cpython/Misc/NEWS.d/3.7.0a4.rst

.. bpo: 31975
.. date: 2018-01-05-20-54-27
.. nonce: AmftlU
.. release date: 2018-01-08
.. section: Core and Builtins

The default warning filter list now starts with a
"default::DeprecationWarning:__main__" entry, so deprecation warnings are
once again shown by default in single-file scripts and at the interactive
prompt.

..

.. bpo: 32226
.. date: 2018-01-04-15-06-15
.. nonce: 7cAvRG
.. section: Core and Builtins

``__class_getitem__`` is now an automatic class method.

..

.. bpo: 32399
.. date: 2017-12-22-13-38-17
.. nonce: wlH12z
.. section: Core and Builtins

Add AIX uuid library support for RFC4122 using uuid_create() in libc.a

..

.. bpo: 32390
.. date: 2017-12-22-13-28-07
.. nonce: QPj083
.. section: Core and Builtins

Fix the compilation failure on AIX after the f_fsid field has been added to
the object returned by os.statvfs() (issue #32143). Original patch by
Michael Felt.

..

.. bpo: 32379
.. date: 2017-12-19-21-14-41
.. nonce: B7mOmI
.. section: Core and Builtins

Make MRO computation faster when a class inherits from a single base.

..

.. bpo: 32259
.. date: 2017-12-16-14-30-21
.. nonce: GoOJiX
.. section: Core and Builtins

The error message of a TypeError raised when unpack non-iterable is now more
specific.

..

.. bpo: 27169
.. date: 2017-12-15-11-50-06
.. nonce: VO84fQ
.. section: Core and Builtins

The ``__debug__`` constant is now optimized out at compile time. This fixes
also bpo-22091.

..

.. bpo: 32329
.. date: 2017-12-15-00-13-04
.. nonce: q47IN2
.. section: Core and Builtins

The :option:`-R` option now turns on hash randomization when the
:envvar:`PYTHONHASHSEED` environment variable is set to ``0``. Previously,
the option was ignored. Moreover, ``sys.flags.hash_randomization`` is now
properly set to 0 when hash randomization is turned off by
``PYTHONHASHSEED=0``.

..

.. bpo: 30416
.. date: 2017-12-14-11-48-19
.. nonce: hlHo_9
.. section: Core and Builtins

The optimizer is now protected from spending much time doing complex
calculations and consuming much memory for creating large constants in
constant folding. Increased limits for constants that can be produced in
constant folding.

..

.. bpo: 32282
.. date: 2017-12-12-14-02-28
.. nonce: xFVMTn
.. section: Core and Builtins

Fix an unnecessary ifdef in the include of VersionHelpers.h in socketmodule
on Windows.

..

.. bpo: 30579
.. date: 2017-12-11-01-52-42
.. nonce: X6cEzf
.. section: Core and Builtins

Implement TracebackType.__new__ to allow Python-level creation of traceback
objects, and make TracebackType.tb_next mutable.

..

.. bpo: 32260
.. date: 2017-12-09-11-03-51
.. nonce: 1DAO-p
.. section: Core and Builtins

Don't byte swap the input keys to the SipHash algorithm on big-endian
platforms. This should ensure siphash gives consistent results across
platforms.

..

.. bpo: 31506
.. date: 2017-12-07-23-44-29
.. nonce: j1U2fU
.. section: Core and Builtins

Improve the error message logic for object.__new__ and object.__init__.
Patch by Sanyam Khurana.

..

.. bpo: 20361
.. date: 2017-12-07-17-22-30
.. nonce: zQUmbi
.. section: Core and Builtins

``-b`` and ``-bb`` now inject ``'default::BytesWarning'`` and
``error::BytesWarning`` entries into ``sys.warnoptions``, ensuring that they
take precedence over any other warning filters configured via the ``-W``
option or the ``PYTHONWARNINGS`` environment variable.

..

.. bpo: 32230
.. date: 2017-12-06-20-18-34
.. nonce: PgGQaB
.. section: Core and Builtins

`-X dev` now injects a ``'default'`` entry into sys.warnoptions, ensuring
that it behaves identically to actually passing ``-Wdefault`` at the command
line.

..

.. bpo: 29240
.. date: 2017-12-05-23-10-58
.. nonce: qpJP5l
.. section: Core and Builtins

Add a new UTF-8 mode: implementation of the :pep:`540`.

..

.. bpo: 32226
.. date: 2017-12-05-21-42-58
.. nonce: G8fqb6
.. section: Core and Builtins

:pep:`560`: Add support for ``__mro_entries__`` and ``__class_getitem__``. Implemented
by Ivan Levkivskyi.

..

.. bpo: 32225
.. date: 2017-12-05-21-33-47
.. nonce: ucKjvw
.. section: Core and Builtins

:pep:`562`: Add support for module ``__getattr__`` and ``__dir__``. Implemented
by Ivan Levkivskyi.

..

.. bpo: 31901
.. date: 2017-11-28-15-04-14
.. nonce: mDeCLK
.. section: Core and Builtins

The `atexit` module now has its callback stored per interpreter.

..

.. bpo: 31650
.. date: 2017-11-26-14-38-44
.. nonce: JWf_Im
.. section: Core and Builtins

Implement :pep:`552` (Deterministic pycs). Python now supports invalidating
bytecode cache files bashed on a source content hash rather than source
last-modified time.

..

.. bpo: 29469
.. date: 2017-07-26-00-20-15
.. nonce: potmyI
.. section: Core and Builtins

Move constant folding from bytecode layer to AST layer. Original patch by
Eugene Toder.

..

.. bpo: 32506
.. date: 2018-01-07-11-32-42
.. nonce: MaT-zU
.. section: Library

Now that dict is defined as keeping insertion order, drop OrderedDict and
just use plain dict.

..

.. bpo: 32279
.. date: 2018-01-06-16-50-11
.. nonce: 1xOpU8
.. section: Library

Add params to dataclasses.make_dataclasses(): init, repr, eq, order, hash,
and frozen.  Pass them through to dataclass().

..

.. bpo: 32278
.. date: 2018-01-06-15-15-34
.. nonce: bGnGc0
.. section: Library

Make type information optional on dataclasses.make_dataclass(). If omitted,
the string 'typing.Any' is used.

..

.. bpo: 32499
.. date: 2018-01-06-10-54-16
.. nonce: koyY-4
.. section: Library

Add dataclasses.is_dataclass(obj), which returns True if obj is a dataclass
or an instance of one.

..

.. bpo: 32468
.. date: 2017-12-31-20-32-58
.. nonce: YBs__0
.. section: Library

Improve frame repr() to mention filename, code name and current line number.

..

.. bpo: 23749
.. date: 2017-12-29-00-44-42
.. nonce: QL1Cxd
.. section: Library

asyncio: Implement loop.start_tls()

..

.. bpo: 32441
.. date: 2017-12-28-21-30-40
.. nonce: LqlboJ
.. section: Library

Return the new file descriptor (i.e., the second argument) from ``os.dup2``.
Previously, ``None`` was always returned.

..

.. bpo: 32422
.. date: 2017-12-25-20-22-47
.. nonce: 5H3Wq2
.. section: Library

``functools.lru_cache`` uses less memory (3 words for each cached key) and
takes about 1/3 time for cyclic GC.

..

.. bpo: 31721
.. date: 2017-12-25-11-09-46
.. nonce: 5gM972
.. section: Library

Prevent Python crash from happening when Future._log_traceback is set to
True manually.  Now it can only be set to False, or a ValueError is raised.

..

.. bpo: 32415
.. date: 2017-12-23-12-45-00
.. nonce: YufXTU
.. section: Library

asyncio: Add Task.get_loop() and Future.get_loop()

..

.. bpo: 26133
.. date: 2017-12-21-11-08-42
.. nonce: mt81QV
.. section: Library

Don't unsubscribe signals in asyncio UNIX event loop on interpreter
shutdown.

..

.. bpo: 32363
.. date: 2017-12-19-00-37-28
.. nonce: YTeGU0
.. section: Library

Make asyncio.Task.set_exception() and set_result() raise
NotImplementedError. Task._step() and Future.__await__() raise proper
exceptions when they are in an invalid state, instead of raising an
AssertionError.

..

.. bpo: 32357
.. date: 2017-12-18-00-36-41
.. nonce: t1F3sn
.. section: Library

Optimize asyncio.iscoroutine() and loop.create_task() for non-native
coroutines (e.g. async/await compiled with Cython).

'loop.create_task(python_coroutine)' used to be 20% faster than
'loop.create_task(cython_coroutine)'.  Now, the latter is as fast.

..

.. bpo: 32356
.. date: 2017-12-17-22-50-51
.. nonce: roZJpA
.. section: Library

asyncio.transport.resume_reading() and pause_reading() are now idempotent.
New transport.is_reading() method is added.

..

.. bpo: 32355
.. date: 2017-12-17-21-42-24
.. nonce: tbaTWA
.. section: Library

Optimize asyncio.gather(); now up to 15% faster.

..

.. bpo: 32351
.. date: 2017-12-17-14-23-23
.. nonce: 95fh2K
.. section: Library

Use fastpath in asyncio.sleep if delay<0 (2x boost)

..

.. bpo: 32348
.. date: 2017-12-16-18-50-57
.. nonce: 5j__he
.. section: Library

Optimize asyncio.Future schedule/add/remove callback.  The optimization
shows 3-6% performance improvements of async/await code.

..

.. bpo: 32331
.. date: 2017-12-15-23-48-43
.. nonce: fIg1Uc
.. section: Library

Fix socket.settimeout() and socket.setblocking() to keep socket.type as is.
Fix socket.socket() constructor to reset any bit flags applied to socket's
type.  This change only affects OSes that have SOCK_NONBLOCK and/or
SOCK_CLOEXEC.

..

.. bpo: 32248
.. date: 2017-12-15-15-34-12
.. nonce: zmO8G2
.. section: Library

Add :class:`importlib.abc.ResourceReader` as an ABC for loaders to provide a
unified API for reading resources contained within packages.  Also add
:mod:`importlib.resources` as the port of ``importlib_resources``.

..

.. bpo: 32311
.. date: 2017-12-14-17-28-54
.. nonce: DL5Ytn
.. section: Library

Implement asyncio.create_task(coro) shortcut

..

.. bpo: 32327
.. date: 2017-12-14-16-00-25
.. nonce: bbkSxA
.. section: Library

Convert asyncio functions that were documented as coroutines to coroutines.
Affected functions: loop.sock_sendall, loop.sock_recv, loop.sock_accept,
loop.getaddrinfo, loop.getnameinfo.

..

.. bpo: 32323
.. date: 2017-12-14-10-10-10
.. nonce: ideco
.. section: Library

:func:`urllib.parse.urlsplit()` does not convert zone-id (scope) to lower
case for scoped IPv6 addresses in hostnames now.

..

.. bpo: 32302
.. date: 2017-12-13-22-38-08
.. nonce: othtTr
.. section: Library

Fix bdist_wininst of distutils for CRT v142: it binary compatible with CRT
v140.

..

.. bpo: 29711
.. date: 2017-12-13-22-10-36
.. nonce: hJjghA
.. section: Library

Fix ``stop_serving`` in asyncio proactor loop kill all listening servers

..

.. bpo: 32308
.. date: 2017-12-13-20-31-30
.. nonce: CUbsb2
.. section: Library

:func:`re.sub()` now replaces empty matches adjacent to a previous non-empty
match.

..

.. bpo: 29970
.. date: 2017-12-13-19-02-38
.. nonce: uxVOpk
.. section: Library

Abort asyncio SSLProtocol connection if handshake not complete within 10s

..

.. bpo: 32314
.. date: 2017-12-13-16-47-38
.. nonce: W4_U2j
.. section: Library

Implement asyncio.run().

..

.. bpo: 17852
.. date: 2017-12-13-00-00-37
.. nonce: Q8BP8N
.. section: Library

Revert incorrect fix based on misunderstanding of _Py_PyAtExit() semantics.

..

.. bpo: 32296
.. date: 2017-12-12-18-01-01
.. nonce: bwscHz
.. section: Library

Implement asyncio._get_running_loop() and get_event_loop() in C. This makes
them 4x faster.

..

.. bpo: 32250
.. date: 2017-12-12-16-58-20
.. nonce: UljTa0
.. section: Library

Implement ``asyncio.current_task()`` and ``asyncio.all_tasks()``. Add
helpers intended to be used by alternative task implementations:
``asyncio._register_task``, ``asyncio._enter_task``, ``asyncio._leave_task``
and ``asyncio._unregister_task``. Deprecate ``asyncio.Task.current_task()``
and ``asyncio.Task.all_tasks()``.

..

.. bpo: 32255
.. date: 2017-12-12-07-29-06
.. nonce: 2bfNmM
.. section: Library

A single empty field is now always quoted when written into a CSV file. This
allows to distinguish an empty row from a row consisting of a single empty
field. Patch by Licht Takeuchi.

..

.. bpo: 32277
.. date: 2017-12-11-09-53-14
.. nonce: jkKiVC
.. section: Library

Raise ``NotImplementedError`` instead of ``SystemError`` on platforms where
``chmod(..., follow_symlinks=False)`` is not supported.  Patch by Anthony
Sottile.

..

.. bpo: 30050
.. date: 2017-12-10-23-44-56
.. nonce: 4SZ3lY
.. section: Library

New argument warn_on_full_buffer to signal.set_wakeup_fd lets you control
whether Python prints a warning on stderr when the wakeup fd buffer
overflows.

..

.. bpo: 29137
.. date: 2017-12-10-21-19-14
.. nonce: CFcON1
.. section: Library

The ``fpectl`` library has been removed. It was never enabled by default,
never worked correctly on x86-64, and it changed the Python ABI in ways that
caused unexpected breakage of C extensions.

..

.. bpo: 32273
.. date: 2017-12-10-19-14-55
.. nonce: 5KKlCv
.. section: Library

Move asyncio.test_utils to test.test_asyncio.

..

.. bpo: 32272
.. date: 2017-12-10-18-59-13
.. nonce: Mu84Am
.. section: Library

Remove asyncio.async() function.

..

.. bpo: 32269
.. date: 2017-12-10-12-30-13
.. nonce: Q85pKj
.. section: Library

Add asyncio.get_running_loop() function.

..

.. bpo: 32265
.. date: 2017-12-10-00-57-51
.. nonce: kELtTE
.. section: Library

All class and static methods of builtin types now are correctly classified
by inspect.classify_class_attrs() and grouped in pydoc ouput. Added
types.ClassMethodDescriptorType for unbound class methods of builtin types.

..

.. bpo: 32253
.. date: 2017-12-09-11-30-35
.. nonce: TQHSYF
.. section: Library

Deprecate ``yield from lock``, ``await lock``, ``with (yield from lock)``
and ``with await lock`` for asyncio synchronization primitives.

..

.. bpo: 22589
.. date: 2017-12-08-15-09-41
.. nonce: 8ouqI6
.. section: Library

Changed MIME type of .bmp from 'image/x-ms-bmp' to 'image/bmp'

..

.. bpo: 32193
.. date: 2017-12-08-11-02-26
.. nonce: NJe_TQ
.. section: Library

Convert asyncio to use *async/await* syntax. Old styled ``yield from`` is
still supported too.

..

.. bpo: 32206
.. date: 2017-12-07-13-14-40
.. nonce: obm4OM
.. section: Library

Add support to run modules with pdb

..

.. bpo: 32227
.. date: 2017-12-05-13-25-15
.. nonce: 3vnWFS
.. section: Library

``functools.singledispatch`` now supports registering implementations using
type annotations.

..

.. bpo: 15873
.. date: 2017-12-04-17-41-40
.. nonce: -T4TRK
.. section: Library

Added new alternate constructors :meth:`datetime.datetime.fromisoformat`,
:meth:`datetime.time.fromisoformat` and :meth:`datetime.date.fromisoformat`
as the inverse operation of each classes's respective ``isoformat`` methods.

..

.. bpo: 32199
.. date: 2017-12-04-12-23-26
.. nonce: nGof4v
.. section: Library

The getnode() ip getter now uses 'ip link' instead of 'ip link list'.

..

.. bpo: 32143
.. date: 2017-11-26-17-28-26
.. nonce: o7YdXL
.. section: Library

os.statvfs() includes the f_fsid field from statvfs(2)

..

.. bpo: 26439
.. date: 2017-11-24-08-35-43
.. nonce: IC45_f
.. section: Library

Fix ctypes.util.find_library() for AIX by implementing
ctypes._aix.find_library() Patch by: Michael Felt

..

.. bpo: 31993
.. date: 2017-11-10-00-05-08
.. nonce: -OMNg8
.. section: Library

The pickler now uses less memory when serializing large bytes and str
objects into a file.  Pickles created with protocol 4 will require less
memory for unpickling large bytes and str objects.

..

.. bpo: 27456
.. date: 2017-11-02-11-57-41
.. nonce: snzyTC
.. section: Library

Ensure TCP_NODELAY is set on Linux. Tests by Victor Stinner.

..

.. bpo: 31778
.. date: 2017-10-18-17-29-30
.. nonce: B6vAkP
.. section: Library

ast.literal_eval() is now more strict. Addition and subtraction of arbitrary
numbers no longer allowed.

..

.. bpo: 31802
.. date: 2017-10-17-14-52-14
.. nonce: sYj2Zv
.. section: Library

Importing native path module (``posixpath``, ``ntpath``) now works even if
the ``os`` module still is not imported.

..

.. bpo: 30241
.. date: 2017-10-10-18-56-46
.. nonce: F_go20
.. section: Library

Add contextlib.AbstractAsyncContextManager. Patch by Jelle Zijlstra.

..

.. bpo: 31699
.. date: 2017-10-05-11-06-32
.. nonce: MF47Y6
.. section: Library

Fix deadlocks in :class:`concurrent.futures.ProcessPoolExecutor` when task
arguments or results cause pickling or unpickling errors. This should make
sure that calls to the :class:`ProcessPoolExecutor` API always eventually
return.

..

.. bpo: 15216
.. date: 2017-09-16-02-56-33
.. nonce: lqXCTT
.. section: Library

``TextIOWrapper.reconfigure()`` supports changing *encoding*, *errors*, and
*newline*.

..

.. bpo: 32418
.. date: 2017-12-24-17-29-37
.. nonce: eZe-ID
.. section: Documentation

Add get_loop() method to Server and AbstractServer classes.

..

.. bpo: 32252
.. date: 2017-12-11-13-31-33
.. nonce: YnFw7J
.. section: Tests

Fix faulthandler_suppress_crash_report() used to prevent core dump files
when testing crashes. getrlimit() returns zero on success.

..

.. bpo: 32002
.. date: 2017-11-11-16-35-18
.. nonce: itDxIo
.. section: Tests

Adjust C locale coercion testing for the empty locale and POSIX locale cases
to more readily adjust to platform dependent behaviour.

..

.. bpo: 19764
.. date: 2017-08-18-18-00-24
.. nonce: ODpc9y
.. section: Windows

Implement support for `subprocess.Popen(close_fds=True)` on Windows. Patch
by Segev Finer.

..

.. bpo: 24960
.. date: 2017-12-22-09-25-51
.. nonce: TGdAgO
.. section: Tools/Demos

2to3 and lib2to3 can now read pickled grammar files using pkgutil.get_data()
rather than probing the filesystem. This lets 2to3 and lib2to3 work when run
from a zipfile.

..

.. bpo: 32030
.. date: 2017-12-20-23-22-32
.. nonce: d1dcwh
.. section: C API

Py_Initialize() doesn't reset the memory allocators to default if the
``PYTHONMALLOC`` environment variable is not set.

..

.. bpo: 29084
.. date: 2017-12-16-09-59-35
.. nonce: ZGJ-LJ
.. section: C API

Undocumented C API for OrderedDict has been excluded from the limited C API.
It was added by mistake and actually never worked in the limited C API.

..

.. bpo: 32264
.. date: 2017-12-12-23-09-46
.. nonce: ahRlOI
.. section: C API

Moved the pygetopt.h header into internal/, since it has no public APIs.

..

.. bpo: 32241
.. date: 2017-12-07-15-58-15
.. nonce: LbyQt6
.. section: C API

:c:func:`Py_SetProgramName` and :c:func:`Py_SetPythonHome` now take the
``const wchar *`` arguments instead of ``wchar *``.