cpython/Doc/whatsnew/3.11.rst

****************************
  What's New In Python 3.11
****************************

: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 bug/patch number as a comment:

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

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

This article explains the new features in Python 3.11, compared to 3.10.

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 3.11 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 3.11.
   Brevity is key.


.. PEP-sized items next.

PEP-654: Exception Groups and ``except*``.
(Contributed by Irit Katriel in :issue:`45292`.)
PEP-673: ``Self`` Type.
(Contributed by James Hilton-Balfe and Pradeep Kumar in :issue:`30924`.)

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

.. _whatsnew311-pep657:

Enhanced error locations in tracebacks
--------------------------------------

When printing tracebacks, the interpreter will now point to the exact expression
that caused the error instead of just the line. For example:

.. code-block:: python

    Traceback (most recent call last):
      File "distance.py", line 11, in <module>
        print(manhattan_distance(p1, p2))
              ^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "distance.py", line 6, in manhattan_distance
        return abs(point_1.x - point_2.x) + abs(point_1.y - point_2.y)
                               ^^^^^^^^^
    AttributeError: 'NoneType' object has no attribute 'x'

Previous versions of the interpreter would point to just the line making it
ambiguous which object was ``None``. These enhanced errors can also be helpful
when dealing with deeply nested dictionary objects and multiple function calls,

.. code-block:: python

    Traceback (most recent call last):
      File "query.py", line 37, in <module>
        magic_arithmetic('foo')
        ^^^^^^^^^^^^^^^^^^^^^^^
      File "query.py", line 18, in magic_arithmetic
        return add_counts(x) / 25
               ^^^^^^^^^^^^^
      File "query.py", line 24, in add_counts
        return 25 + query_user(user1) + query_user(user2)
                    ^^^^^^^^^^^^^^^^^
      File "query.py", line 32, in query_user
        return 1 + query_count(db, response['a']['b']['c']['user'], retry=True)
                                   ~~~~~~~~~~~~~~~~~~^^^^^
    TypeError: 'NoneType' object is not subscriptable

as well as complex arithmetic expressions:

.. code-block:: python

    Traceback (most recent call last):
      File "calculation.py", line 54, in <module>
        result = (x / y / z) * (a / b / c)
                  ~~~~~~^~~
    ZeroDivisionError: division by zero

See :pep:`657` for more details. (Contributed by Pablo Galindo, Batuhan Taskaya
and Ammar Askar in :issue:`43950`.)

.. note::
   This feature requires storing column positions in code objects which may
   result in a small increase of disk usage of compiled Python files or
   interpreter memory usage. To avoid storing the extra information and/or
   deactivate printing the extra traceback information, the
   :option:`-X` ``no_debug_ranges`` command line flag or the :envvar:`PYTHONNODEBUGRANGES`
   environment variable can be used.

Column information for code objects
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The information used by the enhanced traceback feature is made available as a
general API that can be used to correlate bytecode instructions with source
code. This information can be retrieved using:

- The :meth:`codeobject.co_positions` method in Python.
- The :c:func:`PyCode_Addr2Location` function in the C-API.

The :option:`-X` ``no_debug_ranges`` option and the environment variable
:envvar:`PYTHONNODEBUGRANGES` can be used to disable this feature.

See :pep:`657` for more details. (Contributed by Pablo Galindo, Batuhan Taskaya
and Ammar Askar in :issue:`43950`.)

Exceptions can be enriched with a string ``__note__``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``__note__`` field was added to :exc:`BaseException`. It is ``None``
by default but can be set to a string which is added to the exception's
traceback. (Contributed by Irit Katriel in :issue:`45607`.)

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

* Asynchronous comprehensions are now allowed inside comprehensions in
  asynchronous functions. Outer comprehensions implicitly become
  asynchronous. (Contributed by Serhiy Storchaka in :issue:`33346`.)

* A :exc:`TypeError` is now raised instead of an :exc:`AttributeError` in
  :meth:`contextlib.ExitStack.enter_context` and
  :meth:`contextlib.AsyncExitStack.enter_async_context` for objects which do not
  support the :term:`context manager` or :term:`asynchronous context manager`
  protocols correspondingly.
  (Contributed by Serhiy Storchaka in :issue:`44471`.)

* A :exc:`TypeError` is now raised instead of an :exc:`AttributeError` in
  :keyword:`with` and :keyword:`async with` statements for objects which do not
  support the :term:`context manager` or :term:`asynchronous context manager`
  protocols correspondingly.
  (Contributed by Serhiy Storchaka in :issue:`12022`.)


Other CPython Implementation Changes
====================================

* Special methods :meth:`complex.__complex__` and :meth:`bytes.__bytes__` are implemented to
  support :class:`typing.SupportsComplex` and :class:`typing.SupportsBytes` protocols.
  (Contributed by Mark Dickinson and Dong-hee Na in :issue:`24234`.)

* ``siphash13`` is added as a new internal hashing algorithms. It's has similar security
  properties as ``siphash24`` but it is slightly faster for long inputs. ``str``, ``bytes``,
  and some other types now use it as default algorithm for ``hash()``. :pep:`552`
  hash-based pyc files now use ``siphash13``, too.
  (Contributed by Inada Naoki in :issue:`29410`.)

* When an active exception is re-raised by a :keyword:`raise` statement with no parameters,
  the traceback attached to this exception is now always ``sys.exc_info()[1].__traceback__``.
  This means that changes made to the traceback in the current :keyword:`except` clause are
  reflected in the re-raised exception.
  (Contributed by Irit Katriel in :issue:`45711`.)

* The interpreter state's representation of handled exceptions (a.k.a exc_info, or
  _PyErr_StackItem) now has only the ``exc_value`` field, ``exc_type`` and ``exc_traceback``
  have been removed as their values can be derived from ``exc_value``.
  (Contributed by Irit Katriel in :issue:`45711`.)

* A new command line option for the Windows installer ``AppendPath`` has beend added.
  It behaves similiar to ``PrependPath`` but appends the install and scripts directories
  instead of prepending it.
  (Contributed by Bastian Neuburger in :issue:`44934`.)


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

* None yet.


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

fractions
---------

* Support :PEP:`515`-style initialization of :class:`~fractions.Fraction` from
  string.  (Contributed by Sergey B Kirpichev in :issue:`44258`.)

* :class:`~fractions.Fraction` now implements an ``__int__`` method, so
  that an ``isinstance(some_fraction, typing.SupportsInt)`` check passes.
  (Contributed by Mark Dickinson in :issue:`44547`.)


IDLE and idlelib
----------------

* Apply syntax highlighting to `.pyi` files. (Contributed by Alex
  Waygood and Terry Jan Reedy in :issue:`45447`.)

inspect
-------
* Add :func:`inspect.getmembers_static`: return all members without
  triggering dynamic lookup via the descriptor protocol. (Contributed by
  Weipeng Hong in :issue:`30533`.)

* Add :func:`inspect.ismethodwrapper` for checking if the type of an object is a
  :class:`~types.MethodWrapperType`. (Contributed by Hakan Çelik in :issue:`29418`.)

math
----
* Add :func:`math.exp2`: return 2 raised to the power of x.
  (Contributed by Gideon Mitchell in :issue:`45917`.)

* Add :func:`math.cbrt`: return the cube root of x.
  (Contributed by Ajith Ramachandran in :issue:`44357`.)

* The behaviour of two :func:`math.pow` corner cases was changed, for
  consistency with the IEEE 754 specification. The operations
  ``math.pow(0.0, -math.inf)`` and ``math.pow(-0.0, -math.inf)`` now return
  ``inf``. Previously they raised :exc:`ValueError`. (Contributed by Mark
  Dickinson in :issue:`44339`.)


operator
--------

* A new function ``operator.call`` has been added, such that
  ``operator.call(obj, *args, **kwargs) == obj(*args, **kwargs)``.
  (Contributed by Antony Lee in :issue:`44019`.)


os
--

* On Windows, :func:`os.urandom` now uses ``BCryptGenRandom()``,
  instead of ``CryptGenRandom()`` which is deprecated.
  (Contributed by Dong-hee Na in :issue:`44611`.)


socket
------

* Add CAN Socket support for NetBSD.
  (Contributed by Thomas Klausner in :issue:`30512`.)


sqlite3
-------

* You can now disable the authorizer by passing :const:`None` to
  :meth:`~sqlite3.Connection.set_authorizer`.
  (Contributed by Erlend E. Aasland in :issue:`44491`.)

* Collation name :meth:`~sqlite3.Connection.create_collation` can now
  contain any Unicode character.  Collation names with invalid characters
  now raise :exc:`UnicodeEncodeError` instead of :exc:`sqlite3.ProgrammingError`.
  (Contributed by Erlend E. Aasland in :issue:`44688`.)

* :mod:`sqlite3` exceptions now include the SQLite extended error code as
  :attr:`~sqlite3.Error.sqlite_errorcode` and the SQLite error name as
  :attr:`~sqlite3.Error.sqlite_errorname`.
  (Contributed by Aviv Palivoda, Daniel Shahaf, and Erlend E. Aasland in
  :issue:`16379` and :issue:`24139`.)

* Add :meth:`~sqlite3.Connection.setlimit` and
  :meth:`~sqlite3.Connection.getlimit` to :class:`sqlite3.Connection` for
  setting and getting SQLite limits by connection basis.
  (Contributed by Erlend E. Aasland in :issue:`45243`.)

* :mod:`sqlite3` now sets :attr:`sqlite3.threadsafety` based on the default
  threading mode the underlying SQLite library has been compiled with.
  (Contributed by Erlend E. Aasland in :issue:`45613`.)

* :mod:`sqlite3` C callbacks now use unraisable exceptions if callback
  tracebacks are enabled. Users can now register an
  :func:`unraisable hook handler <sys.unraisablehook>` to improve their debug
  experience.
  (Contributed by Erlend E. Aasland in :issue:`45828`.)

* Fetch across rollback no longer raises :exc:`~sqlite3.InterfaceError`.
  Instead we leave it to the SQLite library to handle these cases.
  (Contributed by Erlend E. Aasland in :issue:`44092`.)


sys
---

* :func:`sys.exc_info` now derives the ``type`` and ``traceback`` fields
  from the ``value`` (the exception instance), so when an exception is
  modified while it is being handled, the changes are reflected in
  the results of subsequent calls to :func:`exc_info`.
  (Contributed by Irit Katriel in :issue:`45711`.)

* Add :func:`sys.exception` which returns the active exception instance
  (equivalent to ``sys.exc_info()[1]``).
  (Contributed by Irit Katriel in :issue:`46328`.)

threading
---------

* On Unix, if the ``sem_clockwait()`` function is available in the C library
  (glibc 2.30 and newer), the :meth:`threading.Lock.acquire` method now uses
  the monotonic clock (:data:`time.CLOCK_MONOTONIC`) for the timeout, rather
  than using the system clock (:data:`time.CLOCK_REALTIME`), to not be affected
  by system clock changes.
  (Contributed by Victor Stinner in :issue:`41710`.)


time
----

* On Unix, :func:`time.sleep` now uses the ``clock_nanosleep()`` or
  ``nanosleep()`` function, if available, which has a resolution of 1 nanosecond
  (10\ :sup:`-9` seconds), rather than using ``select()`` which has a resolution
  of 1 microsecond (10\ :sup:`-6` seconds).
  (Contributed by Benjamin Szőke and Victor Stinner in :issue:`21302`.)

* On Windows 8.1 and newer, :func:`time.sleep` now uses a waitable timer based
  on `high-resolution timers
  <https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/high-resolution-timers>`_
  which has a resolution of 100 nanoseconds (10\ :sup:`-7` seconds). Previously,
  it had a resolution of 1 millisecond (10\ :sup:`-3` seconds).
  (Contributed by Benjamin Szőke, Dong-hee Na, Eryk Sun and Victor Stinner in :issue:`21302` and :issue:`45429`.)


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

* The Unicode database has been updated to version 14.0.0. (:issue:`45190`).


fcntl
-----

* On FreeBSD, the :attr:`F_DUP2FD` and :attr:`F_DUP2FD_CLOEXEC` flags respectively
  are supported, the former equals to ``dup2`` usage while the latter set
  the ``FD_CLOEXEC`` flag in addition.


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

* Compiler now optimizes simple C-style formatting with literal format
  containing only format codes ``%s``, ``%r`` and ``%a`` and makes it as
  fast as corresponding f-string expression.
  (Contributed by Serhiy Storchaka in :issue:`28307`.)

* "Zero-cost" exceptions are implemented. The cost of ``try`` statements is
  almost eliminated when no exception is raised.
  (Contributed by Mark Shannon in :issue:`40222`.)

* Method calls with keywords are now faster due to bytecode
  changes which avoid creating bound method instances. Previously, this
  optimization was applied only to method calls with purely positional
  arguments.
  (Contributed by Ken Jin and Mark Shannon in :issue:`26110`, based on ideas
  implemented in PyPy.)

* Pure ASCII strings are now normalized in constant time by :func:`unicodedata.normalize`.
  (Contributed by Dong-hee Na in :issue:`44987`.)

* :mod:`math` functions :func:`~math.comb` and :func:`~math.perm` are now up
  to 10 times or more faster for large arguments (the speed up is larger for
  larger *k*).
  (Contributed by Serhiy Storchaka in :issue:`37295`.)


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

* Replaced all numeric ``BINARY_*`` and ``INPLACE_*`` instructions with a single
  :opcode:`BINARY_OP` implementation.

* Replaced the three call instructions: :opcode:`CALL_FUNCTION`,
  :opcode:`CALL_FUNCTION_KW` and :opcode:`CALL_METHOD` with
  :opcode:`PRECALL_FUNCTION`, :opcode:`PRECALL_METHOD`, :opcode:`CALL`,
  and :opcode:`KW_NAMES`.
  This decouples the argument shifting for methods from the handling of
  keyword arguments and allows better specialization of calls.

* Removed ``COPY_DICT_WITHOUT_KEYS`` and ``GEN_START``.

* :opcode:`MATCH_CLASS` and :opcode:`MATCH_KEYS` no longer push an additional
  boolean value indicating whether the match succeeded or failed. Instead, they
  indicate failure with :const:`None` (where a tuple of extracted values would
  otherwise be).

* Replace several stack manipulation instructions (``DUP_TOP``, ``DUP_TOP_TWO``,
  ``ROT_TWO``, ``ROT_THREE``, ``ROT_FOUR``, and ``ROT_N``) with new
  :opcode:`COPY` and :opcode:`SWAP` instructions.

* Add :opcode:`POP_JUMP_IF_NOT_NONE` and :opcode:`POP_JUMP_IF_NONE` opcodes to
  speed up conditional jumps.

* :opcode:`JUMP_IF_NOT_EXC_MATCH` no longer pops the active exception.


Deprecated
==========

* The :mod:`lib2to3` package and ``2to3`` tool are now deprecated and may not
  be able to parse Python 3.10 or newer. See the :pep:`617` (New PEG parser for
  CPython).  (Contributed by Victor Stinner in :issue:`40360`.)

* :class:`webbrowser.MacOSX` is deprecated and will be removed in Python 3.13.
  It is untested and undocumented and also not used by webbrowser itself.
  (Contributed by Dong-hee Na in :issue:`42255`.)

* The behavior of returning a value from a :class:`~unittest.TestCase` and
  :class:`~unittest.IsolatedAsyncioTestCase` test methods (other than the
  default ``None`` value), is now deprecated.

* Deprecated the following :mod:`unittest` functions, scheduled for removal in
  Python 3.13:

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

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

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

  (Contributed by Erlend E. Aasland in :issue:`5846`.)

* The :meth:`turtle.RawTurtle.settiltangle` is deprecated since Python 3.1,
  it now emits a deprecation warning and will be removed in Python 3.13. Use
  :meth:`turtle.RawTurtle.tiltangle` instead (it was earlier incorrectly marked
  as deprecated, its docstring is now corrected).
  (Contributed by Hugo van Kemenade in :issue:`45837`.)

* The delegation of :func:`int` to :meth:`__trunc__` is now deprecated. Calling
  ``int(a)`` when ``type(a)`` implements :meth:`__trunc__` but not
  :meth:`__int__` or :meth:`__index__` now raises a :exc:`DeprecationWarning`.
  (Contributed by Zackery Spytz in :issue:`44977`.)

* The following have been deprecated in :mod:`configparser` since Python 3.2.
  Their deprecation warnings have now been updated to note they will removed in
  Python 3.12:

  * the :class:`configparser.SafeConfigParser` class
  * the :attr:`configparser.ParsingError.filename` property
  * the :meth:`configparser.ParsingError.readfp` method

  (Contributed by Hugo van Kemenade in :issue:`45173`.)


Removed
=======

* :class:`smtpd.MailmanProxy` is now removed as it is unusable without
  an external module, ``mailman``. (Contributed by Dong-hee Na in :issue:`35800`.)

* The ``binhex`` module, deprecated in Python 3.9, is now removed.
  The following :mod:`binascii` functions, deprecated in Python 3.9, are now
  also removed:

  * ``a2b_hqx()``, ``b2a_hqx()``;
  * ``rlecode_hqx()``, ``rledecode_hqx()``.

  The :func:`binascii.crc_hqx` function remains available.

  (Contributed by Victor Stinner in :issue:`45085`.)

* The distutils ``bdist_msi`` command, deprecated in Python 3.9, is now removed.
  Use ``bdist_wheel`` (wheel packages) instead.
  (Contributed by Hugo van Kemenade in :issue:`45124`.)

* Due to significant security concerns, the *reuse_address* parameter of
  :meth:`asyncio.loop.create_datagram_endpoint`, disabled in Python 3.9, is
  now entirely removed. This is because of the behavior of the socket option
  ``SO_REUSEADDR`` in UDP.
  (Contributed by Hugo van Kemenade in :issue:`45129`.)

* Removed :meth:`__getitem__` methods of
  :class:`xml.dom.pulldom.DOMEventStream`, :class:`wsgiref.util.FileWrapper`
  and :class:`fileinput.FileInput`, deprecated since Python 3.9.
  (Contributed by Hugo van Kemenade in :issue:`45132`.)

* The following deprecated functions and methods are removed in the :mod:`gettext`
  module: :func:`~gettext.lgettext`, :func:`~gettext.ldgettext`,
  :func:`~gettext.lngettext` and :func:`~gettext.ldngettext`.

  Function :func:`~gettext.bind_textdomain_codeset`, methods
  :meth:`~gettext.NullTranslations.output_charset` and
  :meth:`~gettext.NullTranslations.set_output_charset`, and the *codeset*
  parameter of functions :func:`~gettext.translation` and
  :func:`~gettext.install` are also removed, since they are only used for
  the ``l*gettext()`` functions.
  (Contributed by Dong-hee Na and Serhiy Storchaka in :issue:`44235`.)

* The :func:`@asyncio.coroutine <asyncio.coroutine>` :term:`decorator` enabling
  legacy generator-based coroutines to be compatible with async/await code.
  The function has been deprecated since Python 3.8 and the removal was
  initially scheduled for Python 3.10. Use :keyword:`async def` instead.
  (Contributed by Illia Volochii in :issue:`43216`.)

* :class:`asyncio.coroutines.CoroWrapper` used for wrapping legacy
  generator-based coroutine objects in the debug mode.
  (Contributed by Illia Volochii in :issue:`43216`.)

* Removed the deprecated ``split()`` method of :class:`_tkinter.TkappType`.
  (Contributed by Erlend E. Aasland in :issue:`38371`.)

* Removed from the :mod:`inspect` module:

  * the ``getargspec`` function, deprecated since Python 3.0;
    use :func:`inspect.signature` or :func:`inspect.getfullargspec` instead.

  * the ``formatargspec`` function, deprecated since Python 3.5;
    use the :func:`inspect.signature` function and :class:`Signature` object
    directly.

  * the undocumented ``Signature.from_builtin`` and ``Signature.from_function``
    functions, deprecated since Python 3.5; use the
    :meth:`Signature.from_callable() <inspect.Signature.from_callable>` method
    instead.

  (Contributed by Hugo van Kemenade in :issue:`45320`.)

* Remove namespace package support from unittest discovery. It was introduced in
  Python 3.4 but has been broken since Python 3.7.
  (Contributed by Inada Naoki in :issue:`23882`.)

* Remove ``__class_getitem__`` method from :class:`pathlib.PurePath`,
  because it was not used and added by mistake in previous versions.
  (Contributed by Nikita Sobolev in :issue:`46483`.)

Porting to Python 3.11
======================

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


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

* Prohibited passing non-:class:`concurrent.futures.ThreadPoolExecutor`
  executors to :meth:`loop.set_default_executor` following a deprecation in
  Python 3.8.
  (Contributed by Illia Volochii in :issue:`43234`.)

* :func:`open`, :func:`io.open`, :func:`codecs.open` and
  :class:`fileinput.FileInput` no longer accept ``'U'`` ("universal newline")
  in the file mode. This flag was deprecated since Python 3.3. In Python 3, the
  "universal newline" is used by default when a file is open in text mode.  The
  :ref:`newline parameter <open-newline-parameter>` of :func:`open` controls
  how universal newlines works.
  (Contributed by Victor Stinner in :issue:`37330`.)

* The :mod:`pdb` module now reads the :file:`.pdbrc` configuration file with
  the ``'utf-8'`` encoding.
  (Contributed by Srinivas Reddy Thatiparthy (శ్రీనివాస్  రెడ్డి తాటిపర్తి) in :issue:`41137`.)

* When sorting using tuples as keys, the order of the result may differ
  from earlier releases if the tuple elements don't define a total
  ordering (see :ref:`expressions-value-comparisons` for
  information on total ordering).  It's generally true that the result
  of sorting simply isn't well-defined in the absence of a total ordering
  on list elements.

* :mod:`calendar`: The :class:`calendar.LocaleTextCalendar` and
  :class:`calendar.LocaleHTMLCalendar` classes now use
  :func:`locale.getlocale`, instead of using :func:`locale.getdefaultlocale`,
  if no locale is specified.
  (Contributed by Victor Stinner in :issue:`46659`.)


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

* CPython can now be built with the ThinLTO option via ``--with-lto=thin``.
  (Contributed by Dong-hee Na and Brett Holman in :issue:`44340`.)

* libpython is no longer linked against libcrypt.
  (Contributed by Mike Gilbert in :issue:`45433`.)

* Building Python now requires a C99 ``<math.h>`` header file providing
  the following functions: ``copysign()``, ``hypot()``, ``isfinite()``,
  ``isinf()``, ``isnan()``, ``round()``.
  (Contributed by Victor Stinner in :issue:`45440`.)

* Building Python now requires a C99 ``<math.h>`` header file providing
  a ``NAN`` constant, or the ``__builtin_nan()`` built-in function. If a
  platform does not support Not-a-Number (NaN), the ``Py_NO_NAN`` macro can be
  defined in the ``pyconfig.h`` file.
  (Contributed by Victor Stinner in :issue:`46640`.)

* Freelists for object structs can now be disabled. A new :program:`configure`
  option :option:`!--without-freelists` can be used to disable all freelists
  except empty tuple singleton.
  (Contributed by Christian Heimes in :issue:`45522`)

* ``Modules/Setup`` and ``Modules/makesetup`` have been improved and tied up.
  Extension modules can now be built through ``makesetup``. All except some
  test modules can be linked statically into main binary or library.
  (Contributed by Brett Cannon and Christian Heimes in :issue:`45548`,
  :issue:`45570`, :issue:`45571`, and :issue:`43974`.)

* Build dependencies, compiler flags, and linker flags for most stdlib
  extension modules are now detected by :program:`configure`. libffi, libnsl,
  libsqlite3, zlib, bzip2, liblzma, libcrypt, and uuid flags are detected by
  ``pkg-config`` (when available).
  (Contributed by Christian Heimes and Erlend Egeberg Aasland in
  :issue:`bpo-45847`, :issue:`45747`, and :issue:`45763`.)

* CPython now has experimental support for cross compiling to WebAssembly
  platform ``wasm32-emscripten``. The effort is inspired by previous work
  like Pyodide.
  (Contributed by Christian Heimes and Ethan Smith in :issue:`40280`.)

* CPython will now use 30-bit digits by default for the Python :class:`int`
  implementation. Previously, the default was to use 30-bit digits on platforms
  with ``SIZEOF_VOID_P >= 8``, and 15-bit digits otherwise. It's still possible
  to explicitly request use of 15-bit digits via either the
  ``--enable-big-digits`` option to the configure script or (for Windows) the
  ``PYLONG_BITS_IN_DIGIT`` variable in ``PC/pyconfig.h``, but this option may
  be removed at some point in the future. (Contributed by Mark Dickinson in
  :issue:`45569`.)


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

* :c:func:`PyErr_SetExcInfo()` no longer uses the ``type`` and ``traceback``
  arguments, the interpreter now derives those values from the exception
  instance (the ``value`` argument). The function still steals references
  of all three arguments.
  (Contributed by Irit Katriel in :issue:`45711`.)

* :c:func:`PyErr_GetExcInfo()` now derives the ``type`` and ``traceback``
  fields of the result from the exception instance (the ``value`` field).
  (Contributed by Irit Katriel in :issue:`45711`.)

* :c:struct:`_frozen` has a new ``is_package`` field to indicate whether
  or not the frozen module is a package.  Previously, a negative value
  in the ``size`` field was the indicator.  Now only non-negative values
  be used for ``size``.
  (Contributed by Kumar Aditya in :issue:`46608`.)

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

* Add a new :c:func:`PyType_GetName` function to get type's short name.
  (Contributed by Hai Shi in :issue:`42035`.)

* Add a new :c:func:`PyType_GetQualName` function to get type's qualified name.
  (Contributed by Hai Shi in :issue:`42035`.)

* Add new :c:func:`PyThreadState_EnterTracing` and
  :c:func:`PyThreadState_LeaveTracing` functions to the limited C API to
  suspend and resume tracing and profiling.
  (Contributed by Victor Stinner in :issue:`43760`.)

* Added the :c:data:`Py_Version` constant which bears the same value as
  :c:macro:`PY_VERSION_HEX`.
  (Contributed by  Gabriele N. Tornetta in :issue:`43931`.)

* :c:type:`Py_buffer` and APIs are now part of the limited API and the stable
  ABI:

  * :c:func:`PyObject_CheckBuffer`
  * :c:func:`PyObject_GetBuffer`
  * :c:func:`PyBuffer_GetPointer`
  * :c:func:`PyBuffer_SizeFromFormat`
  * :c:func:`PyBuffer_ToContiguous`
  * :c:func:`PyBuffer_FromContiguous`
  * :c:func:`PyBuffer_CopyData`
  * :c:func:`PyBuffer_IsContiguous`
  * :c:func:`PyBuffer_FillContiguousStrides`
  * :c:func:`PyBuffer_FillInfo`
  * :c:func:`PyBuffer_Release`
  * :c:func:`PyMemoryView_FromBuffer`
  * :c:member:`~PyBufferProcs.bf_getbuffer` and
    :c:member:`~PyBufferProcs.bf_releasebuffer` type slots

  (Contributed by Christian Heimes in :issue:`45459`.)

* Added the :c:data:`PyType_GetModuleByDef` function, used to get the module
  in which a method was defined, in cases where this information is not
  available directly (via :c:type:`PyCMethod`).
  (Contributed by Petr Viktorin in :issue:`46613`.)


Porting to Python 3.11
----------------------

* The old trashcan macros (``Py_TRASHCAN_SAFE_BEGIN``/``Py_TRASHCAN_SAFE_END``)
  are now deprecated. 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.

  To support older Python versions in the same codebase, you
  can define the following macros and use them throughout
  the code (credit: these were copied from the ``mypy`` codebase)::

    #if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 8
    #  define CPy_TRASHCAN_BEGIN(op, dealloc) Py_TRASHCAN_BEGIN(op, dealloc)
    #  define CPy_TRASHCAN_END(op) Py_TRASHCAN_END
    #else
    #  define CPy_TRASHCAN_BEGIN(op, dealloc) Py_TRASHCAN_SAFE_BEGIN(op)
    #  define CPy_TRASHCAN_END(op) Py_TRASHCAN_SAFE_END(op)
    #endif

* The :c:func:`PyType_Ready` function now raises an error if a type is defined
  with the :const:`Py_TPFLAGS_HAVE_GC` flag set but has no traverse function
  (:c:member:`PyTypeObject.tp_traverse`).
  (Contributed by Victor Stinner in :issue:`44263`.)

* Heap types with the :const:`Py_TPFLAGS_IMMUTABLETYPE` flag can now inherit
  the :pep:`590` vectorcall protocol.  Previously, this was only possible for
  :ref:`static types <static-types>`.
  (Contributed by Erlend E. Aasland in :issue:`43908`)

* Since :c:func:`Py_TYPE()` is changed to a inline static function,
  ``Py_TYPE(obj) = new_type`` must be replaced with
  ``Py_SET_TYPE(obj, new_type)``: see the :c:func:`Py_SET_TYPE()` function
  (available since Python 3.9). For backward compatibility, this macro can be
  used::

      #if PY_VERSION_HEX < 0x030900A4 && !defined(Py_SET_TYPE)
      static inline void _Py_SET_TYPE(PyObject *ob, PyTypeObject *type)
      { ob->ob_type = type; }
      #define Py_SET_TYPE(ob, type) _Py_SET_TYPE((PyObject*)(ob), type)
      #endif

  (Contributed by Victor Stinner in :issue:`39573`.)

* Since :c:func:`Py_SIZE()` is changed to a inline static function,
  ``Py_SIZE(obj) = new_size`` must be replaced with
  ``Py_SET_SIZE(obj, new_size)``: see the :c:func:`Py_SET_SIZE()` function
  (available since Python 3.9). For backward compatibility, this macro can be
  used::

      #if PY_VERSION_HEX < 0x030900A4 && !defined(Py_SET_SIZE)
      static inline void _Py_SET_SIZE(PyVarObject *ob, Py_ssize_t size)
      { ob->ob_size = size; }
      #define Py_SET_SIZE(ob, size) _Py_SET_SIZE((PyVarObject*)(ob), size)
      #endif

  (Contributed by Victor Stinner in :issue:`39573`.)

* ``<Python.h>`` no longer includes the header files ``<stdlib.h>``,
  ``<stdio.h>``, ``<errno.h>`` and ``<string.h>`` when the ``Py_LIMITED_API``
  macro is set to ``0x030b0000`` (Python 3.11) or higher. C extensions should
  explicitly include the header files after ``#include <Python.h>``.
  (Contributed by Victor Stinner in :issue:`45434`.)

* The non-limited API files ``cellobject.h``, ``classobject.h``, ``context.h``,
  ``funcobject.h``, ``genobject.h`` and ``longintrepr.h`` have been moved to
  the ``Include/cpython`` directory. Moreover, the ``eval.h`` header file was
  removed. These files must not be included directly, as they are already
  included in ``Python.h``: :ref:`Include Files <api-includes>`. If they have
  been included directly, consider including ``Python.h`` instead.
  (Contributed by Victor Stinner in :issue:`35134`.)

* The :c:func:`PyUnicode_CHECK_INTERNED` macro has been excluded from the
  limited C API. It was never usable there, because it used internal structures
  which are not available in the limited C API.
  (Contributed by Victor Stinner in :issue:`46007`.)

* Changes of the private :c:type:`PyFrameObject` structure members.

  While the documentation notes that the fields of ``PyFrameObject`` are
  subject to change at any time, they have been stable for a long time
  and were used in several popular extensions.
  In Python 3.11, the frame struct was reorganized to allow performance
  optimizations. Rather than reading the fields directly, extensions should
  use functions:

  * ``f_code``: removed, use :c:func:`PyFrame_GetCode` instead.
    Warning: the function returns a :term:`strong reference`, need to call
    :c:func:`Py_DECREF`.
  * ``f_back``: changed (see below), use :c:func:`PyFrame_GetBack`.
  * ``f_builtins``: removed,
    use ``PyObject_GetAttrString((PyObject*)frame, "f_builtins")``.
  * ``f_globals``: removed,
    use ``PyObject_GetAttrString((PyObject*)frame, "f_globals")``.
  * ``f_locals``: removed,
    use ``PyObject_GetAttrString((PyObject*)frame, "f_locals")``.
  * ``f_lasti``: removed,
    use ``PyObject_GetAttrString((PyObject*)frame, "f_lasti")``.

  The following fields were removed entirely, as they were details
  of the old implementation:

  * ``f_valuesstack``
  * ``f_stackdepth``
  * ``f_gen``
  * ``f_iblock``
  * ``f_state``
  * ``f_blockstack``
  * ``f_localsplus``

  The Python frame object is now created lazily. A side effect is that the
  ``f_back`` member must not be accessed directly, since its value is now also
  computed lazily. The :c:func:`PyFrame_GetBack` function must be called
  instead.

  Code defining ``PyFrame_GetCode()`` on Python 3.8 and older::

      #if PY_VERSION_HEX < 0x030900B1
      static inline PyCodeObject* PyFrame_GetCode(PyFrameObject *frame)
      {
          Py_INCREF(frame->f_code);
          return frame->f_code;
      }
      #endif

  Code defining ``PyFrame_GetBack()`` on Python 3.8 and older::

      #if PY_VERSION_HEX < 0x030900B1
      static inline PyFrameObject* PyFrame_GetBack(PyFrameObject *frame)
      {
          Py_XINCREF(frame->f_back);
          return frame->f_back;
      }
      #endif

  Or use `the pythoncapi_compat project
  <https://github.com/pythoncapi/pythoncapi_compat>`__ to get these APIs
  on older Python versions.

* Changes of the :c:type:`PyThreadState` structure members:

  * ``frame``: removed, use :c:func:`PyThreadState_GetFrame` (function added
    to Python 3.9 by :issue:`40429`).
    Warning: the function returns a :term:`strong reference`, need to call
    :c:func:`Py_XDECREF`.
  * ``tracing``: changed, use :c:func:`PyThreadState_EnterTracing`
    and :c:func:`PyThreadState_LeaveTracing`
    (functions added to Python 3.11 by :issue:`43760`).
  * ``recursion_depth``: removed,
    use ``(tstate->recursion_limit - tstate->recursion_remaining)`` instead.
  * ``stackcheck_counter``: removed.

  Code defining ``PyThreadState_GetFrame()`` on Python 3.8 and older::

      #if PY_VERSION_HEX < 0x030900B1
      static inline PyFrameObject* PyThreadState_GetFrame(PyThreadState *tstate)
      {
          Py_XINCREF(tstate->frame);
          return tstate->frame;
      }
      #endif

  Code defining ``PyThreadState_EnterTracing()`` and
  ``PyThreadState_LeaveTracing()`` on Python 3.10 and older::

      #if PY_VERSION_HEX < 0x030B00A2
      static inline void PyThreadState_EnterTracing(PyThreadState *tstate)
      {
          tstate->tracing++;
      #if PY_VERSION_HEX >= 0x030A00A1
          tstate->cframe->use_tracing = 0;
      #else
          tstate->use_tracing = 0;
      #endif
      }

      static inline void PyThreadState_LeaveTracing(PyThreadState *tstate)
      {
          int use_tracing = (tstate->c_tracefunc != NULL || tstate->c_profilefunc != NULL);
          tstate->tracing--;
      #if PY_VERSION_HEX >= 0x030A00A1
          tstate->cframe->use_tracing = use_tracing;
      #else
          tstate->use_tracing = use_tracing;
      #endif
      }
      #endif

  Or use `the pythoncapi_compat project
  <https://github.com/pythoncapi/pythoncapi_compat>`__ to get these functions
  on old Python functions.


Deprecated
----------

* Deprecate the following functions to configure the Python initialization:

  * :c:func:`PySys_AddWarnOptionUnicode`
  * :c:func:`PySys_AddWarnOption`
  * :c:func:`PySys_AddXOption`
  * :c:func:`PySys_HasWarnOptions`
  * :c:func:`Py_SetPath`
  * :c:func:`Py_SetProgramName`
  * :c:func:`Py_SetPythonHome`
  * :c:func:`Py_SetStandardStreamEncoding`
  * :c:func:`_Py_SetProgramFullPath`

  Use the new :c:type:`PyConfig` API of the :ref:`Python Initialization Configuration
  <init-config>` instead (:pep:`587`).
  (Contributed by Victor Stinner in :issue:`44113`.)

Removed
-------

* :c:func:`PyFrame_BlockSetup` and :c:func:`PyFrame_BlockPop` have been
  removed.
  (Contributed by Mark Shannon in :issue:`40222`.)

* Remove the following math macros using the ``errno`` variable:

  * ``Py_ADJUST_ERANGE1()``
  * ``Py_ADJUST_ERANGE2()``
  * ``Py_OVERFLOWED()``
  * ``Py_SET_ERANGE_IF_OVERFLOW()``
  * ``Py_SET_ERRNO_ON_MATH_ERROR()``

  (Contributed by Victor Stinner in :issue:`45412`.)

* Remove ``Py_UNICODE_COPY()`` and ``Py_UNICODE_FILL()`` macros, deprecated
  since Python 3.3. Use ``PyUnicode_CopyCharacters()`` or ``memcpy()``
  (``wchar_t*`` string), and ``PyUnicode_Fill()`` functions instead.
  (Contributed by Victor Stinner in :issue:`41123`.)

* Remove the ``pystrhex.h`` header file. It only contains private functions.
  C extensions should only include the main ``<Python.h>`` header file.
  (Contributed by Victor Stinner in :issue:`45434`.)

* Remove the ``Py_FORCE_DOUBLE()`` macro. It was used by the
  ``Py_IS_INFINITY()`` macro.
  (Contributed by Victor Stinner in :issue:`45440`.)

* The following items are no longer available when :c:macro:`Py_LIMITED_API`
  is defined:

  * :c:func:`PyMarshal_WriteLongToFile`
  * :c:func:`PyMarshal_WriteObjectToFile`
  * :c:func:`PyMarshal_ReadObjectFromString`
  * :c:func:`PyMarshal_WriteObjectToString`
  * the ``Py_MARSHAL_VERSION`` macro

  These are not part of the :ref:`limited API <stable-abi-list>`.

  (Contributed by Victor Stinner in :issue:`45474`.)

* Exclude :c:func:`PyWeakref_GET_OBJECT` from the limited C API. It never
  worked since the :c:type:`PyWeakReference` structure is opaque in the
  limited C API.
  (Contributed by Victor Stinner in :issue:`35134`.)

* Remove the ``PyHeapType_GET_MEMBERS()`` macro. It was exposed in the
  public C API by mistake, it must only be used by Python internally.
  Use the ``PyTypeObject.tp_members`` member instead.
  (Contributed by Victor Stinner in :issue:`40170`.)