cpython/Misc/NEWS.d/3.9.0a2.rst

.. bpo: 38945
.. date: 2019-12-01-22-44-40
.. nonce: ztmNXc
.. release date: 2019-12-18
.. section: Security

Newline characters have been escaped when performing uu encoding to prevent
them from overflowing into to content section of the encoded file. This
prevents malicious or accidental modification of data during the decoding
process.

..

.. bpo: 37228
.. date: 2019-11-21-21-36-54
.. nonce: yBZnFG
.. section: Security

Due to significant security concerns, the *reuse_address* parameter of
:meth:`asyncio.loop.create_datagram_endpoint` is no longer supported. This
is because of the behavior of ``SO_REUSEADDR`` in UDP. For more details, see
the documentation for ``loop.create_datagram_endpoint()``. (Contributed by
Kyle Stanley, Antoine Pitrou, and Yury Selivanov in :issue:`37228`.)

..

.. bpo: 38804
.. date: 2019-11-15-00-54-42
.. nonce: vjbM8V
.. section: Security

Fixes a ReDoS vulnerability in :mod:`http.cookiejar`. Patch by Ben Caller.

..

.. bpo: 39028
.. date: 2019-12-17-23-20-51
.. nonce: SND4TB
.. section: Core and Builtins

Slightly improve the speed of keyword argument parsing with many kwargs by
strengthening the assumption that kwargs are interned strings.

..

.. bpo: 39080
.. date: 2019-12-17-21-45-36
.. nonce: OrxEVS
.. section: Core and Builtins

Fix the value of *end_col_offset* for Starred Expression AST nodes when they
are among the elements in the *args* attribute of Call AST nodes.

..

.. bpo: 39031
.. date: 2019-12-12-21-05-43
.. nonce: imlCYZ
.. section: Core and Builtins

When parsing an "elif" node, lineno and col_offset of the node now point to
the "elif" keyword and not to its condition, making it consistent with the
"if" node. Patch by Lysandros Nikolaou.

..

.. bpo: 20443
.. date: 2019-12-09-17-05-53
.. nonce: 8OyT5P
.. section: Core and Builtins

In Python 3.9.0a1, sys.argv[0] was made an absolute path if a filename was
specified on the command line. Revert this change, since most users expect
sys.argv to be unmodified.

..

.. bpo: 39008
.. date: 2019-12-09-10-38-51
.. nonce: Rrp6f1
.. section: Core and Builtins

:c:func:`PySys_Audit` now requires ``Py_ssize_t`` to be used for size
arguments in the format string, regardless of whether ``PY_SSIZE_T_CLEAN``
was defined at include time.

..

.. bpo: 38673
.. date: 2019-12-01-00-17-44
.. nonce: K_Tze-
.. section: Core and Builtins

In REPL mode, don't switch to PS2 if the line starts with comment or
whitespace. Based on work by Batuhan Taşkaya.

..

.. bpo: 38922
.. date: 2019-11-26-12-20-34
.. nonce: i6ja-i
.. section: Core and Builtins

Calling ``replace`` on a code object now raises the ``code.__new__`` audit
event.

..

.. bpo: 38920
.. date: 2019-11-26-09-16-47
.. nonce: Vx__sT
.. section: Core and Builtins

Add audit hooks for when :func:`sys.excepthook` and
:func:`sys.unraisablehook` are invoked.

..

.. bpo: 38892
.. date: 2019-11-22-22-18-50
.. nonce: LS586s
.. section: Core and Builtins

Improve documentation for audit events table and functions.

..

.. bpo: 38852
.. date: 2019-11-22-09-55-21
.. nonce: y7oPEa
.. section: Core and Builtins

Set the thread stack size to 8 Mb for debug builds on android platforms.

..

.. bpo: 38858
.. date: 2019-11-21-09-02-49
.. nonce: bDLH04
.. section: Core and Builtins

Each Python subinterpreter now has its own "small integer singletons":
numbers in [-5; 257] range. It is no longer possible to change the number of
small integers at build time by overriding ``NSMALLNEGINTS`` and
``NSMALLPOSINTS`` macros: macros should now be modified manually in
``pycore_pystate.h`` header file.

..

.. bpo: 36854
.. date: 2019-11-20-12-01-37
.. nonce: Zga_md
.. section: Core and Builtins

The garbage collector state becomes per interpreter
(``PyInterpreterState.gc``), rather than being global
(``_PyRuntimeState.gc``).

..

.. bpo: 38835
.. date: 2019-11-18-16-37-49
.. nonce: -U4se1
.. section: Core and Builtins

The ``PyFPE_START_PROTECT()`` and ``PyFPE_END_PROTECT()`` macros are empty:
they have been doing nothing for the last year, so stop using them.

..

.. bpo: 38328
.. date: 2019-11-11-23-44-15
.. nonce: IFrrjq
.. section: Core and Builtins

Sped up the creation time of constant :class:`list` and :class:`set`
displays. Patch by Brandt Bucher.

..

.. bpo: 38707
.. date: 2019-11-08-00-36-10
.. nonce: SZL036
.. section: Core and Builtins

``MainThread.native_id`` is now correctly reset in child processes spawned
using :class:`multiprocessing.Process`, instead of retaining the parent's
value.

..

.. bpo: 38629
.. date: 2019-10-29-17-11-15
.. nonce: 3qinhF
.. section: Core and Builtins

Added ``__floor__`` and ``__ceil__`` methods to float object. Patch by
Batuhan Taşkaya.

..

.. bpo: 27145
.. date: 2019-09-06-16-40-12
.. nonce: njuCXU
.. section: Core and Builtins

int + int and int - int operators can now return small integer singletons.
Patch by hongweipeng.

..

.. bpo: 38021
.. date: 2019-09-03-19-16-57
.. nonce: KnUhdB
.. section: Core and Builtins

Provide a platform tag for AIX that is sufficient for PEP425 binary
distribution identification. Patch by Michael Felt.

..

.. bpo: 35409
.. date: 2019-07-13-18-01-13
.. nonce: ozbcsR
.. section: Core and Builtins

Ignore GeneratorExit exceptions when throwing an exception into the aclose
coroutine of an asynchronous generator.

..

.. bpo: 33387
.. date: 2018-03-13-14-46-03
.. nonce: v821M7
.. section: Core and Builtins

Removed WITH_CLEANUP_START, WITH_CLEANUP_FINISH, BEGIN_FINALLY, END_FINALLY,
CALL_FINALLY and POP_FINALLY bytecodes. Replaced with RERAISE and
WITH_EXCEPT_START bytecodes. The compiler now generates different code for
exceptional and non-exceptional branches for 'with' and 'try-except'
statements. For 'try-finally' statements the 'finally' block is replicated
for each exit from the 'try' body.

..

.. bpo: 39033
.. date: 2019-12-13-18-54-49
.. nonce: cepuyD
.. section: Library

Fix :exc:`NameError` in :mod:`zipimport`. Patch by Karthikeyan Singaravelan.

..

.. bpo: 39022
.. date: 2019-12-10-23-34-48
.. nonce: QDtIxI
.. section: Library

Update importlib.metadata to include improvements from importlib_metadata
1.3 including better serialization of EntryPoints and improved documentation
for custom finders.

..

.. bpo: 39006
.. date: 2019-12-09-14-40-09
.. nonce: v4VsPg
.. section: Library

Fix asyncio when the ssl module is missing: only check for ssl.SSLSocket
instance if the ssl module is available.

..

.. bpo: 38708
.. date: 2019-12-07-22-25-39
.. nonce: rZTUfk
.. section: Library

Fix a potential IndexError in email parser when parsing an empty msg-id.

..

.. bpo: 38698
.. date: 2019-12-07-21-49-50
.. nonce: HxoSym
.. section: Library

Add a new ``InvalidMessageID`` token to email parser to represent invalid
Message-ID headers.  Also, add defects when there is remaining value after
parsing the header.

..

.. bpo: 38994
.. date: 2019-12-07-18-58-44
.. nonce: IJYhz_
.. section: Library

Implement ``__class_getitem__`` for ``os.PathLike``, ``pathlib.Path``.

..

.. bpo: 38979
.. date: 2019-12-07-16-32-42
.. nonce: q0sIHy
.. section: Library

Return class from ``ContextVar.__class_getitem__`` to simplify subclassing.

..

.. bpo: 38978
.. date: 2019-12-07-13-40-52
.. nonce: R3gHZI
.. section: Library

Implement ``__class_getitem__`` on asyncio objects (Future, Task, Queue).
Patch by Batuhan Taskaya.

..

.. bpo: 38916
.. date: 2019-12-06-18-47-56
.. nonce: K-raU8
.. section: Library

:class:`array.array`: Remove ``tostring()`` and ``fromstring()`` methods.
They were aliases to ``tobytes()`` and ``frombytes()``, deprecated since
Python 3.2.

..

.. bpo: 38986
.. date: 2019-12-06-15-11-42
.. nonce: bg6iZt
.. section: Library

Make repr of C accelerated TaskWakeupMethWrapper the same as of pure Python
version.

..

.. bpo: 38982
.. date: 2019-12-05-18-21-26
.. nonce: W3u-03
.. section: Library

Fix asyncio ``PidfdChildWatcher``: handle ``waitpid()`` error. If
``waitpid()`` is called elsewhere, ``waitpid()`` call fails with
:exc:`ChildProcessError`: use return code 255 in this case, and log a
warning. It ensures that the pidfd file descriptor is closed if this error
occurs.

..

.. bpo: 38529
.. date: 2019-12-05-16-13-25
.. nonce: yvQgx3
.. section: Library

Drop too noisy asyncio warning about deletion of a stream without explicit
``.close()`` call.

..

.. bpo: 27413
.. date: 2019-12-05-02-02-58
.. nonce: 212Th2
.. section: Library

Added ability to pass through ``ensure_ascii`` options to json.dumps in the
``json.tool`` command-line interface.

..

.. bpo: 38634
.. date: 2019-12-04-15-56-28
.. nonce: pq0ZWa
.. section: Library

The :mod:`readline` module now detects if Python is linked to libedit at
runtime on all platforms.  Previously, the check was only done on macOS.

..

.. bpo: 33684
.. date: 2019-12-04-15-28-40
.. nonce: QeSmQP
.. section: Library

Fix ``json.tool`` failed to read a JSON file with non-ASCII characters when
locale encoding is not UTF-8.

..

.. bpo: 38698
.. date: 2019-12-02-10-35-19
.. nonce: WZnAPQ
.. section: Library

Prevent UnboundLocalError to pop up in parse_message_id.

parse_message_id() was improperly using a token defined inside an exception
handler, which was raising `UnboundLocalError` on parsing an invalid value.
Patch by Claudiu Popa.

..

.. bpo: 38927
.. date: 2019-11-27-17-47-00
.. nonce: qT7xKY
.. section: Library

Use ``python -m pip`` instead of ``pip`` to upgrade dependencies in venv.

..

.. bpo: 26730
.. date: 2019-11-27-16-30-02
.. nonce: 56cdBn
.. section: Library

Fix ``SpooledTemporaryFile.rollover()`` might corrupt the file when it is in
text mode. Patch by Serhiy Storchaka.

..

.. bpo: 38881
.. date: 2019-11-22-20-03-46
.. nonce: 7HV1Q0
.. section: Library

random.choices() now raises a ValueError when all the weights are zero.

..

.. bpo: 38876
.. date: 2019-11-22-10-58-58
.. nonce: qqy1Vp
.. section: Library

Raise pickle.UnpicklingError when loading an item from memo for invalid
input.

The previous code was raising a `KeyError` for both the Python and C
implementation. This was caused by the specified index of an invalid input
which did not exist in the memo structure, where the pickle stores what
objects it has seen. The malformed input would have caused either a `BINGET`
or `LONG_BINGET` load from the memo, leading to a `KeyError` as the
determined index was bogus. Patch by Claudiu Popa

..

.. bpo: 38688
.. date: 2019-11-22-10-45-03
.. nonce: iKx23z
.. section: Library

Calling func:`shutil.copytree` to copy a directory tree from one directory
to another subdirectory resulted in an endless loop and a RecursionError. A
fix was added to consume an iterator and create the list of the entries to
be copied, avoiding the recursion for newly created directories. Patch by
Bruno P. Kinoshita.

..

.. bpo: 38863
.. date: 2019-11-21-16-30-00
.. nonce: RkdTjf
.. section: Library

Improve :func:`is_cgi` function in :mod:`http.server`, which enables
processing the case that cgi directory is a child of another directory other
than root.

..

.. bpo: 37838
.. date: 2019-11-21-11-39-17
.. nonce: lRFcEC
.. section: Library

:meth:`typing.get_type_hints` properly handles functions decorated with
:meth:`functools.wraps`.

..

.. bpo: 38870
.. date: 2019-11-20-22-43-48
.. nonce: rLVZEv
.. section: Library

Expose :func:`ast.unparse` as a function of the :mod:`ast` module that can
be used to unparse an :class:`ast.AST` object and produce a string with code
that would produce an equivalent :class:`ast.AST` object when parsed. Patch
by Pablo Galindo and Batuhan Taskaya.

..

.. bpo: 38859
.. date: 2019-11-19-16-30-46
.. nonce: AZUzL8
.. section: Library

AsyncMock now returns StopAsyncIteration on the exhaustion of a side_effects
iterable. Since PEP-479 its Impossible to raise a StopIteration exception
from a coroutine.

..

.. bpo: 38857
.. date: 2019-11-19-16-28-25
.. nonce: YPUkU9
.. section: Library

AsyncMock fix for return values that are awaitable types.  This also covers
side_effect iterable values that happened to be awaitable, and wraps
callables that return an awaitable type. Before these awaitables were being
awaited instead of being returned as is.

..

.. bpo: 38834
.. date: 2019-11-18-17-08-23
.. nonce: abcdef
.. section: Library

:class:`typing.TypedDict` subclasses now track which keys are optional using
the ``__required_keys__`` and ``__optional_keys__`` attributes, to enable
runtime validation by downstream projects.  Patch by Zac Hatfield-Dodds.

..

.. bpo: 38821
.. date: 2019-11-16-23-26-25
.. nonce: -albNN
.. section: Library

Fix unhandled exceptions in :mod:`argparse` when internationalizing error
messages for arguments with ``nargs`` set to special (non-integer) values.
Patch by Federico Bond.

..

.. bpo: 38820
.. date: 2019-11-16-16-09-07
.. nonce: ivhUSV
.. section: Library

Make Python compatible with OpenSSL 3.0.0. :func:`ssl.SSLSocket.getpeercert`
no longer returns IPv6 addresses with a trailing new line.

..

.. bpo: 38811
.. date: 2019-11-15-18-06-04
.. nonce: AmdQ6M
.. section: Library

Fix an unhandled exception in :mod:`pathlib` when :meth:`os.link` is
missing. Patch by Toke Høiland-Jørgensen.

..

.. bpo: 38686
.. date: 2019-11-06-15-26-15
.. nonce: HNFBce
.. section: Library

Added support for multiple ``qop`` values in
:class:`urllib.request.AbstractDigestAuthHandler`.

..

.. bpo: 38712
.. date: 2019-11-05-21-10-12
.. nonce: ezJ0TP
.. section: Library

Add the Linux-specific :func:`signal.pidfd_send_signal` function, which
allows sending a signal to a process identified by a file descriptor rather
than a pid.

..

.. bpo: 38348
.. date: 2019-10-02-18-15-28
.. nonce: _-5eq2
.. section: Library

Add ``-i`` and ``--indent`` (indentation level), and ``--no-type-comments``
(type comments) command line options to ast parsing tool.

..

.. bpo: 37523
.. date: 2019-10-02-02-55-37
.. nonce: GguwJ6
.. section: Library

Change :class:`zipfile.ZipExtFile` to raise ``ValueError`` when trying to
access the underlying file object after it has been closed. This new
behavior is consistent with how accessing closed files is handled in other
parts of Python.

..

.. bpo: 38045
.. date: 2019-09-30-12-09-41
.. nonce: VDRtd3
.. section: Library

Improve the performance of :func:`enum._decompose` in :mod:`enum`. Patch by
hongweipeng.

..

.. bpo: 36820
.. date: 2019-05-06-15-34-17
.. nonce: Eh5mIB
.. section: Library

Break cycle generated when saving an exception in socket.py, codeop.py and
dyld.py as they keep alive not only the exception but user objects through
the ``__traceback__`` attribute. Patch by Mario Corchero.

..

.. bpo: 36406
.. date: 2019-03-24-12-12-27
.. nonce: mCEkOl
.. section: Library

Handle namespace packages in :mod:`doctest`. Patch by Karthikeyan
Singaravelan.

..

.. bpo: 34776
.. date: 2018-09-23-14-24-37
.. nonce: 1SrQe3
.. section: Library

Fix dataclasses to support forward references in type annotations

..

.. bpo: 20928
.. date: 2018-03-30-16-18-12
.. nonce: ieXu6I
.. section: Library

ElementTree supports recursive XInclude processing.  Patch by Stefan Behnel.

..

.. bpo: 29636
.. date: 2018-02-22-11-24-33
.. nonce: ogGRE2
.. section: Library

Add whitespace options for formatting JSON with the ``json.tool`` CLI. The
following mutually exclusive options are now supported: ``--indent`` for
setting the indent level in spaces; ``--tab`` for indenting with tabs;
``--no-indent`` for suppressing newlines; and ``--compact`` for suppressing
all whitespace. The default behavior remains the same as ``--indent=4``.

..

.. bpo: 38928
.. date: 2019-11-27-17-51-27
.. nonce: AfgvfO
.. section: Documentation

Correct when venv's ``upgrade_dependencies()`` and ``--upgrade-deps`` are
added.

..

.. bpo: 38899
.. date: 2019-11-22-15-57-29
.. nonce: 4aYPW2
.. section: Documentation

Update documentation to state that to activate virtual environments under
fish one should use `source`, not `.` as documented at
https://fishshell.com/docs/current/commands.html#source.

..

.. bpo: 22377
.. date: 2019-10-01-10-53-46
.. nonce: 5ni-iC
.. section: Documentation

Improves documentation of the values that :meth:`datetime.datetime.strptime`
accepts for ``%Z``. Patch by Karl Dubost.

..

.. bpo: 38546
.. date: 2019-12-18-14-52-08
.. nonce: 2kxNuM
.. section: Tests

Fix test_ressources_gced_in_workers() of test_concurrent_futures: explicitly
stop the manager to prevent leaking a child process running in the
background after the test completes.

..

.. bpo: 38546
.. date: 2019-12-17-15-27-07
.. nonce: 82JwN2
.. section: Tests

Multiprocessing and concurrent.futures tests now stop the resource tracker
process when tests complete.

..

.. bpo: 38614
.. date: 2019-12-10-14-26-23
.. nonce: 89JpNh
.. section: Tests

Replace hardcoded timeout constants in tests with new :mod:`test.support`
constants: :data:`~test.support.LOOPBACK_TIMEOUT`,
:data:`~test.support.INTERNET_TIMEOUT`, :data:`~test.support.SHORT_TIMEOUT`
and :data:`~test.support.LONG_TIMEOUT`. It becomes easier to adjust these
four timeout constants for all tests at once, rather than having to adjust
every single test file.

..

.. bpo: 38547
.. date: 2019-12-09-11-32-34
.. nonce: Juw54e
.. section: Tests

Fix test_pty: if the process is the session leader, closing the master file
descriptor raises a SIGHUP signal: simply ignore SIGHUP when running the
tests.

..

.. bpo: 38992
.. date: 2019-12-08-15-11-06
.. nonce: cVoHOZ
.. section: Tests

Fix a test for :func:`math.fsum` that was failing due to constant folding.

..

.. bpo: 38991
.. date: 2019-12-07-00-52-09
.. nonce: JE3_o-
.. section: Tests

:mod:`test.support`: :func:`~test.support.run_python_until_end`,
:func:`~test.support.assert_python_ok` and
:func:`~test.support.assert_python_failure` functions no longer strip
whitespaces from stderr. Remove ``test.support.strip_python_stderr()``
function.

..

.. bpo: 38965
.. date: 2019-12-04-17-08-55
.. nonce: yqax3m
.. section: Tests

Fix test_faulthandler on GCC 10. Use the "volatile" keyword in
``faulthandler._stack_overflow()`` to prevent tail call optimization on any
compiler, rather than relying on compiler specific pragma.

..

.. bpo: 38875
.. date: 2019-11-21-09-11-06
.. nonce: wSZJal
.. section: Tests

test_capi: trashcan tests now require the test "cpu" resource.

..

.. bpo: 38841
.. date: 2019-11-20-16-08-19
.. nonce: 5F5Lbw
.. section: Tests

Skip asyncio test_create_datagram_endpoint_existing_sock_unix on platforms
lacking a functional bind() for named unix domain sockets.

..

.. bpo: 38692
.. date: 2019-11-20-15-42-06
.. nonce: aqAvyF
.. section: Tests

Skip the test_posix.test_pidfd_open() test if ``os.pidfd_open()`` fails with
a :exc:`PermissionError`. This situation can happen in a Linux sandbox using
a syscall whitelist which doesn't allow the ``pidfd_open()`` syscall yet.

..

.. bpo: 38839
.. date: 2019-11-18-22-10-55
.. nonce: di6tXv
.. section: Tests

Fix some unused functions in tests. Patch by Adam Johnson.

..

.. bpo: 38669
.. date: 2019-11-04-02-54-16
.. nonce: pazXZ8
.. section: Tests

Raise :exc:`TypeError` when passing target as a string with
:meth:`unittest.mock.patch.object`.

..

.. bpo: 37957
.. date: 2019-10-30-00-01-43
.. nonce: X1r78F
.. section: Tests

test.regrtest now can receive a list of test patterns to ignore (using the
-i/--ignore argument) or a file with a list of patterns to ignore (using the
--ignore-file argument). Patch by Pablo Galindo.

..

.. bpo: 37404
.. date: 2019-12-01-21-45-24
.. nonce: cNsA7S
.. section: Build

:mod:`asyncio` now raises :exc:`TyperError` when calling incompatible
methods with an :class:`ssl.SSLSocket` socket.  Patch by Ido Michael.

..

.. bpo: 36500
.. date: 2019-04-02-01-59-26
.. nonce: fyG6_U
.. section: Build

Added an optional "regen" project to the Visual Studio solution that will
regenerate all grammar, tokens, and opcodes.

..

.. bpo: 39007
.. date: 2019-12-09-10-40-34
.. nonce: vtarxo
.. section: Windows

Add auditing events to functions in :mod:`winreg`.

..

.. bpo: 33125
.. date: 2019-11-14-08-57-50
.. nonce: EN5MWS
.. section: Windows

Add support for building and releasing Windows ARM64 packages.

..

.. bpo: 37931
.. date: 2019-08-23-12-14-34
.. nonce: goYgQj
.. section: macOS

Fixed a crash on OSX dynamic builds that occurred when re-initializing the
posix module after a Py_Finalize if the environment had changed since the
previous `import posix`. Patch by Benoît Hudson.

..

.. bpo: 38944
.. date: 2019-11-30-12-10-36
.. nonce: _3xjKG
.. section: IDLE

Escape key now closes IDLE completion windows.  Patch by Johnny Najera.

..

.. bpo: 38943
.. date: 2019-11-29-23-44-11
.. nonce: 8pUKKs
.. section: IDLE

Fix IDLE autocomplete windows not always appearing on some systems. Patch by
Johnny Najera.

..

.. bpo: 38862
.. date: 2019-11-23-21-50-57
.. nonce: KQ9A0m
.. section: IDLE

'Strip Trailing Whitespace' on the Format menu removes extra newlines at the
end of non-shell files.

..

.. bpo: 38636
.. date: 2019-10-30-22-11-16
.. nonce: hUhDeB
.. section: IDLE

Fix IDLE Format menu tab toggle and file indent width. These functions
(default shortcuts Alt-T and Alt-U) were mistakenly disabled in 3.7.5 and
3.8.0.

..

.. bpo: 38896
.. date: 2019-11-22-19-43-43
.. nonce: 6wvNMJ
.. section: C API

Remove ``PyUnicode_ClearFreeList()`` function: the Unicode free list has
been removed in Python 3.3.

..

.. bpo: 37340
.. date: 2019-11-20-11-08-06
.. nonce: JBQJMS
.. section: C API

Remove ``PyMethod_ClearFreeList()`` and ``PyCFunction_ClearFreeList()``
functions: the free lists of bound method objects have been removed.

..

.. bpo: 38835
.. date: 2019-11-18-15-38-23
.. nonce: II8Szd
.. section: C API

Exclude ``PyFPE_START_PROTECT()`` and ``PyFPE_END_PROTECT()`` macros of
``pyfpe.h`` from ``Py_LIMITED_API`` (stable API).