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[3.13] pythonGH-109975: Copyedit 3.13 What's New: Other Language Chan…
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pythonGH-109975: Copyedit 3.13 What's New: Other Language Changes (pythonGH-123086)
(cherry picked from commit d60b97a)

Co-authored-by: Adam Turner <[email protected]>
Co-authored-by: Hugo van Kemenade <[email protected]>
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@miss-islington @AA-Turner @hugovk
3 people authored Aug 17, 2024
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258 changes: 156 additions & 102 deletions Doc/whatsnew/3.13.rst
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Expand Up @@ -242,6 +242,7 @@ Windows support contributed by Dino Viehland and Anthony Shaw.)

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


.. _whatsnew313-improved-error-messages:

Improved error messages
Expand Down Expand Up @@ -492,138 +493,123 @@ Incremental garbage collection
The cycle garbage collector is now incremental.
This means that maximum pause times are reduced
by an order of magnitude or more for larger heaps.
(Contributed by Mark Shannon in :gh:`108362`.)


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

* Classes have a new :attr:`~class.__static_attributes__` attribute, populated by the compiler,
with a tuple of names of attributes of this class which are assigned
through ``self.X`` from any function in its body. (Contributed by Irit Katriel
in :gh:`115775`.)
* The compiler now strips common common leading whitespace
from every line in a docstring.
This reduces the size of the :term:`bytecode cache <bytecode>`
(such as ``.pyc`` files), with reductions in file size of around 5%,
for example in :mod:`!sqlalchemy.orm.session` from SQLAlchemy 2.0.
This change affects tools that use docstrings, such as :mod:`doctest`.

.. doctest::

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

* The :func:`exec` and :func:`eval` built-ins now accept their ``globals``
and ``locals`` namespace arguments as keywords.
(Contributed by Raphael Gaschignard in :gh:`105879`)
(Contributed by Inada Naoki in :gh:`81283`.)

* Allow the *count* argument of :meth:`str.replace` to be a keyword.
(Contributed by Hugo van Kemenade in :gh:`106487`.)
* :ref:`Annotation scopes <annotation-scopes>` within class scopes
can now contain lambdas and comprehensions.
Comprehensions that are located within class scopes
are not inlined into their parent scope.

* Compiler now strip indents from docstrings.
This will reduce the size of :term:`bytecode cache <bytecode>` (e.g. ``.pyc`` file).
For example, cache file size for ``sqlalchemy.orm.session`` in SQLAlchemy 2.0
is reduced by about 5%.
This change will affect tools using docstrings, like :mod:`doctest`.
(Contributed by Inada Naoki in :gh:`81283`.)
.. code-block:: python
* The :func:`compile` built-in can now accept a new flag,
``ast.PyCF_OPTIMIZED_AST``, which is similar to ``ast.PyCF_ONLY_AST``
except that the returned ``AST`` is optimized according to the value
of the ``optimize`` argument.
(Contributed by Irit Katriel in :gh:`108113`).
class C[T]:
type Alias = lambda: T
* :mod:`multiprocessing`, :mod:`concurrent.futures`, :mod:`compileall`:
Replace :func:`os.cpu_count` with :func:`os.process_cpu_count` to select the
default number of worker threads and processes. Get the CPU affinity
if supported.
(Contributed by Victor Stinner in :gh:`109649`.)
(Contributed by Jelle Zijlstra in :gh:`109118` and :gh:`118160`.)

* :func:`os.path.realpath` now resolves MS-DOS style file names even if
the file is not accessible.
(Contributed by Moonsik Park in :gh:`82367`.)
* :ref:`Future statements <future>` are no longer triggered by
relative imports of the :mod:`__future__` module,
meaning that statements of the form ``from .__future__ import ...``
are now simply standard relative imports, with no special features activated.
(Contributed by Jeremiah Gabriel Pascual in :gh:`118216`.)

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

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

* Added a new environment variable :envvar:`PYTHON_FROZEN_MODULES`. It
determines whether or not frozen modules are ignored by the import machinery,
equivalent of the :option:`-X frozen_modules <-X>` command-line option.
* Add :envvar:`PYTHON_FROZEN_MODULES`, a new environment variable that
determines whether frozen modules are ignored by the import machinery,
equivalent to the :option:`-X frozen_modules <-X>` command-line option.
(Contributed by Yilei Yang in :gh:`111374`.)

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

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

* Add :exc:`PythonFinalizationError` exception. This exception derived from
:exc:`RuntimeError` is raised when an operation is blocked during
the :term:`Python finalization <interpreter shutdown>`.

The following functions now raise PythonFinalizationError, instead of
:exc:`RuntimeError`:

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

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

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

* Allow controlling Expat >=2.6.0 reparse deferral (:cve:`2023-52425`)
by adding five new methods:
* Add :ref:`support for the perf profiler <perf_profiling>` working
without `frame pointers <https://en.wikipedia.org/wiki/Call_stack>`_ through
the new environment variable :envvar:`PYTHON_PERF_JIT_SUPPORT`
and command-line option :option:`-X perf_jit <-X>`.
(Contributed by Pablo Galindo in :gh:`118518`.)

* :meth:`xml.etree.ElementTree.XMLParser.flush`
* :meth:`xml.etree.ElementTree.XMLPullParser.flush`
* :meth:`xml.parsers.expat.xmlparser.GetReparseDeferralEnabled`
* :meth:`xml.parsers.expat.xmlparser.SetReparseDeferralEnabled`
* :meth:`!xml.sax.expatreader.ExpatParser.flush`
* The location of a :file:`.python_history` file can be changed via the
new :envvar:`PYTHON_HISTORY` environment variable.
(Contributed by Levi Sabah, Zackery Spytz and Hugo van Kemenade
in :gh:`73965`.)

(Contributed by Sebastian Pipping in :gh:`115623`.)
* Classes have a new :attr:`~class.__static_attributes__` attribute.
This is populated by the compiler with a tuple of the class's attribute names
which are assigned through ``self.<name>`` from any function in its body.
(Contributed by Irit Katriel in :gh:`115775`.)

* The :func:`ssl.create_default_context` API now includes
:data:`ssl.VERIFY_X509_PARTIAL_CHAIN` and :data:`ssl.VERIFY_X509_STRICT`
in its default flags.
* The compiler now creates a :attr:`!__firstlineno__` attribute on classes
with the line number of the first line of the class definition.
(Contributed by Serhiy Storchaka in :gh:`118465`.)

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

:data:`ssl.VERIFY_X509_STRICT` may reject pre-:rfc:`5280` or malformed
certificates that the underlying OpenSSL implementation otherwise would
accept. While disabling this is not recommended, you can do so using::
* The :func:`compile` builtin now accepts a new flag,
``ast.PyCF_OPTIMIZED_AST``, which is similar to ``ast.PyCF_ONLY_AST``
except that the returned AST is optimized according to
the value of the *optimize* argument.
(Contributed by Irit Katriel in :gh:`108113`).

ctx = ssl.create_default_context()
ctx.verify_flags &= ~ssl.VERIFY_X509_STRICT
* Add :exc:`PythonFinalizationError`, a new exception derived from
:exc:`RuntimeError` and used to signal when operations are blocked
during :term:`finalization <interpreter shutdown>`.
The following callables now raise :exc:`!PythonFinalizationError`,
instead of :exc:`RuntimeError`:

(Contributed by William Woodruff in :gh:`112389`.)
* :func:`_thread.start_new_thread`
* :func:`os.fork`
* :func:`os.forkpty`
* :class:`subprocess.Popen`

* The :class:`configparser.ConfigParser` now accepts unnamed sections before named
ones if configured to do so.
(Contributed by Pedro Sousa Lacerda in :gh:`66449`.)
(Contributed by Victor Stinner in :gh:`114570`.)

* :ref:`annotation scope <annotation-scopes>` within class scopes can now
contain lambdas and comprehensions. Comprehensions that are located within
class scopes are not inlined into their parent scope. (Contributed by
Jelle Zijlstra in :gh:`109118` and :gh:`118160`.)
* Allow the *count* argument of :meth:`str.replace` to be a keyword.
(Contributed by Hugo van Kemenade in :gh:`106487`.)

* Classes have a new :attr:`!__firstlineno__` attribute,
populated by the compiler, with the line number of the first line
of the class definition.
(Contributed by Serhiy Storchaka in :gh:`118465`.)
* Many functions now emit a warning if a boolean value is passed as
a file descriptor argument.
This can help catch some errors earlier.
(Contributed by Serhiy Storchaka in :gh:`82626`.)

* ``from __future__ import ...`` statements are now just normal
relative imports if dots are present before the module name.
(Contributed by Jeremiah Gabriel Pascual in :gh:`118216`.)
* Added :attr:`!name` and :attr:`!mode` attributes
for compressed and archived file-like objects in
the :mod:`bz2`, :mod:`lzma`, :mod:`tarfile`, and :mod:`zipfile` modules.
(Contributed by Serhiy Storchaka in :gh:`115961`.)


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

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


Expand Down Expand Up @@ -748,6 +734,23 @@ base64
See the `Z85 specification <https://rfc.zeromq.org/spec/32/>`_ for more information.
(Contributed by Matan Perelman in :gh:`75299`.)


compileall
----------

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


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

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


copy
----

Expand Down Expand Up @@ -953,6 +956,15 @@ mmap
is inaccessible due to file system errors or access violations.
(Contributed by Jannis Weigend in :gh:`118209`.)


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

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


opcode
------

Expand Down Expand Up @@ -1017,10 +1029,15 @@ os.path
* Add :func:`os.path.isreserved` to check if a path is reserved on the current
system. This function is only available on Windows.
(Contributed by Barney Gale in :gh:`88569`.)

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

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

* Add support of *dir_fd* and *follow_symlinks* keyword arguments in
:func:`shutil.chown`.
(Contributed by Berker Peksag and Tahia K in :gh:`62308`)
Expand Down Expand Up @@ -1120,6 +1137,26 @@ sqlite3
for filtering database objects to dump.
(Contributed by Mariusz Felisiak in :gh:`91602`.)


ssl
---

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

.. note::

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

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

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


statistics
----------

Expand Down Expand Up @@ -1285,13 +1322,26 @@ warnings
warning may also be emitted when a decorated function or class is used at runtime.
See :pep:`702`. (Contributed by Jelle Zijlstra in :gh:`104003`.)

xml.etree.ElementTree
---------------------

xml
---

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

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

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

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


zipimport
---------

Expand Down Expand Up @@ -1447,6 +1497,10 @@ PEP 594: dead batteries (and other module removals)
configparser
------------

* The :class:`configparser.ConfigParser` now accepts unnamed sections
before named ones if configured to do so.
(Contributed by Pedro Sousa Lacerda in :gh:`66449`.)

* Remove the undocumented :class:`!configparser.LegacyInterpolation` class,
deprecated in the docstring since Python 3.2,
and with a deprecation warning since Python 3.11.
Expand Down

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