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Fixes and improvements to 3.8 whatsnew #16535

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0407b7b
Several improvements to whatsnew 3.8
aeros Oct 2, 2019
30129c2
Fix line width
aeros Oct 2, 2019
2da2059
Fix sphinx role
aeros Oct 2, 2019
a6abf44
Fix sphinx role
aeros Oct 2, 2019
1abee7b
Grammar fix
aeros Oct 5, 2019
a018f9a
Grammar Fixes
aeros Oct 5, 2019
fd6fd07
Apply suggestions
aeros Oct 6, 2019
ad0c22c
Fix word wrapping from suggestion
aeros Oct 6, 2019
7e9c550
Fix Sphinx role
aeros Oct 6, 2019
f101ad1
Fix sphinx role
aeros Oct 6, 2019
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109 changes: 58 additions & 51 deletions Doc/whatsnew/3.8.rst
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Expand Up @@ -405,8 +405,9 @@ Other Language Changes

(Contributed by Jonathan Eunice and Serhiy Storchaka in :issue:`30688`.)

* Dict and dictviews are now iterable in reversed insertion order using
:func:`reversed`. (Contributed by Rémi Lapeyre in :issue:`33462`.)
* :class:`dict` and :term:`dictionary views <dictionary view>` are now iterable
in reversed insertion order using :func:`reversed`.
(Contributed by Rémi Lapeyre in :issue:`33462`.)

* The syntax allowed for keyword names in function calls was further
restricted. In particular, ``f((keyword)=arg)`` is no longer allowed. It was
Expand All @@ -415,7 +416,7 @@ Other Language Changes

* Generalized iterable unpacking in :keyword:`yield` and
:keyword:`return` statements no longer requires enclosing parentheses.
This brings the *yield* and *return* syntax into better agreement with
This brings the ``yield`` and ``return`` syntax into better agreement with
normal assignment syntax::

>>> def parse(family):
Expand All @@ -439,7 +440,7 @@ Other Language Changes
an instance of the subclass, rather than the base class. This also affects
the return type of operations whose implementation (directly or indirectly)
uses :class:`datetime.timedelta` arithmetic, such as
:meth:`datetime.datetime.astimezone`.
:meth:`~datetime.datetime.astimezone`.
(Contributed by Paul Ganssle in :issue:`32417`.)

* When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the
Expand Down Expand Up @@ -554,9 +555,10 @@ Improved Modules
ast
---

AST nodes now have ``end_lineno`` and ``end_col_offset`` attributes,
which give the precise location of the end of the node. (This only
applies to nodes that have ``lineno`` and ``col_offset`` attributes.)
AST nodes now have :attr:`~ast.AST.end_lineno` and
:attr:`~ast.AST.end_col_offset` attributes, which give the precise location of
the end of the node. (This only applies to nodes that have ``lineno`` and
``col_offset`` attributes.)

The :func:`ast.parse` function has some new flags:

Expand All @@ -568,7 +570,7 @@ The :func:`ast.parse` function has some new flags:

* ``feature_version=(3, N)`` allows specifying an earlier Python 3
version. (For example, ``feature_version=(3, 4)`` will treat
``async`` and ``await`` as non-reserved words.)
:keyword:`async` and :keyword:`await` as non-reserved words.)

New function :func:`ast.get_source_segment` returns the source code
for a specific AST node.
Expand All @@ -593,20 +595,22 @@ builtins

The :func:`compile` built-in has been improved to accept the
``ast.PyCF_ALLOW_TOP_LEVEL_AWAIT`` flag. With this new flag passed,
:func:`compile` will allow top-level ``await``, ``async for`` and ``async with``
constructs that are usually considered invalid syntax. Asynchronous code object
marked with the ``CO_COROUTINE`` flag may then be returned.
:func:`compile` will allow top-level :keyword:`await`, :keyword:`async for` and
:keyword:`async with` constructs that are usually considered invalid syntax.
Asynchronous code objects marked with the :data:`inspect.CO_COROUTINE` flag may
then be returned.

(Contributed by Matthias Bussonnier in :issue:`34616`)

collections
-----------

The :meth:`_asdict()` method for :func:`collections.namedtuple` now returns
a :class:`dict` instead of a :class:`collections.OrderedDict`. This works because
regular dicts have guaranteed ordering since Python 3.7. If the extra
features of :class:`OrderedDict` are required, the suggested remediation is
to cast the result to the desired type: ``OrderedDict(nt._asdict())``.
The :meth:`~collections.somenamedtuple._asdict` method for
:func:`collections.namedtuple` now returns
a :class:`dict` instead of a :class:`collections.OrderedDict`. This works
because regular dicts have guaranteed ordering since Python 3.7. If the extra
features of :class:`collections.OrderedDict` are required, the suggested
remediation is to cast the result to the desired type: ``OrderedDict(nt._asdict())``.
(Contributed by Raymond Hettinger in :issue:`35864`.)


Expand Down Expand Up @@ -682,10 +686,10 @@ The changes above have been backported to 3.7 maintenance releases.
inspect
-------

The :func:`inspect.getdoc` function can now find docstrings for ``__slots__``
if that attribute is a :class:`dict` where the values are docstrings.
This provides documentation options similar to what we already have
for :func:`property`, :func:`classmethod`, and :func:`staticmethod`::
The :func:`inspect.getdoc` function can now find docstrings for
:attr:`~object.__slots__` if that attribute is a :class:`dict` where the values
are docstrings. This provides documentation options similar to what we already
have for :func:`property`, :func:`classmethod`, and :func:`staticmethod`::

class AudioClip:
__slots__ = {'bit_rate': 'expressed in kilohertz to one decimal place',
Expand Down Expand Up @@ -745,7 +749,7 @@ The changes above have been backported to 3.7 maintenance releases.
json.tool
---------

Add option ``--json-lines`` to parse every input line as separate JSON object.
Add option ``--json-lines`` to parse every input line as a separate JSON object.
(Contributed by Weipeng Hong in :issue:`31553`.)


Expand Down Expand Up @@ -875,7 +879,7 @@ pickle

Reduction methods can now include a 6th item in the tuple they return. This
item should specify a custom state-setting method that's called instead of the
regular ``__setstate__`` method.
regular :meth:`object.__setstate__` method.
(Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`)

:mod:`pickle` extensions subclassing the C-optimized :class:`~pickle.Pickler`
Expand Down Expand Up @@ -935,8 +939,8 @@ recursively removing their contents first.
ssl
---

Added :attr:`SSLContext.post_handshake_auth` to enable and
:meth:`ssl.SSLSocket.verify_client_post_handshake` to initiate TLS 1.3
Added :attr:`~ssl.SSLContext.post_handshake_auth` to enable and
:meth:`~ssl.SSLSocket.verify_client_post_handshake` to initiate TLS 1.3
post-handshake authentication.
(Contributed by Christian Heimes in :issue:`34670`.)

Expand Down Expand Up @@ -1096,8 +1100,9 @@ unicodedata
unittest
--------

* Added :class:`AsyncMock` to support an asynchronous version of :class:`Mock`.
Appropriate new assert functions for testing have been added as well.
* Added :class:`~unittest.mock.AsyncMock` to support an asynchronous version of
:class:`~unittest.mock.Mock`. Appropriate new assert functions for testing have
been added as well.
(Contributed by Lisa Roach in :issue:`26467`).

* Added :func:`~unittest.addModuleCleanup()` and
Expand All @@ -1110,7 +1115,7 @@ unittest
failure. (Contributed by Petter Strandmark in :issue:`35047`.)

* :mod:`unittest` module gained support for coroutines to be used as test cases
with :class:`unittest.IsolatedAsyncioTestCase`.
with :class:`~unittest.IsolatedAsyncioTestCase`.
(Contributed by Andrew Svetlov in :issue:`32972`.)

Example::
Expand Down Expand Up @@ -1219,7 +1224,8 @@ Optimizations
objects (e.g. tuple, list, dict) size is reduced 4 or 8 bytes.
(Contributed by Inada Naoki in :issue:`33597`)

* :class:`uuid.UUID` now uses ``__slots__`` to reduce its memory footprint.
* :class:`uuid.UUID` now uses :attr:`~object.__slots__` to
reduce its memory footprint.

* Improved performance of :func:`operator.itemgetter` by 33%. Optimized
argument handling and added a fast path for the common case of a single
Expand All @@ -1233,9 +1239,10 @@ Optimizations
Joe Jevnik, Serhiy Storchaka in :issue:`32492`.)

* The :class:`list` constructor does not overallocate the internal item buffer
if the input iterable has a known length (the input implements ``__len__``).
This makes the created list 12% smaller on average. (Contributed by
Raymond Hettinger and Pablo Galindo in :issue:`33234`.)
if the input iterable has a known length (the input implements
:meth:`~object.__len__`). This makes the created list 12% smaller
on average.
(Contributed by Raymond Hettinger and Pablo Galindo in :issue:`33234`.)

* Doubled the speed of class variable writes. When a non-dunder attribute
was updated, there was an unnecessary call to update slots.
Expand Down Expand Up @@ -1327,13 +1334,13 @@ Build and C API Changes
:c:func:`PyArg_ParseTuple` with integer converting format units like ``'i'``
will now use the :meth:`~object.__index__` special method instead of
:meth:`~object.__int__`, if available. The deprecation warning will be
emitted for objects with the ``__int__()`` method but without the
``__index__()`` method (like :class:`~decimal.Decimal` and
emitted for objects with the :meth:`~object.__int__` method but without the
:meth:`~object.__index__` method (like :class:`~decimal.Decimal` and
:class:`~fractions.Fraction`). :c:func:`PyNumber_Check` will now return
``1`` for objects implementing ``__index__()``.
``1`` for objects implementing :meth:`~object.__index__`.
:c:func:`PyNumber_Long`, :c:func:`PyNumber_Float` and
:c:func:`PyFloat_AsDouble` also now use the ``__index__()`` method if
available.
:c:func:`PyFloat_AsDouble` also now use the :meth:`object.__index__` method
if available.
(Contributed by Serhiy Storchaka in :issue:`36048` and :issue:`20092`.)

* Heap-allocated type objects will now increase their reference count
Expand Down Expand Up @@ -1372,18 +1379,18 @@ Deprecated
deprecated and will be prohibited in Python 3.9.
(Contributed by Elvis Pranskevichus in :issue:`34075`.)

* The :meth:`__getitem__` methods of :class:`xml.dom.pulldom.DOMEventStream`,
:class:`wsgiref.util.FileWrapper` and :class:`fileinput.FileInput` have been
deprecated.
* The :meth:`object.__getitem__` methods of
:class:`~xml.dom.pulldom.DOMEventStream`, :class:`wsgiref.util.FileWrapper`
and :class:`fileinput.FileInput` have been deprecated.

Implementations of these methods have been ignoring their *index* parameter,
and returning the next item instead.

(Contributed by Berker Peksag in :issue:`9372`.)

* The :class:`typing.NamedTuple` class has deprecated the ``_field_types``
attribute in favor of the ``__annotations__`` attribute which has the same
information. (Contributed by Raymond Hettinger in :issue:`36320`.)
attribute in favor of the :attr:`~object.__annotations__` attribute which has
the same information. (Contributed by Raymond Hettinger in :issue:`36320`.)

* :mod:`ast` classes ``Num``, ``Str``, ``Bytes``, ``NameConstant`` and
``Ellipsis`` are considered deprecated and will be removed in future Python
Expand Down Expand Up @@ -1510,9 +1517,9 @@ that may require changes to your code.
Changes in Python behavior
--------------------------

* Yield expressions (both ``yield`` and ``yield from`` clauses) are now disallowed
in comprehensions and generator expressions (aside from the iterable expression
in the leftmost :keyword:`!for` clause).
* :ref:`Yield expressions <yieldexpr>` (both :keyword:`yield` and ``yield from``
clauses) are now disallowed in comprehensions and generator expressions
(aside from the iterable expression in the leftmost :keyword:`!for` clause).
(Contributed by Serhiy Storchaka in :issue:`10544`.)

* The compiler now produces a :exc:`SyntaxWarning` when identity checks
Expand All @@ -1527,11 +1534,11 @@ Changes in Python behavior
raised when getting the attribute from the type dictionary are no longer
ignored. (Contributed by Serhiy Storchaka in :issue:`35459`.)

* Removed ``__str__`` implementations from builtin types :class:`bool`,
:class:`int`, :class:`float`, :class:`complex` and few classes from
the standard library. They now inherit ``__str__()`` from :class:`object`.
As result, defining the ``__repr__()`` method in the subclass of these
classes will affect their string representation.
* Removed :meth:`~object.__str__` implementations from builtin types
:class:`bool`, :class:`int`, :class:`float`, :class:`complex` and few classes
from the standard library. They now inherit :meth:`~object.__str__` from
:class:`object`. As result, defining the :meth:`~object.__repr__` method
in the subclass of these classes will affect their string representation.
(Contributed by Serhiy Storchaka in :issue:`36793`.)

* On AIX, :attr:`sys.platform` doesn't contain the major version anymore.
Expand Down Expand Up @@ -1568,7 +1575,7 @@ Changes in the Python API
(Contributed by Eric Snow in :issue:`34651`, modified by Christian Heimes
in :issue:`37951`.)

* The :meth:`imap.IMAP4.logout` method no longer ignores silently arbitrary
* The :meth:`imaplib.IMAP4.logout` method no longer silently ignores arbitrary
exceptions.

* The function :func:`platform.popen` has been removed, it was deprecated since
Expand Down Expand Up @@ -1622,7 +1629,7 @@ Changes in the Python API
* The ``PyGC_Head`` struct has changed completely. All code that touched the
struct member should be rewritten. (See :issue:`33597`)

* The ``PyInterpreterState`` struct has been moved into the "internal"
* The :c:type:`PyInterpreterState` struct has been moved into the "internal"
header files (specifically Include/internal/pycore_pystate.h). An
opaque ``PyInterpreterState`` is still available as part of the public
API (and stable ABI). The docs indicate that none of the struct's
Expand Down