From 2357d5ba48cd9685cb36bcf92a0eaed86a85f4de Mon Sep 17 00:00:00 2001 From: Matt Delengowski Date: Fri, 27 Sep 2024 17:10:29 -0400 Subject: gh-90190: Add doc for using `singledispatch` with precise collection type hints (#116544) --- Doc/library/functools.rst | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst index c2c25ca..46136de 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` and pre-existing functions, the :func:`register` attribute can also be used in a functional form:: -- cgit v0.12