bpo-37759: Second round of edits to Whatsnew 3.8 (GH-15204) (GH-15240)
(cherry picked from commit 66a34d35e4)
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Raymond Hettinger
GitHub
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@ -39,7 +39,7 @@
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module.
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(Contributed by P.Y. Developer in :issue:`12345`.)
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This saves the maintainer the effort of going through the Mercurial log
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This saves the maintainer the effort of going through the Git log
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when researching a change.
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:Editor: Raymond Hettinger
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@ -59,6 +59,7 @@ notable items not yet covered are:
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from datetime import date
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from math import cos, radians
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from unicodedata import normalize
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import re
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import math
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@ -383,9 +384,13 @@ Other Language Changes
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was lifted.
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(Contributed by Serhiy Storchaka in :issue:`32489`.)
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* The :class:`int` type now has a new :meth:`~int.as_integer_ratio` method
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compatible with the existing :meth:`float.as_integer_ratio` method.
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(Contributed by Lisa Roach in :issue:`33073`.)
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* The :class:`bool`, :class:`int`, and :class:`fractions.Fraction` types
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now have an :meth:`~int.as_integer_ratio` method like that found in
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:class:`float` and :class:`decimal.Decimal`. This minor API extension
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makes it possible to write ``numerator, denominator =
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x.as_integer_ratio()`` and have it work across multiple numeric types.
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(Contributed by Lisa Roach in :issue:`33073` and Raymond Hettinger in
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:issue:`37819`.)
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* Constructors of :class:`int`, :class:`float` and :class:`complex` will now
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use the :meth:`~object.__index__` special method, if available and the
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@ -410,19 +415,26 @@ Other Language Changes
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never intended to permit more than a bare name on the left-hand side of a
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keyword argument assignment term. See :issue:`34641`.
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* Iterable unpacking is now allowed without parentheses in :keyword:`yield`
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and :keyword:`return` statements.
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* Generalized iterable unpacking in :keyword:`yield` and
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:keyword:`return` statements no longer requires enclosing parentheses.
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This brings the *yield* and *return* syntax into better agreement with
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normal assignment syntax::
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>>> def parse(family):
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lastname, *members = family.split()
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return lastname.upper(), *members
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>>> parse('simpsons homer marge bart lisa sally')
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('SIMPSONS', 'homer', 'marge', 'bart', 'lisa', 'sally')
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(Contributed by David Cuthbert and Jordan Chapman in :issue:`32117`.)
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* The compiler now produces a :exc:`SyntaxWarning` in some cases when a comma
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is missed before tuple or list. For example::
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data = [
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(1, 2, 3) # oops, missing comma!
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(4, 5, 6)
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]
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(Contributed by Serhiy Storchaka in :issue:`15248`.)
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* When a comma is missed in code such as ``[(10, 20) (30, 40)]``, the
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compiler displays a :exc:`SyntaxWarning` with a helpful suggestion.
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This improves on just having a :exc:`TypeError` indicating that the
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first tuple was not callable. (Contributed by Serhiy Storchaka in
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:issue:`15248`.)
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* Arithmetic operations between subclasses of :class:`datetime.date` or
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:class:`datetime.datetime` and :class:`datetime.timedelta` objects now return
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@ -439,7 +451,25 @@ Other Language Changes
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and Windows use this to properly terminate scripts in interactive sessions.
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(Contributed by Google via Gregory P. Smith in :issue:`1054041`.)
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* Added new ``replace()`` method to the code type (:class:`types.CodeType`).
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* Some advanced styles of programming require updating the
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:class:`types.CodeType` object for an existing function. Since code
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objects are immutable, a new code object needs to be created, one
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that is modeled on the existing code object. With 19 parameters,
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this was somewhat tedious. Now, the new ``replace()`` method makes
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it possible to create a clone with a few altered parameters.
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Here's an example that alters the :func:`statistics.mean` function to
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prevent the *data* parameter from being used as a keyword argument::
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>>> from statistics import mean
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>>> mean(data=[10, 20, 90])
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40
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>>> mean.__code__ = mean.__code__.replace(co_posonlyargcount=1)
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>>> mean(data=[10, 20, 90])
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Traceback (most recent call last):
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...
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TypeError: mean() got some positional-only arguments passed as keyword arguments: 'data'
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(Contributed by Victor Stinner in :issue:`37032`.)
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* For integers, the three-argument form of the :func:`pow` function now
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@ -468,14 +498,55 @@ Other Language Changes
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(Contributed by Mark Dickinson in :issue:`36027`.)
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* When dictionary comprehensions are evaluated, the key is now evaluated before
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the value, as proposed by :pep:`572`.
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* Dict comprehensions have been synced-up with dict literals so that the
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key is computed first and the value second::
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>>> # Dict comprehension
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>>> cast = {input('role? '): input('actor? ') for i in range(2)}
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role? King Arthur
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actor? Chapman
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role? Black Knight
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actor? Cleese
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>>> # Dict literal
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>>> cast = {input('role? '): input('actor? ')}
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role? Sir Robin
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actor? Eric Idle
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The guaranteed execution order is helpful with assignment expressions
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because variables assigned in the key expression will be available in
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the value expression::
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>>> names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald']
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>>> {(n := normalize('NFC', name)).casefold() : n for name in names}
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{'martin von löwis': 'Martin von Löwis',
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'łukasz langa': 'Łukasz Langa',
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'walter dörwald': 'Walter Dörwald'}
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New Modules
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===========
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* None yet.
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* The new :mod:`importlib.metadata` module provides (provisional) support for
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reading metadata from third-party packages. For example, it can extract an
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installed package's version number, list of entry points, and more::
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>>> # Note following example requires that the popular "requests"
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>>> # package has been installed.
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>>>
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>>> from importlib.metadata import version, requires, files
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>>> version('requests')
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'2.22.0'
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>>> list(requires('requests'))
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['chardet (<3.1.0,>=3.0.2)']
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>>> list(files('requests'))[:5]
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[PackagePath('requests-2.22.0.dist-info/INSTALLER'),
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PackagePath('requests-2.22.0.dist-info/LICENSE'),
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PackagePath('requests-2.22.0.dist-info/METADATA'),
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PackagePath('requests-2.22.0.dist-info/RECORD'),
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PackagePath('requests-2.22.0.dist-info/WHEEL')]
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(Contributed in :issue:`34632` by Barry Warsaw and Jason R. Coombs.)
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Improved Modules
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