cpython/Misc/NEWS.d/3.11.0a3.rst

.. bpo: 46009
.. date: 2021-12-08-11-06-53
.. nonce: cL8pH0
.. release date: 2021-12-08
.. section: Core and Builtins

Restore behavior from 3.9 and earlier when sending non-None to newly started
generator. In 3.9 this did not affect the state of the generator. In 3.10.0
and 3.10.1 ``gen_func().send(0)`` is equivalent to
``gen_func().throw(TypeError(...)`` which exhausts the generator. In 3.10.2
onward, the behavior has been reverted to that of 3.9.

..

.. bpo: 46004
.. date: 2021-12-07-11-24-24
.. nonce: TTEU1p
.. section: Core and Builtins

Fix the :exc:`SyntaxError` location for errors involving for loops with
invalid targets. Patch by Pablo Galindo

..

.. bpo: 45711
.. date: 2021-12-05-17-36-08
.. nonce: 3TmTSw
.. section: Core and Builtins

:c:func:`_PyErr_ChainStackItem` no longer normalizes ``exc_info`` (including
setting the traceback on the exception instance) because ``exc_info`` is
always normalized.

..

.. bpo: 45607
.. date: 2021-12-01-15-38-04
.. nonce: JhuF8b
.. section: Core and Builtins

The ``__note__`` field was added to :exc:`BaseException`. It is ``None`` by
default but can be set to a string which is added to the exception's
traceback.

..

.. bpo: 45947
.. date: 2021-12-01-14-06-36
.. nonce: 1XPPm_
.. section: Core and Builtins

Place pointers to dict and values immediately before GC header. This reduces
number of dependent memory loads to access either dict or values from 3 to
1.

..

.. bpo: 45915
.. date: 2021-11-28-11-25-08
.. nonce: TSGcLF
.. section: Core and Builtins

``is_valid_fd`` now uses faster ``fcntl(fd, F_GETFD)`` on Linux, macOS, and
Windows.

..

.. bpo: 44530
.. date: 2021-11-26-23-26-25
.. nonce: EZ0gel
.. section: Core and Builtins

Reverts a change to the ``code.__new__`` :ref:`audit event <audit-events>`
from an earlier prerelease.

..

.. bpo: 42268
.. date: 2021-11-26-22-31-22
.. nonce: 3wl-09
.. section: Core and Builtins

Fail the configure step if the selected compiler doesn't support memory
sanitizer. Patch by Pablo Galindo

..

.. bpo: 45711
.. date: 2021-11-25-17-51-29
.. nonce: D2igmz
.. section: Core and Builtins

The three values of ``exc_info`` are now always consistent with each other.
In particular, the ``type`` and ``traceback`` fields are now derived from
the exception instance. This impacts the return values of
:func:`sys.exc_info` and :c:func:`PyErr_GetExcInfo()` if the exception
instance is modified while the exception is handled, as well as
:c:func:`PyErr_SetExcInfo()`, which now ignores the ``type`` and
``traceback`` arguments provided to it.

..

.. bpo: 45727
.. date: 2021-11-24-18-24-49
.. nonce: _xVbbo
.. section: Core and Builtins

Refine the custom syntax error that suggests that a comma may be missing to
trigger only when the expressions are detected between parentheses or
brackets. Patch by Pablo Galindo

..

.. bpo: 45885
.. date: 2021-11-23-21-01-56
.. nonce: 3IxeCX
.. section: Core and Builtins

Specialized the ``COMPARE_OP`` opcode using the PEP 659 machinery.

..

.. bpo: 45786
.. date: 2021-11-23-15-25-00
.. nonce: UdEciD
.. section: Core and Builtins

Allocate space for the interpreter frame in the frame object, to avoid an
additional allocation when the frame object outlives the frame activation.

..

.. bpo: 45614
.. date: 2021-11-23-12-06-41
.. nonce: fIekgI
.. section: Core and Builtins

Fix :mod:`traceback` display for exceptions with invalid module name.

..

.. bpo: 45813
.. date: 2021-11-22-11-28-13
.. nonce: ZMaWE2
.. section: Core and Builtins

Fix crash when calling coro.cr_frame.clear() after coroutine has been freed.

..

.. bpo: 45811
.. date: 2021-11-20-02-25-06
.. nonce: B-1Gsr
.. section: Core and Builtins

Improve the tokenizer errors when encountering invisible control characters
in the parser. Patch by Pablo Galindo

..

.. bpo: 45848
.. date: 2021-11-19-22-57-42
.. nonce: HgVBJ5
.. section: Core and Builtins

Allow the parser to obtain error lines directly from encoded files. Patch by
Pablo Galindo

..

.. bpo: 45709
.. date: 2021-11-19-13-17-47
.. nonce: H_t7ut
.. section: Core and Builtins

Restore behavior from 3.10 when tracing an exception raised within a with
statement.

..

.. bpo: 44525
.. date: 2021-11-18-10-02-02
.. nonce: M4xwn_
.. section: Core and Builtins

Adds new :opcode:`COPY_FREE_VARS` opcode, to make copying of free variables
from function to frame explicit. Helps optimization of calls to Python
function.

..

.. bpo: 45829
.. date: 2021-11-17-10-14-35
.. nonce: 5Cf6fY
.. section: Core and Builtins

Specialize :opcode:`BINARY_SUBSCR` for classes with a ``__getitem__`` method
implemented in Python

..

.. bpo: 45826
.. date: 2021-11-17-08-05-27
.. nonce: OERoTm
.. section: Core and Builtins

Fixed a crash when calling ``.with_traceback(None)`` on ``NameError``. This
occurs internally in ``unittest.TestCase.assertRaises()``.

..

.. bpo: 45822
.. date: 2021-11-16-19-41-04
.. nonce: OT6ueS
.. section: Core and Builtins

Fixed a bug in the parser that was causing it to not respect :pep:`263`
coding cookies when no flags are provided. Patch by Pablo Galindo

..

.. bpo: 45820
.. date: 2021-11-16-19-00-27
.. nonce: 2X6Psr
.. section: Core and Builtins

Fix a segfault when the parser fails without reading any input. Patch by
Pablo Galindo

..

.. bpo: 45636
.. date: 2021-11-15-13-32-54
.. nonce: RDlTdL
.. section: Core and Builtins

Simplify the implementation of :opcode:`BINARY_OP` by indexing into an array
of function pointers (rather than switching on the oparg).

..

.. bpo: 42540
.. date: 2021-11-15-12-08-27
.. nonce: V2w107
.. section: Core and Builtins

Fix crash when :func:`os.fork` is called with an active non-default memory
allocator.

..

.. bpo: 45738
.. date: 2021-11-14-00-14-45
.. nonce: e0cgKd
.. section: Core and Builtins

Fix computation of error location for invalid continuation characters in the
parser. Patch by Pablo Galindo.

..

.. bpo: 45636
.. date: 2021-11-11-19-11-57
.. nonce: 2fyIVm
.. section: Core and Builtins

Remove an existing "fast path" for old-style string formatting, since it no
longer appears to have any measurable impact.

..

.. bpo: 45753
.. date: 2021-11-11-17-14-21
.. nonce: nEBFcC
.. section: Core and Builtins

Make recursion checks a bit more efficient by tracking amount of calls left
before overflow.

..

.. bpo: 45773
.. date: 2021-11-09-13-01-35
.. nonce: POU8A4
.. section: Core and Builtins

Fix a compiler hang when attempting to optimize certain jump patterns.

..

.. bpo: 45764
.. date: 2021-11-09-12-19-22
.. nonce: 8RLhWL
.. section: Core and Builtins

The parser now gives a better error message when leaving out the opening
parenthesis ``(`` after a ``def``-statement::

    >>> def f:
      File "<stdin>", line 1
        def f:
             ^
    SyntaxError: expected '('

..

.. bpo: 45609
.. date: 2021-10-27-21-00-49
.. nonce: L1GKPX
.. section: Core and Builtins

Specialized the ``STORE_SUBSCR`` opcode using the PEP 659 machinery.

..

.. bpo: 45636
.. date: 2021-10-27-15-14-31
.. nonce: K2X7QS
.. section: Core and Builtins

Replace all numeric ``BINARY_*`` and ``INPLACE_*`` instructions with a
single :opcode:`BINARY_OP` implementation.

..

.. bpo: 45582
.. date: 2021-10-23-00-39-31
.. nonce: YONPuo
.. section: Core and Builtins

Path calculation (known as ``getpath``) has been reimplemented as a frozen
Python module. This should have no visible impact, but may affect
calculation of all paths referenced in :mod:`sys` and :mod:`sysconfig`.

..

.. bpo: 45450
.. date: 2021-10-12-18-22-44
.. nonce: d9a-bX
.. section: Core and Builtins

Improve the syntax error message for parenthesized arguments. Patch by Pablo
Galindo.

..

.. bpo: 27946
.. date: 2021-12-04-20-08-42
.. nonce: -Vuarf
.. section: Library

Fix possible crash when getting an attribute of
class:`xml.etree.ElementTree.Element` simultaneously with replacing the
``attrib`` dict.

..

.. bpo: 45711
.. date: 2021-12-02-17-22-06
.. nonce: D6jsdv
.. section: Library

Make :mod:`asyncio` normalize exceptions as soon as they are captured with
:c:func:`PyErr_Fetch`, and before they are stored as an exc_info triplet.
This brings :mod:`asyncio` in line with the rest of the codebase, where an
exc_info triplet is always normalized.

..

.. bpo: 23819
.. date: 2021-12-02-14-37-30
.. nonce: An6vkT
.. section: Library

Replaced asserts with exceptions in asyncio, patch by Kumar Aditya.

..

.. bpo: 13236
.. date: 2021-11-30-13-52-02
.. nonce: FmJIkO
.. section: Library

:class:`unittest.TextTestResult` and :class:`unittest.TextTestRunner` flush
now the output stream more often.

..

.. bpo: 45917
.. date: 2021-11-28-17-24-11
.. nonce: J5TIrd
.. section: Library

Added :func:`math.exp2`:, which returns 2 raised to the power of x.

..

.. bpo: 37658
.. date: 2021-11-28-15-30-34
.. nonce: 8Hno7d
.. section: Library

Fix issue when on certain conditions ``asyncio.wait_for()`` may allow a
coroutine to complete successfully, but fail to return the result,
potentially causing memory leaks or other issues.

..

.. bpo: 45876
.. date: 2021-11-23-15-36-56
.. nonce: NO8Yaj
.. section: Library

Improve the accuracy of stdev() and pstdev() in the statistics module.  When
the inputs are floats or fractions, the output is a correctly rounded float

..

.. bpo: 44649
.. date: 2021-11-21-20-50-42
.. nonce: E8M936
.. section: Library

Handle dataclass(slots=True) with a field that has default a default value,
but for which init=False.

..

.. bpo: 45803
.. date: 2021-11-20-17-04-25
.. nonce: wSgFOy
.. section: Library

Added missing kw_only parameter to dataclasses.make_dataclass().

..

.. bpo: 45837
.. date: 2021-11-18-13-13-19
.. nonce: aGyr1I
.. section: Library

The :meth:`turtle.RawTurtle.settiltangle` is deprecated since Python 3.1, it
now emits a deprecation warning and will be removed in Python 3.13.

Use :meth:`turtle.RawTurtle.tiltangle` instead.

:meth:`turtle.RawTurtle.tiltangle` was earlier incorrectly marked as
deprecated, its docstring has been corrected.

Patch by Hugo van Kemenade.

..

.. bpo: 45831
.. date: 2021-11-17-19-25-37
.. nonce: 9-TojK
.. section: Library

:mod:`faulthandler` can now write ASCII-only strings (like filenames and
function names) with a single write() syscall when dumping a traceback. It
reduces the risk of getting an unreadable dump when two threads or two
processes dump a traceback to the same file (like stderr) at the same time.
Patch by Victor Stinner.

..

.. bpo: 45828
.. date: 2021-11-17-11-40-21
.. nonce: kQU35U
.. section: Library

:mod:`sqlite` C callbacks now use unraisable exceptions if callback
tracebacks are enabled. Patch by Erlend E. Aasland.

..

.. bpo: 41735
.. date: 2021-11-16-18-13-49
.. nonce: D72UY1
.. section: Library

Fix thread lock in ``zlib.Decompress.flush()`` method before
``PyObject_GetBuffer``.

..

.. bpo: 45235
.. date: 2021-11-11-13-03-17
.. nonce: 8ZbkHa
.. section: Library

Reverted an argparse bugfix that caused regression in the handling of
default arguments for subparsers.  This prevented leaf level arguments from
taking precedence over root level arguments.

..

.. bpo: 45754
.. date: 2021-11-09-15-48-38
.. nonce: c-JDto
.. section: Library

Fix a regression in Python 3.11a1 and 3.11a2 where :mod:`sqlite3`
incorrectly would use ``SQLITE_LIMIT_LENGTH`` when checking SQL statement
lengths. Now, ``SQLITE_LIMIT_SQL_LENGTH`` is used. Patch by Erlend E.
Aasland.

..

.. bpo: 45766
.. date: 2021-11-09-09-18-06
.. nonce: dvbcMf
.. section: Library

Added *proportional* option to :meth:`statistics.linear_regression`.

..

.. bpo: 45765
.. date: 2021-11-09-09-04-19
.. nonce: JVobxK
.. section: Library

In importlib.metadata, fix distribution discovery for an empty path.

..

.. bpo: 45757
.. date: 2021-11-08-23-22-14
.. nonce: MHZHt3
.. section: Library

Fix bug where :mod:`dis` produced an incorrect oparg when
:opcode:`EXTENDED_ARG` is followed by an opcode that does not use its
argument.

..

.. bpo: 45644
.. date: 2021-11-06-17-47-46
.. nonce: ZMqHD_
.. section: Library

In-place JSON file formatting using ``python3 -m json.tool infile infile``
now works correctly, previously it left the file empty.  Patch by Chris
Wesseling.

..

.. bpo: 45703
.. date: 2021-11-03-13-41-49
.. nonce: 35AagL
.. section: Library

When a namespace package is imported before another module from the same
namespace is created/installed in a different :data:`sys.path` location
while the program is running, calling the
:func:`importlib.invalidate_caches` function will now also guarantee the new
module is noticed.

..

.. bpo: 45535
.. date: 2021-10-29-16-28-06
.. nonce: n8NiOE
.. section: Library

Improve output of ``dir()`` with Enums.

..

.. bpo: 45664
.. date: 2021-10-28-23-40-54
.. nonce: 7dqtxQ
.. section: Library

Fix :func:`types.resolve_bases` and :func:`types.new_class` for
:class:`types.GenericAlias` instance as a base.

..

.. bpo: 45663
.. date: 2021-10-28-23-11-59
.. nonce: J90N5R
.. section: Library

Fix :func:`dataclasses.is_dataclass` for dataclasses which are subclasses of
:class:`types.GenericAlias`.

..

.. bpo: 45662
.. date: 2021-10-28-22-58-14
.. nonce: sJd7Ir
.. section: Library

Fix the repr of :data:`dataclasses.InitVar` with a type alias to the
built-in class, e.g. ``InitVar[list[int]]``.

..

.. bpo: 43137
.. date: 2021-10-25-12-51-02
.. nonce: apo7jY
.. section: Library

Launch GNOME web browsers via gio tool instead of obsolete gvfs-open

..

.. bpo: 45429
.. date: 2021-10-25-01-22-49
.. nonce: VaEyN9
.. section: Library

On Windows, :func:`time.sleep` now uses a waitable timer which supports
high-resolution timers. Patch by Dong-hee Na and Eryk Sun.

..

.. bpo: 37295
.. date: 2021-10-18-16-08-55
.. nonce: wBEWH2
.. section: Library

Optimize :func:`math.comb` and :func:`math.perm`.

..

.. bpo: 45514
.. date: 2021-10-18-14-25-35
.. nonce: YmlzIl
.. section: Library

Deprecated legacy functions in :mod:`importlib.resources`.

..

.. bpo: 45507
.. date: 2021-10-18-14-00-01
.. nonce: lDotNV
.. section: Library

Add tests for truncated/missing trailers in gzip.decompress implementation.

..

.. bpo: 45359
.. date: 2021-10-03-22-27-35
.. nonce: LX_uxe
.. section: Library

Implement :pep:`585` for :class:`graphlib.TopologicalSorter`.

..

.. bpo: 44733
.. date: 2021-07-26-13-33-37
.. nonce: 88LrP1
.. section: Library

Add ``max_tasks_per_child`` to
:class:`concurrent.futures.ProcessPoolExecutor`. This allows users to
specify the maximum number of tasks a single process should execute before
the process needs to be restarted.

..

.. bpo: 28806
.. date: 2021-05-24-13-48-34
.. nonce: PkNw5D
.. section: Library

Improve netrc library. netrc file no longer needs to contain all tokens. And
if the login name is anonymous, security check is no longer need.

..

.. bpo: 43498
.. date: 2021-04-20-14-14-16
.. nonce: L_Hq-8
.. section: Library

Avoid a possible *"RuntimeError: dictionary changed size during iteration"*
when adjusting the process count of :class:`ProcessPoolExecutor`.

..

.. bpo: 42158
.. date: 2020-11-10-17-46-12
.. nonce: OhxAiH
.. section: Library

Add MIME types for N-quads, N-triples, Notation3 and TriG to ``mimetypes``.

..

.. bpo: 30533
.. date: 2020-06-16-18-00-56
.. nonce: StL57t
.. section: Library

Add :func:`inspect.getmembers_static` , it return all members without
triggering dynamic lookup via the descriptor protocol. Patch by Weipeng
Hong.

..

.. bpo: 42238
.. date: 2021-11-20-02-46-39
.. nonce: hlfMIc
.. section: Documentation

``make -C Doc suspicious`` will be removed soon in favor of ``make -C Doc
check``, mark it as deprecated.

..

.. bpo: 45840
.. date: 2021-11-19-02-02-32
.. nonce: A51B2S
.. section: Documentation

Improve cross-references in the documentation for the data model.

..

.. bpo: 45640
.. date: 2021-11-18-16-44-12
.. nonce: lSpc2A
.. section: Documentation

Properly marked-up grammar tokens in the documentation are now clickable and
take you to the definition of a given piece of grammar.  Patch by Arthur
Milchior.

..

.. bpo: 45788
.. date: 2021-11-18-00-07-40
.. nonce: qibUoB
.. section: Documentation

Link doc for sys.prefix to sysconfig doc on installation paths.

..

.. bpo: 45772
.. date: 2021-11-09-13-10-55
.. nonce: EdrM3t
.. section: Documentation

``socket.socket`` documentation is corrected to a class from a function.

..

.. bpo: 45392
.. date: 2021-11-06-10-54-17
.. nonce: JZnVOz
.. section: Documentation

Update the docstring of the :class:`type` built-in to remove a redundant
line and to mention keyword arguments for the constructor.

..

.. bpo: 45250
.. date: 2021-10-22-12-09-18
.. nonce: Iit5-Y
.. section: Documentation

Update the documentation to note that CPython does not consistently require
iterators to define ``__iter__``.

..

.. bpo: 25381
.. date: 2021-06-21-17-51-51
.. nonce: 7Kn-_H
.. section: Documentation

In the extending chapter of the extending doc, update a paragraph about the
global variables containing exception information.

..

.. bpo: 43905
.. date: 2021-05-24-05-00-12
.. nonce: tBIndE
.. section: Documentation

Expanded :func:`~dataclasses.astuple` and :func:`~dataclasses.asdict` docs,
warning about deepcopy being applied and providing a workaround.

..

.. bpo: 45695
.. date: 2021-12-03-14-19-16
.. nonce: QKBn2E
.. section: Tests

Out-of-tree builds with a read-only source directory are now tested by CI.

..

.. bpo: 19460
.. date: 2021-11-28-15-25-02
.. nonce: lr0aWs
.. section: Tests

Add new Test for ``Lib/email/mime/nonmultipart.py::MIMENonMultipart``.

..

.. bpo: 45835
.. date: 2021-11-17-14-28-08
.. nonce: Mgyhjx
.. section: Tests

Fix race condition in test_queue tests with multiple "feeder" threads.

..

.. bpo: 45783
.. date: 2021-11-11-13-56-00
.. nonce: 8k1Rng
.. section: Tests

The test for the freeze tool now handles file moves and deletions.

..

.. bpo: 45745
.. date: 2021-11-10-12-01-28
.. nonce: wX5B3K
.. section: Tests

Remove the ``--findleaks`` command line option of regrtest: use the
``--fail-env-changed`` option instead. Since Python 3.7, it was a deprecated
alias to the ``--fail-env-changed`` option.

..

.. bpo: 45701
.. date: 2021-10-31-10-58-45
.. nonce: r0LAUL
.. section: Tests

Add tests with ``tuple`` type with :func:`functools.lru_cache` to
``test_functools``.

..

.. bpo: 44035
.. date: 2021-12-06-09-31-27
.. nonce: BiO4XC
.. section: Build

CI now verifies that autoconf files have been regenerated with a current and
unpatched autoconf package.

..

.. bpo: 45950
.. date: 2021-12-01-17-28-39
.. nonce: eEVLoz
.. section: Build

The build system now uses a :program:`_bootstrap_python` interpreter for
freezing and deepfreezing again. To speed up build process the build tools
:program:`_bootstrap_python` and :program:`_freeze_module` are no longer
build with LTO.

..

.. bpo: 45881
.. date: 2021-11-29-16-32-55
.. nonce: 7597J6
.. section: Build

The :program:`configure` script now accepts ``--with-build-python`` and
``--with-freeze-module`` options to make cross compiling easier.

..

.. bpo: 40280
.. date: 2021-11-29-14-37-29
.. nonce: UlTMR8
.. section: Build

Emscripten platform now uses ``.wasm`` suffix by default.

..

.. bpo: 40280
.. date: 2021-11-29-11-24-45
.. nonce: Knx7d7
.. section: Build

Disable unusable core extension modules on WASM/Emscripten targets.

..

.. bpo: 40280
.. date: 2021-11-26-14-09-04
.. nonce: ZLpwQf
.. section: Build

``configure`` now checks for socket ``shutdown`` function. The check makes
it possible to disable ``SYS_shutdown`` with ``ac_cv_func_shutdown=no`` in
CONFIG_SITE.

..

.. bpo: 40280
.. date: 2021-11-26-09-10-19
.. nonce: xmiMJl
.. section: Build

``configure`` now checks for functions ``fork1, getegid, geteuid, getgid,
getppid, getuid, opendir, pipe, system, wait, ttyname``.

..

.. bpo: 33393
.. date: 2021-11-25-20-26-06
.. nonce: 24YNtM
.. section: Build

Update ``config.guess`` to 2021-06-03 and ``config.sub`` to 2021-08-14.
``Makefile`` now has an ``update-config`` target to make updating more
convenient.

..

.. bpo: 45866
.. date: 2021-11-25-13-53-36
.. nonce: ZH1W8N
.. section: Build

``make regen-all`` now produces the same output when run from a directory
other than the source tree: when building Python out of the source tree.
pegen now strips directory of the "generated by pygen from <FILENAME>"
header Patch by Victor Stinner.

..

.. bpo: 40280
.. date: 2021-11-25-10-55-03
.. nonce: E9-gsQ
.. section: Build

``configure`` now accepts machine ``wasm32`` or ``wasm64`` and OS ``wasi``
or ``emscripten`` for cross building, e.g. ``wasm32-unknown-emscripten``,
``wasm32-wasi``, or ``wasm32-unknown-wasi``.

..

.. bpo: 41498
.. date: 2021-11-25-09-15-04
.. nonce: qAk5eo
.. section: Build

Python now compiles on platforms without ``sigset_t``. Several functions in
:mod:`signal` are not available when ``sigset_t`` is missing.

Based on patch by Roman Yurchak for pyodide.

..

.. bpo: 45881
.. date: 2021-11-24-17-14-06
.. nonce: GTXXLk
.. section: Build

``setup.py`` now uses ``CC`` from environment first to discover multiarch
and cross compile paths.

..

.. bpo: 45886
.. date: 2021-11-23-23-37-49
.. nonce: _Ulnh-
.. section: Build

The ``_freeze_module`` program path can now be overridden on the command
line, e.g. ``make FREEZE_MODULE=../x86_64/Program/_freeze_module``.

..

.. bpo: 45873
.. date: 2021-11-23-04-28-40
.. nonce: 9dldZ4
.. section: Build

Get rid of the ``_bootstrap_python`` build step. The deepfreeze.py script is
now run using ``$(PYTHON_FOR_REGEN)`` which can be Python 3.7 or newer (on
Windows, 3.8 or newer).

..

.. bpo: 45847
.. date: 2021-11-19-17-57-57
.. nonce: 9phcpd
.. section: Build

Port builtin hashlib extensions to ``PY_STDLIB_MOD`` macro and ``addext()``.

..

.. bpo: 45723
.. date: 2021-11-19-15-42-27
.. nonce: vwIJWI
.. section: Build

Add ``autoconf`` helpers for saving and restoring environment variables:

* ``SAVE_ENV``: Save ``$CFLAGS``, ``$LDFLAGS``, ``$LIBS``, and
  ``$CPPFLAGS``.
* ``RESTORE_ENV``: Restore ``$CFLAGS``, ``$LDFLAGS``, ``$LIBS``, and
  ``$CPPFLAGS``.
* ``WITH_SAVE_ENV([SCRIPT])``: Run ``SCRIPT`` wrapped with ``SAVE_ENV`` and
  ``RESTORE_ENV``.

Patch by Erlend E. Aasland.

..

.. bpo: 45573
.. date: 2021-11-18-13-31-02
.. nonce: LCjGB8
.. section: Build

Mandatory core modules, that are required to bootstrap Python, are now in
``Modules/Setup.bootstrap``.

..

.. bpo: 45573
.. date: 2021-11-18-12-18-43
.. nonce: xsMZzn
.. section: Build

``configure`` now creates ``Modules/Setup.stdlib`` with conditionally
enabled/disabled extension module lines. The file is not used, yet.

..

.. bpo: 45573
.. date: 2021-11-17-19-02-51
.. nonce: GMNdun
.. section: Build

``configure`` now uses a unified format to set state, compiler flags, and
linker flags in Makefile. The new macro ``PY_STDLIB_MOD`` sets three
variables that are consumed by ``Modules/Setup`` and ``setup.py``.

..

.. bpo: 45816
.. date: 2021-11-16-14-44-06
.. nonce: nbdmVK
.. section: Build

Python now supports building with Visual Studio 2022 (MSVC v143, VS Version
17.0). Patch by Jeremiah Vivian.

..

.. bpo: 45800
.. date: 2021-11-13-16-40-05
.. nonce: 5Hz6nr
.. section: Build

Settings for :mod:`pyexpat` C extension are now detected by ``configure``.
The bundled ``expat`` library is built in ``Makefile``.

..

.. bpo: 45798
.. date: 2021-11-13-10-18-22
.. nonce: IraaTs
.. section: Build

Settings for :mod:`decimal` internal C extension are now detected by
``configure``. The bundled ``libmpdec`` library is built in ``Makefile``.

..

.. bpo: 45723
.. date: 2021-11-10-16-13-02
.. nonce: B5gCB1
.. section: Build

:program:`configure` has a new option ``--with-pkg-config`` to disable or
require pkg-config.

..

.. bpo: 45774
.. date: 2021-11-09-23-30-12
.. nonce: Mwm3ZR
.. section: Build

The build dependencies for :mod:`sqlite3` are now detected by ``configure``
and ``pkg-config``. Patch by Erlend E. Aasland.

..

.. bpo: 45763
.. date: 2021-11-09-10-15-33
.. nonce: gP-vrX
.. section: Build

The build dependencies for :mod:`zlib`, :mod:`bz2`, and :mod:`lzma` are now
detected by ``configure``.

..

.. bpo: 45747
.. date: 2021-11-08-11-31-48
.. nonce: AODmk_
.. section: Build

gdbm and dbm build dependencies are now detected by ``configure``.

..

.. bpo: 45743
.. date: 2021-11-08-08-58-06
.. nonce: fZ8CTi
.. section: Build

On macOS, the build system no longer passes ``search_paths_first`` to the
linker. The flag has been the default since Xcode 4 / macOS 10.6.

..

.. bpo: 45723
.. date: 2021-11-07-10-45-40
.. nonce: AreusF
.. section: Build

``configure.ac`` is now compatible with autoconf 2.71. Deprecated checks
``STDC_HEADERS`` and ``AC_HEADER_TIME`` have been removed.

..

.. bpo: 45723
.. date: 2021-11-07-10-36-12
.. nonce: JNwKSG
.. section: Build

``configure`` now prints a warning when pkg-config is missing.

..

.. bpo: 45731
.. date: 2021-11-05-20-56-29
.. nonce: 9SDnDf
.. section: Build

``configure --enable-loadable-sqlite-extensions`` is now handled by new
``PY_SQLITE_ENABLE_LOAD_EXTENSION`` macro instead of logic in setup.py.

..

.. bpo: 45723
.. date: 2021-11-05-15-09-49
.. nonce: gfSxur
.. section: Build

configure.ac now uses custom helper macros and ``AC_CACHE_CHECK`` to
simplify and speed up configure runs.

..

.. bpo: 45696
.. date: 2021-11-03-00-19-50
.. nonce: eKs46f
.. section: Build

Skip the marshal step for frozen modules by generating C code that produces
a set of ready-to-use code objects. This speeds up startup time by another
10% or more.

..

.. bpo: 45561
.. date: 2021-10-21-14-38-30
.. nonce: PVqhZE
.. section: Build

Run smelly.py tool from $(srcdir).

..

.. bpo: 46105
.. date: 2021-12-08-16-36-20
.. nonce: t1mJ6Q
.. section: Windows

Fixed calculation of :data:`sys.path` in a venv on Windows.

..

.. bpo: 45901
.. date: 2021-11-26-18-17-41
.. nonce: c5IBqM
.. section: Windows

When installed through the Microsoft Store and set as the default app for
:file:`*.py` files, command line arguments will now be passed to Python when
invoking a script without explicitly launching Python (that is, ``script.py
args`` rather than ``python script.py args``).

..

.. bpo: 45616
.. date: 2021-11-23-11-44-42
.. nonce: K52PLZ
.. section: Windows

Fix Python Launcher's ability to distinguish between versions 3.1 and 3.10
when either one is explicitly requested.  Previously, 3.1 would be used if
3.10 was requested but not installed, and 3.10 would be used if 3.1 was
requested but 3.10 was installed.

..

.. bpo: 45850
.. date: 2021-11-20-00-06-59
.. nonce: q9lofz
.. section: Windows

Implement changes to build with deep-frozen modules on Windows. Note that we
now require Python 3.10 as the "bootstrap" or "host" Python.

..

.. bpo: 45732
.. date: 2021-11-08-21-53-11
.. nonce: idl5kx
.. section: Windows

Updates bundled Tcl/Tk to 8.6.12.

..

.. bpo: 45720
.. date: 2021-11-05-01-05-46
.. nonce: 47Nc5I
.. section: Windows

Internal reference to :file:`shlwapi.dll` was dropped to help improve
startup time. This DLL will no longer be loaded at the start of every Python
process.

..

.. bpo: 45732
.. date: 2021-12-05-23-52-03
.. nonce: -BWrnh
.. section: macOS

Update python.org macOS installer to use Tcl/Tk 8.6.12.

..

.. bpo: 39026
.. date: 2021-11-09-15-42-11
.. nonce: sUnYWn
.. section: C API

Fix Python.h to build C extensions with Xcode: remove a relative include
from ``Include/cpython/pystate.h``.