2230 lines
87 KiB
ReStructuredText
2230 lines
87 KiB
ReStructuredText
****************************
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What's New In Python 3.8
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****************************
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.. Rules for maintenance:
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* Anyone can add text to this document. Do not spend very much time
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on the wording of your changes, because your text will probably
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get rewritten to some degree.
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* The maintainer will go through Misc/NEWS periodically and add
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changes; it's therefore more important to add your changes to
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Misc/NEWS than to this file.
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* This is not a complete list of every single change; completeness
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is the purpose of Misc/NEWS. Some changes I consider too small
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or esoteric to include. If such a change is added to the text,
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I'll just remove it. (This is another reason you shouldn't spend
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too much time on writing your addition.)
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* If you want to draw your new text to the attention of the
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maintainer, add 'XXX' to the beginning of the paragraph or
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section.
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* It's OK to just add a fragmentary note about a change. For
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example: "XXX Describe the transmogrify() function added to the
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socket module." The maintainer will research the change and
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write the necessary text.
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* You can comment out your additions if you like, but it's not
|
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necessary (especially when a final release is some months away).
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* Credit the author of a patch or bugfix. Just the name is
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sufficient; the e-mail address isn't necessary.
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* It's helpful to add the bug/patch number as a comment:
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XXX Describe the transmogrify() function added to the socket
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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 Git log
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when researching a change.
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:Editor: Raymond Hettinger
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This article explains the new features in Python 3.8, compared to 3.7.
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For full details, see the :ref:`changelog <changelog>`.
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.. testsetup::
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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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Summary -- Release highlights
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=============================
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.. This section singles out the most important changes in Python 3.8.
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Brevity is key.
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.. PEP-sized items next.
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New Features
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============
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Assignment expressions
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----------------------
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There is new syntax ``:=`` that assigns values to variables as part of a larger
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expression. It is affectionately known as "the walrus operator" due to
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its resemblance to `the eyes and tusks of a walrus
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<https://en.wikipedia.org/wiki/Walrus#/media/File:Pacific_Walrus_-_Bull_(8247646168).jpg>`_.
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In this example, the assignment expression helps avoid calling
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:func:`len` twice::
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if (n := len(a)) > 10:
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print(f"List is too long ({n} elements, expected <= 10)")
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A similar benefit arises during regular expression matching where
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match objects are needed twice, once to test whether a match
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occurred and another to extract a subgroup::
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discount = 0.0
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if (mo := re.search(r'(\d+)% discount', advertisement)):
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discount = float(mo.group(1)) / 100.0
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The operator is also useful with while-loops that compute
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a value to test loop termination and then need that same
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value again in the body of the loop::
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# Loop over fixed length blocks
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while (block := f.read(256)) != '':
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process(block)
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Another motivating use case arises in list comprehensions where
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a value computed in a filtering condition is also needed in
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the expression body::
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[clean_name.title() for name in names
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if (clean_name := normalize('NFC', name)) in allowed_names]
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Try to limit use of the walrus operator to clean cases that reduce
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complexity and improve readability.
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See :pep:`572` for a full description.
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(Contributed by Emily Morehouse in :issue:`35224`.)
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Positional-only parameters
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--------------------------
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There is a new function parameter syntax ``/`` to indicate that some
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function parameters must be specified positionally and cannot be used as
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keyword arguments. This is the same notation shown by ``help()`` for C
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functions annotated with Larry Hastings' `Argument Clinic
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<https://docs.python.org/3/howto/clinic.html>`_ tool.
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In the following example, parameters *a* and *b* are positional-only,
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while *c* or *d* can be positional or keyword, and *e* or *f* are
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required to be keywords::
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def f(a, b, /, c, d, *, e, f):
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print(a, b, c, d, e, f)
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The following is a valid call::
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f(10, 20, 30, d=40, e=50, f=60)
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However, these are invalid calls::
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f(10, b=20, c=30, d=40, e=50, f=60) # b cannot be a keyword argument
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f(10, 20, 30, 40, 50, f=60) # e must be a keyword argument
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One use case for this notation is that it allows pure Python functions
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to fully emulate behaviors of existing C coded functions. For example,
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the built-in :func:`divmod` function does not accept keyword arguments::
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def divmod(a, b, /):
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"Emulate the built in divmod() function"
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return (a // b, a % b)
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Another use case is to preclude keyword arguments when the parameter
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name is not helpful. For example, the builtin :func:`len` function has
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the signature ``len(obj, /)``. This precludes awkward calls such as::
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len(obj='hello') # The "obj" keyword argument impairs readability
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A further benefit of marking a parameter as positional-only is that it
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allows the parameter name to be changed in the future without risk of
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breaking client code. For example, in the :mod:`statistics` module, the
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parameter name *dist* may be changed in the future. This was made
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possible with the following function specification::
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def quantiles(dist, /, *, n=4, method='exclusive')
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...
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Since the parameters to the left of ``/`` are not exposed as possible
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keywords, the parameters names remain available for use in ``**kwargs``::
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>>> def f(a, b, /, **kwargs):
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... print(a, b, kwargs)
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...
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>>> f(10, 20, a=1, b=2, c=3) # a and b are used in two ways
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10 20 {'a': 1, 'b': 2, 'c': 3}
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This greatly simplifies the implementation of functions and methods
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that need to accept arbitrary keyword arguments. For example, here
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is an excerpt from code in the :mod:`collections` module::
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class Counter(dict):
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def __init__(self, iterable=None, /, **kwds):
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# Note "iterable" is a possible keyword argument
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See :pep:`570` for a full description.
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(Contributed by Pablo Galindo in :issue:`36540`.)
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.. TODO: Pablo will sprint on docs at PyCon US 2019.
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Parallel filesystem cache for compiled bytecode files
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-----------------------------------------------------
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The new :envvar:`PYTHONPYCACHEPREFIX` setting (also available as
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:option:`-X` ``pycache_prefix``) configures the implicit bytecode
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cache to use a separate parallel filesystem tree, rather than
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the default ``__pycache__`` subdirectories within each source
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directory.
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The location of the cache is reported in :data:`sys.pycache_prefix`
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(:const:`None` indicates the default location in ``__pycache__``
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subdirectories).
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(Contributed by Carl Meyer in :issue:`33499`.)
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Debug build uses the same ABI as release build
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-----------------------------------------------
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Python now uses the same ABI whether it's built in release or debug mode. On
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Unix, when Python is built in debug mode, it is now possible to load C
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extensions built in release mode and C extensions built using the stable ABI.
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Release builds and debug builds are now ABI compatible: defining the
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``Py_DEBUG`` macro no longer implies the ``Py_TRACE_REFS`` macro, which
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introduces the only ABI incompatibility. The ``Py_TRACE_REFS`` macro, which
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adds the :func:`sys.getobjects` function and the :envvar:`PYTHONDUMPREFS`
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environment variable, can be set using the new ``./configure --with-trace-refs``
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build option.
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(Contributed by Victor Stinner in :issue:`36465`.)
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On Unix, C extensions are no longer linked to libpython except on Android
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and Cygwin.
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It is now possible
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for a statically linked Python to load a C extension built using a shared
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library Python.
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(Contributed by Victor Stinner in :issue:`21536`.)
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On Unix, when Python is built in debug mode, import now also looks for C
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extensions compiled in release mode and for C extensions compiled with the
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stable ABI.
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(Contributed by Victor Stinner in :issue:`36722`.)
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To embed Python into an application, a new ``--embed`` option must be passed to
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``python3-config --libs --embed`` to get ``-lpython3.8`` (link the application
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to libpython). To support both 3.8 and older, try ``python3-config --libs
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--embed`` first and fallback to ``python3-config --libs`` (without ``--embed``)
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if the previous command fails.
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Add a pkg-config ``python-3.8-embed`` module to embed Python into an
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application: ``pkg-config python-3.8-embed --libs`` includes ``-lpython3.8``.
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To support both 3.8 and older, try ``pkg-config python-X.Y-embed --libs`` first
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and fallback to ``pkg-config python-X.Y --libs`` (without ``--embed``) if the
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previous command fails (replace ``X.Y`` with the Python version).
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On the other hand, ``pkg-config python3.8 --libs`` no longer contains
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``-lpython3.8``. C extensions must not be linked to libpython (except on
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Android and Cygwin, whose cases are handled by the script);
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this change is backward incompatible on purpose.
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(Contributed by Victor Stinner in :issue:`36721`.)
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f-strings support ``=`` for self-documenting expressions and debugging
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----------------------------------------------------------------------
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Added an ``=`` specifier to :term:`f-string`\s. An f-string such as
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``f'{expr=}'`` will expand to the text of the expression, an equal sign,
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then the representation of the evaluated expression. For example:
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>>> user = 'eric_idle'
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>>> member_since = date(1975, 7, 31)
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>>> f'{user=} {member_since=}'
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"user='eric_idle' member_since=datetime.date(1975, 7, 31)"
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The usual :ref:`f-string format specifiers <f-strings>` allow more
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control over how the result of the expression is displayed::
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>>> delta = date.today() - member_since
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>>> f'{user=!s} {delta.days=:,d}'
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'user=eric_idle delta.days=16,075'
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The ``=`` specifier will display the whole expression so that
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calculations can be shown::
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>>> print(f'{theta=} {cos(radians(theta))=:.3f}')
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theta=30 cos(radians(theta))=0.866
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(Contributed by Eric V. Smith and Larry Hastings in :issue:`36817`.)
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PEP 578: Python Runtime Audit Hooks
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-----------------------------------
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The PEP adds an Audit Hook and Verified Open Hook. Both are available from
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Python and native code, allowing applications and frameworks written in pure
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Python code to take advantage of extra notifications, while also allowing
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embedders or system administrators to deploy builds of Python where auditing is
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always enabled.
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See :pep:`578` for full details.
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PEP 587: Python Initialization Configuration
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--------------------------------------------
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The :pep:`587` adds a new C API to configure the Python Initialization
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providing finer control on the whole configuration and better error reporting.
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New structures:
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* :c:type:`PyConfig`
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* :c:type:`PyPreConfig`
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* :c:type:`PyStatus`
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* :c:type:`PyWideStringList`
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New functions:
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* :c:func:`PyConfig_Clear`
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* :c:func:`PyConfig_InitIsolatedConfig`
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* :c:func:`PyConfig_InitPythonConfig`
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* :c:func:`PyConfig_Read`
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* :c:func:`PyConfig_SetArgv`
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* :c:func:`PyConfig_SetBytesArgv`
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* :c:func:`PyConfig_SetBytesString`
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* :c:func:`PyConfig_SetString`
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* :c:func:`PyPreConfig_InitIsolatedConfig`
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* :c:func:`PyPreConfig_InitPythonConfig`
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||
* :c:func:`PyStatus_Error`
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* :c:func:`PyStatus_Exception`
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* :c:func:`PyStatus_Exit`
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* :c:func:`PyStatus_IsError`
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||
* :c:func:`PyStatus_IsExit`
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||
* :c:func:`PyStatus_NoMemory`
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||
* :c:func:`PyStatus_Ok`
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* :c:func:`PyWideStringList_Append`
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* :c:func:`PyWideStringList_Insert`
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* :c:func:`Py_BytesMain`
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||
* :c:func:`Py_ExitStatusException`
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* :c:func:`Py_InitializeFromConfig`
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* :c:func:`Py_PreInitialize`
|
||
* :c:func:`Py_PreInitializeFromArgs`
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||
* :c:func:`Py_PreInitializeFromBytesArgs`
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* :c:func:`Py_RunMain`
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||
|
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This PEP also adds ``_PyRuntimeState.preconfig`` (:c:type:`PyPreConfig` type)
|
||
and ``PyInterpreterState.config`` (:c:type:`PyConfig` type) fields to these
|
||
internal structures. ``PyInterpreterState.config`` becomes the new
|
||
reference configuration, replacing global configuration variables and
|
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other private variables.
|
||
|
||
See :ref:`Python Initialization Configuration <init-config>` for the
|
||
documentation.
|
||
|
||
See :pep:`587` for a full description.
|
||
|
||
(Contributed by Victor Stinner in :issue:`36763`.)
|
||
|
||
|
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PEP 590: Vectorcall: a fast calling protocol for CPython
|
||
--------------------------------------------------------
|
||
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:ref:`vectorcall` is added to the Python/C API.
|
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It is meant to formalize existing optimizations which were already done
|
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for various classes.
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Any static type implementing a callable can use this protocol.
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This is currently provisional.
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||
The aim is to make it fully public in Python 3.9.
|
||
|
||
See :pep:`590` for a full description.
|
||
|
||
(Contributed by Jeroen Demeyer, Mark Shannon and Petr Viktorin in :issue:`36974`.)
|
||
|
||
|
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Pickle protocol 5 with out-of-band data buffers
|
||
-----------------------------------------------
|
||
|
||
When :mod:`pickle` is used to transfer large data between Python processes
|
||
in order to take advantage of multi-core or multi-machine processing,
|
||
it is important to optimize the transfer by reducing memory copies, and
|
||
possibly by applying custom techniques such as data-dependent compression.
|
||
|
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The :mod:`pickle` protocol 5 introduces support for out-of-band buffers
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||
where :pep:`3118`-compatible data can be transmitted separately from the
|
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main pickle stream, at the discretion of the communication layer.
|
||
|
||
See :pep:`574` for a full description.
|
||
|
||
(Contributed by Antoine Pitrou in :issue:`36785`.)
|
||
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Other Language Changes
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======================
|
||
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* A :keyword:`continue` statement was illegal in the :keyword:`finally` clause
|
||
due to a problem with the implementation. In Python 3.8 this restriction
|
||
was lifted.
|
||
(Contributed by Serhiy Storchaka in :issue:`32489`.)
|
||
|
||
* The :class:`bool`, :class:`int`, and :class:`fractions.Fraction` types
|
||
now have an :meth:`~int.as_integer_ratio` method like that found in
|
||
:class:`float` and :class:`decimal.Decimal`. This minor API extension
|
||
makes it possible to write ``numerator, denominator =
|
||
x.as_integer_ratio()`` and have it work across multiple numeric types.
|
||
(Contributed by Lisa Roach in :issue:`33073` and Raymond Hettinger in
|
||
:issue:`37819`.)
|
||
|
||
* Constructors of :class:`int`, :class:`float` and :class:`complex` will now
|
||
use the :meth:`~object.__index__` special method, if available and the
|
||
corresponding method :meth:`~object.__int__`, :meth:`~object.__float__`
|
||
or :meth:`~object.__complex__` is not available.
|
||
(Contributed by Serhiy Storchaka in :issue:`20092`.)
|
||
|
||
* Added support of ``\N{name}`` escapes in :mod:`regular expressions <re>`::
|
||
|
||
>>> notice = 'Copyright © 2019'
|
||
>>> copyright_year_pattern = re.compile(r'\N{copyright sign}\s*(\d{4})')
|
||
>>> int(copyright_year_pattern.search(notice).group(1))
|
||
2019
|
||
|
||
(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`.)
|
||
|
||
* The syntax allowed for keyword names in function calls was further
|
||
restricted. In particular, ``f((keyword)=arg)`` is no longer allowed. It was
|
||
never intended to permit more than a bare name on the left-hand side of a
|
||
keyword argument assignment term.
|
||
(Contributed by Benjamin Peterson in :issue:`34641`.)
|
||
|
||
* 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
|
||
normal assignment syntax::
|
||
|
||
>>> def parse(family):
|
||
lastname, *members = family.split()
|
||
return lastname.upper(), *members
|
||
|
||
>>> parse('simpsons homer marge bart lisa maggie')
|
||
('SIMPSONS', 'homer', 'marge', 'bart', 'lisa', 'maggie')
|
||
|
||
(Contributed by David Cuthbert and Jordan Chapman in :issue:`32117`.)
|
||
|
||
* When a comma is missed in code such as ``[(10, 20) (30, 40)]``, the
|
||
compiler displays a :exc:`SyntaxWarning` with a helpful suggestion.
|
||
This improves on just having a :exc:`TypeError` indicating that the
|
||
first tuple was not callable. (Contributed by Serhiy Storchaka in
|
||
:issue:`15248`.)
|
||
|
||
* Arithmetic operations between subclasses of :class:`datetime.date` or
|
||
:class:`datetime.datetime` and :class:`datetime.timedelta` objects now return
|
||
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`.
|
||
(Contributed by Paul Ganssle in :issue:`32417`.)
|
||
|
||
* When the Python interpreter is interrupted by Ctrl-C (SIGINT) and the
|
||
resulting :exc:`KeyboardInterrupt` exception is not caught, the Python process
|
||
now exits via a SIGINT signal or with the correct exit code such that the
|
||
calling process can detect that it died due to a Ctrl-C. Shells on POSIX
|
||
and Windows use this to properly terminate scripts in interactive sessions.
|
||
(Contributed by Google via Gregory P. Smith in :issue:`1054041`.)
|
||
|
||
* Some advanced styles of programming require updating the
|
||
:class:`types.CodeType` object for an existing function. Since code
|
||
objects are immutable, a new code object needs to be created, one
|
||
that is modeled on the existing code object. With 19 parameters,
|
||
this was somewhat tedious. Now, the new ``replace()`` method makes
|
||
it possible to create a clone with a few altered parameters.
|
||
|
||
Here's an example that alters the :func:`statistics.mean` function to
|
||
prevent the *data* parameter from being used as a keyword argument::
|
||
|
||
>>> from statistics import mean
|
||
>>> mean(data=[10, 20, 90])
|
||
40
|
||
>>> mean.__code__ = mean.__code__.replace(co_posonlyargcount=1)
|
||
>>> mean(data=[10, 20, 90])
|
||
Traceback (most recent call last):
|
||
...
|
||
TypeError: mean() got some positional-only arguments passed as keyword arguments: 'data'
|
||
|
||
(Contributed by Victor Stinner in :issue:`37032`.)
|
||
|
||
* For integers, the three-argument form of the :func:`pow` function now
|
||
permits the exponent to be negative in the case where the base is
|
||
relatively prime to the modulus. It then computes a modular inverse to
|
||
the base when the exponent is ``-1``, and a suitable power of that
|
||
inverse for other negative exponents. For example, to compute the
|
||
`modular multiplicative inverse
|
||
<https://en.wikipedia.org/wiki/Modular_multiplicative_inverse>`_ of 38
|
||
modulo 137, write::
|
||
|
||
>>> pow(38, -1, 137)
|
||
119
|
||
>>> 119 * 38 % 137
|
||
1
|
||
|
||
Modular inverses arise in the solution of `linear Diophantine
|
||
equations <https://en.wikipedia.org/wiki/Diophantine_equation>`_.
|
||
For example, to find integer solutions for ``4258𝑥 + 147𝑦 = 369``,
|
||
first rewrite as ``4258𝑥 ≡ 369 (mod 147)`` then solve:
|
||
|
||
>>> x = 369 * pow(4258, -1, 147) % 147
|
||
>>> y = (4258 * x - 369) // -147
|
||
>>> 4258 * x + 147 * y
|
||
369
|
||
|
||
(Contributed by Mark Dickinson in :issue:`36027`.)
|
||
|
||
* Dict comprehensions have been synced-up with dict literals so that the
|
||
key is computed first and the value second::
|
||
|
||
>>> # Dict comprehension
|
||
>>> cast = {input('role? '): input('actor? ') for i in range(2)}
|
||
role? King Arthur
|
||
actor? Chapman
|
||
role? Black Knight
|
||
actor? Cleese
|
||
|
||
>>> # Dict literal
|
||
>>> cast = {input('role? '): input('actor? ')}
|
||
role? Sir Robin
|
||
actor? Eric Idle
|
||
|
||
The guaranteed execution order is helpful with assignment expressions
|
||
because variables assigned in the key expression will be available in
|
||
the value expression::
|
||
|
||
>>> names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald']
|
||
>>> {(n := normalize('NFC', name)).casefold() : n for name in names}
|
||
{'martin von löwis': 'Martin von Löwis',
|
||
'łukasz langa': 'Łukasz Langa',
|
||
'walter dörwald': 'Walter Dörwald'}
|
||
|
||
(Contributed by Jörn Heissler in :issue:`35224`.)
|
||
|
||
* The :meth:`object.__reduce__` method can now return a tuple from two to
|
||
six elements long. Formerly, five was the limit. The new, optional sixth
|
||
element is a callable with a ``(obj, state)`` signature. This allows the
|
||
direct control over the state-updating behavior of a specific object. If
|
||
not *None*, this callable will have priority over the object's
|
||
:meth:`~__setstate__` method.
|
||
(Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`.)
|
||
|
||
New Modules
|
||
===========
|
||
|
||
* The new :mod:`importlib.metadata` module provides (provisional) support for
|
||
reading metadata from third-party packages. For example, it can extract an
|
||
installed package's version number, list of entry points, and more::
|
||
|
||
>>> # Note following example requires that the popular "requests"
|
||
>>> # package has been installed.
|
||
>>>
|
||
>>> from importlib.metadata import version, requires, files
|
||
>>> version('requests')
|
||
'2.22.0'
|
||
>>> list(requires('requests'))
|
||
['chardet (<3.1.0,>=3.0.2)']
|
||
>>> list(files('requests'))[:5]
|
||
[PackagePath('requests-2.22.0.dist-info/INSTALLER'),
|
||
PackagePath('requests-2.22.0.dist-info/LICENSE'),
|
||
PackagePath('requests-2.22.0.dist-info/METADATA'),
|
||
PackagePath('requests-2.22.0.dist-info/RECORD'),
|
||
PackagePath('requests-2.22.0.dist-info/WHEEL')]
|
||
|
||
(Contributed by Barry Warsaw and Jason R. Coombs in :issue:`34632`.)
|
||
|
||
|
||
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.)
|
||
|
||
New function :func:`ast.get_source_segment` returns the source code
|
||
for a specific AST node.
|
||
|
||
(Contributed by Ivan Levkivskyi in :issue:`33416`.)
|
||
|
||
The :func:`ast.parse` function has some new flags:
|
||
|
||
* ``type_comments=True`` causes it to return the text of :pep:`484` and
|
||
:pep:`526` type comments associated with certain AST nodes;
|
||
|
||
* ``mode='func_type'`` can be used to parse :pep:`484` "signature type
|
||
comments" (returned for function definition AST nodes);
|
||
|
||
* ``feature_version=(3, N)`` allows specifying an earlier Python 3
|
||
version. For example, ``feature_version=(3, 4)`` will treat
|
||
:keyword:`async` and :keyword:`await` as non-reserved words.
|
||
|
||
(Contributed by Guido van Rossum in :issue:`35766`.)
|
||
|
||
|
||
asyncio
|
||
-------
|
||
|
||
:func:`asyncio.run` has graduated from the provisional to stable API. This
|
||
function can be used to execute a :term:`coroutine` and return the result while
|
||
automatically managing the event loop. For example::
|
||
|
||
import asyncio
|
||
|
||
async def main():
|
||
await asyncio.sleep(0)
|
||
return 42
|
||
|
||
asyncio.run(main())
|
||
|
||
This is *roughly* equivalent to::
|
||
|
||
import asyncio
|
||
|
||
async def main():
|
||
await asyncio.sleep(0)
|
||
return 42
|
||
|
||
loop = asyncio.new_event_loop()
|
||
asyncio.set_event_loop(loop)
|
||
try:
|
||
loop.run_until_complete(main())
|
||
finally:
|
||
asyncio.set_event_loop(None)
|
||
loop.close()
|
||
|
||
|
||
The actual implementation is significantly more complex. Thus,
|
||
:func:`asyncio.run` should be the preferred way of running asyncio programs.
|
||
|
||
(Contributed by Yury Selivanov in :issue:`32314`.)
|
||
|
||
Running ``python -m asyncio`` launches a natively async REPL. This allows rapid
|
||
experimentation with code that has a top-level :keyword:`await`. There is no
|
||
longer a need to directly call ``asyncio.run()`` which would spawn a new event
|
||
loop on every invocation:
|
||
|
||
.. code-block:: none
|
||
|
||
$ python -m asyncio
|
||
asyncio REPL 3.8.0
|
||
Use "await" directly instead of "asyncio.run()".
|
||
Type "help", "copyright", "credits" or "license" for more information.
|
||
>>> import asyncio
|
||
>>> await asyncio.sleep(10, result='hello')
|
||
hello
|
||
|
||
(Contributed by Yury Selivanov in :issue:`37028`.)
|
||
|
||
The exception :class:`asyncio.CancelledError` now inherits from
|
||
:class:`BaseException` rather than :class:`Exception` and no longer inherits
|
||
from :class:`concurrent.futures.CancelledError`.
|
||
(Contributed by Yury Selivanov in :issue:`32528`.)
|
||
|
||
On Windows, the default event loop is now :class:`~asyncio.ProactorEventLoop`.
|
||
(Contributed by Victor Stinner in :issue:`34687`.)
|
||
|
||
:class:`~asyncio.ProactorEventLoop` now also supports UDP.
|
||
(Contributed by Adam Meily and Andrew Svetlov in :issue:`29883`.)
|
||
|
||
:class:`~asyncio.ProactorEventLoop` can now be interrupted by
|
||
:exc:`KeyboardInterrupt` ("CTRL+C").
|
||
(Contributed by Vladimir Matveev in :issue:`23057`.)
|
||
|
||
Added :meth:`asyncio.Task.get_coro` for getting the wrapped coroutine
|
||
within an :class:`asyncio.Task`.
|
||
(Contributed by Alex Grönholm in :issue:`36999`.)
|
||
|
||
Asyncio tasks can now be named, either by passing the ``name`` keyword
|
||
argument to :func:`asyncio.create_task` or
|
||
the :meth:`~asyncio.loop.create_task` event loop method, or by
|
||
calling the :meth:`~asyncio.Task.set_name` method on the task object. The
|
||
task name is visible in the ``repr()`` output of :class:`asyncio.Task` and
|
||
can also be retrieved using the :meth:`~asyncio.Task.get_name` method.
|
||
(Contributed by Alex Grönholm in :issue:`34270`.)
|
||
|
||
Added support for
|
||
`Happy Eyeballs <https://en.wikipedia.org/wiki/Happy_Eyeballs>`_ to
|
||
:func:`asyncio.loop.create_connection`. To specify the behavior, two new
|
||
parameters have been added: *happy_eyeballs_delay* and *interleave*. The Happy
|
||
Eyeballs algorithm improves responsiveness in applications that support IPv4
|
||
and IPv6 by attempting to simultaneously connect using both.
|
||
(Contributed by twisteroid ambassador in :issue:`33530`.)
|
||
|
||
|
||
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.
|
||
(Contributed by Matthias Bussonnier in :issue:`34616`)
|
||
|
||
|
||
collections
|
||
-----------
|
||
|
||
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:`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`.)
|
||
|
||
|
||
cProfile
|
||
--------
|
||
|
||
The :class:`cProfile.Profile <profile.Profile>` class can now be used as a context manager.
|
||
Profile a block of code by running::
|
||
|
||
import cProfile
|
||
|
||
with cProfile.Profile() as profiler:
|
||
# code to be profiled
|
||
...
|
||
|
||
(Contributed by Scott Sanderson in :issue:`29235`.)
|
||
|
||
|
||
csv
|
||
---
|
||
|
||
The :class:`csv.DictReader` now returns instances of :class:`dict` instead of
|
||
a :class:`collections.OrderedDict`. The tool is now faster and uses less
|
||
memory while still preserving the field order.
|
||
(Contributed by Michael Selik in :issue:`34003`.)
|
||
|
||
|
||
curses
|
||
-------
|
||
|
||
Added a new variable holding structured version information for the
|
||
underlying ncurses library: :data:`~curses.ncurses_version`.
|
||
(Contributed by Serhiy Storchaka in :issue:`31680`.)
|
||
|
||
|
||
ctypes
|
||
------
|
||
|
||
On Windows, :class:`~ctypes.CDLL` and subclasses now accept a *winmode* parameter
|
||
to specify flags for the underlying ``LoadLibraryEx`` call. The default flags are
|
||
set to only load DLL dependencies from trusted locations, including the path
|
||
where the DLL is stored (if a full or partial path is used to load the initial
|
||
DLL) and paths added by :func:`~os.add_dll_directory`.
|
||
(Contributed by Steve Dower in :issue:`36085`.)
|
||
|
||
|
||
datetime
|
||
--------
|
||
|
||
Added new alternate constructors :meth:`datetime.date.fromisocalendar` and
|
||
:meth:`datetime.datetime.fromisocalendar`, which construct :class:`date` and
|
||
:class:`datetime` objects respectively from ISO year, week number, and weekday;
|
||
these are the inverse of each class's ``isocalendar`` method.
|
||
(Contributed by Paul Ganssle in :issue:`36004`.)
|
||
|
||
|
||
functools
|
||
---------
|
||
|
||
:func:`functools.lru_cache` can now be used as a straight decorator rather
|
||
than as a function returning a decorator. So both of these are now supported::
|
||
|
||
@lru_cache
|
||
def f(x):
|
||
...
|
||
|
||
@lru_cache(maxsize=256)
|
||
def f(x):
|
||
...
|
||
|
||
(Contributed by Raymond Hettinger in :issue:`36772`.)
|
||
|
||
Added a new :func:`functools.cached_property` decorator, for computed properties
|
||
cached for the life of the instance. ::
|
||
|
||
import functools
|
||
import statistics
|
||
|
||
class Dataset:
|
||
def __init__(self, sequence_of_numbers):
|
||
self.data = sequence_of_numbers
|
||
|
||
@functools.cached_property
|
||
def variance(self):
|
||
return statistics.variance(self.data)
|
||
|
||
(Contributed by Carl Meyer in :issue:`21145`)
|
||
|
||
|
||
Added a new :func:`functools.singledispatchmethod` decorator that converts
|
||
methods into :term:`generic functions <generic function>` using
|
||
:term:`single dispatch`::
|
||
|
||
from functools import singledispatchmethod
|
||
from contextlib import suppress
|
||
|
||
class TaskManager:
|
||
|
||
def __init__(self, tasks):
|
||
self.tasks = list(tasks)
|
||
|
||
@singledispatchmethod
|
||
def discard(self, value):
|
||
with suppress(ValueError):
|
||
self.tasks.remove(value)
|
||
|
||
@discard.register(list)
|
||
def _(self, tasks):
|
||
targets = set(tasks)
|
||
self.tasks = [x for x in self.tasks if x not in targets]
|
||
|
||
(Contributed by Ethan Smith in :issue:`32380`)
|
||
|
||
gc
|
||
--
|
||
|
||
:func:`~gc.get_objects` can now receive an optional *generation* parameter
|
||
indicating a generation to get objects from.
|
||
(Contributed by Pablo Galindo in :issue:`36016`.)
|
||
|
||
|
||
gettext
|
||
-------
|
||
|
||
Added :func:`~gettext.pgettext` and its variants.
|
||
(Contributed by Franz Glasner, Éric Araujo, and Cheryl Sabella in :issue:`2504`.)
|
||
|
||
|
||
gzip
|
||
----
|
||
|
||
Added the *mtime* parameter to :func:`gzip.compress` for reproducible output.
|
||
(Contributed by Guo Ci Teo in :issue:`34898`.)
|
||
|
||
A :exc:`~gzip.BadGzipFile` exception is now raised instead of :exc:`OSError`
|
||
for certain types of invalid or corrupt gzip files.
|
||
(Contributed by Filip Gruszczyński, Michele Orrù, and Zackery Spytz in
|
||
:issue:`6584`.)
|
||
|
||
|
||
IDLE and idlelib
|
||
----------------
|
||
|
||
Output over N lines (50 by default) is squeezed down to a button.
|
||
N can be changed in the PyShell section of the General page of the
|
||
Settings dialog. Fewer, but possibly extra long, lines can be squeezed by
|
||
right clicking on the output. Squeezed output can be expanded in place
|
||
by double-clicking the button or into the clipboard or a separate window
|
||
by right-clicking the button. (Contributed by Tal Einat in :issue:`1529353`.)
|
||
|
||
Add "Run Customized" to the Run menu to run a module with customized
|
||
settings. Any command line arguments entered are added to sys.argv.
|
||
They also re-appear in the box for the next customized run. One can also
|
||
suppress the normal Shell main module restart. (Contributed by Cheryl
|
||
Sabella, Terry Jan Reedy, and others in :issue:`5680` and :issue:`37627`.)
|
||
|
||
Added optional line numbers for IDLE editor windows. Windows
|
||
open without line numbers unless set otherwise in the General
|
||
tab of the configuration dialog. Line numbers for an existing
|
||
window are shown and hidden in the Options menu.
|
||
(Contributed by Tal Einat and Saimadhav Heblikar in :issue:`17535`.)
|
||
|
||
OS native encoding is now used for converting between Python strings and Tcl
|
||
objects. This allows IDLE to work with emoji and other non-BMP characters.
|
||
These characters can be displayed or copied and pasted to or from the
|
||
clipboard. Converting strings from Tcl to Python and back now never fails.
|
||
(Many people worked on this for eight years but the problem was finally
|
||
solved by Serhiy Storchaka in :issue:`13153`.)
|
||
|
||
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`::
|
||
|
||
class AudioClip:
|
||
__slots__ = {'bit_rate': 'expressed in kilohertz to one decimal place',
|
||
'duration': 'in seconds, rounded up to an integer'}
|
||
def __init__(self, bit_rate, duration):
|
||
self.bit_rate = round(bit_rate / 1000.0, 1)
|
||
self.duration = ceil(duration)
|
||
|
||
(Contributed by Raymond Hettinger in :issue:`36326`.)
|
||
|
||
|
||
io
|
||
--
|
||
|
||
In development mode (:option:`-X` ``env``) and in debug build, the
|
||
:class:`io.IOBase` finalizer now logs the exception if the ``close()`` method
|
||
fails. The exception is ignored silently by default in release build.
|
||
(Contributed by Victor Stinner in :issue:`18748`.)
|
||
|
||
|
||
itertools
|
||
---------
|
||
|
||
The :func:`itertools.accumulate` function added an option *initial* keyword
|
||
argument to specify an initial value::
|
||
|
||
>>> from itertools import accumulate
|
||
>>> list(accumulate([10, 5, 30, 15], initial=1000))
|
||
[1000, 1010, 1015, 1045, 1060]
|
||
|
||
(Contributed by Lisa Roach in :issue:`34659`.)
|
||
|
||
|
||
json.tool
|
||
---------
|
||
|
||
Add option ``--json-lines`` to parse every input line as a separate JSON object.
|
||
(Contributed by Weipeng Hong in :issue:`31553`.)
|
||
|
||
|
||
logging
|
||
-------
|
||
|
||
Added a *force* keyword argument to :func:`logging.basicConfig()`
|
||
When set to true, any existing handlers attached
|
||
to the root logger are removed and closed before carrying out the
|
||
configuration specified by the other arguments.
|
||
|
||
This solves a long-standing problem. Once a logger or *basicConfig()* had
|
||
been called, subsequent calls to *basicConfig()* were silently ignored.
|
||
This made it difficult to update, experiment with, or teach the various
|
||
logging configuration options using the interactive prompt or a Jupyter
|
||
notebook.
|
||
|
||
(Suggested by Raymond Hettinger, implemented by Dong-hee Na, and
|
||
reviewed by Vinay Sajip in :issue:`33897`.)
|
||
|
||
|
||
math
|
||
----
|
||
|
||
Added new function :func:`math.dist` for computing Euclidean distance
|
||
between two points. (Contributed by Raymond Hettinger in :issue:`33089`.)
|
||
|
||
Expanded the :func:`math.hypot` function to handle multiple dimensions.
|
||
Formerly, it only supported the 2-D case.
|
||
(Contributed by Raymond Hettinger in :issue:`33089`.)
|
||
|
||
Added new function, :func:`math.prod`, as analogous function to :func:`sum`
|
||
that returns the product of a 'start' value (default: 1) times an iterable of
|
||
numbers::
|
||
|
||
>>> prior = 0.8
|
||
>>> likelihoods = [0.625, 0.84, 0.30]
|
||
>>> math.prod(likelihoods, start=prior)
|
||
0.126
|
||
|
||
(Contributed by Pablo Galindo in :issue:`35606`.)
|
||
|
||
Added two new combinatoric functions :func:`math.perm` and :func:`math.comb`::
|
||
|
||
>>> math.perm(10, 3) # Permutations of 10 things taken 3 at a time
|
||
720
|
||
>>> math.comb(10, 3) # Combinations of 10 things taken 3 at a time
|
||
120
|
||
|
||
(Contributed by Yash Aggarwal, Keller Fuchs, Serhiy Storchaka, and Raymond
|
||
Hettinger in :issue:`37128`, :issue:`37178`, and :issue:`35431`.)
|
||
|
||
Added a new function :func:`math.isqrt` for computing accurate integer square
|
||
roots without conversion to floating point. The new function supports
|
||
arbitrarily large integers. It is faster than ``floor(sqrt(n))`` but slower
|
||
than :func:`math.sqrt`::
|
||
|
||
>>> r = 650320427
|
||
>>> s = r ** 2
|
||
>>> isqrt(s - 1) # correct
|
||
650320426
|
||
>>> floor(sqrt(s - 1)) # incorrect
|
||
650320427
|
||
|
||
(Contributed by Mark Dickinson in :issue:`36887`.)
|
||
|
||
The function :func:`math.factorial` no longer accepts arguments that are not
|
||
int-like. (Contributed by Pablo Galindo in :issue:`33083`.)
|
||
|
||
|
||
mmap
|
||
----
|
||
|
||
The :class:`mmap.mmap` class now has an :meth:`~mmap.mmap.madvise` method to
|
||
access the ``madvise()`` system call.
|
||
(Contributed by Zackery Spytz in :issue:`32941`.)
|
||
|
||
|
||
multiprocessing
|
||
---------------
|
||
|
||
Added new :mod:`multiprocessing.shared_memory` module.
|
||
(Contributed by Davin Potts in :issue:`35813`.)
|
||
|
||
On macOS, the *spawn* start method is now used by default.
|
||
(Contributed by Victor Stinner in :issue:`33725`.)
|
||
|
||
|
||
os
|
||
--
|
||
|
||
Added new function :func:`~os.add_dll_directory` on Windows for providing
|
||
additional search paths for native dependencies when importing extension
|
||
modules or loading DLLs using :mod:`ctypes`.
|
||
(Contributed by Steve Dower in :issue:`36085`.)
|
||
|
||
A new :func:`os.memfd_create` function was added to wrap the
|
||
``memfd_create()`` syscall.
|
||
(Contributed by Zackery Spytz and Christian Heimes in :issue:`26836`.)
|
||
|
||
On Windows, much of the manual logic for handling reparse points (including
|
||
symlinks and directory junctions) has been delegated to the operating system.
|
||
Specifically, :func:`os.stat` will now traverse anything supported by the
|
||
operating system, while :func:`os.lstat` will only open reparse points that
|
||
identify as "name surrogates" while others are opened as for :func:`os.stat`.
|
||
In all cases, :attr:`stat_result.st_mode` will only have ``S_IFLNK`` set for
|
||
symbolic links and not other kinds of reparse points. To identify other kinds
|
||
of reparse point, check the new :attr:`stat_result.st_reparse_tag` attribute.
|
||
|
||
On Windows, :func:`os.readlink` is now able to read directory junctions. Note
|
||
that :func:`~os.path.islink` will return ``False`` for directory junctions,
|
||
and so code that checks ``islink`` first will continue to treat junctions as
|
||
directories, while code that handles errors from :func:`os.readlink` may now
|
||
treat junctions as links.
|
||
|
||
(Contributed by Steve Dower in :issue:`37834`.)
|
||
|
||
|
||
os.path
|
||
-------
|
||
|
||
:mod:`os.path` functions that return a boolean result like
|
||
:func:`~os.path.exists`, :func:`~os.path.lexists`, :func:`~os.path.isdir`,
|
||
:func:`~os.path.isfile`, :func:`~os.path.islink`, and :func:`~os.path.ismount`
|
||
now return ``False`` instead of raising :exc:`ValueError` or its subclasses
|
||
:exc:`UnicodeEncodeError` and :exc:`UnicodeDecodeError` for paths that contain
|
||
characters or bytes unrepresentable at the OS level.
|
||
(Contributed by Serhiy Storchaka in :issue:`33721`.)
|
||
|
||
:func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE`
|
||
environment variable and does not use :envvar:`HOME`, which is not normally set
|
||
for regular user accounts.
|
||
(Contributed by Anthony Sottile in :issue:`36264`.)
|
||
|
||
:func:`~os.path.isdir` on Windows no longer returns ``True`` for a link to a
|
||
non-existent directory.
|
||
|
||
:func:`~os.path.realpath` on Windows now resolves reparse points, including
|
||
symlinks and directory junctions.
|
||
|
||
(Contributed by Steve Dower in :issue:`37834`.)
|
||
|
||
|
||
pathlib
|
||
-------
|
||
|
||
:mod:`pathlib.Path` methods that return a boolean result like
|
||
:meth:`~pathlib.Path.exists()`, :meth:`~pathlib.Path.is_dir()`,
|
||
:meth:`~pathlib.Path.is_file()`, :meth:`~pathlib.Path.is_mount()`,
|
||
:meth:`~pathlib.Path.is_symlink()`, :meth:`~pathlib.Path.is_block_device()`,
|
||
:meth:`~pathlib.Path.is_char_device()`, :meth:`~pathlib.Path.is_fifo()`,
|
||
:meth:`~pathlib.Path.is_socket()` now return ``False`` instead of raising
|
||
:exc:`ValueError` or its subclass :exc:`UnicodeEncodeError` for paths that
|
||
contain characters unrepresentable at the OS level.
|
||
(Contributed by Serhiy Storchaka in :issue:`33721`.)
|
||
|
||
Added :meth:`pathlib.Path.link_to()` which creates a hard link pointing
|
||
to a path.
|
||
(Contributed by Joannah Nanjekye in :issue:`26978`)
|
||
|
||
|
||
pickle
|
||
------
|
||
|
||
:mod:`pickle` extensions subclassing the C-optimized :class:`~pickle.Pickler`
|
||
can now override the pickling logic of functions and classes by defining the
|
||
special :meth:`~pickle.Pickler.reducer_override` method.
|
||
(Contributed by Pierre Glaser and Olivier Grisel in :issue:`35900`.)
|
||
|
||
|
||
plistlib
|
||
--------
|
||
|
||
Added new :class:`plistlib.UID` and enabled support for reading and writing
|
||
NSKeyedArchiver-encoded binary plists.
|
||
(Contributed by Jon Janzen in :issue:`26707`.)
|
||
|
||
|
||
pprint
|
||
------
|
||
|
||
The :mod:`pprint` module added a *sort_dicts* parameter to several functions.
|
||
By default, those functions continue to sort dictionaries before rendering or
|
||
printing. However, if *sort_dicts* is set to false, the dictionaries retain
|
||
the order that keys were inserted. This can be useful for comparison to JSON
|
||
inputs during debugging.
|
||
|
||
In addition, there is a convenience new function, :func:`pprint.pp` that is
|
||
like :func:`pprint.pprint` but with *sort_dicts* defaulting to ``False``::
|
||
|
||
>>> from pprint import pprint, pp
|
||
>>> d = dict(source='input.txt', operation='filter', destination='output.txt')
|
||
>>> pp(d, width=40) # Original order
|
||
{'source': 'input.txt',
|
||
'operation': 'filter',
|
||
'destination': 'output.txt'}
|
||
>>> pprint(d, width=40) # Keys sorted alphabetically
|
||
{'destination': 'output.txt',
|
||
'operation': 'filter',
|
||
'source': 'input.txt'}
|
||
|
||
(Contributed by Rémi Lapeyre in :issue:`30670`.)
|
||
|
||
|
||
py_compile
|
||
----------
|
||
|
||
:func:`py_compile.compile` now supports silent mode.
|
||
(Contributed by Joannah Nanjekye in :issue:`22640`.)
|
||
|
||
|
||
shlex
|
||
-----
|
||
|
||
The new :func:`shlex.join` function acts as the inverse of :func:`shlex.split`.
|
||
(Contributed by Bo Bayles in :issue:`32102`.)
|
||
|
||
|
||
shutil
|
||
------
|
||
|
||
:func:`shutil.copytree` now accepts a new ``dirs_exist_ok`` keyword argument.
|
||
(Contributed by Josh Bronson in :issue:`20849`.)
|
||
|
||
:func:`shutil.make_archive` now defaults to the modern pax (POSIX.1-2001)
|
||
format for new archives to improve portability and standards conformance,
|
||
inherited from the corresponding change to the :mod:`tarfile` module.
|
||
(Contributed by C.A.M. Gerlach in :issue:`30661`.)
|
||
|
||
:func:`shutil.rmtree` on Windows now removes directory junctions without
|
||
recursively removing their contents first.
|
||
(Contributed by Steve Dower in :issue:`37834`.)
|
||
|
||
|
||
socket
|
||
------
|
||
|
||
Added :meth:`~socket.create_server()` and :meth:`~socket.has_dualstack_ipv6()`
|
||
convenience functions to automate the necessary tasks usually involved when
|
||
creating a server socket, including accepting both IPv4 and IPv6 connections
|
||
on the same socket. (Contributed by Giampaolo Rodolà in :issue:`17561`.)
|
||
|
||
The :func:`socket.if_nameindex()`, :func:`socket.if_nametoindex()`, and
|
||
:func:`socket.if_indextoname()` functions have been implemented on Windows.
|
||
(Contributed by Zackery Spytz in :issue:`37007`.)
|
||
|
||
|
||
ssl
|
||
---
|
||
|
||
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`.)
|
||
|
||
|
||
statistics
|
||
----------
|
||
|
||
Added :func:`statistics.fmean` as a faster, floating point variant of
|
||
:func:`statistics.mean()`. (Contributed by Raymond Hettinger and
|
||
Steven D'Aprano in :issue:`35904`.)
|
||
|
||
Added :func:`statistics.geometric_mean()`
|
||
(Contributed by Raymond Hettinger in :issue:`27181`.)
|
||
|
||
Added :func:`statistics.multimode` that returns a list of the most
|
||
common values. (Contributed by Raymond Hettinger in :issue:`35892`.)
|
||
|
||
Added :func:`statistics.quantiles` that divides data or a distribution
|
||
in to equiprobable intervals (e.g. quartiles, deciles, or percentiles).
|
||
(Contributed by Raymond Hettinger in :issue:`36546`.)
|
||
|
||
Added :class:`statistics.NormalDist`, a tool for creating
|
||
and manipulating normal distributions of a random variable.
|
||
(Contributed by Raymond Hettinger in :issue:`36018`.)
|
||
|
||
::
|
||
|
||
>>> temperature_feb = NormalDist.from_samples([4, 12, -3, 2, 7, 14])
|
||
>>> temperature_feb.mean
|
||
6.0
|
||
>>> temperature_feb.stdev
|
||
6.356099432828281
|
||
|
||
>>> temperature_feb.cdf(3) # Chance of being under 3 degrees
|
||
0.3184678262814532
|
||
>>> # Relative chance of being 7 degrees versus 10 degrees
|
||
>>> temperature_feb.pdf(7) / temperature_feb.pdf(10)
|
||
1.2039930378537762
|
||
|
||
>>> el_niño = NormalDist(4, 2.5)
|
||
>>> temperature_feb += el_niño # Add in a climate effect
|
||
>>> temperature_feb
|
||
NormalDist(mu=10.0, sigma=6.830080526611674)
|
||
|
||
>>> temperature_feb * (9/5) + 32 # Convert to Fahrenheit
|
||
NormalDist(mu=50.0, sigma=12.294144947901014)
|
||
>>> temperature_feb.samples(3) # Generate random samples
|
||
[7.672102882379219, 12.000027119750287, 4.647488369766392]
|
||
|
||
|
||
sys
|
||
---
|
||
|
||
Add new :func:`sys.unraisablehook` function which can be overridden to control
|
||
how "unraisable exceptions" are handled. It is called when an exception has
|
||
occurred but there is no way for Python to handle it. For example, when a
|
||
destructor raises an exception or during garbage collection
|
||
(:func:`gc.collect`).
|
||
(Contributed by Victor Stinner in :issue:`36829`.)
|
||
|
||
|
||
tarfile
|
||
-------
|
||
|
||
The :mod:`tarfile` module now defaults to the modern pax (POSIX.1-2001)
|
||
format for new archives, instead of the previous GNU-specific one.
|
||
This improves cross-platform portability with a consistent encoding (UTF-8)
|
||
in a standardized and extensible format, and offers several other benefits.
|
||
(Contributed by C.A.M. Gerlach in :issue:`36268`.)
|
||
|
||
|
||
threading
|
||
---------
|
||
|
||
Add a new :func:`threading.excepthook` function which handles uncaught
|
||
:meth:`threading.Thread.run` exception. It can be overridden to control how
|
||
uncaught :meth:`threading.Thread.run` exceptions are handled.
|
||
(Contributed by Victor Stinner in :issue:`1230540`.)
|
||
|
||
Add a new :func:`threading.get_native_id` function and
|
||
a :data:`~threading.Thread.native_id`
|
||
attribute to the :class:`threading.Thread` class. These return the native
|
||
integral Thread ID of the current thread assigned by the kernel.
|
||
This feature is only available on certain platforms, see
|
||
:func:`get_native_id <threading.get_native_id>` for more information.
|
||
(Contributed by Jake Tesler in :issue:`36084`.)
|
||
|
||
|
||
tokenize
|
||
--------
|
||
|
||
The :mod:`tokenize` module now implicitly emits a ``NEWLINE`` token when
|
||
provided with input that does not have a trailing new line. This behavior
|
||
now matches what the C tokenizer does internally.
|
||
(Contributed by Ammar Askar in :issue:`33899`.)
|
||
|
||
|
||
tkinter
|
||
-------
|
||
|
||
Added methods :meth:`~tkinter.Spinbox.selection_from`,
|
||
:meth:`~tkinter.Spinbox.selection_present`,
|
||
:meth:`~tkinter.Spinbox.selection_range` and
|
||
:meth:`~tkinter.Spinbox.selection_to`
|
||
in the :class:`tkinter.Spinbox` class.
|
||
(Contributed by Juliette Monsel in :issue:`34829`.)
|
||
|
||
Added method :meth:`~tkinter.Canvas.moveto`
|
||
in the :class:`tkinter.Canvas` class.
|
||
(Contributed by Juliette Monsel in :issue:`23831`.)
|
||
|
||
The :class:`tkinter.PhotoImage` class now has
|
||
:meth:`~tkinter.PhotoImage.transparency_get` and
|
||
:meth:`~tkinter.PhotoImage.transparency_set` methods. (Contributed by
|
||
Zackery Spytz in :issue:`25451`.)
|
||
|
||
|
||
time
|
||
----
|
||
|
||
Added new clock :data:`~time.CLOCK_UPTIME_RAW` for macOS 10.12.
|
||
(Contributed by Joannah Nanjekye in :issue:`35702`.)
|
||
|
||
|
||
typing
|
||
------
|
||
|
||
The :mod:`typing` module incorporates several new features:
|
||
|
||
* A dictionary type with per-key types. See :pep:`589` and
|
||
:class:`typing.TypedDict`.
|
||
TypedDict uses only string keys. By default, every key is required
|
||
to be present. Specify "total=False" to allow keys to be optional::
|
||
|
||
class Location(TypedDict, total=False):
|
||
lat_long: tuple
|
||
grid_square: str
|
||
xy_coordinate: tuple
|
||
|
||
* Literal types. See :pep:`586` and :class:`typing.Literal`.
|
||
Literal types indicate that a parameter or return value
|
||
is constrained to one or more specific literal values::
|
||
|
||
def get_status(port: int) -> Literal['connected', 'disconnected']:
|
||
...
|
||
|
||
* "Final" variables, functions, methods and classes. See :pep:`591`,
|
||
:class:`typing.Final` and :func:`typing.final`.
|
||
The final qualifier instructs a static type checker to restrict
|
||
subclassing, overriding, or reassignment::
|
||
|
||
pi: Final[float] = 3.1415926536
|
||
|
||
* Protocol definitions. See :pep:`544`, :class:`typing.Protocol` and
|
||
:func:`typing.runtime_checkable`. Simple ABCs like
|
||
:class:`typing.SupportsInt` are now ``Protocol`` subclasses.
|
||
|
||
* New protocol class :class:`typing.SupportsIndex`.
|
||
|
||
* New functions :func:`typing.get_origin` and :func:`typing.get_args`.
|
||
|
||
|
||
unicodedata
|
||
-----------
|
||
|
||
The :mod:`unicodedata` module has been upgraded to use the `Unicode 12.1.0
|
||
<http://blog.unicode.org/2019/05/unicode-12-1-en.html>`_ release.
|
||
|
||
New function :func:`~unicodedata.is_normalized` can be used to verify a string
|
||
is in a specific normal form, often much faster than by actually normalizing
|
||
the string. (Contributed by Max Belanger, David Euresti, and Greg Price in
|
||
:issue:`32285` and :issue:`37966`).
|
||
|
||
|
||
unittest
|
||
--------
|
||
|
||
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
|
||
:meth:`~unittest.TestCase.addClassCleanup()` to unittest to support
|
||
cleanups for :func:`~unittest.setUpModule()` and
|
||
:meth:`~unittest.TestCase.setUpClass()`.
|
||
(Contributed by Lisa Roach in :issue:`24412`.)
|
||
|
||
Several mock assert functions now also print a list of actual calls upon
|
||
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`.
|
||
(Contributed by Andrew Svetlov in :issue:`32972`.)
|
||
|
||
Example::
|
||
|
||
import unittest
|
||
|
||
|
||
class TestRequest(unittest.IsolatedAsyncioTestCase):
|
||
|
||
async def asyncSetUp(self):
|
||
self.connection = await AsyncConnection()
|
||
|
||
async def test_get(self):
|
||
response = await self.connection.get("https://example.com")
|
||
self.assertEqual(response.status_code, 200)
|
||
|
||
async def asyncTearDown(self):
|
||
await self.connection.close()
|
||
|
||
|
||
if __name__ == "__main__":
|
||
unittest.main()
|
||
|
||
|
||
venv
|
||
----
|
||
|
||
:mod:`venv` now includes an ``Activate.ps1`` script on all platforms for
|
||
activating virtual environments under PowerShell Core 6.1.
|
||
(Contributed by Brett Cannon in :issue:`32718`.)
|
||
|
||
|
||
weakref
|
||
-------
|
||
|
||
The proxy objects returned by :func:`weakref.proxy` now support the matrix
|
||
multiplication operators ``@`` and ``@=`` in addition to the other
|
||
numeric operators. (Contributed by Mark Dickinson in :issue:`36669`.)
|
||
|
||
|
||
xml
|
||
---
|
||
|
||
As mitigation against DTD and external entity retrieval, the
|
||
:mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process
|
||
external entities by default.
|
||
(Contributed by Christian Heimes in :issue:`17239`.)
|
||
|
||
The ``.find*()`` methods in the :mod:`xml.etree.ElementTree` module
|
||
support wildcard searches like ``{*}tag`` which ignores the namespace
|
||
and ``{namespace}*`` which returns all tags in the given namespace.
|
||
(Contributed by Stefan Behnel in :issue:`28238`.)
|
||
|
||
The :mod:`xml.etree.ElementTree` module provides a new function
|
||
:func:`–xml.etree.ElementTree.canonicalize()` that implements C14N 2.0.
|
||
(Contributed by Stefan Behnel in :issue:`13611`.)
|
||
|
||
The target object of :class:`xml.etree.ElementTree.XMLParser` can
|
||
receive namespace declaration events through the new callback methods
|
||
``start_ns()`` and ``end_ns()``. Additionally, the
|
||
:class:`xml.etree.ElementTree.TreeBuilder` target can be configured
|
||
to process events about comments and processing instructions to include
|
||
them in the generated tree.
|
||
(Contributed by Stefan Behnel in :issue:`36676` and :issue:`36673`.)
|
||
|
||
|
||
xmlrpc
|
||
------
|
||
|
||
:class:`xmlrpc.client.ServerProxy` now supports an optional *headers* keyword
|
||
argument for a sequence of HTTP headers to be sent with each request. Among
|
||
other things, this makes it possible to upgrade from default basic
|
||
authentication to faster session authentication.
|
||
(Contributed by Cédric Krier in :issue:`35153`.)
|
||
|
||
|
||
Optimizations
|
||
=============
|
||
|
||
* The :mod:`subprocess` module can now use the :func:`os.posix_spawn` function
|
||
in some cases for better performance. Currently, it is only used on macOS
|
||
and Linux (using glibc 2.24 or newer) if all these conditions are met:
|
||
|
||
* *close_fds* is false;
|
||
* *preexec_fn*, *pass_fds*, *cwd* and *start_new_session* parameters
|
||
are not set;
|
||
* the *executable* path contains a directory.
|
||
|
||
(Contributed by Joannah Nanjekye and Victor Stinner in :issue:`35537`.)
|
||
|
||
* :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`,
|
||
:func:`shutil.copytree` and :func:`shutil.move` use platform-specific
|
||
"fast-copy" syscalls on Linux and macOS in order to copy the file
|
||
more efficiently.
|
||
"fast-copy" means that the copying operation occurs within the kernel,
|
||
avoiding the use of userspace buffers in Python as in
|
||
"``outfd.write(infd.read())``".
|
||
On Windows :func:`shutil.copyfile` uses a bigger default buffer size (1 MiB
|
||
instead of 16 KiB) and a :func:`memoryview`-based variant of
|
||
:func:`shutil.copyfileobj` is used.
|
||
The speedup for copying a 512 MiB file within the same partition is about
|
||
+26% on Linux, +50% on macOS and +40% on Windows. Also, much less CPU cycles
|
||
are consumed.
|
||
See :ref:`shutil-platform-dependent-efficient-copy-operations` section.
|
||
(Contributed by Giampaolo Rodolà in :issue:`33671`.)
|
||
|
||
* :func:`shutil.copytree` uses :func:`os.scandir` function and all copy
|
||
functions depending from it use cached :func:`os.stat` values. The speedup
|
||
for copying a directory with 8000 files is around +9% on Linux, +20% on
|
||
Windows and +30% on a Windows SMB share. Also the number of :func:`os.stat`
|
||
syscalls is reduced by 38% making :func:`shutil.copytree` especially faster
|
||
on network filesystems. (Contributed by Giampaolo Rodolà in :issue:`33695`.)
|
||
|
||
* The default protocol in the :mod:`pickle` module is now Protocol 4,
|
||
first introduced in Python 3.4. It offers better performance and smaller
|
||
size compared to Protocol 3 available since Python 3.0.
|
||
|
||
* Removed one ``Py_ssize_t`` member from ``PyGC_Head``. All GC tracked
|
||
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.
|
||
(Contributed by Wouter Bolsterlee and Tal Einat in :issue:`30977`)
|
||
|
||
* Improved performance of :func:`operator.itemgetter` by 33%. Optimized
|
||
argument handling and added a fast path for the common case of a single
|
||
non-negative integer index into a tuple (which is the typical use case in
|
||
the standard library). (Contributed by Raymond Hettinger in
|
||
:issue:`35664`.)
|
||
|
||
* Sped-up field lookups in :func:`collections.namedtuple`. They are now more
|
||
than two times faster, making them the fastest form of instance variable
|
||
lookup in Python. (Contributed by Raymond Hettinger, Pablo Galindo, and
|
||
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`.)
|
||
|
||
* Doubled the speed of class variable writes. When a non-dunder attribute
|
||
was updated, there was an unnecessary call to update slots.
|
||
(Contributed by Stefan Behnel, Pablo Galindo Salgado, Raymond Hettinger,
|
||
Neil Schemenauer, and Serhiy Storchaka in :issue:`36012`.)
|
||
|
||
* Reduced an overhead of converting arguments passed to many builtin functions
|
||
and methods. This sped up calling some simple builtin functions and
|
||
methods up to 20--50%. (Contributed by Serhiy Storchaka in :issue:`23867`,
|
||
:issue:`35582` and :issue:`36127`.)
|
||
|
||
* ``LOAD_GLOBAL`` instruction now uses new "per opcode cache" mechanism.
|
||
It is about 40% faster now. (Contributed by Yury Selivanov and Inada Naoki in
|
||
:issue:`26219`.)
|
||
|
||
|
||
Build and C API Changes
|
||
=======================
|
||
|
||
* Default :data:`sys.abiflags` became an empty string: the ``m`` flag for
|
||
pymalloc became useless (builds with and without pymalloc are ABI compatible)
|
||
and so has been removed. (Contributed by Victor Stinner in :issue:`36707`.)
|
||
|
||
Example of changes:
|
||
|
||
* Only ``python3.8`` program is installed, ``python3.8m`` program is gone.
|
||
* Only ``python3.8-config`` script is installed, ``python3.8m-config`` script
|
||
is gone.
|
||
* The ``m`` flag has been removed from the suffix of dynamic library
|
||
filenames: extension modules in the standard library as well as those
|
||
produced and installed by third-party packages, like those downloaded from
|
||
PyPI. On Linux, for example, the Python 3.7 suffix
|
||
``.cpython-37m-x86_64-linux-gnu.so`` became
|
||
``.cpython-38-x86_64-linux-gnu.so`` in Python 3.8.
|
||
|
||
* The header files have been reorganized to better separate the different kinds
|
||
of APIs:
|
||
|
||
* ``Include/*.h`` should be the portable public stable C API.
|
||
* ``Include/cpython/*.h`` should be the unstable C API specific to CPython;
|
||
public API, with some private API prefixed by ``_Py`` or ``_PY``.
|
||
* ``Include/internal/*.h`` is the private internal C API very specific to
|
||
CPython. This API comes with no backward compatibility warranty and should
|
||
not be used outside CPython. It is only exposed for very specific needs
|
||
like debuggers and profiles which has to access to CPython internals
|
||
without calling functions. This API is now installed by ``make install``.
|
||
|
||
(Contributed by Victor Stinner in :issue:`35134` and :issue:`35081`,
|
||
work initiated by Eric Snow in Python 3.7.)
|
||
|
||
* Some macros have been converted to static inline functions: parameter types
|
||
and return type are well defined, they don't have issues specific to macros,
|
||
variables have a local scopes. Examples:
|
||
|
||
* :c:func:`Py_INCREF`, :c:func:`Py_DECREF`
|
||
* :c:func:`Py_XINCREF`, :c:func:`Py_XDECREF`
|
||
* :c:func:`PyObject_INIT`, :c:func:`PyObject_INIT_VAR`
|
||
* Private functions: :c:func:`_PyObject_GC_TRACK`,
|
||
:c:func:`_PyObject_GC_UNTRACK`, :c:func:`_Py_Dealloc`
|
||
|
||
(Contributed by Victor Stinner in :issue:`35059`.)
|
||
|
||
* The :c:func:`PyByteArray_Init` and :c:func:`PyByteArray_Fini` functions have
|
||
been removed. They did nothing since Python 2.7.4 and Python 3.2.0, were
|
||
excluded from the limited API (stable ABI), and were not documented.
|
||
(Contributed by Victor Stinner in :issue:`35713`.)
|
||
|
||
* The result of :c:func:`PyExceptionClass_Name` is now of type
|
||
``const char *`` rather of ``char *``.
|
||
(Contributed by Serhiy Storchaka in :issue:`33818`.)
|
||
|
||
* The duality of ``Modules/Setup.dist`` and ``Modules/Setup`` has been
|
||
removed. Previously, when updating the CPython source tree, one had
|
||
to manually copy ``Modules/Setup.dist`` (inside the source tree) to
|
||
``Modules/Setup`` (inside the build tree) in order to reflect any changes
|
||
upstream. This was of a small benefit to packagers at the expense of
|
||
a frequent annoyance to developers following CPython development, as
|
||
forgetting to copy the file could produce build failures.
|
||
|
||
Now the build system always reads from ``Modules/Setup`` inside the source
|
||
tree. People who want to customize that file are encouraged to maintain
|
||
their changes in a git fork of CPython or as patch files, as they would do
|
||
for any other change to the source tree.
|
||
|
||
(Contributed by Antoine Pitrou in :issue:`32430`.)
|
||
|
||
* Functions that convert Python number to C integer like
|
||
:c:func:`PyLong_AsLong` and argument parsing functions like
|
||
: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
|
||
:class:`~fractions.Fraction`). :c:func:`PyNumber_Check` will now return
|
||
``1`` for objects implementing ``__index__()``.
|
||
:c:func:`PyNumber_Long`, :c:func:`PyNumber_Float` and
|
||
:c:func:`PyFloat_AsDouble` also now use the ``__index__()`` method if
|
||
available.
|
||
(Contributed by Serhiy Storchaka in :issue:`36048` and :issue:`20092`.)
|
||
|
||
* Heap-allocated type objects will now increase their reference count
|
||
in :c:func:`PyObject_Init` (and its parallel macro ``PyObject_INIT``)
|
||
instead of in :c:func:`PyType_GenericAlloc`. Types that modify instance
|
||
allocation or deallocation may need to be adjusted.
|
||
(Contributed by Eddie Elizondo in :issue:`35810`.)
|
||
|
||
* The new function :c:func:`PyCode_NewWithPosOnlyArgs` allows to create
|
||
code objects like :c:func:`PyCode_New`, but with an extra *posonlyargcount*
|
||
parameter for indicating the number of positional-only arguments.
|
||
(Contributed by Pablo Galindo in :issue:`37221`.)
|
||
|
||
* :c:func:`Py_SetPath` now sets :data:`sys.executable` to the program full
|
||
path (:c:func:`Py_GetProgramFullPath`) rather than to the program name
|
||
(:c:func:`Py_GetProgramName`).
|
||
(Contributed by Victor Stinner in :issue:`38234`.)
|
||
|
||
|
||
Deprecated
|
||
==========
|
||
|
||
* The distutils ``bdist_wininst`` command is now deprecated, use
|
||
``bdist_wheel`` (wheel packages) instead.
|
||
(Contributed by Victor Stinner in :issue:`37481`.)
|
||
|
||
* Deprecated methods ``getchildren()`` and ``getiterator()`` in
|
||
the :mod:`~xml.etree.ElementTree` module now emit a
|
||
:exc:`DeprecationWarning` instead of :exc:`PendingDeprecationWarning`.
|
||
They will be removed in Python 3.9.
|
||
(Contributed by Serhiy Storchaka in :issue:`29209`.)
|
||
|
||
* Passing an object that is not an instance of
|
||
:class:`concurrent.futures.ThreadPoolExecutor` to
|
||
:meth:`loop.set_default_executor() <asyncio.loop.set_default_executor>` is
|
||
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.
|
||
|
||
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`.)
|
||
|
||
* :mod:`ast` classes ``Num``, ``Str``, ``Bytes``, ``NameConstant`` and
|
||
``Ellipsis`` are considered deprecated and will be removed in future Python
|
||
versions. :class:`~ast.Constant` should be used instead.
|
||
(Contributed by Serhiy Storchaka in :issue:`32892`.)
|
||
|
||
* :class:`ast.NodeVisitor` methods ``visit_Num()``, ``visit_Str()``,
|
||
``visit_Bytes()``, ``visit_NameConstant()`` and ``visit_Ellipsis()`` are
|
||
deprecated now and will not be called in future Python versions.
|
||
Add the :meth:`~ast.NodeVisitor.visit_Constant` method to handle all
|
||
constant nodes.
|
||
(Contributed by Serhiy Storchaka in :issue:`36917`.)
|
||
|
||
* The :func:`asyncio.coroutine` :term:`decorator` is deprecated and will be
|
||
removed in version 3.10. Instead of ``@asyncio.coroutine``, use
|
||
:keyword:`async def` instead.
|
||
(Contributed by Andrew Svetlov in :issue:`36921`.)
|
||
|
||
* In :mod:`asyncio`, the explicit passing of a *loop* argument has been
|
||
deprecated and will be removed in version 3.10 for the following:
|
||
:func:`asyncio.sleep`, :func:`asyncio.gather`, :func:`asyncio.shield`,
|
||
:func:`asyncio.wait_for`, :func:`asyncio.wait`, :func:`asyncio.as_completed`,
|
||
:class:`asyncio.Task`, :class:`asyncio.Lock`, :class:`asyncio.Event`,
|
||
:class:`asyncio.Condition`, :class:`asyncio.Semaphore`,
|
||
:class:`asyncio.BoundedSemaphore`, :class:`asyncio.Queue`,
|
||
:func:`asyncio.create_subprocess_exec`, and
|
||
:func:`asyncio.create_subprocess_shell`.
|
||
|
||
* The explicit passing of coroutine objects to :func:`asyncio.wait` has been
|
||
deprecated and will be removed in version 3.11.
|
||
(Contributed by Yury Selivanov in :issue:`34790`.)
|
||
|
||
* The following functions and methods are deprecated in the :mod:`gettext`
|
||
module: :func:`~gettext.lgettext`, :func:`~gettext.ldgettext`,
|
||
:func:`~gettext.lngettext` and :func:`~gettext.ldngettext`.
|
||
They return encoded bytes, and it's possible that you will get unexpected
|
||
Unicode-related exceptions if there are encoding problems with the
|
||
translated strings. It's much better to use alternatives which return
|
||
Unicode strings in Python 3. These functions have been broken for a long time.
|
||
|
||
Function :func:`~gettext.bind_textdomain_codeset`, methods
|
||
:meth:`~gettext.NullTranslations.output_charset` and
|
||
:meth:`~gettext.NullTranslations.set_output_charset`, and the *codeset*
|
||
parameter of functions :func:`~gettext.translation` and
|
||
:func:`~gettext.install` are also deprecated, since they are only used for
|
||
for the ``l*gettext()`` functions.
|
||
(Contributed by Serhiy Storchaka in :issue:`33710`.)
|
||
|
||
* The :meth:`~threading.Thread.isAlive()` method of :class:`threading.Thread`
|
||
has been deprecated.
|
||
(Contributed by Dong-hee Na in :issue:`35283`.)
|
||
|
||
* Many builtin and extension functions that take integer arguments will
|
||
now emit a deprecation warning for :class:`~decimal.Decimal`\ s,
|
||
:class:`~fractions.Fraction`\ s and any other objects that can be converted
|
||
to integers only with a loss (e.g. that have the :meth:`~object.__int__`
|
||
method but do not have the :meth:`~object.__index__` method). In future
|
||
version they will be errors.
|
||
(Contributed by Serhiy Storchaka in :issue:`36048`.)
|
||
|
||
* Deprecated passing the following arguments as keyword arguments:
|
||
|
||
- *func* in :func:`functools.partialmethod`, :func:`weakref.finalize`,
|
||
:meth:`profile.Profile.runcall`, :meth:`cProfile.Profile.runcall`,
|
||
:meth:`bdb.Bdb.runcall`, :meth:`trace.Trace.runfunc` and
|
||
:func:`curses.wrapper`.
|
||
- *function* in :meth:`unittest.TestCase.addCleanup`.
|
||
- *fn* in the :meth:`~concurrent.futures.Executor.submit` method of
|
||
:class:`concurrent.futures.ThreadPoolExecutor` and
|
||
:class:`concurrent.futures.ProcessPoolExecutor`.
|
||
- *callback* in :meth:`contextlib.ExitStack.callback`,
|
||
:meth:`contextlib.AsyncExitStack.callback` and
|
||
:meth:`contextlib.AsyncExitStack.push_async_callback`.
|
||
- *c* and *typeid* in the :meth:`~multiprocessing.managers.Server.create`
|
||
method of :class:`multiprocessing.managers.Server` and
|
||
:class:`multiprocessing.managers.SharedMemoryServer`.
|
||
- *obj* in :func:`weakref.finalize`.
|
||
|
||
In future releases of Python, they will be :ref:`positional-only
|
||
<positional-only_parameter>`.
|
||
(Contributed by Serhiy Storchaka in :issue:`36492`.)
|
||
|
||
|
||
API and Feature Removals
|
||
========================
|
||
|
||
The following features and APIs have been removed from Python 3.8:
|
||
|
||
* Starting with Python 3.3, importing ABCs from :mod:`collections` was
|
||
deprecated, and importing should be done from :mod:`collections.abc`. Being
|
||
able to import from collections was marked for removal in 3.8, but has been
|
||
delayed to 3.9. (See :issue:`36952`.)
|
||
|
||
* The :mod:`macpath` module, deprecated in Python 3.7, has been removed.
|
||
(Contributed by Victor Stinner in :issue:`35471`.)
|
||
|
||
* The function :func:`platform.popen` has been removed, after having been
|
||
deprecated since Python 3.3: use :func:`os.popen` instead.
|
||
(Contributed by Victor Stinner in :issue:`35345`.)
|
||
|
||
* The function :func:`time.clock` has been removed, after having been
|
||
deprecated since Python 3.3: use :func:`time.perf_counter` or
|
||
:func:`time.process_time` instead, depending
|
||
on your requirements, to have well-defined behavior.
|
||
(Contributed by Matthias Bussonnier in :issue:`36895`.)
|
||
|
||
* The ``pyvenv`` script has been removed in favor of ``python3.8 -m venv``
|
||
to help eliminate confusion as to what Python interpreter the ``pyvenv``
|
||
script is tied to. (Contributed by Brett Cannon in :issue:`25427`.)
|
||
|
||
* ``parse_qs``, ``parse_qsl``, and ``escape`` are removed from the :mod:`cgi`
|
||
module. They are deprecated in Python 3.2 or older. They should be imported
|
||
from the ``urllib.parse`` and ``html`` modules instead.
|
||
|
||
* ``filemode`` function is removed from the :mod:`tarfile` module.
|
||
It is not documented and deprecated since Python 3.3.
|
||
|
||
* The :class:`~xml.etree.ElementTree.XMLParser` constructor no longer accepts
|
||
the *html* argument. It never had an effect and was deprecated in Python 3.4.
|
||
All other parameters are now :ref:`keyword-only <keyword-only_parameter>`.
|
||
(Contributed by Serhiy Storchaka in :issue:`29209`.)
|
||
|
||
* Removed the ``doctype()`` method of :class:`~xml.etree.ElementTree.XMLParser`.
|
||
(Contributed by Serhiy Storchaka in :issue:`29209`.)
|
||
|
||
* "unicode_internal" codec is removed.
|
||
(Contributed by Inada Naoki in :issue:`36297`.)
|
||
|
||
* The ``Cache`` and ``Statement`` objects of the :mod:`sqlite3` module are not
|
||
exposed to the user.
|
||
(Contributed by Aviv Palivoda in :issue:`30262`.)
|
||
|
||
* The ``bufsize`` keyword argument of :func:`fileinput.input` and
|
||
:func:`fileinput.FileInput` which was ignored and deprecated since Python 3.6
|
||
has been removed. :issue:`36952` (Contributed by Matthias Bussonnier.)
|
||
|
||
* The functions :func:`sys.set_coroutine_wrapper` and
|
||
:func:`sys.get_coroutine_wrapper` deprecated in Python 3.7 have been removed;
|
||
:issue:`36933` (Contributed by Matthias Bussonnier.)
|
||
|
||
|
||
Porting to Python 3.8
|
||
=====================
|
||
|
||
This section lists previously described changes and other bugfixes
|
||
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).
|
||
(Contributed by Serhiy Storchaka in :issue:`10544`.)
|
||
|
||
* The compiler now produces a :exc:`SyntaxWarning` when identity checks
|
||
(``is`` and ``is not``) are used with certain types of literals
|
||
(e.g. strings, numbers). These can often work by accident in CPython,
|
||
but are not guaranteed by the language spec. The warning advises users
|
||
to use equality tests (``==`` and ``!=``) instead.
|
||
(Contributed by Serhiy Storchaka in :issue:`34850`.)
|
||
|
||
* The CPython interpreter can swallow exceptions in some circumstances.
|
||
In Python 3.8 this happens in fewer cases. In particular, exceptions
|
||
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.
|
||
(Contributed by Serhiy Storchaka in :issue:`36793`.)
|
||
|
||
* On AIX, :attr:`sys.platform` doesn't contain the major version anymore.
|
||
It is always ``'aix'``, instead of ``'aix3'`` .. ``'aix7'``. Since
|
||
older Python versions include the version number, so it is recommended to
|
||
always use ``sys.platform.startswith('aix')``.
|
||
(Contributed by M. Felt in :issue:`36588`.)
|
||
|
||
* :c:func:`PyEval_AcquireLock` and :c:func:`PyEval_AcquireThread` now
|
||
terminate the current thread if called while the interpreter is
|
||
finalizing, making them consistent with :c:func:`PyEval_RestoreThread`,
|
||
:c:func:`Py_END_ALLOW_THREADS`, and :c:func:`PyGILState_Ensure`. If this
|
||
behavior is not desired, guard the call by checking :c:func:`_Py_IsFinalizing`
|
||
or :c:func:`sys.is_finalizing`.
|
||
(Contributed by Joannah Nanjekye in :issue:`36475`.)
|
||
|
||
|
||
Changes in the Python API
|
||
-------------------------
|
||
|
||
* The :func:`os.getcwdb` function now uses the UTF-8 encoding on Windows,
|
||
rather than the ANSI code page: see :pep:`529` for the rationale. The
|
||
function is no longer deprecated on Windows.
|
||
(Contributed by Victor Stinner in :issue:`37412`.)
|
||
|
||
* :class:`subprocess.Popen` can now use :func:`os.posix_spawn` in some cases
|
||
for better performance. On Windows Subsystem for Linux and QEMU User
|
||
Emulation, the :class:`Popen` constructor using :func:`os.posix_spawn` no longer raises an
|
||
exception on errors like "missing program". Instead the child process fails with a
|
||
non-zero :attr:`~Popen.returncode`.
|
||
(Contributed by Joannah Nanjekye and Victor Stinner in :issue:`35537`.)
|
||
|
||
* The *preexec_fn* argument of * :class:`subprocess.Popen` is no longer
|
||
compatible with subinterpreters. The use of the parameter in a
|
||
subinterpreter now raises :exc:`RuntimeError`.
|
||
(Contributed by Eric Snow in :issue:`34651`, modified by Christian Heimes
|
||
in :issue:`37951`.)
|
||
|
||
* The :meth:`imap.IMAP4.logout` method no longer silently ignores arbitrary
|
||
exceptions.
|
||
(Contributed by Victor Stinner in :issue:`36348`.)
|
||
|
||
* The function :func:`platform.popen` has been removed, after having been deprecated since
|
||
Python 3.3: use :func:`os.popen` instead.
|
||
(Contributed by Victor Stinner in :issue:`35345`.)
|
||
|
||
* The :func:`statistics.mode` function no longer raises an exception
|
||
when given multimodal data. Instead, it returns the first mode
|
||
encountered in the input data. (Contributed by Raymond Hettinger
|
||
in :issue:`35892`.)
|
||
|
||
* The :meth:`~tkinter.ttk.Treeview.selection` method of the
|
||
:class:`tkinter.ttk.Treeview` class no longer takes arguments. Using it with
|
||
arguments for changing the selection was deprecated in Python 3.6. Use
|
||
specialized methods like :meth:`~tkinter.ttk.Treeview.selection_set` for
|
||
changing the selection. (Contributed by Serhiy Storchaka in :issue:`31508`.)
|
||
|
||
* The :meth:`writexml`, :meth:`toxml` and :meth:`toprettyxml` methods of
|
||
:mod:`xml.dom.minidom`, and the :meth:`write` method of :mod:`xml.etree`,
|
||
now preserve the attribute order specified by the user.
|
||
(Contributed by Diego Rojas and Raymond Hettinger in :issue:`34160`.)
|
||
|
||
* A :mod:`dbm.dumb` database opened with flags ``'r'`` is now read-only.
|
||
:func:`dbm.dumb.open` with flags ``'r'`` and ``'w'`` no longer creates
|
||
a database if it does not exist.
|
||
(Contributed by Serhiy Storchaka in :issue:`32749`.)
|
||
|
||
* The ``doctype()`` method defined in a subclass of
|
||
:class:`~xml.etree.ElementTree.XMLParser` will no longer be called and will
|
||
emit a :exc:`RuntimeWarning` instead of a :exc:`DeprecationWarning`.
|
||
Define the :meth:`doctype() <xml.etree.ElementTree.TreeBuilder.doctype>`
|
||
method on a target for handling an XML doctype declaration.
|
||
(Contributed by Serhiy Storchaka in :issue:`29209`.)
|
||
|
||
* A :exc:`RuntimeError` is now raised when the custom metaclass doesn't
|
||
provide the ``__classcell__`` entry in the namespace passed to
|
||
``type.__new__``. A :exc:`DeprecationWarning` was emitted in Python
|
||
3.6--3.7. (Contributed by Serhiy Storchaka in :issue:`23722`.)
|
||
|
||
* The :class:`cProfile.Profile` class can now be used as a context
|
||
manager. (Contributed by Scott Sanderson in :issue:`29235`.)
|
||
|
||
* :func:`shutil.copyfile`, :func:`shutil.copy`, :func:`shutil.copy2`,
|
||
:func:`shutil.copytree` and :func:`shutil.move` use platform-specific
|
||
"fast-copy" syscalls (see
|
||
:ref:`shutil-platform-dependent-efficient-copy-operations` section).
|
||
|
||
* :func:`shutil.copyfile` default buffer size on Windows was changed from
|
||
16 KiB to 1 MiB.
|
||
|
||
* The ``PyGC_Head`` struct has changed completely. All code that touched the
|
||
struct member should be rewritten. (See :issue:`33597`.)
|
||
|
||
* 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
|
||
fields are public, so we hope no one has been using them. However,
|
||
if you do rely on one or more of those private fields and have no
|
||
alternative then please open a BPO issue. We'll work on helping
|
||
you adjust (possibly including adding accessor functions to the
|
||
public API). (See :issue:`35886`.)
|
||
|
||
* The :meth:`mmap.flush() <mmap.mmap.flush>` method now returns ``None`` on
|
||
success and raises an exception on error under all platforms. Previously,
|
||
its behavior was platform-dependent: a nonzero value was returned on success;
|
||
zero was returned on error under Windows. A zero value was returned on
|
||
success; an exception was raised on error under Unix.
|
||
(Contributed by Berker Peksag in :issue:`2122`.)
|
||
|
||
* :mod:`xml.dom.minidom` and :mod:`xml.sax` modules no longer process
|
||
external entities by default.
|
||
(Contributed by Christian Heimes in :issue:`17239`.)
|
||
|
||
* Deleting a key from a read-only :mod:`dbm` database (:mod:`dbm.dumb`,
|
||
:mod:`dbm.gnu` or :mod:`dbm.ndbm`) raises :attr:`error` (:exc:`dbm.dumb.error`,
|
||
:exc:`dbm.gnu.error` or :exc:`dbm.ndbm.error`) instead of :exc:`KeyError`.
|
||
(Contributed by Xiang Zhang in :issue:`33106`.)
|
||
|
||
* Simplified AST for literals. All constants will be represented as
|
||
:class:`ast.Constant` instances. Instantiating old classes ``Num``,
|
||
``Str``, ``Bytes``, ``NameConstant`` and ``Ellipsis`` will return
|
||
an instance of ``Constant``.
|
||
(Contributed by Serhiy Storchaka in :issue:`32892`.)
|
||
|
||
* :func:`~os.path.expanduser` on Windows now prefers the :envvar:`USERPROFILE`
|
||
environment variable and does not use :envvar:`HOME`, which is not normally
|
||
set for regular user accounts.
|
||
(Contributed by Anthony Sottile in :issue:`36264`.)
|
||
|
||
* The exception :class:`asyncio.CancelledError` now inherits from
|
||
:class:`BaseException` rather than :class:`Exception` and no longer inherits
|
||
from :class:`concurrent.futures.CancelledError`.
|
||
(Contributed by Yury Selivanov in :issue:`32528`.)
|
||
|
||
* The function :func:`asyncio.wait_for` now correctly waits for cancellation
|
||
when using an instance of :class:`asyncio.Task`. Previously, upon reaching
|
||
*timeout*, it was cancelled and immediately returned.
|
||
(Contributed by Elvis Pranskevichus in :issue:`32751`.)
|
||
|
||
* The function :func:`asyncio.BaseTransport.get_extra_info` now returns a safe
|
||
to use socket object when 'socket' is passed to the *name* parameter.
|
||
(Contributed by Yury Selivanov in :issue:`37027`.)
|
||
|
||
* :class:`asyncio.BufferedProtocol` has graduated to the stable API.
|
||
|
||
.. _bpo-36085-whatsnew:
|
||
|
||
* DLL dependencies for extension modules and DLLs loaded with :mod:`ctypes` on
|
||
Windows are now resolved more securely. Only the system paths, the directory
|
||
containing the DLL or PYD file, and directories added with
|
||
:func:`~os.add_dll_directory` are searched for load-time dependencies.
|
||
Specifically, :envvar:`PATH` and the current working directory are no longer
|
||
used, and modifications to these will no longer have any effect on normal DLL
|
||
resolution. If your application relies on these mechanisms, you should check
|
||
for :func:`~os.add_dll_directory` and if it exists, use it to add your DLLs
|
||
directory while loading your library. Note that Windows 7 users will need to
|
||
ensure that Windows Update KB2533623 has been installed (this is also verified
|
||
by the installer).
|
||
(Contributed by Steve Dower in :issue:`36085`.)
|
||
|
||
* The header files and functions related to pgen have been removed after its
|
||
replacement by a pure Python implementation. (Contributed by Pablo Galindo
|
||
in :issue:`36623`.)
|
||
|
||
* :class:`types.CodeType` has a new parameter in the second position of the
|
||
constructor (*posonlyargcount*) to support positional-only arguments defined
|
||
in :pep:`570`. The first argument (*argcount*) now represents the total
|
||
number of positional arguments (including positional-only arguments). The new
|
||
``replace()`` method of :class:`types.CodeType` can be used to make the code
|
||
future-proof.
|
||
|
||
|
||
Changes in the C API
|
||
--------------------
|
||
|
||
* The :c:type:`PyCompilerFlags` structure got a new *cf_feature_version*
|
||
field. It should be initialized to ``PY_MINOR_VERSION``. The field is ignored
|
||
by default, and is used if and only if ``PyCF_ONLY_AST`` flag is set in
|
||
*cf_flags*.
|
||
(Contributed by Guido van Rossum in :issue:`35766`.)
|
||
|
||
* The :c:func:`PyEval_ReInitThreads` function has been removed from the C API.
|
||
It should not be called explicitly: use :c:func:`PyOS_AfterFork_Child`
|
||
instead.
|
||
(Contributed by Victor Stinner in :issue:`36728`.)
|
||
|
||
* On Unix, C extensions are no longer linked to libpython except on Android
|
||
and Cygwin. When Python is embedded, ``libpython`` must not be loaded with
|
||
``RTLD_LOCAL``, but ``RTLD_GLOBAL`` instead. Previously, using
|
||
``RTLD_LOCAL``, it was already not possible to load C extensions which
|
||
were not linked to ``libpython``, like C extensions of the standard
|
||
library built by the ``*shared*`` section of ``Modules/Setup``.
|
||
(Contributed by Victor Stinner in :issue:`21536`.)
|
||
|
||
* Use of ``#`` variants of formats in parsing or building value (e.g.
|
||
:c:func:`PyArg_ParseTuple`, :c:func:`Py_BuildValue`, :c:func:`PyObject_CallFunction`,
|
||
etc.) without ``PY_SSIZE_T_CLEAN`` defined raises ``DeprecationWarning`` now.
|
||
It will be removed in 3.10 or 4.0. Read :ref:`arg-parsing` for detail.
|
||
(Contributed by Inada Naoki in :issue:`36381`.)
|
||
|
||
* Instances of heap-allocated types (such as those created with
|
||
:c:func:`PyType_FromSpec`) hold a reference to their type object.
|
||
Increasing the reference count of these type objects has been moved from
|
||
:c:func:`PyType_GenericAlloc` to the more low-level functions,
|
||
:c:func:`PyObject_Init` and :c:func:`PyObject_INIT`.
|
||
This makes types created through :c:func:`PyType_FromSpec` behave like
|
||
other classes in managed code.
|
||
|
||
Statically allocated types are not affected.
|
||
|
||
For the vast majority of cases, there should be no side effect.
|
||
However, types that manually increase the reference count after allocating
|
||
an instance (perhaps to work around the bug) may now become immortal.
|
||
To avoid this, these classes need to call Py_DECREF on the type object
|
||
during instance deallocation.
|
||
|
||
To correctly port these types into 3.8, please apply the following
|
||
changes:
|
||
|
||
* Remove :c:macro:`Py_INCREF` on the type object after allocating an
|
||
instance - if any.
|
||
This may happen after calling :c:func:`PyObject_New`,
|
||
:c:func:`PyObject_NewVar`, :c:func:`PyObject_GC_New`,
|
||
:c:func:`PyObject_GC_NewVar`, or any other custom allocator that uses
|
||
:c:func:`PyObject_Init` or :c:func:`PyObject_INIT`.
|
||
|
||
Example:
|
||
|
||
.. code-block:: c
|
||
|
||
static foo_struct *
|
||
foo_new(PyObject *type) {
|
||
foo_struct *foo = PyObject_GC_New(foo_struct, (PyTypeObject *) type);
|
||
if (foo == NULL)
|
||
return NULL;
|
||
#if PY_VERSION_HEX < 0x03080000
|
||
// Workaround for Python issue 35810; no longer necessary in Python 3.8
|
||
PY_INCREF(type)
|
||
#endif
|
||
return foo;
|
||
}
|
||
|
||
* Ensure that all custom ``tp_dealloc`` functions of heap-allocated types
|
||
decrease the type's reference count.
|
||
|
||
Example:
|
||
|
||
.. code-block:: c
|
||
|
||
static void
|
||
foo_dealloc(foo_struct *instance) {
|
||
PyObject *type = Py_TYPE(instance);
|
||
PyObject_GC_Del(instance);
|
||
#if PY_VERSION_HEX >= 0x03080000
|
||
// This was not needed before Python 3.8 (Python issue 35810)
|
||
Py_DECREF(type);
|
||
#endif
|
||
}
|
||
|
||
(Contributed by Eddie Elizondo in :issue:`35810`.)
|
||
|
||
* The :c:macro:`Py_DEPRECATED()` macro has been implemented for MSVC.
|
||
The macro now must be placed before the symbol name.
|
||
|
||
Example:
|
||
|
||
.. code-block:: c
|
||
|
||
Py_DEPRECATED(3.8) PyAPI_FUNC(int) Py_OldFunction(void);
|
||
|
||
(Contributed by Zackery Spytz in :issue:`33407`.)
|
||
|
||
* The interpreter does not pretend to support binary compatibility of
|
||
extension types across feature releases, anymore. A :c:type:`PyTypeObject`
|
||
exported by a third-party extension module is supposed to have all the
|
||
slots expected in the current Python version, including
|
||
:c:member:`~PyTypeObject.tp_finalize` (:const:`Py_TPFLAGS_HAVE_FINALIZE`
|
||
is not checked anymore before reading :c:member:`~PyTypeObject.tp_finalize`).
|
||
|
||
(Contributed by Antoine Pitrou in :issue:`32388`.)
|
||
|
||
* The :c:func:`PyCode_New` has a new parameter in the second position (*posonlyargcount*)
|
||
to support :pep:`570`, indicating the number of positional-only arguments.
|
||
|
||
* The functions :c:func:`PyNode_AddChild` and :c:func:`PyParser_AddToken` now accept
|
||
two additional ``int`` arguments *end_lineno* and *end_col_offset*.
|
||
|
||
* The :file:`libpython38.a` file to allow MinGW tools to link directly against
|
||
:file:`python38.dll` is no longer included in the regular Windows distribution.
|
||
If you require this file, it may be generated with the ``gendef`` and
|
||
``dlltool`` tools, which are part of the MinGW binutils package:
|
||
|
||
.. code-block:: shell
|
||
|
||
gendef - python38.dll > tmp.def
|
||
dlltool --dllname python38.dll --def tmp.def --output-lib libpython38.a
|
||
|
||
The location of an installed :file:`pythonXY.dll` will depend on the
|
||
installation options and the version and language of Windows. See
|
||
:ref:`using-on-windows` for more information. The resulting library should be
|
||
placed in the same directory as :file:`pythonXY.lib`, which is generally the
|
||
:file:`libs` directory under your Python installation.
|
||
|
||
(Contributed by Steve Dower in :issue:`37351`.)
|
||
|
||
|
||
CPython bytecode changes
|
||
------------------------
|
||
|
||
* The interpreter loop has been simplified by moving the logic of unrolling
|
||
the stack of blocks into the compiler. The compiler emits now explicit
|
||
instructions for adjusting the stack of values and calling the
|
||
cleaning-up code for :keyword:`break`, :keyword:`continue` and
|
||
:keyword:`return`.
|
||
|
||
Removed opcodes :opcode:`BREAK_LOOP`, :opcode:`CONTINUE_LOOP`,
|
||
:opcode:`SETUP_LOOP` and :opcode:`SETUP_EXCEPT`. Added new opcodes
|
||
:opcode:`ROT_FOUR`, :opcode:`BEGIN_FINALLY`, :opcode:`CALL_FINALLY` and
|
||
:opcode:`POP_FINALLY`. Changed the behavior of :opcode:`END_FINALLY`
|
||
and :opcode:`WITH_CLEANUP_START`.
|
||
|
||
(Contributed by Mark Shannon, Antoine Pitrou and Serhiy Storchaka in
|
||
:issue:`17611`.)
|
||
|
||
* Added new opcode :opcode:`END_ASYNC_FOR` for handling exceptions raised
|
||
when awaiting a next item in an :keyword:`async for` loop.
|
||
(Contributed by Serhiy Storchaka in :issue:`33041`.)
|
||
|
||
* The :opcode:`MAP_ADD` now expects the value as the first element in the
|
||
stack and the key as the second element. This change was made so the key
|
||
is always evaluated before the value in dictionary comprehensions, as
|
||
proposed by :pep:`572`. (Contributed by Jörn Heissler in :issue:`35224`.)
|
||
|
||
|
||
Demos and Tools
|
||
---------------
|
||
|
||
Added a benchmark script for timing various ways to access variables:
|
||
``Tools/scripts/var_access_benchmark.py``.
|
||
(Contributed by Raymond Hettinger in :issue:`35884`.)
|
||
|
||
Here's a summary of performance improvements since Python 3.3:
|
||
|
||
.. code-block:: none
|
||
|
||
Python version 3.3 3.4 3.5 3.6 3.7 3.8
|
||
-------------- --- --- --- --- --- ---
|
||
|
||
Variable and attribute read access:
|
||
read_local 4.0 7.1 7.1 5.4 5.1 3.9
|
||
read_nonlocal 5.3 7.1 8.1 5.8 5.4 4.4
|
||
read_global 13.3 15.5 19.0 14.3 13.6 7.6
|
||
read_builtin 20.0 21.1 21.6 18.5 19.0 7.5
|
||
read_classvar_from_class 20.5 25.6 26.5 20.7 19.5 18.4
|
||
read_classvar_from_instance 18.5 22.8 23.5 18.8 17.1 16.4
|
||
read_instancevar 26.8 32.4 33.1 28.0 26.3 25.4
|
||
read_instancevar_slots 23.7 27.8 31.3 20.8 20.8 20.2
|
||
read_namedtuple 68.5 73.8 57.5 45.0 46.8 18.4
|
||
read_boundmethod 29.8 37.6 37.9 29.6 26.9 27.7
|
||
|
||
Variable and attribute write access:
|
||
write_local 4.6 8.7 9.3 5.5 5.3 4.3
|
||
write_nonlocal 7.3 10.5 11.1 5.6 5.5 4.7
|
||
write_global 15.9 19.7 21.2 18.0 18.0 15.8
|
||
write_classvar 81.9 92.9 96.0 104.6 102.1 39.2
|
||
write_instancevar 36.4 44.6 45.8 40.0 38.9 35.5
|
||
write_instancevar_slots 28.7 35.6 36.1 27.3 26.6 25.7
|
||
|
||
Data structure read access:
|
||
read_list 19.2 24.2 24.5 20.8 20.8 19.0
|
||
read_deque 19.9 24.7 25.5 20.2 20.6 19.8
|
||
read_dict 19.7 24.3 25.7 22.3 23.0 21.0
|
||
read_strdict 17.9 22.6 24.3 19.5 21.2 18.9
|
||
|
||
Data structure write access:
|
||
write_list 21.2 27.1 28.5 22.5 21.6 20.0
|
||
write_deque 23.8 28.7 30.1 22.7 21.8 23.5
|
||
write_dict 25.9 31.4 33.3 29.3 29.2 24.7
|
||
write_strdict 22.9 28.4 29.9 27.5 25.2 23.1
|
||
|
||
Stack (or queue) operations:
|
||
list_append_pop 144.2 93.4 112.7 75.4 74.2 50.8
|
||
deque_append_pop 30.4 43.5 57.0 49.4 49.2 42.5
|
||
deque_append_popleft 30.8 43.7 57.3 49.7 49.7 42.8
|
||
|
||
Timing loop:
|
||
loop_overhead 0.3 0.5 0.6 0.4 0.3 0.3
|
||
|
||
The benchmarks were measured on an
|
||
`Intel® Core™ i7-4960HQ processor
|
||
<https://ark.intel.com/content/www/us/en/ark/products/76088/intel-core-i7-4960hq-processor-6m-cache-up-to-3-80-ghz.html>`_
|
||
running the macOS 64-bit builds found at
|
||
`python.org <https://www.python.org/downloads/mac-osx/>`_.
|
||
The benchmark script displays timings in nanoseconds.
|
||
|
||
|
||
Notable changes in Python 3.8.1
|
||
===============================
|
||
|
||
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 the socket option ``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`.)
|