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.



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`.)


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`.)


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`.)


math
----

* 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`.)


os
--

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


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 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`.)


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`.)

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.)

* :file:`.pdbrc` is now read with ``'utf-8'`` encoding.


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

* Added a new :opcode:`CALL_METHOD_KW` opcode.  Calls a method in a similar
  fashion as :opcode:`CALL_METHOD`, but also supports keyword arguments.  Works
  in tandem with :opcode:`LOAD_METHOD`.


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


Deprecated
==========

* The :mod:`lib2to3` package is 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`.)


Removed
=======

* 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`.)

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`.)


C API Changes
=============
* 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`.)

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

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`)

Deprecated
----------

Removed
-------

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

* 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`.)

* 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 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.