path: root/Doc/whatsnew/3.12.rst

****************************
  What's New In Python 3.12
****************************

:Release: |release|
:Date: |today|

.. 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 3.12, compared to 3.11.

For full details, see the :ref:`changelog <changelog>`.

.. note::

   Prerelease users should be aware that this document is currently in draft
   form. It will be updated substantially as Python 3.12 moves towards release,
   so it's worth checking back even after reading earlier versions.


Summary -- Release highlights
=============================

.. This section singles out the most important changes in Python 3.12.
   Brevity is key.


.. PEP-sized items next.

Important deprecations, removals or restrictions:

* :pep:`623`, Remove wstr from Unicode


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

* Add :ref:`perf_profiling` through the new
  environment variable :envvar:`PYTHONPERFSUPPORT`,
  the new command-line option :option:`-X perf <-X>`,
  as well as the new :func:`sys.activate_stack_trampoline`,
  :func:`sys.deactivate_stack_trampoline`,
  and :func:`sys.is_stack_trampoline_active` APIs.
  (Design by Pablo Galindo. Contributed by Pablo Galindo and Christian Heimes
  with contributions from Gregory P. Smith [Google] and Mark Shannon
  in :gh:`96123`.)


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

* :class:`types.MappingProxyType` instances are now hashable if the underlying
  mapping is hashable.
  (Contributed by Serhiy Storchaka in :gh:`87995`.)

* :class:`memoryview` now supports the half-float type (the "e" format code).
  (Contributed by Dong-hee Na and Antoine Pitrou in :gh:`90751`.)

* The parser now raises :exc:`SyntaxError` when parsing source code containing
  null bytes. (Contributed by Pablo Galindo in :gh:`96670`.)

* :func:`ast.parse` now raises :exc:`SyntaxError` instead of :exc:`ValueError`
  when parsing source code containing null bytes. (Contributed by Pablo Galindo
  in :gh:`96670`.)

* The Garbage Collector now runs only on the eval breaker mechanism of the
  Python bytecode evaluation loop instead on object allocations. The GC can
  also run when :c:func:`PyErr_CheckSignals` is called so C extensions that
  need to run for a long time without executing any Python code also have a
  chance to execute the GC periodically. (Contributed by Pablo Galindo in
  :gh:`97922`.)

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

* None yet.


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

array
-----

* The :class:`array.array` class now supports subscripting, making it a
  :term:`generic type`. (Contributed by Jelle Zijlstra in :gh:`98658`.)

asyncio
-------

* On Linux, :mod:`asyncio` uses :class:`~asyncio.PidfdChildWatcher` by default
  if :func:`os.pidfd_open` is available and functional instead of
  :class:`~asyncio.ThreadedChildWatcher`.
  (Contributed by Kumar Aditya in :gh:`98024`.)

* The child watcher classes :class:`~asyncio.MultiLoopChildWatcher`,
  :class:`~asyncio.FastChildWatcher` and
  :class:`~asyncio.SafeChildWatcher` are deprecated and
  will be removed in Python 3.14. It is recommended to not manually
  configure a child watcher as the event loop now uses the best available
  child watcher for each platform (:class:`~asyncio.PidfdChildWatcher`
  if supported and :class:`~asyncio.ThreadedChildWatcher` otherwise).
  (Contributed by Kumar Aditya in :gh:`94597`.)

* :func:`asyncio.set_child_watcher`, :func:`asyncio.get_child_watcher`,
  :meth:`asyncio.AbstractEventLoopPolicy.set_child_watcher` and
  :meth:`asyncio.AbstractEventLoopPolicy.get_child_watcher` are deprecated
  and will be removed in Python 3.14.
  (Contributed by Kumar Aditya in :gh:`94597`.)

pathlib
-------

* Add :meth:`~pathlib.Path.walk` for walking the directory trees and generating
  all file or directory names within them, similar to :func:`os.walk`.
  (Contributed by Stanislav Zmiev in :gh:`90385`.)

* Add *walk_up* optional parameter to :meth:`pathlib.PurePath.relative_to`
  to allow the insertion of ``..`` entries in the result; this behavior is
  more consistent with :func:`os.path.relpath`.
  (Contributed by Domenico Ragusa in :issue:`40358`.)

dis
---

* Pseudo instruction opcodes (which are used by the compiler but
  do not appear in executable bytecode) are now exposed in the
  :mod:`dis` module.
  :data:`~dis.HAVE_ARGUMENT` is still relevant to real opcodes,
  but it is not useful for pseudo instructions. Use the new
  :data:`~dis.hasarg` collection instead.
  (Contributed by Irit Katriel in :gh:`94216`.)

os
--

* Add :data:`os.PIDFD_NONBLOCK` to open a file descriptor
  for a process with :func:`os.pidfd_open` in non-blocking mode.
  (Contributed by Kumar Aditya in :gh:`93312`.)

shutil
------

* :func:`shutil.make_archive` now passes the *root_dir* argument to custom
  archivers which support it.
  In this case it no longer temporarily changes the current working directory
  of the process to *root_dir* to perform archiving.
  (Contributed by Serhiy Storchaka in :gh:`74696`.)


sqlite3
-------

* Add a :ref:`command-line interface <sqlite3-cli>`.
  (Contributed by Erlend E. Aasland in :gh:`77617`.)

threading
---------

* Add :func:`threading.settrace_all_threads` and
  :func:`threading.setprofile_all_threads` that allow to set tracing and
  profiling functions in all running threads in addition to the calling one.
  (Contributed by Pablo Galindo in :gh:`93503`.)

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

* The Unicode database has been updated to version 15.0.0. (Contributed by
  Benjamin Peterson in :gh:`96734`).

tempfile
--------

The :class:`tempfile.NamedTemporaryFile` function has a new optional parameter
*delete_on_close* (Contributed by Evgeny Zorin in :gh:`58451`.)

sys
---

* Add :func:`sys.activate_stack_trampoline` and
  :func:`sys.deactivate_stack_trampoline` for activating and deactivating
  stack profiler trampolines,
  and :func:`sys.is_stack_trampoline_active` for querying if stack profiler
  trampolines are active.
  (Contributed by Pablo Galindo and Christian Heimes
  with contributions from Gregory P. Smith [Google] and Mark Shannon
  in :gh:`96123`.)


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

* Removed ``wstr`` and ``wstr_length`` members from Unicode objects.
  It reduces object size by 8 or 16 bytes on 64bit platform. (:pep:`623`)
  (Contributed by Inada Naoki in :gh:`92536`.)

* Added experimental support for using the BOLT binary optimizer in the build
  process, which improves performance by 1-5%.
  (Contributed by Kevin Modzelewski in :gh:`90536`.)

* Speed up the regular expression substitution (functions :func:`re.sub` and
  :func:`re.subn` and corresponding :class:`re.Pattern` methods) for
  replacement strings containing group references by 2--3 times.
  (Contributed by Serhiy Storchaka in :gh:`91524`.)


CPython bytecode changes
========================

* Removed the :opcode:`LOAD_METHOD` instruction. It has been merged into
  :opcode:`LOAD_ATTR`. :opcode:`LOAD_ATTR` will now behave like the old
  :opcode:`LOAD_METHOD` instruction if the low bit of its oparg is set.
  (Contributed by Ken Jin in :gh:`93429`.)


Demos and Tools
===============

* Remove the ``Tools/demo/`` directory which contained old demo scripts. A copy
  can be found in the `old-demos project
  <https://github.com/gvanrossum/old-demos>`_.
  (Contributed by Victor Stinner in :gh:`97681`.)

* Remove outdated example scripts of the ``Tools/scripts/`` directory.
  A copy can be found in the `old-demos project
  <https://github.com/gvanrossum/old-demos>`_.
  (Contributed by Victor Stinner in :gh:`97669`.)


Deprecated
==========

* :class:`typing.Hashable` and :class:`typing.Sized` aliases for :class:`collections.abc.Hashable`
  and :class:`collections.abc.Sized`. (:gh:`94309`.)

* The :mod:`sqlite3` :ref:`default adapters and converters
  <sqlite3-default-converters>` are now deprecated.
  Instead, use the :ref:`sqlite3-adapter-converter-recipes`
  and tailor them to your needs.
  (Contributed by Erlend E. Aasland in :gh:`90016`.)

* The 3-arg signatures (type, value, traceback) of :meth:`~coroutine.throw`,
  :meth:`~generator.throw` and :meth:`~agen.athrow` are deprecated and
  may be removed in a future version of Python. Use the single-arg versions
  of these functions instead. (Contributed by Ofey Chan in :gh:`89874`.)

* :exc:`DeprecationWarning` is now raised when ``__package__`` on a
  module differs from ``__spec__.parent`` (previously it was
  :exc:`ImportWarning`).
  (Contributed by Brett Cannon in :gh:`65961`.)


Pending Removal in Python 3.13
------------------------------

The following modules and APIs have been deprecated in earlier Python releases,
and will be removed in Python 3.13.

Modules (see :pep:`594`):

* :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`
* :mod:`xdrlib`

APIs:

* :class:`configparser.LegacyInterpolation` (:gh:`90765`)
* :func:`locale.getdefaultlocale` (:gh:`90817`)
* :meth:`turtle.RawTurtle.settiltangle` (:gh:`50096`)
* :func:`unittest.findTestCases` (:gh:`50096`)
* :func:`unittest.makeSuite` (:gh:`50096`)
* :func:`unittest.getTestCaseNames` (:gh:`50096`)
* :class:`webbrowser.MacOSX` (:gh:`86421`)

Pending Removal in Python 3.14
==============================

* Deprecated the following :mod:`importlib.abc` classes, scheduled for removal in
  Python 3.14:

  * :class:`importlib.abc.ResourceReader`
  * :class:`importlib.abc.Traversable`
  * :class:`importlib.abc.TraversableResources`

  Use :mod:`importlib.resources.abc` classes instead:

  * :class:`importlib.resources.abc.TraversableResources`
  * :class:`importlib.resources.abc.Traversable`
  * :class:`importlib.resources.abc.TraversableResources`

  (Contributed by Jason R. Coombs and Hugo van Kemenade in :gh:`93963`.)

* Creating :c:data:`immutable types <Py_TPFLAGS_IMMUTABLETYPE>` with mutable
  bases using the C API.

* ``__package__`` and ``__cached__`` will cease to be set or taken
  into consideration by the import system (:gh:`97879`).


Pending Removal in Future Versions
----------------------------------

The following APIs were deprecated in earlier Python versions and will be removed,
although there is currently no date scheduled for their removal.

* :class:`typing.Text` (:gh:`92332`)

* Currently Python accepts numeric literals immediately followed by keywords,
  for example ``0in x``, ``1or x``, ``0if 1else 2``.  It allows confusing
  and ambiguous expressions like ``[0x1for x in y]`` (which can be
  interpreted as ``[0x1 for x in y]`` or ``[0x1f or x in y]``).
  A syntax warning is raised if the numeric literal is
  immediately followed by one of keywords :keyword:`and`, :keyword:`else`,
  :keyword:`for`, :keyword:`if`, :keyword:`in`, :keyword:`is` and :keyword:`or`.
  In a future release it will be changed to a syntax error. (:gh:`87999`)


Removed
=======

* Removed many old deprecated :mod:`unittest` features:

  - A number of :class:`~unittest.TestCase` method aliases:

    ============================ =============================== ===============
       Deprecated alias           Method Name                     Deprecated in
    ============================ =============================== ===============
     ``failUnless``               :meth:`.assertTrue`             3.1
     ``failIf``                   :meth:`.assertFalse`            3.1
     ``failUnlessEqual``          :meth:`.assertEqual`            3.1
     ``failIfEqual``              :meth:`.assertNotEqual`         3.1
     ``failUnlessAlmostEqual``    :meth:`.assertAlmostEqual`      3.1
     ``failIfAlmostEqual``        :meth:`.assertNotAlmostEqual`   3.1
     ``failUnlessRaises``         :meth:`.assertRaises`           3.1
     ``assert_``                  :meth:`.assertTrue`             3.2
     ``assertEquals``             :meth:`.assertEqual`            3.2
     ``assertNotEquals``          :meth:`.assertNotEqual`         3.2
     ``assertAlmostEquals``       :meth:`.assertAlmostEqual`      3.2
     ``assertNotAlmostEquals``    :meth:`.assertNotAlmostEqual`   3.2
     ``assertRegexpMatches``      :meth:`.assertRegex`            3.2
     ``assertRaisesRegexp``       :meth:`.assertRaisesRegex`      3.2
     ``assertNotRegexpMatches``   :meth:`.assertNotRegex`         3.5
    ============================ =============================== ===============

    You can use https://github.com/isidentical/teyit to automatically modernise
    your unit tests.

  - Undocumented and broken :class:`~unittest.TestCase` method
    ``assertDictContainsSubset`` (deprecated in Python 3.2).

  - Undocumented :meth:`TestLoader.loadTestsFromModule
    <unittest.TestLoader.loadTestsFromModule>` parameter *use_load_tests*
    (deprecated and ignored since Python 3.2).

  - An alias of the :class:`~unittest.TextTestResult` class:
    ``_TextTestResult`` (deprecated in Python 3.2).

  (Contributed by Serhiy Storchaka in :issue:`45162`.)

* Several names deprecated in the :mod:`configparser` way back in 3.2 have
  been removed per :gh:`89336`:

  * :class:`configparser.ParsingError` no longer has a ``filename`` attribute
    or argument. Use the ``source`` attribute and argument instead.
  * :mod:`configparser` no longer has a ``SafeConfigParser`` class. Use the
    shorter :class:`~configparser.ConfigParser` name instead.
  * :class:`configparser.ConfigParser` no longer has a ``readfp`` method.
    Use :meth:`~configparser.ConfigParser.read_file` instead.

* The following undocumented :mod:`sqlite3` features, deprecated in Python
  3.10, are now removed:

  * ``sqlite3.enable_shared_cache()``
  * ``sqlite3.OptimizedUnicode``

  If a shared cache must be used, open the database in URI mode using the
  ``cache=shared`` query parameter.

  The ``sqlite3.OptimizedUnicode`` text factory has been an alias for
  :class:`str` since Python 3.3. Code that previously set the text factory to
  ``OptimizedUnicode`` can either use ``str`` explicitly, or rely on the
  default value which is also ``str``.

  (Contributed by Erlend E. Aasland in :gh:`92548`.)

* ``smtpd`` has been removed according to the schedule in :pep:`594`,
  having been deprecated in Python 3.4.7 and 3.5.4.
  Use aiosmtpd_ PyPI module or any other
  :mod:`asyncio`-based server instead.
  (Contributed by Oleg Iarygin in :gh:`93243`.)

.. _aiosmtpd: https://pypi.org/project/aiosmtpd/

* Remove ``io.OpenWrapper`` and ``_pyio.OpenWrapper``, deprecated in Python
  3.10: just use :func:`open` instead. The :func:`open` (:func:`io.open`)
  function is a built-in function. Since Python 3.10, :func:`_pyio.open` is
  also a static method.
  (Contributed by Victor Stinner in :gh:`94169`.)

* Remove the :func:`ssl.RAND_pseudo_bytes` function, deprecated in Python 3.6:
  use :func:`os.urandom` or :func:`ssl.RAND_bytes` instead.
  (Contributed by Victor Stinner in :gh:`94199`.)

* :mod:`gzip`: Remove the ``filename`` attribute of :class:`gzip.GzipFile`,
  deprecated since Python 2.6, use the :attr:`~gzip.GzipFile.name` attribute
  instead. In write mode, the ``filename`` attribute added ``'.gz'`` file
  extension if it was not present.
  (Contributed by Victor Stinner in :gh:`94196`.)

* Remove the :func:`ssl.match_hostname` function. The
  :func:`ssl.match_hostname` was deprecated in Python 3.7. OpenSSL performs
  hostname matching since Python 3.7, Python no longer uses the
  :func:`ssl.match_hostname` function.
  (Contributed by Victor Stinner in :gh:`94199`.)

* Remove the :func:`locale.format` function, deprecated in Python 3.7:
  use :func:`locale.format_string` instead.
  (Contributed by Victor Stinner in :gh:`94226`.)

* :mod:`hashlib`: Remove the pure Python implementation of
  :func:`hashlib.pbkdf2_hmac()`, deprecated in Python 3.10. Python 3.10 and
  newer requires OpenSSL 1.1.1 (:pep:`644`): this OpenSSL version provides
  a C implementation of :func:`~hashlib.pbkdf2_hmac()` which is faster.
  (Contributed by Victor Stinner in :gh:`94199`.)

* :mod:`xml.etree`: Remove the ``ElementTree.Element.copy()`` method of the
  pure Python implementation, deprecated in Python 3.10, use the
  :func:`copy.copy` function instead.  The C implementation of :mod:`xml.etree`
  has no ``copy()`` method, only a ``__copy__()`` method.
  (Contributed by Victor Stinner in :gh:`94383`.)

* :mod:`zipimport`: Remove ``find_loader()`` and ``find_module()`` methods,
  deprecated in Python 3.10: use the ``find_spec()`` method instead.  See
  :pep:`451` for the rationale.
  (Contributed by Victor Stinner in :gh:`94379`.)

* Remove the :func:`ssl.wrap_socket` function, deprecated in Python 3.7:
  instead, create a :class:`ssl.SSLContext` object and call its
  :class:`ssl.SSLContext.wrap_socket` method. Any package that still uses
  :func:`ssl.wrap_socket` is broken and insecure. The function neither sends a
  SNI TLS extension nor validates server hostname. Code is subject to `CWE-295
  <https://cwe.mitre.org/data/definitions/295.html>`_: Improper Certificate
  Validation.
  (Contributed by Victor Stinner in :gh:`94199`.)

* Many previously deprecated cleanups in :mod:`importlib` have now been
  completed:

  * References to, and support for ``module_repr()`` has been eradicated.


* ``importlib.util.set_package`` has been removed.
  (Contributed by Brett Cannon in :gh:`65961`.)

* Removed the ``suspicious`` rule from the documentation Makefile, and
  removed ``Doc/tools/rstlint.py``, both in favor of `sphinx-lint
  <https://github.com/sphinx-contrib/sphinx-lint>`_.
  (Contributed by Julien Palard in :gh:`98179`.)


Porting to Python 3.12
======================

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

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

* More strict rules are now applied for numerical group references and
  group names in regular expressions.
  Only sequence of ASCII digits is now accepted as a numerical reference.
  The group name in bytes patterns and replacement strings can now only
  contain ASCII letters and digits and underscore.
  (Contributed by Serhiy Storchaka in :gh:`91760`.)

* Removed randrange() functionality deprecated since Python 3.10.  Formerly,
  randrange(10.0) losslessly converted to randrange(10). Now, it raises a
  TypeError. Also, the exception raised for non-integral values such as
  randrange(10.5) or randrange('10') has been changed from ValueError to
  TypeError.  This also prevents bugs where ``randrange(1e25)`` would silently
  select from a larger range than ``randrange(10**25)``.
  (Originally suggested by Serhiy Storchaka gh-86388.)

* :class:`argparse.ArgumentParser` changed encoding and error handler
  for reading arguments from file (e.g. ``fromfile_prefix_chars`` option)
  from default text encoding (e.g. :func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>`)
  to :term:`filesystem encoding and error handler`.
  Argument files should be encoded in UTF-8 instead of ANSI Codepage on Windows.

* Removed the ``asyncore``-based ``smtpd`` module deprecated in Python 3.4.7
  and 3.5.4.  A recommended replacement is the
  :mod:`asyncio`-based aiosmtpd_ PyPI module.

* :func:`shlex.split`: Passing ``None`` for *s* argument now raises an
  exception, rather than reading :data:`sys.stdin`. The feature was deprecated
  in Python 3.9.
  (Contributed by Victor Stinner in :gh:`94352`.)

* The :mod:`os` module no longer accepts bytes-like paths, like
  :class:`bytearray` and :class:`memoryview` types: only the exact
  :class:`bytes` type is accepted for bytes strings.
  (Contributed by Victor Stinner in :gh:`98393`.)


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

* Python no longer uses ``setup.py`` to build shared C extension modules.
  Build parameters like headers and libraries are detected in ``configure``
  script. Extensions are built by ``Makefile``. Most extensions use
  ``pkg-config`` and fall back to manual detection.
  (Contributed by Christian Heimes in :gh:`93939`.)

* ``va_start()`` with two parameters, like ``va_start(args, format),``
  is now required to build Python.
  ``va_start()`` is no longer called with a single parameter.
  (Contributed by Kumar Aditya in :gh:`93207`.)

* CPython now uses the ThinLTO option as the default link time optimization policy
  if the Clang compiler accepts the flag.
  (Contributed by Dong-hee Na in :gh:`89536`.)


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

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

* Added the new limited C API function :c:func:`PyType_FromMetaclass`,
  which generalizes the existing :c:func:`PyType_FromModuleAndSpec` using
  an additional metaclass argument.
  (Contributed by Wenzel Jakob in :gh:`93012`.)

* API for creating objects that can be called using
  :ref:`the vectorcall protocol <vectorcall>` was added to the
  :ref:`Limited API <stable>`:

  * :const:`Py_TPFLAGS_HAVE_VECTORCALL`
  * :c:func:`PyVectorcall_NARGS`
  * :c:func:`PyVectorcall_Call`
  * :c:type:`vectorcallfunc`

  The :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag is now removed from a class
  when the class's :py:meth:`~object.__call__` method is reassigned.
  This makes vectorcall safe to use with mutable types (i.e. heap types
  without the :const:`immutable <Py_TPFLAGS_IMMUTABLETYPE>` flag).
  Mutable types that do not override :c:member:`~PyTypeObject.tp_call` now
  inherit the ``Py_TPFLAGS_HAVE_VECTORCALL`` flag.
  (Contributed by Petr Viktorin in :gh:`93274`.)

  The :const:`Py_TPFLAGS_MANAGED_DICT` and :const:`Py_TPFLAGS_MANAGED_WEAKREF`
  flags have been added. This allows extensions classes to support object
  ``__dict__`` and weakrefs with less bookkeeping,
  using less memory and with faster access.

* Added two new public functions,
  :c:func:`PyEval_SetProfileAllThreads` and
  :c:func:`PyEval_SetTraceAllThreads`, that allow to set tracing and profiling
  functions in all running threads in addition to the calling one. (Contributed
  by Pablo Galindo in :gh:`93503`.)

* Added new function :c:func:`PyFunction_SetVectorcall` to the C API
  which sets the vectorcall field of a given :c:type:`PyFunctionObject`.
  (Contributed by Andrew Frost in :gh:`92257`.)

* The C API now permits registering callbacks via :c:func:`PyDict_AddWatcher`,
  :c:func:`PyDict_AddWatch` and related APIs to be called whenever a dictionary
  is modified. This is intended for use by optimizing interpreters, JIT
  compilers, or debuggers.
  (Contributed by Carl Meyer in :gh:`91052`.)

* Added :c:func:`PyType_AddWatcher` and :c:func:`PyType_Watch` API to register
  callbacks to receive notification on changes to a type.
  (Contributed by Carl Meyer in :gh:`91051`.)


Porting to Python 3.12
----------------------

* Legacy Unicode APIs based on ``Py_UNICODE*`` representation has been removed.
  Please migrate to APIs based on UTF-8 or ``wchar_t*``.

* Argument parsing functions like :c:func:`PyArg_ParseTuple` doesn't support
  ``Py_UNICODE*`` based format (e.g. ``u``, ``Z``) anymore. Please migrate
  to other formats for Unicode like ``s``, ``z``, ``es``, and ``U``.

* ``tp_weaklist`` for all static builtin types is always ``NULL``.
  This is an internal-only field on ``PyTypeObject``
  but we're pointing out the change in case someone happens to be
  accessing the field directly anyway.  To avoid breakage, consider
  using the existing public C-API instead, or, if necessary, the
  (internal-only) ``_PyObject_GET_WEAKREFS_LISTPTR()`` macro.

* This internal-only :c:member:`PyTypeObject.tp_subclasses` may now not be
  a valid object pointer.  Its type was changed to :c:expr:`void *` to
  reflect this.  We mention this in case someone happens to be accessing the
  internal-only field directly.

  To get a list of subclasses, call the Python method
  :py:meth:`~class.__subclasses__` (using :c:func:`PyObject_CallMethod`,
  for example).

* An unrecognized format character in :c:func:`PyUnicode_FromFormat` and
  :c:func:`PyUnicode_FromFormatV` now sets a :exc:`SystemError`.
  In previous versions it caused all the rest of the format string to be
  copied as-is to the result string, and any extra arguments discarded.
  (Contributed by Serhiy Storchaka in :gh:`95781`.)

* Fixed wrong sign placement in :c:func:`PyUnicode_FromFormat` and
  :c:func:`PyUnicode_FromFormatV`.
  (Contributed by Philip Georgi in :gh:`95504`.)

* Extension classes wanting to add a ``__dict__`` or weak reference slot
  should use :const:`Py_TPFLAGS_MANAGED_DICT` and
  :const:`Py_TPFLAGS_MANAGED_WEAKREF` instead of ``tp_dictoffset`` and
  ``tp_weaklistoffset``, respectively.
  The use of ``tp_dictoffset`` and ``tp_weaklistoffset`` is still
  supported, but does not fully support multiple inheritance
  (:gh:`95589`), and performance may be worse.
  Classes declaring :const:`Py_TPFLAGS_MANAGED_DICT` should call
  :c:func:`_PyObject_VisitManagedDict` and :c:func:`_PyObject_ClearManagedDict`
  to traverse and clear their instance's dictionaries.
  To clear weakrefs, call :c:func:`PyObject_ClearWeakRefs`, as before.

* The :c:func:`PyUnicode_FSDecoder` function no longer accepts bytes-like
  paths, like :class:`bytearray` and :class:`memoryview` types: only the exact
  :class:`bytes` type is accepted for bytes strings.
  (Contributed by Victor Stinner in :gh:`98393`.)

Deprecated
----------

* Deprecate global configuration variable:

  * :c:var:`Py_DebugFlag`: use :c:member:`PyConfig.parser_debug`
  * :c:var:`Py_VerboseFlag`: use :c:member:`PyConfig.verbose`
  * :c:var:`Py_QuietFlag`: use :c:member:`PyConfig.quiet`
  * :c:var:`Py_InteractiveFlag`: use :c:member:`PyConfig.interactive`
  * :c:var:`Py_InspectFlag`: use :c:member:`PyConfig.inspect`
  * :c:var:`Py_OptimizeFlag`: use :c:member:`PyConfig.optimization_level`
  * :c:var:`Py_NoSiteFlag`: use :c:member:`PyConfig.site_import`
  * :c:var:`Py_BytesWarningFlag`: use :c:member:`PyConfig.bytes_warning`
  * :c:var:`Py_FrozenFlag`: use :c:member:`PyConfig.pathconfig_warnings`
  * :c:var:`Py_IgnoreEnvironmentFlag`: use :c:member:`PyConfig.use_environment`
  * :c:var:`Py_DontWriteBytecodeFlag`: use :c:member:`PyConfig.write_bytecode`
  * :c:var:`Py_NoUserSiteDirectory`: use :c:member:`PyConfig.user_site_directory`
  * :c:var:`Py_UnbufferedStdioFlag`: use :c:member:`PyConfig.buffered_stdio`
  * :c:var:`Py_HashRandomizationFlag`: use :c:member:`PyConfig.use_hash_seed`
    and :c:member:`PyConfig.hash_seed`
  * :c:var:`Py_IsolatedFlag`: use :c:member:`PyConfig.isolated`
  * :c:var:`Py_LegacyWindowsFSEncodingFlag`: use :c:member:`PyConfig.legacy_windows_fs_encoding`
  * :c:var:`Py_LegacyWindowsStdioFlag`: use :c:member:`PyConfig.legacy_windows_stdio`
  * :c:var:`Py_FileSystemDefaultEncoding`: use :c:member:`PyConfig.filesystem_encoding`
  * :c:var:`Py_FileSystemDefaultEncodeErrors`: use :c:member:`PyConfig.filesystem_errors`
  * :c:var:`Py_UTF8Mode`: use :c:member:`PyPreConfig.utf8_mode` (see :c:func:`Py_PreInitialize`)

  The :c:func:`Py_InitializeFromConfig` API should be used with
  :c:type:`PyConfig` instead.
  (Contributed by Victor Stinner in :gh:`77782`.)

* Creating :c:data:`immutable types <Py_TPFLAGS_IMMUTABLETYPE>` with mutable
  bases is deprecated and will be disabled in Python 3.14.


Removed
-------

* Remove the ``token.h`` header file. There was never any public tokenizer C
  API. The ``token.h`` header file was only designed to be used by Python
  internals.
  (Contributed by Victor Stinner in :gh:`92651`.)

* Leagcy Unicode APIs has been removed. See :pep:`623` for detail.

   * :c:macro:`PyUnicode_WCHAR_KIND`
   * :c:func:`PyUnicode_AS_UNICODE`
   * :c:func:`PyUnicode_AsUnicode`
   * :c:func:`PyUnicode_AsUnicodeAndSize`
   * :c:func:`PyUnicode_AS_DATA`
   * :c:func:`PyUnicode_FromUnicode`
   * :c:func:`PyUnicode_GET_SIZE`
   * :c:func:`PyUnicode_GetSize`
   * :c:func:`PyUnicode_GET_DATA_SIZE`

* Remove the ``PyUnicode_InternImmortal()`` function and the
  ``SSTATE_INTERNED_IMMORTAL`` macro.
  (Contributed by Victor Stinner in :gh:`85858`.)