Allow non-descriptor callables in functools.singledispatchmethod

Bug report

Bug description:

When a non-descriptor callable (such as a lambda or a class instance) is registered as a handler, singledispatchmethod unconditionally attempts to call the __get__ method on that handler during dispatch.
This results in an AttributeError, because non-descriptor callables do not have a get method.
This behavior directly violates the explicit guarantee in singledispatchmethod's own docstring, which states that it does handle non-descriptor callables.

import functools

class MyCallable:
    def __call__(self, host_self, arg):
        return f"Handled {arg} via MyCallable"

class Host:
    @functools.singledispatchmethod
    def my_method(self, arg):
        return f"Base handling for {arg}"

callable_instance = MyCallable()
Host.my_method.register(int, callable_instance)


h = Host()

h.my_method(123)

AttributeError: 'MyCallable' object has no attribute '__get__'. Did you mean: '__ge__'?

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

pythongh-140873: Add support of non-descriptor callables in functools…

This never worked, so it can be considered a new feature.

The docstring should be corrected in 3.14 and older.

I'll categorize this as a new feature as this is the main point of this issue (and considering no one complained until now I think we can safely assume that it wasn't assumed so).

But we need to correct the docstring otherwise (as part of this issue). Adding support for non-descriptors would possibly break existing code so better to consider this a new feature.

Although we have several tests for non-descriptor callable (I think they were added by me). They are passed because the methods were not called, we only tested other their properties.

gh-140873: Add support of non-descriptor callables in functools.singl…

pythongh-140873: Fix the singledispatchmethod documentation

Merge branch 'main' into fix-issue21914

Merge branch 'main' of github.com:python/cpython into fix-Issue18387

Merge branch 'main' of github.com:python/cpython into fix-issue24255

[3.14] gh-140873: Fix the singledispatchmethod documentation (GH-141523)

[3.14] pythongh-140873: Fix the singledispatchmethod documentation (p…

[3.13] gh-140873: Fix the singledispatchmethod documentation (GH-141523…

pythongh-140873: Add support of non-descriptor callables in functools…

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Allow non-descriptor callables in `functools.singledispatchmethod` #140873

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Allow non-descriptor callables in functools.singledispatchmethod #140873

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Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

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serhiy-storchaka commented on Nov 1, 2025

picnixz commented on Nov 2, 2025

serhiy-storchaka commented on Nov 2, 2025

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Allow non-descriptor callables in `functools.singledispatchmethod` #140873