path: root/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.

- Python 3.11 is up to 10-60% faster than Python 3.10. On average, we measured a
  1.22x speedup on the standard benchmark suite. See `Faster CPython`_ for details.

.. PEP-sized items next.

New syntax features:

* :pep:`654`: Exception Groups and ``except*``.
  (Contributed by Irit Katriel in :issue:`45292`.)

New typing features:

* :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 notes (PEP 678)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The :meth:`add_note` method was added to :exc:`BaseException`. It can be
used to enrich exceptions with context information which is not available
at the time when the exception is raised. The notes added appear in the
default traceback. See :pep:`678` for more details. (Contributed by
Irit Katriel in :issue:`45607`.)


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

* Starred expressions can be used in :ref:`for statements<for>`. (See
  :issue:`46725` for more details.)

* 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`.)

* Added :meth:`object.__getstate__` which provides the default
  implementation of the ``__getstate__()`` method.  :mod:`Copying <copy>`
  and :mod:`pickling <pickle>` instances of subclasses of builtin types
  :class:`bytearray`, :class:`set`, :class:`frozenset`,
  :class:`collections.OrderedDict`, :class:`collections.deque`,
  :class:`weakref.WeakSet`, and :class:`datetime.tzinfo` now copies and
  pickles instance attributes implemented as :term:`slots <__slots__>`.
  (Contributed by Serhiy Storchaka in :issue:`26579`.)


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 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 :func:`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 been added.
  It behaves similiar to ``PrependPath`` but appends the install and scripts directories
  instead of prepending them.
  (Contributed by Bastian Neuburger in :issue:`44934`.)


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

* A new module, :mod:`tomllib`, was added for parsing TOML.
  (Contributed by Taneli Hukkinen in :issue:`40059`.)

* :mod:`wsgiref.types`, containing WSGI-specific types for static type
  checking, was added.
  (Contributed by Sebastian Rittau in :issue:`42012`.)


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

asyncio
-------

* Add raw datagram socket functions to the event loop:
  :meth:`~asyncio.AbstractEventLoop.sock_sendto`,
  :meth:`~asyncio.AbstractEventLoop.sock_recvfrom` and
  :meth:`~asyncio.AbstractEventLoop.sock_recvfrom_into`.
  (Contributed by Alex Grönholm in :issue:`46805`.)

* Add :meth:`~asyncio.streams.StreamWriter.start_tls` method for upgrading
  existing stream-based connections to TLS. (Contributed by Ian Good in
  :issue:`34975`.)

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`.)

functools
---------

* :func:`functools.singledispatch` now supports :data:`types.UnionType`
  and :data:`typing.Union` as annotations to the dispatch argument.::

    >>> from functools import singledispatch
    >>> @singledispatch
    ... def fun(arg, verbose=False):
    ...     if verbose:
    ...         print("Let me just say,", end=" ")
    ...     print(arg)
    ...
    >>> @fun.register
    ... def _(arg: int | float, verbose=False):
    ...     if verbose:
    ...         print("Strength in numbers, eh?", end=" ")
    ...     print(arg)
    ...
    >>> from typing import Union
    >>> @fun.register
    ... def _(arg: Union[list, set], verbose=False):
    ...     if verbose:
    ...         print("Enumerate this:")
    ...     for i, elem in enumerate(arg):
    ...         print(i, elem)
    ...

  (Contributed by Yurii Karabas in :issue:`46014`.)

hashlib
-------

* :func:`hashlib.blake2b` and :func:`hashlib.blake2s` now prefer `libb2`_
  over Python's vendored copy.
  (Contributed by Christian Heimes in :issue:`47095`.)

* The internal ``_sha3`` module with SHA3 and SHAKE algorithms now uses
  *tiny_sha3* instead of the *Keccak Code Package* to reduce code and binary
  size. The :mod:`hashlib` module prefers optimized SHA3 and SHAKE
  implementations from OpenSSL. The change affects only installations without
  OpenSSL support.
  (Contributed by Christian Heimes in :issue:`47098`.)

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`.)

locale
------

* Add :func:`locale.getencoding` to get the current locale encoding. It is similar to
  ``locale.getpreferredencoding(False)`` but ignores the
  :ref:`Python UTF-8 Mode <utf8-mode>`.

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`.)

* The :data:`math.nan` value is now always available.
  (Contributed by Victor Stinner in :issue:`46917`.)


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`.)

re
--

* Atomic grouping (``(?>...)``) and possessive quantifiers (``*+``, ``++``,
  ``?+``, ``{m,n}+``) are now supported in regular expressions.
  (Contributed by Jeffrey C. Jacobs and Serhiy Storchaka in :issue:`433030`.)

shutil
------

* Add optional parameter *dir_fd* in :func:`shutil.rmtree`.
  (Contributed by Serhiy Storchaka in :issue:`46245`.)


socket
------

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

* :meth:`~socket.create_connection` has an option to raise, in case of
  failure to connect, an :exc:`ExceptionGroup` containing all errors
  instead of only raising the last error.
  (Contributed by Irit Katriel in :issue:`29980`).

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`.)

* Add :meth:`~sqlite3.Connection.serialize` and
  :meth:`~sqlite3.Connection.deserialize` to :class:`sqlite3.Connection` for
  serializing and deserializing databases.
  (Contributed by Erlend E. Aasland in :issue:`41930`.)

* Add :meth:`~sqlite3.Connection.create_window_function` to
  :class:`sqlite3.Connection` for creating aggregate window functions.
  (Contributed by Erlend E. Aasland in :issue:`34916`.)

* Add :meth:`~sqlite3.Connection.blobopen` to :class:`sqlite3.Connection`.
  :class:`sqlite3.Blob` allows incremental I/O operations on blobs.
  (Contributed by Aviv Palivoda and Erlend E. Aasland in :issue:`24905`)


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`.)


sysconfig
---------

* Two new :ref:`installation schemes <installation_paths>`
  (*posix_venv*, *nt_venv* and *venv*) were added and are used when Python
  creates new virtual environments or when it is running from a virtual
  environment.
  The first two schemes (*posix_venv* and *nt_venv*) are OS-specific
  for non-Windows and Windows, the *venv* is essentially an alias to one of
  them according to the OS Python runs on.
  This is useful for downstream distributors who modify
  :func:`sysconfig.get_preferred_scheme`.
  Third party code that creates new virtual environments should use the new
  *venv* installation scheme to determine the paths, as does :mod:`venv`.
  (Contributed by Miro Hrončok in :issue:`45413`.)


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`).


venv
----

* When new Python virtual environments are created, the *venv*
  :ref:`sysconfig installation scheme <installation_paths>` is used
  to determine the paths inside the environment.
  When Python runs in a virtual environment, the same installation scheme
  is the default.
  That means that downstream distributors can change the default sysconfig install
  scheme without changing behavior of virtual environments.
  Third party code that also creates new virtual environments should do the same.
  (Contributed by Miro Hrončok in :issue:`45413`.)

zipfile
-------

* Added support for specifying member name encoding for reading
  metadata in the zipfile's directory and file headers.
  (Contributed by Stephen J. Turnbull and Serhiy Storchaka in :issue:`28080`.)

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`.)

* 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`.)

* Dict don't store hash value when all inserted keys are Unicode objects.
  This reduces dict size. For example, ``sys.getsizeof(dict.fromkeys("abcdefg"))``
  becomes 272 bytes from 352 bytes on 64bit platform.
  (Contributed by Inada Naoki in :issue:`46845`.)

* :mod:`re`'s regular expression matching engine has been partially refactored,
  and now uses computed gotos (or "threaded code") on supported platforms. As a
  result, Python 3.11 executes the `pyperformance regular expression benchmarks
  <https://pyperformance.readthedocs.io/benchmarks.html#regex-dna>`_ up to 10%
  faster than Python 3.10.


Faster CPython
==============

CPython 3.11 is on average `1.22x faster <https://github.com/faster-cpython/ideas/blob/main/main-vs-310.rst>`_
than CPython 3.10 when measured with the
`pyperformance <https://github.com/python/pyperformance>`_ benchmark suite,
and compiled with GCC on Ubuntu Linux. Depending on your workload, the speedup
could be up to 10-60% faster.

This project focuses on two major areas in Python: faster startup and faster
runtime. Other optimizations not under this project are listed in `Optimizations`_.

Faster Startup
--------------

Frozen imports / Static code objects
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Python caches bytecode in the :ref:`__pycache__<tut-pycache>` directory to
speed up module loading.

Previously in 3.10, Python module execution looked like this:

.. code-block:: text

   Read __pycache__ -> Unmarshal -> Heap allocated code object -> Evaluate

In Python 3.11, the core modules essential for Python startup are "frozen".
This means that their code objects (and bytecode) are statically allocated
by the interpreter. This reduces the steps in module execution process to this:

.. code-block:: text

   Statically allocated code object -> Evaluate

Interpreter startup is now 10-15% faster in Python 3.11. This has a big
impact for short-running programs using Python.

(Contributed by Eric Snow, Guido van Rossum and Kumar Aditya in numerous issues.)


Faster Runtime
--------------

Cheaper, lazy Python frames
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Python frames are created whenever Python calls a Python function. This frame
holds execution information. The following are new frame optimizations:

- Streamlined the frame creation process.
- Avoided memory allocation by generously re-using frame space on the C stack.
- Streamlined the internal frame struct to contain only essential information.
  Frames previously held extra debugging and memory management information.

Old-style frame objects are now created only when required by debuggers. For
most user code, no frame objects are created at all. As a result, nearly all
Python functions calls have sped up significantly. We measured a 3-7% speedup
in pyperformance.

(Contributed by Mark Shannon in :issue:`44590`.)

.. _inline-calls:

Inlined Python function calls
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
During a Python function call, Python will call an evaluating C function to
interpret that function's code. This effectively limits pure Python recursion to
what's safe for the C stack.

In 3.11, when CPython detects Python code calling another Python function,
it sets up a new frame, and "jumps" to the new code inside the new frame. This
avoids calling the C interpreting function altogether.

Most Python function calls now consume no C stack space. This speeds up
most of such calls. In simple recursive functions like fibonacci or
factorial, a 1.7x speedup was observed. This also means recursive functions
can recurse significantly deeper (if the user increases the recursion limit).
We measured a 1-3% improvement in pyperformance.

(Contributed by Pablo Galindo and Mark Shannon in :issue:`45256`.)

PEP 659: Specializing Adaptive Interpreter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:pep:`659` is one of the key parts of the faster CPython project. The general
idea is that while Python is a dynamic language, most code has regions where
objects and types rarely change. This concept is known as *type stability*.

At runtime, Python will try to look for common patterns and type stability
in the executing code. Python will then replace the current operation with a
more specialized one. This specialized operation uses fast paths available only
to those use cases/types, which generally outperform their generic
counterparts. This also brings in another concept called *inline caching*, where
Python caches the results of expensive operations directly in the bytecode.

The specializer will also combine certain common instruction pairs into one
superinstruction. This reduces the overhead during execution.

Python will only specialize
when it sees code that is "hot" (executed multiple times). This prevents Python
from wasting time for run-once code. Python can also de-specialize when code is
too dynamic or when the use changes. Specialization is attempted periodically,
and specialization attempts are not too expensive. This allows specialization
to adapt to new circumstances.

(PEP written by Mark Shannon, with ideas inspired by Stefan Brunthaler.
See :pep:`659` for more information.)

..
   If I missed out anyone, please add them.

+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Operation     | Form               | Specialization                                        | Operation speedup | Contributor(s)    |
|               |                    |                                                       | (up to)           |                   |
+===============+====================+=======================================================+===================+===================+
| Binary        | ``x+x; x*x; x-x;`` | Binary add, multiply and subtract for common types    | 10%               | Mark Shannon,     |
| operations    |                    | such as ``int``, ``float``, and ``str`` take custom   |                   | Dong-hee Na,      |
|               |                    | fast paths for their underlying types.                |                   | Brandt Bucher,    |
|               |                    |                                                       |                   | Dennis Sweeney    |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Subscript     | ``a[i]``           | Subscripting container types such as ``list``,        | 10-25%            | Irit Katriel,     |
|               |                    | ``tuple`` and ``dict`` directly index the underlying  |                   | Mark Shannon      |
|               |                    | data structures.                                      |                   |                   |
|               |                    |                                                       |                   |                   |
|               |                    | Subscripting custom ``__getitem__``                   |                   |                   |
|               |                    | is also inlined similar to :ref:`inline-calls`.       |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Store         | ``a[i] = z``       | Similar to subscripting specialization above.         | 10-25%            | Dennis Sweeney    |
| subscript     |                    |                                                       |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Calls         | ``f(arg)``         | Calls to common builtin (C) functions and types such  | 20%               | Mark Shannon,     |
|               | ``C(arg)``         | as ``len`` and ``str`` directly call their underlying |                   | Ken Jin           |
|               |                    | C version. This avoids going through the internal     |                   |                   |
|               |                    | calling convention.                                   |                   |                   |
|               |                    |                                                       |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Load          | ``print``          | The object's index in the globals/builtins namespace  | [1]_              | Mark Shannon      |
| global        | ``len``            | is cached. Loading globals and builtins require       |                   |                   |
| variable      |                    | zero namespace lookups.                               |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Load          | ``o.attr``         | Similar to loading global variables. The attribute's  | [2]_              | Mark Shannon      |
| attribute     |                    | index inside the class/object's namespace is cached.  |                   |                   |
|               |                    | In most cases, attribute loading will require zero    |                   |                   |
|               |                    | namespace lookups.                                    |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Load          | ``o.meth()``       | The actual address of the method is cached. Method    | 10-20%            | Ken Jin,          |
| methods for   |                    | loading now has no namespace lookups -- even for      |                   | Mark Shannon      |
| call          |                    | classes with long inheritance chains.                 |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Store         | ``o.attr = z``     | Similar to load attribute optimization.               | 2%                | Mark Shannon      |
| attribute     |                    |                                                       | in pyperformance  |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+
| Unpack        | ``*seq``           | Specialized for common containers such as ``list``    | 8%                | Brandt Bucher     |
| Sequence      |                    | and ``tuple``. Avoids internal calling convention.    |                   |                   |
+---------------+--------------------+-------------------------------------------------------+-------------------+-------------------+

.. [1] A similar optimization already existed since Python 3.8.  3.11
       specializes for more forms and reduces some overhead.

.. [2] A similar optimization already existed since Python 3.10.
       3.11 specializes for more forms. Furthermore, all attribute loads should
       be sped up by :issue:`45947`.


Misc
----

* Objects now require less memory due to lazily created object namespaces. Their
  namespace dictionaries now also share keys more freely.
  (Contributed Mark Shannon in :issue:`45340` and :issue:`40116`.)

* A more concise representation of exceptions in the interpreter reduced the
  time required for catching an exception by about 10%.
  (Contributed by Irit Katriel in :issue:`45711`.)

FAQ
---

| Q: How should I write my code to utilize these speedups?
|
| A: You don't have to change your code. Write Pythonic code that follows common
  best practices. The Faster CPython project optimizes for common code
  patterns we observe.
|
|
| Q: Will CPython 3.11 use more memory?
|
| A: Maybe not. We don't expect memory use to exceed 20% more than 3.10.
  This is offset by memory optimizations for frame objects and object
  dictionaries as mentioned above.
|
|
| Q: I don't see any speedups in my workload. Why?
|
| A: Certain code won't have noticeable benefits. If your code spends most of
  its time on I/O operations, or already does most of its
  computation in a C extension library like numpy, there won't be significant
  speedup. This project currently benefits pure-Python workloads the most.
|
| Furthermore, the pyperformance figures are a geometric mean. Even within the
  pyperformance benchmarks, certain benchmarks have slowed down slightly, while
  others have sped up by nearly 2x!
|
|
| Q: Is there a JIT compiler?
|
| A: No. We're still exploring other optimizations.


About
-----

Faster CPython explores optimizations for :term:`CPython`. The main team is
funded by Microsoft to work on this full-time. Pablo Galindo Salgado is also
funded by Bloomberg LP to work on the project part-time. Finally, many
contributors are volunteers from the community.


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:`PUSH_NULL`, :opcode:`PRECALL`, :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.

* Replaced :opcode:`JUMP_IF_NOT_EXC_MATCH` by :opcode:`CHECK_EXC_MATCH` which
  performs the check but does not jump.

* Replaced :opcode:`JUMP_IF_NOT_EG_MATCH` by :opcode:`CHECK_EG_MATCH` which
  performs the check but does not jump.

* Replaced :opcode:`JUMP_ABSOLUTE` by the relative :opcode:`JUMP_BACKWARD`.

* Added :opcode:`JUMP_BACKWARD_NO_INTERRUPT`, which is used in certain loops where it
  is undesirable to handle interrupts.

* Replaced :opcode:`POP_JUMP_IF_TRUE` and :opcode:`POP_JUMP_IF_FALSE` by
  the relative :opcode:`POP_JUMP_FORWARD_IF_TRUE`, :opcode:`POP_JUMP_BACKWARD_IF_TRUE`,
  :opcode:`POP_JUMP_FORWARD_IF_FALSE` and :opcode:`POP_JUMP_BACKWARD_IF_FALSE`.

* Added :opcode:`POP_JUMP_FORWARD_IF_NOT_NONE`, :opcode:`POP_JUMP_BACKWARD_IF_NOT_NONE`,
  :opcode:`POP_JUMP_FORWARD_IF_NONE` and :opcode:`POP_JUMP_BACKWARD_IF_NONE`
  opcodes to speed up conditional jumps.

* :opcode:`JUMP_IF_TRUE_OR_POP` and :opcode:`JUMP_IF_FALSE_OR_POP` are now
  relative rather than absolute.


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`.)

* Undocumented modules ``sre_compile``, ``sre_constants`` and ``sre_parse``
  are now deprecated.
  (Contributed by Serhiy Storchaka in :issue:`47152`.)

* :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`.)

* :class:`configparser.LegacyInterpolation` has been deprecated in the docstring
  since Python 3.2. It now emits a :exc:`DeprecationWarning` and will be removed
  in Python 3.13. Use :class:`configparser.BasicInterpolation` or
  :class:`configparser.ExtendedInterpolation` instead.
  (Contributed by Hugo van Kemenade in :issue:`46607`.)

* The :func:`locale.getdefaultlocale` function is deprecated and will be
  removed in Python 3.13. Use :func:`locale.setlocale`,
  :func:`locale.getpreferredencoding(False) <locale.getpreferredencoding>` and
  :func:`locale.getlocale` functions instead.
  (Contributed by Victor Stinner in :issue:`46659`.)

* The :mod:`asynchat`, :mod:`asyncore` and  :mod:`smtpd` modules have been
  deprecated since at least Python 3.6. Their documentation and deprecation
  warnings have now been updated to note they will removed in Python 3.12
  (:pep:`594`).
  (Contributed by Hugo van Kemenade in :issue:`47022`.)

* :pep:`594` led to the deprecations of the following modules which are
  slated for removal in Python 3.13:

  * :mod:`aifc`
  * :mod:`audioop`
  * :mod:`cgi`
  * :mod:`cgitb`
  * :mod:`chunk`
  * :mod:`crypt`
  * :mod:`imghdr`
  * :mod:`msilib`
  * :mod:`nis`
  * :mod:`nntplib`
  * :mod:`ossaudiodev`
  * :mod:`pipes`

  (Contributed by Brett Cannon in :issue:`47061`.)


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`.)

* Remove the undocumented private ``float.__set_format__()`` method, previously
  known as ``float.__setformat__()`` in Python 3.7. Its docstring said: "You
  probably don't want to use this function. It exists mainly to be used in
  Python's test suite."
  (Contributed by Victor Stinner in :issue:`46852`.)

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`.)

* Global inline flags (e.g. ``(?i)``) can now only be used at the start of
  the regular expressions.  Using them not at the start of expression was
  deprecated since Python 3.6.
  (Contributed by Serhiy Storchaka in :issue:`47066`.)

* :mod:`re` module: Fix a few long-standing bugs where, in rare cases,
  capturing group could get wrong result. So the result may be different than
  before.
  (Contributed by Ma Lin in :issue:`35859`.)

* The *population* parameter of :func:`random.sample` must be a sequence.
  Automatic conversion of sets to lists is no longer supported. If the sample size
  is larger than the population size, a :exc:`ValueError` is raised.
  (Contributed by Raymond Hettinger in :issue:`40465`.)


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

* Building Python now requires a C11 compiler without optional C11 features.
  (Contributed by Victor Stinner in :issue:`46656`.)

* Building Python now requires support of IEEE 754 floating point numbers.
  (Contributed by Victor Stinner in :issue:`46917`.)

* 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.
  (Contributed by Victor Stinner in :issue:`46640`.)

* Building Python now requires support for floating point Not-a-Number (NaN):
  remove the ``Py_NO_NAN`` macro.
  (Contributed by Victor Stinner in :issue:`46656`.)

* 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, Tcl/Tk libs, and uuid flags
  are detected by ``pkg-config`` (when available).
  (Contributed by Christian Heimes and Erlend Egeberg Aasland in
  :issue:`45847`, :issue:`45747`, and :issue:`45763`.)

  .. note::
     Use the environment variables ``TCLTK_CFLAGS`` and ``TCLTK_LIBS`` to
     manually specify the location of Tcl/Tk headers and libraries.
     The :program:`configure` options ``--with-tcltk-includes`` and
     ``--with-tcltk-libs`` have been removed.

* 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`.)

* The :mod:`tkinter` package now requires Tcl/Tk version 8.5.12 or newer.
  (Contributed by Serhiy Storchaka in :issue:`46996`.)


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`.)

* :c:func:`_PyFrameEvalFunction` now takes ``_PyInterpreterFrame*``
  as its second parameter, instead of ``PyFrameObject*``.
  See :pep:`523` for more details of how to use this function pointer type.

* :c:func:`PyCode_New` and :c:func:`PyCode_NewWithPosOnlyArgs` now take
  an additional ``exception_table`` argument.
  Using these functions should be avoided, if at all possible.
  To get a custom code object: create a code object using the compiler,
  then get a modified version with the ``replace`` method.

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`.)

* Add new functions to pack and unpack C double (serialize and deserialize):
  :c:func:`PyFloat_Pack2`, :c:func:`PyFloat_Pack4`, :c:func:`PyFloat_Pack8`,
  :c:func:`PyFloat_Unpack2`, :c:func:`PyFloat_Unpack4` and
  :c:func:`PyFloat_Unpack8`.
  (Contributed by Victor Stinner in :issue:`46906`.)

* Add new functions to get frame object attributes:
  :c:func:`PyFrame_GetBuiltins`, :c:func:`PyFrame_GetGenerator`,
  :c:func:`PyFrame_GetGlobals`, :c:func:`PyFrame_GetLasti`.

* Added two new functions to get and set the active exception instance:
  :c:func:`PyErr_GetHandledException` and :c:func:`PyErr_SetHandledException`.
  These are alternatives to :c:func:`PyErr_SetExcInfo()` and
  :c:func:`PyErr_GetExcInfo()` which work with the legacy 3-tuple
  representation of exceptions.
  (Contributed by Irit Katriel in :issue:`46343`.)


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``, ``code.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`.)

.. _pyframeobject-3.11-hiding:

* The :c:type:`PyFrameObject` structure members have been removed from the
  public C API.

  While the documentation notes that the :c:type:`PyFrameObject` fields 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. Some fields were removed entirely, as they were details of the
  old implementation.

  :c:type:`PyFrameObject` fields:

  * ``f_back``: use :c:func:`PyFrame_GetBack`.
  * ``f_blockstack``: removed.
  * ``f_builtins``: use :c:func:`PyFrame_GetBuiltins`.
  * ``f_code``: use :c:func:`PyFrame_GetCode`.
  * ``f_gen``: use :c:func:`PyFrame_GetGenerator`.
  * ``f_globals``: use :c:func:`PyFrame_GetGlobals`.
  * ``f_iblock``: removed.
  * ``f_lasti``: use :c:func:`PyFrame_GetLasti`.
    Code using ``f_lasti`` with ``PyCode_Addr2Line()`` should use
    :c:func:`PyFrame_GetLineNumber` instead; it may be faster.
  * ``f_lineno``: use :c:func:`PyFrame_GetLineNumber`
  * ``f_locals``: use :c:func:`PyFrame_GetLocals`.
  * ``f_stackdepth``: removed.
  * ``f_state``: no public API (renamed to ``f_frame.f_state``).
  * ``f_trace``: no public API.
  * ``f_trace_lines``: use ``PyObject_GetAttrString((PyObject*)frame, "f_trace_lines")``.
  * ``f_trace_opcodes``: use ``PyObject_GetAttrString((PyObject*)frame, "f_trace_opcodes")``.
  * ``f_localsplus``: no public API (renamed to ``f_frame.localsplus``).
  * ``f_valuestack``: removed.

  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.

  Debuggers that accessed the ``f_locals`` directly *must* call
  :c:func:`PyFrame_GetLocals` instead. They no longer need to call
  :c:func:`PyFrame_FastToLocalsWithError` or :c:func:`PyFrame_LocalsToFast`,
  in fact they should not call those functions. The necessary updating of the
  frame is now managed by the virtual machine.

  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/python/pythoncapi_compat>`__ to get these two
  functions 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/python/pythoncapi_compat>`__ to get these functions
  on old Python functions.

* Distributors are encouraged to build Python with the optimized Blake2
  library `libb2`_.


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`.)

* Deprecate the ``ob_shash`` member of the :c:type:`PyBytesObject`. Use :c:func:`PyObject_Hash` instead.
  (Contributed by Inada Naoki in :issue:`46864`.)

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`.)

* Remove the ``HAVE_PY_SET_53BIT_PRECISION`` macro (moved to the internal C
  API).
  (Contributed by Victor Stinner in :issue:`45412`.)


.. _libb2: https://www.blake2.net/