.. bpo: 44022
.. date: 2021-05-05-17-37-04
.. nonce: bS3XJ9
.. release date: 2021-05-31
.. section: Security

mod:`http.client` now avoids infinitely reading potential HTTP headers after
a ``100 Continue`` status response from the server.

..

.. bpo: 43667
.. date: 2021-05-27-17-34-29
.. nonce: ND9jP3
.. section: Core and Builtins

Improve Unicode support in non-UTF locales on Oracle Solaris. This issue
does not affect other Solaris systems.

..

.. bpo: 44232
.. date: 2021-05-25-18-20-10
.. nonce: DMcCCf
.. section: Core and Builtins

Fix a regression in :func:`type` when a metaclass raises an exception. The C
function :c:func:`type_new` must properly report the exception when a
metaclass constructor raises an exception and the winner class is not the
metaclass. Patch by Victor Stinner.

..

.. bpo: 44201
.. date: 2021-05-21-21-16-03
.. nonce: bGaSjt
.. section: Core and Builtins

Avoid side effects of checking for specialized syntax errors in the REPL
that was causing it to ask for extra tokens after a syntax error had been
detected. Patch by Pablo Galindo

..

.. bpo: 44184
.. date: 2021-05-21-01-42-45
.. nonce: 9qOptC
.. section: Core and Builtins

Fix a crash at Python exit when a deallocator function removes the last
strong reference to a heap type. Patch by Victor Stinner.

..

.. bpo: 44180
.. date: 2021-05-19-20-33-36
.. nonce: mQVaAs
.. section: Core and Builtins

The parser doesn't report generic syntax errors that happen in a position
further away that the one it reached in the first pass. Patch by Pablo
Galindo

..

.. bpo: 44168
.. date: 2021-05-18-11-27-02
.. nonce: mgB-rt
.. section: Core and Builtins

Fix error message in the parser involving keyword arguments with invalid
expressions. Patch by Pablo Galindo

..

.. bpo: 44143
.. date: 2021-05-15-17-30-57
.. nonce: 7UTS6H
.. section: Core and Builtins

Fixed a crash in the parser that manifest when raising tokenizer errors when
an existing exception was present. Patch by Pablo Galindo.

..

.. bpo: 44114
.. date: 2021-05-12-14-26-16
.. nonce: p-WfAE
.. section: Core and Builtins

Fix incorrect dictkeys_reversed and dictitems_reversed function signatures
in C code, which broke webassembly builds.

..

.. bpo: 43149
.. date: 2021-05-08-17-18-37
.. nonce: Kp5FxD
.. section: Core and Builtins

Corrent the syntax error message regarding multiple exception types to not
refer to "exception groups". Patch by Pablo Galindo

..

.. bpo: 44056
.. date: 2021-05-06-12-43-04
.. nonce: 4LWcJW
.. section: Core and Builtins

Syntax errors when default ``except`` is not the last ``except``  are
reported with the correct location. Patch by Mark Shannon.

..

.. bpo: 43822
.. date: 2021-05-04-01-01-04
.. nonce: 9VeCg0
.. section: Core and Builtins

The parser will prioritize tokenizer errors over custom syntax errors when
raising exceptions. Patch by Pablo Galindo.

..

.. bpo: 28146
.. date: 2021-01-13-19-34-41
.. nonce: AZBBkH
.. section: Core and Builtins

Fix a confusing error message in :func:`str.format`.

..

.. bpo: 44254
.. date: 2021-05-29-01-05-43
.. nonce: f06xDm
.. section: Library

On Mac, give turtledemo button text a color that works on both light or dark
background.  Programmers cannot control the latter.

..

.. bpo: 38693
.. date: 2021-05-26-14-50-06
.. nonce: NkMacJ
.. section: Library

Prefer f-strings to ``.format`` in importlib.resources.

..

.. bpo: 33693
.. date: 2021-05-26-13-34-37
.. nonce: 3okzdo
.. section: Library

Importlib.metadata now prefers f-strings to .format.

..

.. bpo: 44241
.. date: 2021-05-26-13-15-51
.. nonce: TBqej8
.. section: Library

Incorporate minor tweaks from importlib_metadata 4.1: SimplePath protocol,
support for Metadata 2.2.

..

.. bpo: 44210
.. date: 2021-05-21-21-23-43
.. nonce: 5afQ3K
.. section: Library

Make importlib.metadata._meta.PackageMetadata public.

..

.. bpo: 43643
.. date: 2021-05-21-12-12-35
.. nonce: GWnmcF
.. section: Library

Declare readers.MultiplexedPath.name as a property per the spec.

..

.. bpo: 33433
.. date: 2021-05-16-17-48-24
.. nonce: MyzO71
.. section: Library

For IPv4 mapped IPv6 addresses (:rfc:`4291` Section 2.5.5.2), the
:mod:`ipaddress.IPv6Address.is_private` check is deferred to the mapped IPv4
address. This solves a bug where public mapped IPv4 addresses were
considered private by the IPv6 check.

..

.. bpo: 44145
.. date: 2021-05-16-00-00-38
.. nonce: ko5SJ7
.. section: Library

:mod:`hmac` computations were not releasing the GIL while calling the
OpenSSL ``HMAC_Update`` C API (a new feature in 3.9).  This unintentionally
prevented parallel computation as other :mod:`hashlib` algorithms support.

..

.. bpo: 37788
.. date: 2021-05-13-19-07-28
.. nonce: adeFcf
.. section: Library

Fix a reference leak when a Thread object is never joined.

..

.. bpo: 38908
.. date: 2021-05-12-16-43-21
.. nonce: nM2_rO
.. section: Library

Subclasses of ``typing.Protocol`` which only have data variables declared
will now raise a ``TypeError`` when checked with ``isinstance`` unless they
are decorated with :func:`runtime_checkable`.  Previously, these checks
passed silently. Patch provided by Yurii Karabas.

..

.. bpo: 44098
.. date: 2021-05-10-17-45-00
.. nonce: _MoxuZ
.. section: Library

``typing.ParamSpec`` will no longer be found in the ``__parameters__`` of
most :mod:`typing` generics except in valid use locations specified by
:pep:`612`. This prevents incorrect usage like ``typing.List[P][int]``. This
change means incorrect usage which may have passed silently in 3.10 beta 1
and earlier will now error.

..

.. bpo: 44089
.. date: 2021-05-09-22-52-34
.. nonce: IoANsN
.. section: Library

Allow subclassing ``csv.Error`` in 3.10 (it was allowed in 3.9 and earlier
but was disallowed in early versions of 3.10).

..

.. bpo: 44059
.. date: 2021-05-06-16-01-55
.. nonce: GF5r6O
.. section: Library

Register the SerenityOS Browser in the :mod:`webbrowser` module.

..

.. bpo: 36515
.. date: 2021-05-05-11-44-49
.. nonce: uOSa3q
.. section: Library

The :mod:`hashlib` module no longer does unaligned memory accesses when
compiled for ARM platforms.

..

.. bpo: 44018
.. date: 2021-05-03-10-07-43
.. nonce: VDyW8f
.. section: Library

random.seed() no longer mutates bytearray inputs.

..

.. bpo: 38352
.. date: 2021-05-02-13-54-25
.. nonce: N9MlhV
.. section: Library

Add ``IO``, ``BinaryIO``, ``TextIO``, ``Match``, and ``Pattern`` to
``typing.__all__``. Patch by Jelle Zijlstra.

..

.. bpo: 43972
.. date: 2021-04-30-16-58-24
.. nonce: Y2r9lg
.. section: Library

When :class:`http.server.SimpleHTTPRequestHandler` sends a ``301 (Moved
Permanently)`` for a directory path not ending with `/`, add a
``Content-Length: 0`` header. This improves the behavior for certain
clients.

..

.. bpo: 28528
.. date: 2021-04-29-00-48-00
.. nonce: JLAVWj
.. section: Library

Fix a bug in :mod:`pdb` where :meth:`~pdb.Pdb.checkline` raises
:exc:`AttributeError` if it is called after :meth:`~pdb.Pdb.reset`.

..

.. bpo: 43650
.. date: 2021-03-29-00-23-30
.. nonce: v01tic
.. section: Library

Fix :exc:`MemoryError` in :func:`shutil.unpack_archive` which fails inside
:func:`shutil._unpack_zipfile` on large files. Patch by Igor Bolshakov.

..

.. bpo: 41730
.. date: 2020-09-10-07-23-24
.. nonce: DyKFi9
.. section: Library

``DeprecationWarning`` is now raised when importing :mod:`tkinter.tix`,
which has been deprecated in documentation since Python 3.6.

..

.. bpo: 42392
.. date: 2021-05-26-11-16-33
.. nonce: oxRx6E
.. section: Documentation

Document the deprecation and removal of the ``loop`` parameter for many
functions and classes in :mod:`asyncio`.

..

.. bpo: 44195
.. date: 2021-05-23-09-11-28
.. nonce: 1bqkOs
.. section: Documentation

Corrected references to ``TraversableResources`` in docs. There is no
``TraversableReader``.

..

.. bpo: 41963
.. date: 2021-05-17-20-03-47
.. nonce: eUz9_o
.. section: Documentation

Document that ``ConfigParser`` strips off comments when reading
configuration files.

..

.. bpo: 44072
.. date: 2021-05-08-09-48-05
.. nonce: fb2x5I
.. section: Documentation

Correct where in the numeric ABC hierarchy ``**`` support is added, i.e., in
numbers.Complex, not numbers.Integral.

..

.. bpo: 43558
.. date: 2021-05-07-12-27-09
.. nonce: UGhA8R
.. section: Documentation

Add the remark to :mod:`dataclasses` documentation that the :meth:`__init__`
of any base class has to be called in :meth:`__post_init__`, along with a
code example.

..

.. bpo: 44025
.. date: 2021-05-03-22-08-08
.. nonce: gcB7iP
.. section: Documentation

Clarify when '_' in match statements is a keyword, and when not.

..

.. bpo: 31904
.. date: 2021-05-07-15-46-04
.. nonce: 8dk3la
.. section: Tests

Ignore error string case in test_py_compile ``test_file_not_exists()``.

..

.. bpo: 42083
.. date: 2021-05-04-18-10-57
.. nonce: EMS2TK
.. section: Tests

Add test to check that ``PyStructSequence_NewType`` accepts a
``PyStructSequence_Desc`` with ``doc`` field set to ``NULL``.

..

.. bpo: 35753
.. date: 2020-10-25-19-20-26
.. nonce: 2LT-hO
.. section: Tests

Fix crash in doctest when doctest parses modules that include unwrappable
functions by skipping those functions.

..

.. bpo: 41282
.. date: 2021-05-24-03-31-17
.. nonce: L8nP44
.. section: Build

Fix broken ``make install`` that caused standard library extension modules
to be unnecessarily and incorrectly rebuilt during the install phase of
cpython.

..

.. bpo: 42686
.. date: 2021-01-01-21-21-03
.. nonce: G_f-TC
.. section: Windows

Build :mod:`sqlite3` with math functions enabled. Patch by Erlend E.
Aasland.

..

.. bpo: 43109
.. date: 2021-05-24-21-15-41
.. nonce: npKJ9c
.. section: macOS

Allow --with-lto configure option to work with Apple-supplied Xcode or
Command Line Tools.

..

.. bpo: 41611
.. date: 2021-05-27-18-22-46
.. nonce: jOKpfc
.. section: IDLE

Avoid uncaught exceptions in ``AutoCompleteWindow.winconfig_event()``.

..

.. bpo: 41611
.. date: 2021-05-27-13-39-43
.. nonce: liNQqj
.. section: IDLE

Fix IDLE sometimes freezing upon tab-completion on macOS.

..

.. bpo: 44010
.. date: 2021-05-09-09-02-09
.. nonce: TaLe9x
.. section: IDLE

Highlight the new :ref:`match <match>` statement's :ref:`soft keywords
<soft-keywords>`: :keyword:`match`, :keyword:`case <match>`, and :keyword:`_
<wildcard-patterns>`. However, this highlighting is not perfect and will be
incorrect in some rare cases, including some ``_``-s in ``case`` patterns.

..

.. bpo: 44026
.. date: 2021-05-05-09-45-24
.. nonce: m2Z0zR
.. section: IDLE

Include interpreter's typo fix suggestions in message line for NameErrors
and AttributeErrors.  Patch by E. Paine.

..

.. bpo: 44074
.. date: 2021-05-08-13-57-00
.. nonce: F09kCK
.. section: Tools/Demos

Make patchcheck automatically detect the correct base branch name
(previously it was hardcoded to 'master')

..

.. bpo: 43795
.. date: 2021-05-19-15-09-47
.. nonce: WAHRxt
.. section: C API

The undocumented function :c:func:`Py_FrozenMain` is removed from the
Limited API.

..

.. bpo: 43795
.. date: 2021-05-05-19-04-50
.. nonce: 9Ojj73
.. section: C API

:c:func:`PyCodec_Unregister` is now properly exported as a function in the
Windows Stable ABI DLL.