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gh-90190: Add doc for using singledispatch with precise collection type hints #116544

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Merged
merged 8 commits into from
Sep 27, 2024
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gh-90190: Add doc for using singledispatch with precise collection type hints #116544

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d95c49d
gh-90190: Adds documentation for singledispatch with GenericAlias ann…
Delengowski Mar 9, 2024
92f8c82
Corrects rst syntax
Delengowski Mar 9, 2024
e8bbb6a
Merge branch 'main' into add-docs-singledispatch-generic-alias-90190
Delengowski May 9, 2024
16cd6f0
Resolves grammatical errors and wording feedback
Delengowski May 10, 2024
b1d9d45
Merge branch 'main' into add-docs-singledispatch-generic-alias-90190
Delengowski May 26, 2024
4b4786f
Merge branch 'main' into add-docs-singledispatch-generic-alias-90190
Delengowski Jul 3, 2024
dc45be5
minor grammar fix
AlexWaygood Sep 27, 2024
9c75412
Merge branch 'main' into add-docs-singledispatch-generic-alias-90190
AlexWaygood Sep 27, 2024
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19 changes: 19 additions & 0 deletions Doc/library/functools.rst
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Expand Up @@ -543,6 +543,25 @@ The :mod:`functools` module defines the following functions:
... print(arg.real, arg.imag)
...

For code that dispatches on a collections type (e.g., ``list``), but wants
to typehint the items of the collection (e.g., ``list[int]``), the
dispatch type should be passed explicitly to the decorator itself with the
typehint going into the function definition::

>>> @fun.register(list)
... def _(arg: list[int], verbose=False):
... if verbose:
... print("Enumerate this:")
... for i, elem in enumerate(arg):
... print(i, elem)

.. note::

At runtime the function will dispatch on an instance of a list regardless
of the type contained within the list i.e. ``[1,2,3]`` will be
dispatched the same as ``["foo", "bar", "baz"]``. The annotation
provided in this example is for static type checkers only and has no
runtime impact.

To enable registering :term:`lambdas<lambda>` and pre-existing functions,
the :func:`register` attribute can also be used in a functional form::
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