`,
  :class:`~ipaddress.IPv4Network`, and :class:`~ipaddress.IPv6Network`.
  (Contributed by Jakub Stasiak in :gh:`113171`.)


itertools
---------

* :func:`~itertools.batched` has a new *strict* parameter,
  which raises a :exc:`ValueError` if the final batch is shorter
  than the specified batch size.
  (Contributed by Raymond Hettinger in :gh:`113202`.)


marshal
-------

* Add the *allow_code* parameter in module functions.
  Passing ``allow_code=False`` prevents serialization and de-serialization
  of code objects which are incompatible between Python versions.
  (Contributed by Serhiy Storchaka in :gh:`113626`.)


math
----

* The new function :func:`~math.fma` performs fused multiply-add operations.
  This computes ``x * y + z`` with only a single round,
  and so avoids any intermediate loss of precision.
  It wraps the ``fma()`` function provided by C99,
  and follows the specification of the IEEE 754 "fusedMultiplyAdd" operation
  for special cases.
  (Contributed by Mark Dickinson and Victor Stinner in :gh:`73468`.)


mimetypes
---------

* Add the :func:`~mimetypes.guess_file_type` function to guess a MIME type
  from a filesystem path.
  Using paths with :func:`~mimetypes.guess_type` is now :term:`soft deprecated`.
  (Contributed by Serhiy Storchaka in :gh:`66543`.)


mmap
----

* :class:`~mmap.mmap` is now protected from crashing on Windows when the
  mapped memory is inaccessible due to file system errors or access violations.
  (Contributed by Jannis Weigend in :gh:`118209`.)

* :class:`~mmap.mmap` has a new :meth:`~mmap.mmap.seekable` method
  that can be used when a seekable file-like object is required.
  The :meth:`~mmap.mmap.seek` method now returns the new absolute position.
  (Contributed by Donghee Na and Sylvie Liberman in :gh:`111835`.)

* The new UNIX-only *trackfd* parameter for :class:`~mmap.mmap` controls
  file descriptor duplication;
  if false, the file descriptor specified by *fileno* will not be duplicated.
  (Contributed by Zackery Spytz and Petr Viktorin in :gh:`78502`.)


multiprocessing
---------------

* The default number of worker threads and processes is now selected using
  :func:`os.process_cpu_count` instead of :func:`os.cpu_count`.
  (Contributed by Victor Stinner in :gh:`109649`.)


os
--

* Add :func:`~os.process_cpu_count` function to get the number
  of logical CPU cores usable by the calling thread of the current process.
  (Contributed by Victor Stinner in :gh:`109649`.)

* :func:`~os.cpu_count` and :func:`~os.process_cpu_count` can be overridden
  through the new environment variable :envvar:`PYTHON_CPU_COUNT`
  or the new command-line option :option:`-X cpu_count <-X>`.
  This option is useful for users who need to limit CPU resources
  of a container system without having to modify application code
  or the container itself.
  (Contributed by Donghee Na in :gh:`109595`.)

* Add a :ref:`low level interface <os-timerfd>` to Linux's
  :manpage:`timer file descriptors <timerfd_create(2)>`
  via :func:`~os.timerfd_create`,
  :func:`~os.timerfd_settime`, :func:`~os.timerfd_settime_ns`,
  :func:`~os.timerfd_gettime`, :func:`~os.timerfd_gettime_ns`,
  :const:`~os.TFD_NONBLOCK`, :const:`~os.TFD_CLOEXEC`,
  :const:`~os.TFD_TIMER_ABSTIME`, and :const:`~os.TFD_TIMER_CANCEL_ON_SET`
  (Contributed by Masaru Tsuchiyama in :gh:`108277`.)

* :func:`~os.lchmod` and the *follow_symlinks* argument of :func:`~os.chmod`
  are both now available on Windows.
  Note that the default value of *follow_symlinks*
  in :func:`!lchmod` is ``False`` on Windows.
  (Contributed by Serhiy Storchaka in :gh:`59616`.)

* :func:`~os.fchmod` and support for file descriptors in :func:`~os.chmod`
  are both now available on Windows.
  (Contributed by Serhiy Storchaka in :gh:`113191`.)

* On Windows, :func:`~os.mkdir` and :func:`~os.makedirs` now support passing
  a *mode* value of ``0o700`` to apply access control to the new directory.
  This implicitly affects :func:`tempfile.mkdtemp`
  and is a mitigation for :cve:`2024-4030`.
  Other values for *mode* continue to be ignored.
  (Contributed by Steve Dower in :gh:`118486`.)

* :func:`~os.posix_spawn` now accepts ``None`` for the *env* argument,
  which makes the newly spawned process use the current process environment.
  (Contributed by Jakub Kulik in :gh:`113119`.)

* :func:`~os.posix_spawn` can now use the :const:`~os.POSIX_SPAWN_CLOSEFROM`
  attribute in the *file_actions* parameter on platforms that support
  :c:func:`!posix_spawn_file_actions_addclosefrom_np`.
  (Contributed by Jakub Kulik in :gh:`113117`.)


os.path
-------

* Add :func:`~os.path.isreserved` to check if a path is reserved
  on the current system.
  This function is only available on Windows.
  (Contributed by Barney Gale in :gh:`88569`.)

* On Windows, :func:`~os.path.isabs` no longer considers paths
  starting with exactly one slash (``\`` or ``/``) to be absolute.
  (Contributed by Barney Gale and Jon Foster in :gh:`44626`.)

* :func:`~os.path.realpath` now resolves MS-DOS style file names
  even if the file is not accessible.
  (Contributed by Moonsik Park in :gh:`82367`.)


pathlib
-------

* Add :exc:`~pathlib.UnsupportedOperation`, which is raised instead of
  :exc:`NotImplementedError` when a path operation isn't supported.
  (Contributed by Barney Gale in :gh:`89812`.)

* Add a new constructor for creating :class:`~pathlib.Path` objects
  from 'file' URIs (``file:///``), :meth:`.Path.from_uri`.
  (Contributed by Barney Gale in :gh:`107465`.)

* Add :meth:`.PurePath.full_match` for matching paths with
  shell-style wildcards, including the recursive wildcard "``**``".
  (Contributed by Barney Gale in :gh:`73435`.)

* Add the :attr:`.PurePath.parser` class attribute to store the
  implementation of :mod:`os.path` used
  for low-level path parsing and joining.
  This will be either :mod:`!posixpath` or :mod:`!ntpath`.

* Add *recurse_symlinks* keyword-only argument to
  :meth:`.Path.glob` and :meth:`~pathlib.Path.rglob`.
  (Contributed by Barney Gale in :gh:`77609`.)

* :meth:`.Path.glob` and :meth:`~pathlib.Path.rglob`
  now return files and directories when given a pattern that ends with "``**``".
  Previously, only directories were returned.
  (Contributed by Barney Gale in :gh:`70303`.)

* Add the *follow_symlinks* keyword-only argument to
  :meth:`Path.is_file <pathlib.Path.is_file>`,
  :meth:`Path.is_dir <pathlib.Path.is_dir>`,
  :meth:`.Path.owner`, and :meth:`.Path.group`.
  (Contributed by Barney Gale in :gh:`105793` and Kamil Turek in :gh:`107962`.)


pdb
---

* :func:`breakpoint` and :func:`~pdb.set_trace` now enter the debugger immediately
  rather than on the next line of code to be executed. This change prevents the
  debugger from breaking outside of the context when :func:`!breakpoint` is positioned
  at the end of the context.
  (Contributed by Tian Gao in :gh:`118579`.)

* ``sys.path[0]`` is no longer replaced by the directory of the script
  being debugged when :attr:`sys.flags.safe_path` is set.
  (Contributed by Tian Gao and Christian Walther in :gh:`111762`.)

* :mod:`zipapp` is now supported as a debugging target.
  (Contributed by Tian Gao in :gh:`118501`.)

* Add ability to move between chained exceptions during
  post-mortem debugging in :func:`~pdb.pm` using
  the new :pdbcmd:`exceptions [exc_number] <exceptions>` command for Pdb.
  (Contributed by Matthias Bussonnier in :gh:`106676`.)

* Expressions and statements whose prefix is a pdb command are now correctly
  identified and executed.
  (Contributed by Tian Gao in :gh:`108464`.)


queue
-----

* Add :meth:`Queue.shutdown <queue.Queue.shutdown>` and :exc:`~queue.ShutDown`
  to manage queue termination.
  (Contributed by Laurie Opperman and Yves Duprat in :gh:`104750`.)


random
------

* Add a :ref:`command-line interface <random-cli>`.
  (Contributed by Hugo van Kemenade in :gh:`118131`.)


re
--

* Rename :exc:`!re.error` to :exc:`~re.PatternError` for improved clarity.
  :exc:`!re.error` is kept for backward compatibility.


shutil
------

* Support the *dir_fd* and *follow_symlinks* keyword arguments
  in :func:`~shutil.chown`.
  (Contributed by Berker Peksag and Tahia K in :gh:`62308`)


site
----

* :file:`.pth` files are now decoded using UTF-8 first,
  and then with the :term:`locale encoding` if UTF-8 decoding fails.
  (Contributed by Inada Naoki in :gh:`117802`.)


sqlite3
-------

* A :exc:`ResourceWarning` is now emitted if a :class:`~sqlite3.Connection`
  object is not :meth:`closed <sqlite3.Connection.close>` explicitly.
  (Contributed by Erlend E. Aasland in :gh:`105539`.)

* Add the *filter* keyword-only parameter to :meth:`.Connection.iterdump`
  for filtering database objects to dump.
  (Contributed by Mariusz Felisiak in :gh:`91602`.)


ssl
---

* The :func:`~ssl.create_default_context` API now includes
  :data:`~ssl.VERIFY_X509_PARTIAL_CHAIN` and :data:`~ssl.VERIFY_X509_STRICT`
  in its default flags.

  .. note::

     :data:`~ssl.VERIFY_X509_STRICT` may reject pre-:rfc:`5280`
     or malformed certificates that the underlying OpenSSL implementation
     might otherwise accept.
     Whilst disabling this is not recommended, you can do so using:

     .. code-block:: python

        import ssl

        ctx = ssl.create_default_context()
        ctx.verify_flags &= ~ssl.VERIFY_X509_STRICT

  (Contributed by William Woodruff in :gh:`112389`.)


statistics
----------

* Add :func:`~statistics.kde` for kernel density estimation.
  This makes it possible to estimate a continuous probability density function
  from a fixed number of discrete samples.
  (Contributed by Raymond Hettinger in :gh:`115863`.)

* Add :func:`~statistics.kde_random` for sampling from an
  estimated probability density function created by :func:`~statistics.kde`.
  (Contributed by Raymond Hettinger in :gh:`115863`.)


.. _whatsnew313-subprocess:

subprocess
----------

* The :mod:`subprocess` module now uses the :func:`~os.posix_spawn` function in
  more situations.

  Notably, when *close_fds* is ``True`` (the default),
  :func:`~os.posix_spawn` will be used when the C library provides
  :c:func:`!posix_spawn_file_actions_addclosefrom_np`,
  which includes recent versions of Linux, FreeBSD, and Solaris.
  On Linux, this should perform similarly to the existing
  Linux :c:func:`!vfork` based code.

  A private control knob :attr:`!subprocess._USE_POSIX_SPAWN` can
  be set to ``False`` if you need to force :mod:`subprocess`
  to never use :func:`~os.posix_spawn`.
  Please report your reason and platform details in
  the :ref:`issue tracker <using-the-tracker>` if you set this
  so that we can improve our API selection logic for everyone.
  (Contributed by Jakub Kulik in :gh:`113117`.)


sys
---

* Add the :func:`~sys._is_interned` function to test if a string was interned.
  This function is not guaranteed to exist in all implementations of Python.
  (Contributed by Serhiy Storchaka in :gh:`78573`.)


tempfile
--------

* On Windows, the default mode ``0o700`` used by :func:`tempfile.mkdtemp` now
  limits access to the new directory due to changes to :func:`os.mkdir`.
  This is a mitigation for :cve:`2024-4030`.
  (Contributed by Steve Dower in :gh:`118486`.)


time
----

* On Windows, :func:`~time.monotonic` now uses the
  ``QueryPerformanceCounter()`` clock for a resolution of 1 microsecond,
  instead of the ``GetTickCount64()`` clock which has
  a resolution of 15.6 milliseconds.
  (Contributed by Victor Stinner in :gh:`88494`.)

* On Windows, :func:`~time.time` now uses the
  ``GetSystemTimePreciseAsFileTime()`` clock for a resolution of 1 microsecond,
  instead of the ``GetSystemTimeAsFileTime()`` clock which has
  a resolution of 15.6 milliseconds.
  (Contributed by Victor Stinner in :gh:`63207`.)


tkinter
-------

* Add :mod:`tkinter` widget methods:
  :meth:`!tk_busy_hold`, :meth:`!tk_busy_configure`,
  :meth:`!tk_busy_cget`, :meth:`!tk_busy_forget`,
  :meth:`!tk_busy_current`, and :meth:`!tk_busy_status`.
  (Contributed by Miguel, klappnase and Serhiy Storchaka in :gh:`72684`.)

* The :mod:`tkinter` widget method :meth:`!wm_attributes` now accepts
  the attribute name without the minus prefix to get window attributes,
  for example ``w.wm_attributes('alpha')``
  and allows specifying attributes and values to set as keyword arguments,
  for example ``w.wm_attributes(alpha=0.5)``.
  (Contributed by Serhiy Storchaka in :gh:`43457`.)

* :meth:`!wm_attributes` can now return attributes as a :class:`dict`,
  by using the new optional keyword-only parameter *return_python_dict*.
  (Contributed by Serhiy Storchaka in :gh:`43457`.)

* :meth:`!Text.count` can now return a simple :class:`int`
  when the new optional keyword-only parameter *return_ints* is used.
  Otherwise, the single count is returned as a 1-tuple or ``None``.
  (Contributed by Serhiy Storchaka in :gh:`97928`.)

* Support the "vsapi" element type in
  the :meth:`~tkinter.ttk.Style.element_create` method of
  :class:`tkinter.ttk.Style`.
  (Contributed by Serhiy Storchaka in :gh:`68166`.)

* Add the :meth:`!after_info` method for Tkinter widgets.
  (Contributed by Cheryl Sabella in :gh:`77020`.)

* Add a new :meth:`!copy_replace` method to :class:`!PhotoImage`
  to copy a region from one image to another,
  possibly with pixel zooming, subsampling, or both.
  (Contributed by Serhiy Storchaka in :gh:`118225`.)

* Add *from_coords* parameter to the :class:`!PhotoImage` methods
  :meth:`!copy`, :meth:`!zoom` and :meth:`!subsample`.
  Add *zoom* and *subsample* parameters to the :class:`!PhotoImage` method
  :meth:`!copy`.
  (Contributed by Serhiy Storchaka in :gh:`118225`.)

* Add the :class:`!PhotoImage` methods
  :meth:`!read` to read an image from a file
  and :meth:`!data` to get the image data.
  Add *background* and *grayscale* parameters to the :meth:`!write` method.
  (Contributed by Serhiy Storchaka in :gh:`118271`.)


traceback
---------

* Add the :attr:`~traceback.TracebackException.exc_type_str` attribute
  to :class:`~traceback.TracebackException`,
  which holds a string display of the *exc_type*.
  Deprecate the :attr:`~traceback.TracebackException.exc_type` attribute,
  which holds the type object itself.
  Add parameter *save_exc_type* (default ``True``)
  to indicate whether ``exc_type`` should be saved.
  (Contributed by Irit Katriel in :gh:`112332`.)

* Add a new *show_group* keyword-only parameter to
  :meth:`.TracebackException.format_exception_only` to (recursively) format
  the nested exceptions of a :exc:`BaseExceptionGroup` instance.
  (Contributed by Irit Katriel in :gh:`105292`.)


types
-----

* :class:`~types.SimpleNamespace` can now take a single positional argument
  to initialise the namespace's arguments.
  This argument must either be a mapping or an iterable of key-value pairs.
  (Contributed by Serhiy Storchaka in :gh:`108191`.)


typing
------

* :pep:`705`: Add :data:`~typing.ReadOnly`, a special typing construct
  to mark a :class:`~typing.TypedDict` item as read-only for type checkers.

* :pep:`742`: Add :data:`~typing.TypeIs`, a typing construct
  that can be used to instruct a type checker how to narrow a type.

* Add :data:`~typing.NoDefault`, a sentinel object used to represent
  the defaults of some parameters in the :mod:`typing` module.
  (Contributed by Jelle Zijlstra in :gh:`116126`.)

* Add :func:`~typing.get_protocol_members` to return the set of members
  defining a :class:`typing.Protocol`.
  (Contributed by Jelle Zijlstra in :gh:`104873`.)

* Add :func:`~typing.is_protocol` to check whether a class
  is a :class:`~typing.Protocol`.
  (Contributed by Jelle Zijlstra in :gh:`104873`.)

* :data:`~typing.ClassVar` can now be nested in :data:`~typing.Final`,
  and vice versa.
  (Contributed by Mehdi Drissi in :gh:`89547`.)


unicodedata
-----------

* Update the Unicode database to `version 15.1.0`__.
  (Contributed by James Gerity in :gh:`109559`.)

  __ https://www.unicode.org/versions/Unicode15.1.0/


venv
----

* Add support for creating source control management (SCM) ignore files
  in a virtual environment's directory.
  By default, Git is supported.
  This is implemented as opt-in via the API,
  which can be extended to support other SCMs
  (:class:`~venv.EnvBuilder` and :func:`~venv.create`),
  and opt-out via the CLI, using :option:`!--without-scm-ignore-files`.
  (Contributed by Brett Cannon in :gh:`108125`.)


warnings
--------

* :pep:`702`: The new :func:`warnings.deprecated` decorator provides a way to
  communicate deprecations to a :term:`static type checker`
  and to warn on usage of deprecated classes and functions.
  A :exc:`DeprecationWarning` may also be emitted when
  a decorated function or class is used at runtime.
  (Contributed by Jelle Zijlstra in :gh:`104003`.)


xml
---

* Allow controlling Expat >=2.6.0 reparse deferral (:cve:`2023-52425`)
  by adding five new methods:

  * :meth:`xml.etree.ElementTree.XMLParser.flush`
  * :meth:`xml.etree.ElementTree.XMLPullParser.flush`
  * :meth:`xml.parsers.expat.xmlparser.GetReparseDeferralEnabled`
  * :meth:`xml.parsers.expat.xmlparser.SetReparseDeferralEnabled`
  * :meth:`!xml.sax.expatreader.ExpatParser.flush`

  (Contributed by Sebastian Pipping in :gh:`115623`.)

* Add the :meth:`!close` method for the iterator returned by
  :func:`~xml.etree.ElementTree.iterparse` for explicit cleanup.
  (Contributed by Serhiy Storchaka in :gh:`69893`.)


zipimport
---------

* Add support for ZIP64_ format files.
  Everybody loves huge data, right?
  (Contributed by Tim Hatch in :gh:`94146`.)

  .. _ZIP64: https://en.wikipedia.org/wiki/Zip_(file_format)#ZIP64


Optimizations
=============

* Several standard library modules have had
  their import times significantly improved.
  For example, the import time of the :mod:`typing` module
  has been reduced by around a third by removing dependencies
  on :mod:`re` and :mod:`contextlib`.
  Other modules to enjoy import-time speedups include
  :mod:`email.utils`, :mod:`enum`, :mod:`functools`,
  :mod:`importlib.metadata`, and :mod:`threading`.
  (Contributed by Alex Waygood, Shantanu Jain, Adam Turner, Daniel Hollas,
  and others in :gh:`109653`.)

* :func:`textwrap.indent` is now around 30% faster than before for large input.
  (Contributed by Inada Naoki in :gh:`107369`.)

* The :mod:`subprocess` module now uses the :func:`~os.posix_spawn` function in
  more situations, including when *close_fds* is ``True`` (the default)
  on many modern platforms.
  This should provide a notable performance increase
  when launching processes on FreeBSD and Solaris.
  See the :ref:`subprocess <whatsnew313-subprocess>` section above for details.
  (Contributed by Jakub Kulik in :gh:`113117`.)


Removed Modules And APIs
========================


.. _whatsnew313-pep594:

PEP 594: Remove "dead batteries" from the standard library
----------------------------------------------------------

:pep:`594` proposed removing 19 modules from the standard library,
colloquially referred to as 'dead batteries' due to their
historic, obsolete, or insecure status.
All of the following modules were deprecated in Python 3.11,
and are now removed:

* :mod:`!aifc`

  * :pypi:`standard-aifc`:
    Use the redistribution of ``aifc`` library from PyPI.

* :mod:`!audioop`

  * :pypi:`audioop-lts`:
    Use ``audioop-lts`` library from PyPI.

* :mod:`!chunk`

  * :pypi:`standard-chunk`:
    Use the redistribution of ``chunk`` library from PyPI.

* :mod:`!cgi` and :mod:`!cgitb`

  * :class:`!cgi.FieldStorage` can typically be replaced with
    :func:`urllib.parse.parse_qsl` for ``GET`` and ``HEAD`` requests,
    and the :mod:`email.message` module or the :pypi:`multipart` library
    for ``POST`` and ``PUT`` requests.

  * :func:`!cgi.parse` can be replaced by calling
    :func:`urllib.parse.parse_qs` directly on the desired query string,
    unless the input is ``multipart/form-data``,
    which should be replaced as described below for :func:`!cgi.parse_multipart`.

  * :func:`!cgi.parse_header` can be replaced with the functionality
    in the :mod:`email` package, which implements the same MIME RFCs.
    For example, with :class:`email.message.EmailMessage`:

    .. code-block:: python

       from email.message import EmailMessage

       msg = EmailMessage()
       msg['content-type'] = 'application/json; charset="utf8"'
       main, params = msg.get_content_type(), msg['content-type'].params

  * :func:`!cgi.parse_multipart` can be replaced with the functionality
    in the :mod:`email` package, which implements the same MIME RFCs,
    or with the :pypi:`multipart` library.
    For example, the :class:`email.message.EmailMessage`
    and :class:`email.message.Message` classes.

  * :pypi:`standard-cgi`: and :pypi:`standard-cgitb`:
    Use the redistribution of ``cgi`` and ``cgitb`` library from PyPI.

* :mod:`!crypt` and the private :mod:`!_crypt` extension.
  The :mod:`hashlib` module may be an appropriate replacement
  when simply hashing a value is required.
  Otherwise, various third-party libraries on PyPI are available:

  * :pypi:`bcrypt`:
    Modern password hashing for your software and your servers.
  * :pypi:`argon2-cffi`:
    The secure Argon2 password hashing algorithm.
  * :pypi:`legacycrypt`:
    :mod:`ctypes` wrapper to the POSIX crypt library call
    and associated functionality.
  * :pypi:`crypt_r`:
    Fork of the :mod:`!crypt` module,
    wrapper to the :manpage:`crypt_r(3)` library call
    and associated functionality.
  * :pypi:`standard-crypt` and :pypi:`deprecated-crypt-alternative`:
    Use the redistribution of ``crypt`` and reimplementation of ``_crypt`` libraries from PyPI.

* :mod:`!imghdr`:
  The :pypi:`filetype`, :pypi:`puremagic`, or :pypi:`python-magic` libraries
  should be used as replacements.
  For example, the :func:`!puremagic.what` function can be used
  to replace the :func:`!imghdr.what` function for all file formats
  that were supported by :mod:`!imghdr`.

  * :pypi:`standard-imghdr`:
    Use the redistribution of ``imghdr`` library from PyPI.

* :mod:`!mailcap`:
  Use the :mod:`mimetypes` module instead.

  * :pypi:`standard-mailcap`:
    Use the redistribution of ``mailcap`` library from PyPI.

* :mod:`!msilib`
* :mod:`!nis`
* :mod:`!nntplib`:
  Use the :pypi:`pynntp` library from PyPI instead.

  * :pypi:`standard-nntplib`:
    Use the redistribution of ``nntplib`` library from PyPI.

* :mod:`!ossaudiodev`:
  For audio playback, use the :pypi:`pygame` library from PyPI instead.
* :mod:`!pipes`:
  Use the :mod:`subprocess` module instead.
  Use :func:`shlex.quote` to replace the undocumented ``pipes.quote``
  function.

  * :pypi:`standard-pipes`:
    Use the redistribution of ``pipes`` library from PyPI.

* :mod:`!sndhdr`:
  The :pypi:`filetype`, :pypi:`puremagic`, or :pypi:`python-magic` libraries
  should be used as replacements.

  * :pypi:`standard-sndhdr`:
    Use the redistribution of ``sndhdr`` library from PyPI.

* :mod:`!spwd`:
  Use the :pypi:`python-pam` library from PyPI instead.
* :mod:`!sunau`

  * :pypi:`standard-sunau`:
    Use the redistribution of ``sunau`` library from PyPI.

* :mod:`!telnetlib`,
  Use the :pypi:`telnetlib3` or :pypi:`Exscript` libraries from PyPI instead.

  * :pypi:`standard-telnetlib`:
    Use the redistribution of ``telnetlib`` library from PyPI.

* :mod:`!uu`:
  Use the :mod:`base64` module instead, as a modern alternative.

  * :pypi:`standard-uu`:
    Use the redistribution of ``uu`` library from PyPI.

* :mod:`!xdrlib`

  * :pypi:`standard-xdrlib`:
    Use the redistribution of ``xdrlib`` library from PyPI.

(Contributed by Victor Stinner and Zachary Ware in :gh:`104773` and :gh:`104780`.)


2to3
----

* Remove the :program:`2to3` program and the :mod:`!lib2to3` module,
  previously deprecated in Python 3.11.
  (Contributed by Victor Stinner in :gh:`104780`.)


builtins
--------

* Remove support for chained :class:`classmethod` descriptors
  (introduced in :gh:`63272`).
  These can no longer be used to wrap other descriptors,
  such as :class:`property`.
  The core design of this feature was flawed and led to several problems.
  To "pass-through" a :class:`classmethod`, consider using
  the :attr:`!__wrapped__` attribute that was added in Python 3.10.
  (Contributed by Raymond Hettinger in :gh:`89519`.)

* Raise a :exc:`RuntimeError` when calling :meth:`frame.clear`
  on a suspended frame (as has always been the case for an executing frame).
  (Contributed by Irit Katriel in :gh:`79932`.)


configparser
------------

* Remove the undocumented :class:`!LegacyInterpolation` class,
  deprecated in the docstring since Python 3.2,
  and at runtime since Python 3.11.
  (Contributed by Hugo van Kemenade in :gh:`104886`.)


importlib.metadata
------------------

* Remove deprecated subscript (:meth:`~object.__getitem__`) access for
  :ref:`EntryPoint <entry-points>` objects.
  (Contributed by Jason R. Coombs in :gh:`113175`.)


locale
------

* Remove the :func:`!locale.resetlocale` function, deprecated in Python 3.11.
  Use ``locale.setlocale(locale.LC_ALL, "")`` instead.
  (Contributed by Victor Stinner in :gh:`104783`.)


opcode
------

* Move :attr:`!opcode.ENABLE_SPECIALIZATION` to :attr:`!_opcode.ENABLE_SPECIALIZATION`.
  This field was added in 3.12, it was never documented,
  and is not intended for external use.
  (Contributed by Irit Katriel in :gh:`105481`.)

* Remove :func:`!opcode.is_pseudo`, :attr:`!opcode.MIN_PSEUDO_OPCODE`,
  and :attr:`!opcode.MAX_PSEUDO_OPCODE`, which were added in Python 3.12,
  but were neither documented nor exposed through :mod:`dis`,
  and were not intended to be used externally.
  (Contributed by Irit Katriel in :gh:`105481`.)


optparse
--------

* This module is no longer considered :term:`soft deprecated`.
  While :mod:`argparse` remains preferred for new projects that
  aren't using a third party command line argument processing
  library, there are aspects of the way ``argparse`` works that
  mean the lower level ``optparse`` module may provide a better
  foundation for *writing* argument processing libraries, and
  for implementing command line applications which adhere more
  strictly than ``argparse`` does to various Unix command line
  processing conventions that originate in the behaviour of the
  C :c:func:`!getopt` function .
  (Contributed by Alyssa Coghlan and Serhiy Storchaka in :gh:`126180`.)


pathlib
-------

* Remove the ability to use :class:`~pathlib.Path` objects as context managers.
  This functionality was deprecated and has had no effect since Python 3.9.
  (Contributed by Barney Gale in :gh:`83863`.)


re
--

* Remove the undocumented, deprecated, and broken
  :func:`!re.template` function and :attr:`!re.TEMPLATE` / :attr:`!re.T` flag.
  (Contributed by Serhiy Storchaka and Nikita Sobolev in :gh:`105687`.)


tkinter.tix
-----------

* Remove the :mod:`!tkinter.tix` module, deprecated in Python 3.6.
  The third-party Tix library which the module wrapped is unmaintained.
  (Contributed by Zachary Ware in :gh:`75552`.)


turtle
------

* Remove the :meth:`!RawTurtle.settiltangle` method,
  deprecated in the documentation since Python 3.1
  and at runtime since Python 3.11.
  (Contributed by Hugo van Kemenade in :gh:`104876`.)


typing
------

* Remove the :mod:`!typing.io` and :mod:`!typing.re` namespaces,
  deprecated since Python 3.8.
  The items in those namespaces can be imported directly
  from the :mod:`typing` module.
  (Contributed by Sebastian Rittau in :gh:`92871`.)

* Remove the keyword-argument method of creating
  :class:`~typing.TypedDict` types, deprecated in Python 3.11.
  (Contributed by Tomas Roun in :gh:`104786`.)


unittest
--------

* Remove the following :mod:`unittest` functions, deprecated in Python 3.11:

  * :func:`!unittest.findTestCases`
  * :func:`!unittest.makeSuite`
  * :func:`!unittest.getTestCaseNames`

  Use :class:`~unittest.TestLoader` methods instead:

  * :meth:`~unittest.TestLoader.loadTestsFromModule`
  * :meth:`~unittest.TestLoader.loadTestsFromTestCase`
  * :meth:`~unittest.TestLoader.getTestCaseNames`

  (Contributed by Hugo van Kemenade in :gh:`104835`.)

* Remove the untested and undocumented :meth:`!TestProgram.usageExit`
  method, deprecated in Python 3.11.
  (Contributed by Hugo van Kemenade in :gh:`104992`.)


urllib
------

* Remove the *cafile*, *capath*, and *cadefault* parameters of the
  :func:`urllib.request.urlopen` function, deprecated in Python 3.6.
  Use the *context* parameter instead with an :class:`~ssl.SSLContext` instance.
  The :meth:`ssl.SSLContext.load_cert_chain` function
  can be used to load specific certificates,
  or let :func:`ssl.create_default_context` select
  the operating system's trusted certificate authority (CA) certificates.
  (Contributed by Victor Stinner in :gh:`105382`.)


webbrowser
----------

* Remove the untested and undocumented :class:`!MacOSX` class,
  deprecated in Python 3.11.
  Use the :class:`!MacOSXOSAScript` class (introduced in Python 3.2) instead.
  (Contributed by Hugo van Kemenade in :gh:`104804`.)

* Remove the deprecated :attr:`!MacOSXOSAScript._name` attribute.
  Use the :attr:`MacOSXOSAScript.name <webbrowser.controller.name>`
  attribute instead.
  (Contributed by Nikita Sobolev in :gh:`105546`.)


New Deprecations
================

* :ref:`User-defined functions <user-defined-funcs>`:

  * Deprecate assignment to a function's :attr:`~function.__code__` attribute,
    where the new code object's type does not match the function's type.
    The different types are:
    plain function, generator, async generator, and coroutine.
    (Contributed by Irit Katriel in :gh:`81137`.)

* :mod:`array`:

  * Deprecate the ``'u'`` format code (:c:type:`wchar_t`) at runtime.
    This format code has been deprecated in documentation since Python 3.3,
    and will be removed in Python 3.16.
    Use the ``'w'`` format code (:c:type:`Py_UCS4`)
    for Unicode characters instead.
    (Contributed by Hugo van Kemenade in :gh:`80480`.)

* :mod:`ctypes`:

  * Deprecate the undocumented :func:`!SetPointerType` function,
    to be removed in Python 3.15.
    (Contributed by Victor Stinner in :gh:`105733`.)

  * :term:`Soft-deprecate <soft deprecated>` the :func:`~ctypes.ARRAY`
    function in favour of ``type * length`` multiplication.
    (Contributed by Victor Stinner in :gh:`105733`.)

* :mod:`decimal`:

  * Deprecate the non-standard and undocumented :class:`~decimal.Decimal`
    format specifier ``'N'``,
    which is only supported in the :mod:`!decimal` module's C implementation.
    (Contributed by Serhiy Storchaka in :gh:`89902`.)

* :mod:`dis`:

  * Deprecate the :attr:`!HAVE_ARGUMENT` separator.
    Check membership in :data:`~dis.hasarg` instead.
    (Contributed by Irit Katriel in :gh:`109319`.)

* :mod:`gettext`:

  * Deprecate non-integer numbers as arguments to functions and methods
    that consider plural forms in the :mod:`!gettext` module,
    even if no translation was found.
    (Contributed by Serhiy Storchaka in :gh:`88434`.)

* :mod:`glob`:

  * Deprecate the undocumented :func:`!glob0` and :func:`!glob1` functions.
    Use :func:`~glob.glob` and pass a :term:`path-like object` specifying
    the root directory to the *root_dir* parameter instead.
    (Contributed by Barney Gale in :gh:`117337`.)

* :mod:`http.server`:

  * Deprecate :class:`!CGIHTTPRequestHandler`,
    to be removed in Python 3.15.
    Process-based CGI HTTP servers have been out of favor for a very long time.
    This code was outdated, unmaintained, and rarely used.
    It has a high potential for both security and functionality bugs.
    (Contributed by Gregory P. Smith in :gh:`109096`.)

  * Deprecate the :option:`!--cgi` flag to
    the :program:`python -m http.server` command-line interface,
    to be removed in Python 3.15.
    (Contributed by Gregory P. Smith in :gh:`109096`.)

* :mod:`mimetypes`:

  * :term:`Soft-deprecate <soft deprecated>` file path arguments
    to :func:`~mimetypes.guess_type`,
    use :func:`~mimetypes.guess_file_type` instead.
    (Contributed by Serhiy Storchaka in :gh:`66543`.)

* :mod:`re`:

  * Deprecate passing the optional *maxsplit*, *count*, or *flags* arguments
    as positional arguments to the module-level
    :func:`~re.split`, :func:`~re.sub`, and :func:`~re.subn` functions.
    These parameters will become :ref:`keyword-only <keyword-only_parameter>`
    in a future version of Python.
    (Contributed by Serhiy Storchaka in :gh:`56166`.)

* :mod:`pathlib`:

  * Deprecate :meth:`!.PurePath.is_reserved`,
    to be removed in Python 3.15.
    Use :func:`os.path.isreserved` to detect reserved paths on Windows.
    (Contributed by Barney Gale in :gh:`88569`.)

* :mod:`platform`:

  * Deprecate :func:`!platform.java_ver`,
    to be removed in Python 3.15.
    This function is only useful for Jython support, has a confusing API,
    and is largely untested.
    (Contributed by Nikita Sobolev in :gh:`116349`.)

* :mod:`pydoc`:

  * Deprecate the undocumented :func:`!ispackage` function.
    (Contributed by Zackery Spytz in :gh:`64020`.)

* :mod:`sqlite3`:

  * Deprecate passing more than one positional argument to
    the :func:`~sqlite3.connect` function
    and the :class:`~sqlite3.Connection` constructor.
    The remaining parameters will become keyword-only in Python 3.15.
    (Contributed by Erlend E. Aasland in :gh:`107948`.)

  * Deprecate passing name, number of arguments, and the callable as keyword
    arguments for :meth:`.Connection.create_function`
    and :meth:`.Connection.create_aggregate`
    These parameters will become positional-only in Python 3.15.
    (Contributed by Erlend E. Aasland in :gh:`108278`.)

  * Deprecate passing the callback callable by keyword for the
    :meth:`~sqlite3.Connection.set_authorizer`,
    :meth:`~sqlite3.Connection.set_progress_handler`, and
    :meth:`~sqlite3.Connection.set_trace_callback`
    :class:`~sqlite3.Connection` methods.
    The callback callables will become positional-only in Python 3.15.
    (Contributed by Erlend E. Aasland in :gh:`108278`.)

* :mod:`sys`:

  * Deprecate the :func:`~sys._enablelegacywindowsfsencoding` function,
    to be removed in Python 3.16.
    Use the :envvar:`PYTHONLEGACYWINDOWSFSENCODING` environment variable instead.
    (Contributed by Inada Naoki in :gh:`73427`.)

* :mod:`tarfile`:

  * Deprecate the undocumented and unused :attr:`!TarFile.tarfile` attribute,
    to be removed in Python 3.16.
    (Contributed in :gh:`115256`.)

* :mod:`traceback`:

  * Deprecate the :attr:`.TracebackException.exc_type` attribute.
    Use :attr:`.TracebackException.exc_type_str` instead.
    (Contributed by Irit Katriel in :gh:`112332`.)

* :mod:`typing`:

  * Deprecate the undocumented keyword argument syntax for creating
    :class:`~typing.NamedTuple` classes
    (e.g. ``Point = NamedTuple("Point", x=int, y=int)``),
    to be removed in Python 3.15.
    Use the class-based syntax or the functional syntax instead.
    (Contributed by Alex Waygood in :gh:`105566`.)

  * Deprecate omitting the *fields* parameter when creating
    a :class:`~typing.NamedTuple` or :class:`typing.TypedDict` class,
    and deprecate passing ``None`` to the *fields* parameter of both types.
    Python 3.15 will require a valid sequence for the *fields* parameter.
    To create a NamedTuple class with zero fields,
    use ``class NT(NamedTuple): pass`` or ``NT = NamedTuple("NT", ())``.
    To create a TypedDict class with zero fields,
    use ``class TD(TypedDict): pass`` or ``TD = TypedDict("TD", {})``.
    (Contributed by Alex Waygood in :gh:`105566` and :gh:`105570`.)

  * Deprecate the :func:`typing.no_type_check_decorator` decorator function,
    to be removed in Python 3.15.
    After eight years in the :mod:`typing` module,
    it has yet to be supported by any major type checker.
    (Contributed by Alex Waygood in :gh:`106309`.)

  * Deprecate :data:`typing.AnyStr`.
    In Python 3.16, it will be removed from ``typing.__all__``,
    and a :exc:`DeprecationWarning` will be emitted at runtime
    when it is imported or accessed.
    It will be removed entirely in Python 3.18.
    Use the new :ref:`type parameter syntax <type-params>` instead.
    (Contributed by Michael The in :gh:`107116`.)

* :mod:`wave`:

  * Deprecate the ``getmark()``, ``setmark()`` and ``getmarkers()`` methods of
    the :class:`~wave.Wave_read` and :class:`~wave.Wave_write` classes,
    to be removed in Python 3.15.
    (Contributed by Victor Stinner in :gh:`105096`.)

.. Add deprecations above alphabetically, not here at the end.

.. include:: ../deprecations/pending-removal-in-3.14.rst

.. include:: ../deprecations/pending-removal-in-3.15.rst

.. include:: ../deprecations/pending-removal-in-3.16.rst

.. include:: ../deprecations/pending-removal-in-3.17.rst

.. include:: ../deprecations/pending-removal-in-3.19.rst

.. include:: ../deprecations/pending-removal-in-3.20.rst

.. include:: ../deprecations/pending-removal-in-future.rst

CPython Bytecode Changes
========================

* The oparg of :opcode:`YIELD_VALUE` is now
  ``1`` if the yield is part of a yield-from or await, and ``0`` otherwise.
  The oparg of :opcode:`RESUME` was changed to add a bit indicating
  if the except-depth is 1, which is needed to optimize closing of generators.
  (Contributed by Irit Katriel in :gh:`111354`.)


C API Changes
=============

New Features
------------

* Add the :ref:`PyMonitoring C API <c-api-monitoring>`
  for generating :pep:`669` monitoring events:

  * :c:type:`PyMonitoringState`
  * :c:func:`PyMonitoring_FirePyStartEvent`
  * :c:func:`PyMonitoring_FirePyResumeEvent`
  * :c:func:`PyMonitoring_FirePyReturnEvent`
  * :c:func:`PyMonitoring_FirePyYieldEvent`
  * :c:func:`PyMonitoring_FireCallEvent`
  * :c:func:`PyMonitoring_FireLineEvent`
  * :c:func:`PyMonitoring_FireJumpEvent`
  * ``PyMonitoring_FireBranchEvent``
  * :c:func:`PyMonitoring_FireCReturnEvent`
  * :c:func:`PyMonitoring_FirePyThrowEvent`
  * :c:func:`PyMonitoring_FireRaiseEvent`
  * :c:func:`PyMonitoring_FireCRaiseEvent`
  * :c:func:`PyMonitoring_FireReraiseEvent`
  * :c:func:`PyMonitoring_FireExceptionHandledEvent`
  * :c:func:`PyMonitoring_FirePyUnwindEvent`
  * :c:func:`PyMonitoring_FireStopIterationEvent`
  * :c:func:`PyMonitoring_EnterScope`
  * :c:func:`PyMonitoring_ExitScope`

  (Contributed by Irit Katriel in :gh:`111997`).

* Add :c:type:`PyMutex`, a lightweight mutex that occupies a single byte,
  and the new :c:func:`PyMutex_Lock` and :c:func:`PyMutex_Unlock` functions.
  :c:func:`!PyMutex_Lock` will release the :term:`GIL` (if currently held)
  if the operation needs to block.
  (Contributed by Sam Gross in :gh:`108724`.)

* Add the :ref:`PyTime C API <c-api-time>` to provide access to system clocks:

  * :c:type:`PyTime_t`.
  * :c:var:`PyTime_MIN` and :c:var:`PyTime_MAX`.
  * :c:func:`PyTime_AsSecondsDouble`.
  * :c:func:`PyTime_Monotonic`.
  * :c:func:`PyTime_MonotonicRaw`.
  * :c:func:`PyTime_PerfCounter`.
  * :c:func:`PyTime_PerfCounterRaw`.
  * :c:func:`PyTime_Time`.
  * :c:func:`PyTime_TimeRaw`.

  (Contributed by Victor Stinner and Petr Viktorin in :gh:`110850`.)

* Add the :c:func:`PyDict_ContainsString` function
  with the same behavior as :c:func:`PyDict_Contains`,
  but *key* is specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
  rather than a :c:expr:`PyObject*`.
  (Contributed by Victor Stinner in :gh:`108314`.)

* Add the :c:func:`PyDict_GetItemRef` and :c:func:`PyDict_GetItemStringRef`
  functions,
  which behave similarly to :c:func:`PyDict_GetItemWithError`,
  but return a  :term:`strong reference` instead of a :term:`borrowed reference`.
  Moreover, these functions return ``-1`` on error,
  removing the need to check :c:func:`!PyErr_Occurred`.
  (Contributed by Victor Stinner in :gh:`106004`.)

* Add the :c:func:`PyDict_SetDefaultRef` function,
  which behaves similarly to :c:func:`PyDict_SetDefault`,
  but returns a :term:`strong reference` instead of a :term:`borrowed reference`.
  This function returns ``-1`` on error,
  ``0`` on insertion,
  and ``1`` if the key was already present in the dictionary.
  (Contributed by Sam Gross in :gh:`112066`.)

* Add the :c:func:`PyDict_Pop` and :c:func:`PyDict_PopString` functions
  to remove a key from a dictionary and optionally return the removed value.
  This is similar to :meth:`dict.pop`,
  though there is no default value,
  and :exc:`KeyError` is not raised for missing keys.
  (Contributed by Stefan Behnel and Victor Stinner in :gh:`111262`.)

* Add the :c:func:`PyMapping_GetOptionalItem`
  and :c:func:`PyMapping_GetOptionalItemString` functions
  as alternatives to :c:func:`PyObject_GetItem`
  and :c:func:`PyMapping_GetItemString` respectively.
  The new functions do not raise :exc:`KeyError`
  if the requested key is missing from the mapping.
  These variants are more convenient and faster
  if a missing key should not be treated as a failure.
  (Contributed by Serhiy Storchaka in :gh:`106307`.)

* Add the :c:func:`PyObject_GetOptionalAttr`
  and :c:func:`PyObject_GetOptionalAttrString` functions
  as alternatives to  :c:func:`PyObject_GetAttr`
  and :c:func:`PyObject_GetAttrString` respectively.
  The new functions do not raise :exc:`AttributeError`
  if the requested attribute is not found on the object.
  These variants are more convenient and faster
  if the missing attribute should not be treated as a failure.
  (Contributed by Serhiy Storchaka in :gh:`106521`.)

* Add the :c:func:`PyErr_FormatUnraisable` function
  as an extension to :c:func:`PyErr_WriteUnraisable`
  that allows customizing the warning message.
  (Contributed by Serhiy Storchaka in :gh:`108082`.)

* Add new functions that return a :term:`strong reference` instead of
  a :term:`borrowed reference` for frame locals, globals, and builtins,
  as part of :ref:`PEP 667 <whatsnew313-locals-semantics>`:

  * :c:func:`PyEval_GetFrameBuiltins` replaces :c:func:`PyEval_GetBuiltins`
  * :c:func:`PyEval_GetFrameGlobals` replaces :c:func:`PyEval_GetGlobals`
  * :c:func:`PyEval_GetFrameLocals` replaces :c:func:`PyEval_GetLocals`

  (Contributed by Mark Shannon and Tian Gao in :gh:`74929`.)

* Add the :c:func:`Py_GetConstant` and :c:func:`Py_GetConstantBorrowed`
  functions to get :term:`strong <strong reference>`
  or :term:`borrowed <borrowed reference>` references to constants.
  For example, ``Py_GetConstant(Py_CONSTANT_ZERO)`` returns a strong reference
  to the constant zero.
  (Contributed by Victor  Stinner in :gh:`115754`.)

* Add the :c:func:`PyImport_AddModuleRef` function
  as a replacement for :c:func:`PyImport_AddModule`
  that returns a :term:`strong reference` instead of a :term:`borrowed reference`.
  (Contributed by Victor Stinner in :gh:`105922`.)

* Add the :c:func:`Py_IsFinalizing` function to check
  whether the main Python interpreter is
  :term:`shutting down <interpreter shutdown>`.
  (Contributed by Victor Stinner in :gh:`108014`.)

* Add the :c:func:`PyList_GetItemRef` function
  as a replacement for :c:func:`PyList_GetItem`
  that returns a :term:`strong reference` instead of a :term:`borrowed reference`.
  (Contributed by Sam Gross in :gh:`114329`.)

* Add the :c:func:`PyList_Extend` and :c:func:`PyList_Clear` functions,
  mirroring the Python :meth:`list.extend` and :meth:`list.clear` methods.
  (Contributed by Victor Stinner in :gh:`111138`.)

* Add the :c:func:`PyLong_AsInt` function.
  It behaves similarly to :c:func:`PyLong_AsLong`,
  but stores the result in a C :c:expr:`int` instead of a C :c:expr:`long`.
  (Contributed by Victor Stinner in :gh:`108014`.)

* Add the :c:func:`PyLong_AsNativeBytes`, :c:func:`PyLong_FromNativeBytes`,
  and :c:func:`PyLong_FromUnsignedNativeBytes` functions
  to simplify converting between native integer types
  and Python :class:`int` objects.
  (Contributed by Steve Dower in :gh:`111140`.)

* Add :c:func:`PyModule_Add` function, which is similar to
  :c:func:`PyModule_AddObjectRef` and :c:func:`PyModule_AddObject`,
  but always steals a reference to the value.
  (Contributed by Serhiy Storchaka in :gh:`86493`.)

* Add the :c:func:`PyObject_GenericHash` function
  that implements the default hashing function of a Python object.
  (Contributed by Serhiy Storchaka in :gh:`113024`.)

* Add the :c:func:`Py_HashPointer` function to hash a raw pointer.
  (Contributed by Victor Stinner in :gh:`111545`.)

* Add the :c:func:`PyObject_VisitManagedDict` and
  :c:func:`PyObject_ClearManagedDict` functions.
  which must be called by the traverse and clear functions of a type using
  the :c:macro:`Py_TPFLAGS_MANAGED_DICT` flag.
  The `pythoncapi-compat project`_ can be used to
  use these functions with Python 3.11 and 3.12.
  (Contributed by Victor Stinner in :gh:`107073`.)

* Add the :c:func:`PyRefTracer_SetTracer`
  and :c:func:`PyRefTracer_GetTracer` functions,
  which enable tracking object creation and destruction
  in the same way that the :mod:`tracemalloc` module does.
  (Contributed by Pablo Galindo in :gh:`93502`.)

* Add the :c:func:`PySys_AuditTuple` function
  as an alternative to :c:func:`PySys_Audit`
  that takes event arguments as a Python :class:`tuple` object.
  (Contributed by Victor Stinner in :gh:`85283`.)

* Add the :c:func:`PyThreadState_GetUnchecked()` function
  as an alternative to :c:func:`PyThreadState_Get()`
  that doesn't kill the process with a fatal error if it is ``NULL``.
  The caller is responsible for checking if the result is ``NULL``.
  (Contributed by Victor Stinner in :gh:`108867`.)

* Add the :c:func:`PyType_GetFullyQualifiedName` function
  to get the type's fully qualified name.
  The module name is prepended if :attr:`type.__module__` is
  a string and is not equal to either ``'builtins'`` or ``'__main__'``.
  (Contributed by Victor Stinner in :gh:`111696`.)

* Add the :c:func:`PyType_GetModuleName` function
  to get the type's module name. This is equivalent to getting the
  :attr:`type.__module__` attribute.
  (Contributed by Eric Snow and Victor Stinner in :gh:`111696`.)

* Add the :c:func:`PyUnicode_EqualToUTF8AndSize`
  and :c:func:`PyUnicode_EqualToUTF8` functions
  to compare a Unicode object with a :c:expr:`const char*` UTF-8 encoded string
  and ``1`` if they are equal or ``0`` otherwise.
  These functions do not raise exceptions.
  (Contributed by Serhiy Storchaka in :gh:`110289`.)

* Add the :c:func:`PyWeakref_GetRef` function
  as an alternative to  :c:func:`!PyWeakref_GetObject`
  that returns a :term:`strong reference`
  or ``NULL`` if the referent is no longer live.
  (Contributed by Victor Stinner in :gh:`105927`.)

* Add fixed variants of functions which silently ignore errors:

  * :c:func:`PyObject_HasAttrWithError` replaces :c:func:`PyObject_HasAttr`.
  * :c:func:`PyObject_HasAttrStringWithError`
    replaces :c:func:`PyObject_HasAttrString`.
  * :c:func:`PyMapping_HasKeyWithError` replaces :c:func:`PyMapping_HasKey`.
  * :c:func:`PyMapping_HasKeyStringWithError`
    replaces :c:func:`PyMapping_HasKeyString`.

  The new functions return ``-1`` for errors
  and the standard ``1`` for true and ``0`` for false.

  (Contributed by Serhiy Storchaka in :gh:`108511`.)


Changed C APIs
--------------

* The *keywords* parameter of :c:func:`PyArg_ParseTupleAndKeywords`
  and :c:func:`PyArg_VaParseTupleAndKeywords`
  now has type :c:expr:`char * const *` in C
  and :c:expr:`const char * const *` in C++,
  instead of :c:expr:`char **`.
  In C++, this makes these functions compatible with arguments
  of type :c:expr:`const char * const *`, :c:expr:`const char **`,
  or :c:expr:`char * const *` without an explicit type cast.
  In C, the functions only support arguments of type :c:expr:`char * const *`.
  This can be overridden with the :c:macro:`PY_CXX_CONST` macro.
  (Contributed by Serhiy Storchaka in :gh:`65210`.)

* :c:func:`PyArg_ParseTupleAndKeywords` now supports
  non-ASCII keyword parameter names.
  (Contributed by Serhiy Storchaka in :gh:`110815`.)

* The :c:func:`!PyCode_GetFirstFree` function is now unstable API
  and is now named :c:func:`PyUnstable_Code_GetFirstFree`.
  (Contributed by Bogdan Romanyuk in :gh:`115781`.)

* The :c:func:`PyDict_GetItem`, :c:func:`PyDict_GetItemString`,
  :c:func:`PyMapping_HasKey`, :c:func:`PyMapping_HasKeyString`,
  :c:func:`PyObject_HasAttr`, :c:func:`PyObject_HasAttrString`,
  and :c:func:`PySys_GetObject` functions,
  each of which clears all errors which occurred when calling them
  now reports these errors using :func:`sys.unraisablehook`.
  You may replace them with other functions as recommended in the documentation.
  (Contributed by Serhiy Storchaka in :gh:`106672`.)

* Add support for the ``%T``, ``%#T``, ``%N`` and ``%#N`` formats
  to :c:func:`PyUnicode_FromFormat`:

  * ``%T``: Get the fully qualified name of an object type
  * ``%#T``: As above, but use a colon as the separator
  * ``%N``: Get the fully qualified name of a type
  * ``%#N``: As above, but use a colon as the separator

  See :pep:`737` for more information.
  (Contributed by Victor Stinner in :gh:`111696`.)

* You no longer have to define the ``PY_SSIZE_T_CLEAN`` macro before
  including :file:`Python.h` when using ``#`` formats in
  :ref:`format codes <arg-parsing-string-and-buffers>`.
  APIs accepting the format codes always use ``Py_ssize_t`` for ``#`` formats.
  (Contributed by Inada Naoki in :gh:`104922`.)

* If Python is built in :ref:`debug mode <debug-build>`
  or :option:`with assertions <--with-assertions>`,
  :c:func:`PyTuple_SET_ITEM` and :c:func:`PyList_SET_ITEM`
  now check the index argument with an assertion.
  (Contributed by Victor Stinner in :gh:`106168`.)


Limited C API Changes
---------------------

* The following functions are now included in the Limited C API:

  * :c:func:`PyMem_RawMalloc`
  * :c:func:`PyMem_RawCalloc`
  * :c:func:`PyMem_RawRealloc`
  * :c:func:`PyMem_RawFree`
  * :c:func:`PySys_Audit`
  * :c:func:`PySys_AuditTuple`
  * :c:func:`PyType_GetModuleByDef`

  (Contributed by Victor Stinner in :gh:`85283`, :gh:`85283`, and :gh:`116936`.)

* Python built with :option:`--with-trace-refs` (tracing references)
  now supports the :ref:`Limited API <limited-c-api>`.
  (Contributed by Victor Stinner in :gh:`108634`.)


Removed C APIs
--------------

* Remove several functions, macros, variables, etc
  with names prefixed by ``_Py`` or ``_PY`` (which are considered private).
  If your project is affected  by one of these removals
  and you believe that the removed API should remain available,
  please :ref:`open a new issue <using-the-tracker>` to request a public C API
  and add ``cc: @vstinner`` to the issue to notify Victor Stinner.
  (Contributed by Victor Stinner in :gh:`106320`.)

* Remove old buffer protocols deprecated in Python 3.0.
  Use :ref:`bufferobjects` instead.

  * :c:func:`!PyObject_CheckReadBuffer`:
    Use :c:func:`PyObject_CheckBuffer` to test
    whether the object supports the buffer protocol.
    Note that :c:func:`PyObject_CheckBuffer` doesn't guarantee
    that :c:func:`PyObject_GetBuffer` will succeed.
    To test if the object is actually readable,
    see the next example of :c:func:`PyObject_GetBuffer`.

  * :c:func:`!PyObject_AsCharBuffer`, :c:func:`!PyObject_AsReadBuffer`:
    Use :c:func:`PyObject_GetBuffer` and :c:func:`PyBuffer_Release` instead:

    .. code-block:: c

       Py_buffer view;
       if (PyObject_GetBuffer(obj, &view, PyBUF_SIMPLE) < 0) {
           return NULL;
       }
       // Use `view.buf` and `view.len` to read from the buffer.
       // You may need to cast buf as `(const char*)view.buf`.
       PyBuffer_Release(&view);

  * :c:func:`!PyObject_AsWriteBuffer`:
    Use :c:func:`PyObject_GetBuffer` and :c:func:`PyBuffer_Release` instead:

    .. code-block:: c

       Py_buffer view;
       if (PyObject_GetBuffer(obj, &view, PyBUF_WRITABLE) < 0) {
           return NULL;
       }
       // Use `view.buf` and `view.len` to write to the buffer.
       PyBuffer_Release(&view);

  (Contributed by Inada Naoki in :gh:`85275`.)

* Remove various functions deprecated in Python 3.9:

  * :c:func:`!PyEval_CallObject`, :c:func:`!PyEval_CallObjectWithKeywords`:
    Use :c:func:`PyObject_CallNoArgs` or :c:func:`PyObject_Call` instead.

    .. warning::

       In :c:func:`PyObject_Call`, positional arguments must be a :class:`tuple`
       and must not be ``NULL``,
       and keyword arguments must be a :class:`dict` or ``NULL``,
       whereas the removed functions checked argument types
       and accepted ``NULL`` positional and keyword arguments.
       To replace ``PyEval_CallObjectWithKeywords(func, NULL, kwargs)`` with
       :c:func:`PyObject_Call`,
       pass an empty tuple as positional arguments using
       :c:func:`PyTuple_New(0) <PyTuple_New>`.

  * :c:func:`!PyEval_CallFunction`:
    Use :c:func:`PyObject_CallFunction` instead.
  * :c:func:`!PyEval_CallMethod`:
    Use :c:func:`PyObject_CallMethod` instead.
  * :c:func:`!PyCFunction_Call`:
    Use :c:func:`PyObject_Call` instead.

  (Contributed by Victor Stinner in :gh:`105107`.)

* Remove the following old functions to configure the Python initialization,
  deprecated in Python 3.11:

  * :c:func:`!PySys_AddWarnOptionUnicode`:
    Use :c:member:`PyConfig.warnoptions` instead.
  * :c:func:`!PySys_AddWarnOption`:
    Use :c:member:`PyConfig.warnoptions` instead.
  * :c:func:`!PySys_AddXOption`:
    Use :c:member:`PyConfig.xoptions` instead.
  * :c:func:`!PySys_HasWarnOptions`:
    Use :c:member:`PyConfig.xoptions` instead.
  * :c:func:`!PySys_SetPath`:
    Set :c:member:`PyConfig.module_search_paths` instead.
  * :c:func:`!Py_SetPath`:
    Set :c:member:`PyConfig.module_search_paths` instead.
  * :c:func:`!Py_SetStandardStreamEncoding`:
    Set :c:member:`PyConfig.stdio_encoding` instead,
    and set also maybe :c:member:`PyConfig.legacy_windows_stdio` (on Windows).
  * :c:func:`!_Py_SetProgramFullPath`:
    Set :c:member:`PyConfig.executable` instead.

  Use the new :c:type:`PyConfig` API of the :ref:`Python Initialization
  Configuration <init-config>` instead (:pep:`587`), added to Python 3.8.
  (Contributed by Victor Stinner in :gh:`105145`.)

* Remove :c:func:`!PyEval_AcquireLock` and :c:func:`!PyEval_ReleaseLock` functions,
  deprecated in Python 3.2.
  They didn't update the current thread state.
  They can be replaced with:

  * :c:func:`PyEval_SaveThread` and :c:func:`PyEval_RestoreThread`;
  * low-level :c:func:`PyEval_AcquireThread` and :c:func:`PyEval_RestoreThread`;
  * or :c:func:`PyGILState_Ensure` and :c:func:`PyGILState_Release`.

  (Contributed by Victor Stinner in :gh:`105182`.)

* Remove the :c:func:`!PyEval_ThreadsInitialized` function,
  deprecated in Python 3.9.
  Since Python 3.7, :c:func:`!Py_Initialize` always creates the GIL:
  calling :c:func:`!PyEval_InitThreads` does nothing and
  :c:func:`!PyEval_ThreadsInitialized` always returns non-zero.
  (Contributed by Victor Stinner in :gh:`105182`.)

* Remove the :c:func:`!_PyInterpreterState_Get` alias to
  :c:func:`PyInterpreterState_Get()`
  which was kept for backward compatibility with Python 3.8.
  The `pythoncapi-compat project`_ can be used to get
  :c:func:`PyInterpreterState_Get()` on Python 3.8 and older.
  (Contributed by Victor Stinner in :gh:`106320`.)

* Remove the private :c:func:`!_PyObject_FastCall` function:
  use :c:func:`!PyObject_Vectorcall` which is available since Python 3.8
  (:pep:`590`).
  (Contributed by Victor Stinner in :gh:`106023`.)

* Remove the ``cpython/pytime.h`` header file,
  which only contained private functions.
  (Contributed by Victor Stinner in :gh:`106316`.)

* Remove the undocumented ``PY_TIMEOUT_MAX`` constant from the limited C API.
  (Contributed by Victor Stinner in :gh:`110014`.)

* Remove the old trashcan macros ``Py_TRASHCAN_SAFE_BEGIN``
  and ``Py_TRASHCAN_SAFE_END``.
  Replace both with the new macros ``Py_TRASHCAN_BEGIN``
  and ``Py_TRASHCAN_END``.
  (Contributed by Irit Katriel in :gh:`105111`.)

Deprecated C APIs
-----------------

* Deprecate old Python initialization functions:

  * :c:func:`!PySys_ResetWarnOptions`:
    Clear :data:`sys.warnoptions` and :data:`!warnings.filters` instead.
  * :c:func:`!Py_GetExecPrefix`:
    Get :data:`sys.exec_prefix` instead.
  * :c:func:`!Py_GetPath`:
    Get :data:`sys.path` instead.
  * :c:func:`!Py_GetPrefix`:
    Get :data:`sys.prefix` instead.
  * :c:func:`!Py_GetProgramFullPath`:
    Get :data:`sys.executable` instead.
  * :c:func:`!Py_GetProgramName`:
    Get :data:`sys.executable` instead.
  * :c:func:`!Py_GetPythonHome`:
    Get :c:member:`PyConfig.home`
    or the :envvar:`PYTHONHOME` environment variable instead.

  (Contributed by Victor Stinner in :gh:`105145`.)

* :term:`Soft deprecate <soft deprecated>` the
  :c:func:`PyEval_GetBuiltins`, :c:func:`PyEval_GetGlobals`,
  and :c:func:`PyEval_GetLocals` functions,
  which return a :term:`borrowed reference`.
  (Soft deprecated as part of :pep:`667`.)

* Deprecate the :c:func:`!PyImport_ImportModuleNoBlock` function,
  which is just an alias to :c:func:`PyImport_ImportModule` since Python 3.3.
  (Contributed by Victor Stinner in :gh:`105396`.)

* :term:`Soft deprecate <soft deprecated>` the
  :c:func:`PyModule_AddObject` function.
  It should be replaced with :c:func:`PyModule_Add`
  or :c:func:`PyModule_AddObjectRef`.
  (Contributed by Serhiy Storchaka in :gh:`86493`.)

* Deprecate the old ``Py_UNICODE`` and ``PY_UNICODE_TYPE`` types
  and the :c:macro:`!Py_UNICODE_WIDE` define.
  Use the :c:type:`wchar_t` type directly instead.
  Since Python 3.3, ``Py_UNICODE`` and ``PY_UNICODE_TYPE``
  are just aliases to :c:type:`!wchar_t`.
  (Contributed by Victor Stinner in :gh:`105156`.)

* Deprecate the :c:func:`!PyWeakref_GetObject` and
  :c:func:`!PyWeakref_GET_OBJECT` functions,
  which return a :term:`borrowed reference`.
  Replace them with the new :c:func:`PyWeakref_GetRef` function,
  which returns a :term:`strong reference`.
  The `pythoncapi-compat project`_ can be used to get
  :c:func:`PyWeakref_GetRef` on Python 3.12 and older.
  (Contributed by Victor Stinner in :gh:`105927`.)

.. Add deprecations above alphabetically, not here at the end.

.. include:: ../deprecations/c-api-pending-removal-in-3.14.rst

.. include:: ../deprecations/c-api-pending-removal-in-3.15.rst

.. include:: ../deprecations/c-api-pending-removal-in-3.16.rst

.. include:: ../deprecations/c-api-pending-removal-in-3.18.rst

.. include:: ../deprecations/c-api-pending-removal-in-future.rst

.. _pythoncapi-compat project: https://github.com/python/pythoncapi-compat/

Build Changes
=============

* ``arm64-apple-ios`` and ``arm64-apple-ios-simulator`` are both
  now :pep:`11` tier 3 platforms.
  (:ref:`PEP 730 <whatsnew313-platform-support>` written
  and implementation contributed by Russell Keith-Magee in :gh:`114099`.)

* ``aarch64-linux-android`` and ``x86_64-linux-android`` are both
  now :pep:`11` tier 3 platforms.
  (:ref:`PEP 738 <whatsnew313-platform-support>` written
  and implementation contributed by Malcolm Smith in :gh:`116622`.)

* ``wasm32-wasi`` is now a :pep:`11` tier 2 platform.
  (Contributed by Brett Cannon in :gh:`115192`.)

* ``wasm32-emscripten`` is no longer a :pep:`11` supported platform.
  (Contributed by Brett Cannon in :gh:`115192`.)

* Building CPython now requires a compiler with support for the C11 atomic
  library, GCC built-in atomic functions, or MSVC interlocked intrinsics.

* Autoconf 2.71 and aclocal 1.16.5 are now required to regenerate
  the :file:`configure` script.
  (Contributed by Christian Heimes in :gh:`89886` and by Victor Stinner in :gh:`112090`.)

* SQLite 3.15.2 or newer is required to build
  the :mod:`sqlite3` extension module.
  (Contributed by Erlend Aasland in :gh:`105875`.)

* CPython now bundles the `mimalloc library`_ by default.
  It is licensed under the MIT license;
  see :ref:`mimalloc license <mimalloc-license>`.
  The bundled mimalloc has custom changes, see :gh:`113141` for details.
  (Contributed by Dino Viehland in :gh:`109914`.)

  .. _mimalloc library: https://github.com/microsoft/mimalloc/

* The :file:`configure` option :option:`--with-system-libmpdec`
  now defaults to ``yes``.
  The bundled copy of ``libmpdec`` will be removed in Python 3.16.

* Python built with :file:`configure` :option:`--with-trace-refs`
  (tracing references) is now ABI compatible with the Python release build
  and :ref:`debug build <debug-build>`.
  (Contributed by Victor Stinner in :gh:`108634`.)

* On POSIX systems, the pkg-config (``.pc``) filenames now include the ABI
  flags.  For example, the free-threaded build generates ``python-3.13t.pc``
  and the debug build generates ``python-3.13d.pc``.

* The ``errno``, ``fcntl``, ``grp``, ``md5``, ``pwd``, ``resource``,
  ``termios``, ``winsound``,
  ``_ctypes_test``, ``_multiprocessing.posixshmem``, ``_scproxy``, ``_stat``,
  ``_statistics``, ``_testconsole``, ``_testimportmultiple`` and ``_uuid``
  C extensions are now built with the :ref:`limited C API <limited-c-api>`.
  (Contributed by Victor Stinner in :gh:`85283`.)


Porting to Python 3.13
======================

This section lists previously described changes and other bugfixes
that may require changes to your code.

Changes in the Python API
-------------------------

.. _pep667-porting-notes-py:

* :ref:`PEP 667 <whatsnew313-locals-semantics>` introduces several changes
  to the semantics of :func:`locals` and :attr:`f_locals <frame.f_locals>`:

  * Calling :func:`locals` in an :term:`optimized scope` now produces an
    independent snapshot on each call, and hence no longer implicitly updates
    previously returned references. Obtaining the legacy CPython behavior now
    requires explicit calls to update the initially returned dictionary with the
    results of subsequent calls to :func:`!locals`. Code execution functions that
    implicitly target :func:`!locals` (such as ``exec`` and ``eval``) must be
    passed an explicit namespace to access their results in an optimized scope.
    (Changed as part of :pep:`667`.)

  * Calling :func:`locals` from a comprehension at module or class scope
    (including via ``exec`` or ``eval``) once more behaves as if the comprehension
    were running as an independent nested function (i.e. the local variables from
    the containing scope are not included). In Python 3.12, this had changed
    to include the local variables from the containing scope when implementing
    :pep:`709`. (Changed as part of :pep:`667`.)

  * Accessing :attr:`FrameType.f_locals <frame.f_locals>` in an
    :term:`optimized scope` now returns a write-through proxy rather than a
    snapshot that gets updated at ill-specified times. If a snapshot is desired,
    it must be created explicitly with ``dict`` or the proxy's ``.copy()`` method.
    (Changed as part of :pep:`667`.)

* :class:`functools.partial` now emits a :exc:`FutureWarning`
  when used as a method.
  The behavior will change in future Python versions.
  Wrap it in :func:`staticmethod` if you want to preserve the old behavior.
  (Contributed by Serhiy Storchaka in :gh:`121027`.)

* An :exc:`OSError` is now raised by :func:`getpass.getuser`
  for any failure to retrieve a username,
  instead of :exc:`ImportError` on non-Unix platforms
  or :exc:`KeyError` on Unix platforms where the password database is empty.

* The value of the :attr:`!mode` attribute of :class:`gzip.GzipFile`
  is now a string (``'rb'`` or ``'wb'``) instead of an integer (``1`` or ``2``).
  The value of the :attr:`!mode` attribute of the readable file-like object
  returned by :meth:`zipfile.ZipFile.open` is now ``'rb'`` instead of ``'r'``.
  (Contributed by Serhiy Storchaka in :gh:`115961`.)

* :class:`mailbox.Maildir` now ignores files with a leading dot (``.``).
  (Contributed by Zackery Spytz in :gh:`65559`.)

* :meth:`pathlib.Path.glob` and :meth:`~pathlib.Path.rglob` now return both
  files and directories if a pattern that ends with "``**``" is given,
  rather than directories only.
  Add a trailing slash to keep the previous behavior and only match directories.

* The :mod:`threading` module now expects the :mod:`!_thread` module
  to have an :func:`!_is_main_interpreter` function.
  This function takes no arguments and returns ``True``
  if the current interpreter is the main interpreter.

  Any library or application that provides a custom :mod:`!_thread` module
  must provide :func:`!_is_main_interpreter`,
  just like the module's other "private" attributes.
  (:gh:`112826`.)


Changes in the C API
--------------------

* ``Python.h`` no longer includes the ``<ieeefp.h>`` standard header. It was
  included for the :c:func:`!finite` function which is now provided by the
  ``<math.h>`` header. It should now be included explicitly if needed. Remove
  also the ``HAVE_IEEEFP_H`` macro.
  (Contributed by Victor Stinner in :gh:`108765`.)

* ``Python.h`` no longer includes these standard header files: ``<time.h>``,
  ``<sys/select.h>`` and ``<sys/time.h>``. If needed, they should now be
  included explicitly. For example, ``<time.h>`` provides the :c:func:`!clock` and
  :c:func:`!gmtime` functions, ``<sys/select.h>`` provides the :c:func:`!select`
  function, and ``<sys/time.h>`` provides the :c:func:`!futimes`, :c:func:`!gettimeofday`
  and :c:func:`!setitimer` functions.
  (Contributed by Victor Stinner in :gh:`108765`.)

* On Windows, ``Python.h`` no longer includes the ``<stddef.h>`` standard
  header file. If needed, it should now be included explicitly. For example, it
  provides :c:func:`!offsetof` function, and ``size_t`` and ``ptrdiff_t`` types.
  Including ``<stddef.h>`` explicitly was already needed by all other
  platforms, the ``HAVE_STDDEF_H`` macro is only defined on Windows.
  (Contributed by Victor Stinner in :gh:`108765`.)

* If the :c:macro:`Py_LIMITED_API` macro is defined, :c:macro:`!Py_BUILD_CORE`,
  :c:macro:`!Py_BUILD_CORE_BUILTIN` and :c:macro:`!Py_BUILD_CORE_MODULE` macros
  are now undefined by ``<Python.h>``.
  (Contributed by Victor Stinner in :gh:`85283`.)

* The old trashcan macros ``Py_TRASHCAN_SAFE_BEGIN`` and ``Py_TRASHCAN_SAFE_END``
  were removed. They should be replaced by the new macros ``Py_TRASHCAN_BEGIN``
  and ``Py_TRASHCAN_END``.

  A ``tp_dealloc`` function that has the old macros, such as::

    static void
    mytype_dealloc(mytype *p)
    {
        PyObject_GC_UnTrack(p);
        Py_TRASHCAN_SAFE_BEGIN(p);
        ...
        Py_TRASHCAN_SAFE_END
    }

  should migrate to the new macros as follows::

    static void
    mytype_dealloc(mytype *p)
    {
        PyObject_GC_UnTrack(p);
        Py_TRASHCAN_BEGIN(p, mytype_dealloc)
        ...
        Py_TRASHCAN_END
    }

  Note that ``Py_TRASHCAN_BEGIN`` has a second argument which
  should be the deallocation function it is in. The new macros were
  added in Python 3.8 and the old macros were deprecated in Python 3.11.
  (Contributed by Irit Katriel in :gh:`105111`.)

.. _pep667-porting-notes-c:

* :ref:`PEP 667 <whatsnew313-locals-semantics>` introduces several changes
  to frame-related functions:

  * The effects of mutating the dictionary returned from
    :c:func:`PyEval_GetLocals` in an :term:`optimized scope` have changed.
    New dict entries added this way will now *only* be visible to
    subsequent :c:func:`PyEval_GetLocals` calls in that frame,
    as :c:func:`PyFrame_GetLocals`, :func:`locals`,
    and :attr:`FrameType.f_locals <frame.f_locals>` no longer access
    the same underlying cached dictionary.
    Changes made to entries for actual variable names and names added via
    the write-through proxy interfaces will be overwritten on subsequent calls
    to :c:func:`PyEval_GetLocals` in that frame.
    The recommended code update depends on how the function was being used,
    so refer to the deprecation notice on the function for details.

  * Calling :c:func:`PyFrame_GetLocals` in an :term:`optimized scope`
    now returns a write-through proxy rather than a snapshot
    that gets updated at ill-specified times.
    If a snapshot is desired, it must be created explicitly
    (e.g. with :c:func:`PyDict_Copy`),
    or by calling the new :c:func:`PyEval_GetFrameLocals` API.

  * :c:func:`!PyFrame_FastToLocals` and :c:func:`!PyFrame_FastToLocalsWithError`
    no longer have any effect.
    Calling these functions has been redundant since Python 3.11,
    when :c:func:`PyFrame_GetLocals` was first introduced.

  * :c:func:`!PyFrame_LocalsToFast` no longer has any effect.
    Calling this function is redundant now that :c:func:`PyFrame_GetLocals`
    returns a write-through proxy for :term:`optimized scopes <optimized scope>`.

* Python 3.13 removed many private functions. Some of them can be replaced using these
  alternatives:

  * ``_PyDict_Pop()``: :c:func:`PyDict_Pop` or :c:func:`PyDict_PopString`;
  * ``_PyDict_GetItemWithError()``: :c:func:`PyDict_GetItemRef`;
  * ``_PyErr_WriteUnraisableMsg()``:  :c:func:`PyErr_FormatUnraisable`;
  * ``_PyEval_SetTrace()``: :c:func:`PyEval_SetTrace` or :c:func:`PyEval_SetTraceAllThreads`;
  * ``_PyList_Extend()``: :c:func:`PyList_Extend`;
  * ``_PyLong_AsInt()``: :c:func:`PyLong_AsInt`;
  * ``_PyMem_RawStrdup()``: ``strdup()``;
  * ``_PyMem_Strdup()``: ``strdup()``;
  * ``_PyObject_ClearManagedDict()``: :c:func:`PyObject_ClearManagedDict`;
  * ``_PyObject_VisitManagedDict()``: :c:func:`PyObject_VisitManagedDict`;
  * ``_PyThreadState_UncheckedGet()``: :c:func:`PyThreadState_GetUnchecked()`;
  * ``_PyTime_AsSecondsDouble()``: :c:func:`PyTime_AsSecondsDouble`;
  * ``_PyTime_GetMonotonicClock()``: :c:func:`PyTime_Monotonic` or :c:func:`PyTime_MonotonicRaw`;
  * ``_PyTime_GetPerfCounter()``: :c:func:`PyTime_PerfCounter` or :c:func:`PyTime_PerfCounterRaw`;
  * ``_PyTime_GetSystemClock()``: :c:func:`PyTime_Time` or :c:func:`PyTime_TimeRaw`;
  * ``_PyTime_MAX``: :c:var:`PyTime_MAX`;
  * ``_PyTime_MIN``: :c:var:`PyTime_MIN`;
  * ``_PyTime_t``: :c:type:`PyTime_t`;
  * ``_Py_HashPointer()``: :c:func:`Py_HashPointer`;
  * ``_Py_IsFinalizing()``: :c:func:`Py_IsFinalizing`.

  The `pythoncapi-compat project`_ can be used to get most of these new
  functions on Python 3.12 and older.

Regression Test Changes
=======================

* Python built with :file:`configure` :option:`--with-pydebug` now
  supports a :option:`-X presite=package.module <-X>` command-line
  option. If used, it specifies a module that should be imported early
  in the lifecycle of the interpreter, before ``site.py`` is executed.
  (Contributed by Łukasz Langa in :gh:`110769`.)
