.. bpo: 44600
.. date: 2021-07-25-20-04-54
.. nonce: 0WMldg
.. release date: 2021-08-02
.. section: Security

Fix incorrect line numbers while tracing some failed patterns in :ref:`match
<match>` statements. Patch by Charles Burkland.

..

.. bpo: 44792
.. date: 2021-07-31-12-12-57
.. nonce: mOReTW
.. section: Core and Builtins

Improve syntax errors for if expressions. Patch by Miguel Brito

..

.. bpo: 34013
.. date: 2021-07-27-11-14-22
.. nonce: SjLFe-
.. section: Core and Builtins

Generalize the invalid legacy statement custom error message (like the one
generated when "print" is called without parentheses) to include more
generic expressions. Patch by Pablo Galindo

..

.. bpo: 44732
.. date: 2021-07-26-15-27-03
.. nonce: IxObt3
.. section: Core and Builtins

Rename ``types.Union`` to ``types.UnionType``.

..

.. bpo: 44698
.. date: 2021-07-21-15-26-56
.. nonce: DA4_0o
.. section: Core and Builtins

Fix undefined behaviour in complex object exponentiation.

..

.. bpo: 44653
.. date: 2021-07-19-20-49-06
.. nonce: WcqGyI
.. section: Core and Builtins

Support :mod:`typing` types in parameter substitution in the union type.

..

.. bpo: 44676
.. date: 2021-07-19-19-53-46
.. nonce: WgIMvh
.. section: Core and Builtins

Add ability to serialise ``types.Union`` objects. Patch provided by Yurii
Karabas.

..

.. bpo: 44633
.. date: 2021-07-17-21-04-04
.. nonce: 5-zKeI
.. section: Core and Builtins

Parameter substitution of the union type with wrong types now raises
``TypeError`` instead of returning ``NotImplemented``.

..

.. bpo: 44662
.. date: 2021-07-17-13-41-58
.. nonce: q22kWR
.. section: Core and Builtins

Add ``__module__`` to ``types.Union``. This also fixes ``types.Union``
issues with ``typing.Annotated``. Patch provided by Yurii Karabas.

..

.. bpo: 44655
.. date: 2021-07-16-21-35-14
.. nonce: 95I7M6
.. section: Core and Builtins

Include the name of the type in unset __slots__ attribute errors. Patch by
Pablo Galindo

..

.. bpo: 44655
.. date: 2021-07-16-20-25-37
.. nonce: I3wRjL
.. section: Core and Builtins

Don't include a missing attribute with the same name as the failing one when
offering suggestions for missing attributes. Patch by Pablo Galindo

..

.. bpo: 44646
.. date: 2021-07-16-09-59-13
.. nonce: Yb6s05
.. section: Core and Builtins

Fix the hash of the union type: it no longer depends on the order of
arguments.

..

.. bpo: 44636
.. date: 2021-07-16-09-36-12
.. nonce: ZWebi8
.. section: Core and Builtins

Collapse union of equal types. E.g. the result of ``int | int`` is now
``int``. Fix comparison of the union type with non-hashable objects. E.g.
``int | str == {}`` no longer raises a TypeError.

..

.. bpo: 44635
.. date: 2021-07-14-13-54-07
.. nonce: 7ZMAdB
.. section: Core and Builtins

Convert ``None`` to ``type(None)`` in the union type constructor.

..

.. bpo: 44589
.. date: 2021-07-13-23-19-41
.. nonce: 59OH8T
.. section: Core and Builtins

Mapping patterns in ``match`` statements with two or more equal literal keys
will now raise a :exc:`SyntaxError` at compile-time.

..

.. bpo: 44606
.. date: 2021-07-13-20-22-12
.. nonce: S3Bv2w
.. section: Core and Builtins

Fix ``__instancecheck__`` and ``__subclasscheck__`` for the union type.

..

.. bpo: 42073
.. date: 2021-07-13-17-47-32
.. nonce: 9wopiC
.. section: Core and Builtins

The ``@classmethod`` decorator can now wrap other classmethod-like
descriptors.

..

.. bpo: 44490
.. date: 2021-07-06-22-22-15
.. nonce: BJxPbZ
.. section: Core and Builtins

:mod:`typing` now searches for type parameters in ``types.Union`` objects.
``get_type_hints`` will also properly resolve annotations with nested
``types.Union`` objects. Patch provided by Yurii Karabas.

..

.. bpo: 44490
.. date: 2021-07-01-11-59-34
.. nonce: xY80VR
.. section: Core and Builtins

Add ``__parameters__`` attribute and ``__getitem__`` operator to
``types.Union``. Patch provided by Yurii Karabas.

..

.. bpo: 44472
.. date: 2021-06-21-11-19-54
.. nonce: Vvm1yn
.. section: Core and Builtins

Fix ltrace functionality when exceptions are raised. Patch by Pablo Galindo

..

.. bpo: 44806
.. date: 2021-08-02-14-37-32
.. nonce: wOW_Qn
.. section: Library

Non-protocol subclasses of :class:`typing.Protocol` ignore now the
``__init__`` method inherited from protocol base classes.

..

.. bpo: 44793
.. date: 2021-07-31-20-28-20
.. nonce: woaQSg
.. section: Library

Fix checking the number of arguments when subscribe a generic type with
``ParamSpec`` parameter.

..

.. bpo: 44784
.. date: 2021-07-31-08-45-31
.. nonce: fIMIDS
.. section: Library

In importlib.metadata tests, override warnings behavior under expected
DeprecationWarnings (importlib_metadata 4.6.3).

..

.. bpo: 44667
.. date: 2021-07-30-23-27-30
.. nonce: tu0Xrv
.. section: Library

The :func:`tokenize.tokenize` doesn't incorrectly generate a ``NEWLINE``
token if the source doesn't end with a new line character but the last line
is a comment, as the function is already generating a ``NL`` token. Patch by
Pablo Galindo

..

.. bpo: 44752
.. date: 2021-07-27-22-11-29
.. nonce: _bvbrZ
.. section: Library

:mod:`rcompleter` does not call :func:`getattr` on :class:`property` objects
to avoid the side-effect of  evaluating the corresponding method.

..

.. bpo: 44720
.. date: 2021-07-24-02-17-59
.. nonce: shU5Qm
.. section: Library

``weakref.proxy`` objects referencing non-iterators now raise ``TypeError``
rather than dereferencing the null ``tp_iternext`` slot and crashing.

..

.. bpo: 44704
.. date: 2021-07-21-23-16-30
.. nonce: iqHLxQ
.. section: Library

The implementation of ``collections.abc.Set._hash()`` now matches that of
``frozenset.__hash__()``.

..

.. bpo: 44666
.. date: 2021-07-21-10-43-22
.. nonce: CEThkv
.. section: Library

Fixed issue in :func:`compileall.compile_file` when ``sys.stdout`` is
redirected. Patch by Stefan Hölzl.

..

.. bpo: 42854
.. date: 2021-07-20-21-51-35
.. nonce: ThuDMI
.. section: Library

Fixed a bug in the :mod:`_ssl` module that was throwing :exc:`OverflowError`
when using :meth:`_ssl._SSLSocket.write` and :meth:`_ssl._SSLSocket.read`
for a big value of the ``len`` parameter. Patch by Pablo Galindo

..

.. bpo: 44353
.. date: 2021-07-19-22-43-15
.. nonce: HF81_Q
.. section: Library

Refactor ``typing.NewType`` from function into callable class. Patch
provided by Yurii Karabas.

..

.. bpo: 44524
.. date: 2021-07-19-14-04-42
.. nonce: Nbf2JC
.. section: Library

Add missing ``__name__`` and ``__qualname__`` attributes to ``typing``
module classes. Patch provided by Yurii Karabas.

..

.. bpo: 40897
.. date: 2021-07-16-13-40-31
.. nonce: aveAre
.. section: Library

Give priority to using the current class constructor in
:func:`inspect.signature`. Patch by Weipeng Hong.

..

.. bpo: 44648
.. date: 2021-07-15-16-51-32
.. nonce: 2o49TB
.. section: Library

Fixed wrong error being thrown by :func:`inspect.getsource` when examining a
class in the interactive session. Instead of :exc:`TypeError`, it should be
:exc:`OSError` with appropriate error message.

..

.. bpo: 44608
.. date: 2021-07-13-09-01-33
.. nonce: R3IcM1
.. section: Library

Fix memory leak in :func:`_tkinter._flatten` if it is called with a sequence
or set, but not list or tuple.

..

.. bpo: 44559
.. date: 2021-07-12-10-43-31
.. nonce: YunVKY
.. section: Library

[Enum] module reverted to 3.9; 3.10 changes pushed until 3.11

..

.. bpo: 41928
.. date: 2021-07-09-07-14-37
.. nonce: Q1jMrr
.. section: Library

Update :func:`shutil.copyfile` to raise :exc:`FileNotFoundError` instead of
confusing :exc:`IsADirectoryError` when a path ending with a
:const:`os.path.sep` does not exist; :func:`shutil.copy` and
:func:`shutil.copy2` are also affected.

..

.. bpo: 44566
.. date: 2021-07-05-18-13-25
.. nonce: o51Bd1
.. section: Library

handle StopIteration subclass raised from @contextlib.contextmanager
generator

..

.. bpo: 41249
.. date: 2021-07-04-11-33-34
.. nonce: sHdwBE
.. section: Library

Fixes ``TypedDict`` to work with ``typing.get_type_hints()`` and postponed
evaluation of annotations across modules.

..

.. bpo: 44461
.. date: 2021-06-29-21-17-17
.. nonce: acqRnV
.. section: Library

Fix bug with :mod:`pdb`'s handling of import error due to a package which
does not have a ``__main__`` module

..

.. bpo: 43625
.. date: 2021-06-29-07-27-08
.. nonce: ZlAxhp
.. section: Library

Fix a bug in the detection of CSV file headers by
:meth:`csv.Sniffer.has_header` and improve documentation of same.

..

.. bpo: 42892
.. date: 2021-06-24-19-16-20
.. nonce: qvRNhI
.. section: Library

Fixed an exception thrown while parsing a malformed multipart email by
:class:`email.message.EmailMessage`.

..

.. bpo: 27827
.. date: 2021-06-12-21-25-35
.. nonce: TMWh1i
.. section: Library

:meth:`pathlib.PureWindowsPath.is_reserved` now identifies a greater range
of reserved filenames, including those with trailing spaces or colons.

..

.. bpo: 38741
.. date: 2019-11-12-18-59-33
.. nonce: W7IYkq
.. section: Library

:mod:`configparser`: using ']' inside a section header will no longer cut
the section name short at the ']'

..

.. bpo: 27513
.. date: 2019-06-03-23-53-25
.. nonce: qITN7d
.. section: Library

:func:`email.utils.getaddresses` now accepts :class:`email.header.Header`
objects along with string values. Patch by Zackery Spytz.

..

.. bpo: 29298
.. date: 2017-09-20-14-43-03
.. nonce: _78CSN
.. section: Library

Fix ``TypeError`` when required subparsers without ``dest`` do not receive
arguments. Patch by Anthony Sottile.

..

.. bpo: 44740
.. date: 2021-07-26-23-48-31
.. nonce: zMFGMV
.. section: Documentation

Replaced occurences of uppercase "Web" and "Internet" with lowercase
versions per the 2016 revised Associated Press Style Book.

..

.. bpo: 44693
.. date: 2021-07-25-23-04-15
.. nonce: JuCbNq
.. section: Documentation

Update the definition of __future__ in the glossary by replacing the
confusing word "pseudo-module" with a more accurate description.

..

.. bpo: 35183
.. date: 2021-07-22-08-28-03
.. nonce: p9BWTB
.. section: Documentation

Add typical examples to os.path.splitext docs

..

.. bpo: 30511
.. date: 2021-07-20-21-03-18
.. nonce: eMFkRi
.. section: Documentation

Clarify that :func:`shutil.make_archive` is not thread-safe due to reliance
on changing the current working directory.

..

.. bpo: 44561
.. date: 2021-07-18-22-43-14
.. nonce: T7HpWm
.. section: Documentation

Update of three expired hyperlinks in Doc/distributing/index.rst: "Project
structure", "Building and packaging the project", and "Uploading the project
to the Python Packaging Index".

..

.. bpo: 44613
.. date: 2021-07-12-11-39-20
.. nonce: DIXNzc
.. section: Documentation

importlib.metadata is no longer provisional.

..

.. bpo: 44544
.. date: 2021-07-02-14-02-29
.. nonce: _5_aCz
.. section: Documentation

List all kwargs for :func:`textwrap.wrap`, :func:`textwrap.fill`, and
:func:`textwrap.shorten`. Now, there are nav links to attributes of
:class:`TextWrap`, which makes navigation much easier while minimizing
duplication in the documentation.

..

.. bpo: 44453
.. date: 2021-06-18-06-44-45
.. nonce: 3PIkj2
.. section: Documentation

Fix documentation for the return type of :func:`sysconfig.get_path`.

..

.. bpo: 44734
.. date: 2021-07-24-20-09-15
.. nonce: KKsNOV
.. section: Tests

Fixed floating point precision issue in turtle tests.

..

.. bpo: 44708
.. date: 2021-07-22-16-38-39
.. nonce: SYNaac
.. section: Tests

Regression tests, when run with -w, are now re-running only the affected
test methods instead of re-running the entire test file.

..

.. bpo: 44647
.. date: 2021-07-16-14-02-33
.. nonce: 5LzqIy
.. section: Tests

Added a permanent Unicode-valued environment variable to regression tests to
ensure they handle this use case in the future. If your test environment
breaks because of that, report a bug to us, and temporarily set
PYTHONREGRTEST_UNICODE_GUARD=0 in your test environment.

..

.. bpo: 44515
.. date: 2021-06-26-18-37-36
.. nonce: e9fO6f
.. section: Tests

Adjust recently added contextlib tests to avoid assuming the use of a
refcounted GC

..

.. bpo: 44572
.. date: 2021-07-13-15-32-49
.. nonce: gXvhDc
.. section: Windows

Avoid consuming standard input in the :mod:`platform` module

..

.. bpo: 40263
.. date: 2020-04-13-15-20-28
.. nonce: 1KKEbu
.. section: Windows

This is a follow-on bug from https://bugs.python.org/issue26903. Once that
is applied we run into an off-by-one assertion problem. The assert was not
correct.

..

.. bpo: 41972
.. date: 2021-07-12-15-42-02
.. nonce: yUjE8j
.. section: macOS

The framework build's user header path in sysconfig is changed to add a
'pythonX.Y' component to match distutils's behavior.

..

.. bpo: 34932
.. date: 2021-03-29-21-11-23
.. nonce: f3Hdyd
.. section: macOS

Add socket.TCP_KEEPALIVE support for macOS. Patch by Shane Harvey.

..

.. bpo: 44756
.. date: 2021-07-28-00-51-55
.. nonce: pvAajB
.. section: Tools/Demos

In the Makefile for documentation (:file:`Doc/Makefile`), the ``build`` rule
is dependent on the ``venv`` rule. Therefore, ``html``, ``latex``, and other
build-dependent rules are also now dependent on ``venv``. The ``venv`` rule
only performs an action if ``$(VENVDIR)`` does not exist.
:file:`Doc/README.rst` was updated; most users now only need to type ``make
html``.

..

.. bpo: 41103
.. date: 2021-07-29-16-04-28
.. nonce: hiKKcF
.. section: C API

Reverts removal of the old buffer protocol because they are part of stable
ABI.

..

.. bpo: 42747
.. date: 2021-07-20-16-21-06
.. nonce: rRxjUY
.. section: C API

The ``Py_TPFLAGS_HAVE_VERSION_TAG`` type flag now does nothing. The
``Py_TPFLAGS_HAVE_AM_SEND`` flag (which was added in 3.10) is removed. Both
were unnecessary because it is not possible to have type objects with the
relevant fields missing.