GH-109975: Copyedit 3.13 What's New: Other Language Changes (#123086)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Author: AA-Turner

Doc/whatsnew/3.13.rst

@@ -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
@@ -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`.)
 
 
@@ -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
 ----
 
@@ -965,6 +968,15 @@ 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
 ------
 
@@ -1029,10 +1041,15 @@ 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`)
@@ -1132,6 +1149,26 @@ 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
 ----------
 
@@ -1297,13 +1334,26 @@ 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
 ---------
 
@@ -1459,6 +1509,10 @@ 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.