8000 bpo-42741: Sync what's new in 3.9 with 3.9 branch by Fidget-Spinner · Pull Request #23943 · python/cpython · GitHub
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Dec 25, 2020
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bpo-42741: Sync what's new in 3.9 with 3.9 branch #23943

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35 changes: 34 additions & 1 deletion Doc/whatsnew/3.9.rst
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Expand Up @@ -1482,4 +1482,37 @@ and to match the behavior of static type checkers specified in the PEP.
File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'set'

(Contributed by Yurii Karabas in :issue:`42345`.)
(Contributed by Yurii Karabas in :issue:`42345`.)

macOS 11.0 (Big Sur) and Apple Silicon Mac support
--------------------------------------------------

As of 3.9.1, Python now fully supports building and running on macOS 11.0
(Big Sur) and on Apple Silicon Macs (based on the ``ARM64`` architecture).
A new universal build variant, ``universal2``, is now available to natively
support both ``ARM64`` and ``Intel 64`` in one set of executables. Binaries
can also now be built on current versions of macOS to be deployed on a range
of older macOS versions (tested to 10.9) while making some newer OS
functions and options conditionally available based on the operating system
version in use at runtime ("weaklinking").

(Contributed by Ronald Oussoren and Lawrence D'Anna in :issue:`41100`.)

Notable changes in Python 3.9.2
===============================

collections.abc
---------------

:class:`collections.abc.Callable` generic now flattens type parameters, similar
to what :data:`typing.Callable` currently does. This means that
``collections.abc.Callable[[int, str], str]`` will have ``__args__`` of
``(int, str, str)``; previously this was ``([int, str], str)``. To allow this
change, :class:`types.GenericAlias` can now be subclassed, and a subclass will
be returned when subscripting the :class:`collections.abc.Callable` type.
Code which accesses the arguments via :func:`typing.get_args` or ``__args__``
need to account for this change. A :exc:`DeprecationWarning` may be emitted for
invalid forms of parameterizing :class:`collections.abc.Callable` which may have
passed silently in Python 3.9.1. This :exc:`DeprecationWarning` will
become a :exc:`TypeError` in Python 3.10.
(Contributed by Ken Jin in :issue:`42195`.)
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