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Merged
gvanrossum merged 1 commit into from
Dec 18, 2020
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bpo-42675: Document collections.abc.Callable changes #23839

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4 changes: 4 additions & 0 deletions Doc/library/types.rst
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Expand Up @@ -280,6 +280,10 @@ Standard names are defined for the following types:

.. versionadded:: 3.9

.. versionchanged:: 3.9.2
This type can now be subclassed.


.. data:: Union

The type of :ref:`union type expressions<types-union>`.
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24 changes: 24 additions & 0 deletions Doc/whatsnew/3.10.rst
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Expand Up @@ -179,6 +179,21 @@ codecs
Add a :func:`codecs.unregister` function to unregister a codec search function.
(Contributed by Hai Shi in :issue:`41842`.)

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

The ``__args__`` of the :ref:`parameterized generic <types-genericalias>` for
:class:`collections.abc.Callable` are now consistent with :data:`typing.Callable`.
: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. Note
that a :exc:`TypeError` may be raised for invalid forms of parameterizing
:class:`collections.abc.Callable` which may have passed silently in Python 3.9.
(Contributed by Ken Jin in :issue:`42195`.)

contextlib
----------

Expand Down Expand Up @@ -507,6 +522,15 @@ Changes in the Python API
ignored.
(Contributed by Victor Stinner in :issue:`42639`.)

* :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)``. Code which
accesses the arguments via :func:`typing.get_args` or ``__args__`` need to account
for this change. Furthermore, :exc:`TypeError` may be raised for invalid forms
of parameterizing :class:`collections.abc.Callable` which may have passed
silently in Python 3.9.
(Contributed by Ken Jin in :issue:`42195`.)

CPython bytecode changes
========================
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