https://github.com/python/cpython/commit/2357d5ba48cd9685cb36bcf92a0eaed86a85f4de
commit: 2357d5ba48cd9685cb36bcf92a0eaed86a85f4de
branch: main
author: Matt Delengowski <[email protected]>
committer: AlexWaygood <[email protected]>
date: 2024-09-27T21:10:29Z
summary:
gh-90190: Add doc for using `singledispatch` with precise collection type hints
(#116544)
files:
M Doc/library/functools.rst
diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst
index c2c25ca67f338a..46136def06dc05 100644
--- a/Doc/library/functools.rst
+++ b/Doc/library/functools.rst
@@ -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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