Description

T90REAL

opened on Nov 1, 2025

Issue body actions

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

• gh-140873: Add support of non-descriptor callables in functools.singledispatchmethod() #140884
• [3.14] gh-140873: Fix the singledispatchmethod documentation #141523
• [3.13] gh-140873: Fix the singledispatchmethod documentation (GH-141523) #141710

Activity

1. T90REAL

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Nov 1, 2025
2. picnixz

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Nov 1, 2025
3. serhiy-storchaka

   self-assigned this

   on Nov 1, 2025
4. serhiy-storchaka

   added a commit that references this issue on Nov 1, 2025

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

   ab8e8e9
5. serhiy-storchaka commented on Nov 1, 2025

   

   serhiy-storchaka

   on Nov 1, 2025

   Member

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

   The docstring should be corrected in 3.14 and older.
6. picnixz

   added

   type-featureA feature request or enhancementA feature request or enhancement

   and removed

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Nov 2, 2025
7. picnixz

   changed the title [-]`functools.singledispatchmethod` crashes with `AttributeError` for registered non-descriptor callables, violating documentation guarantee[/-] [+]Allow non-descriptor callables in `functools.singledispatchmethod`[/+] on Nov 2, 2025
8. picnixz commented on Nov 2, 2025

   

   picnixz

   on Nov 2, 2025

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   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.
9. serhiy-storchaka commented on Nov 2, 2025

   

   serhiy-storchaka

   on Nov 2, 2025

   Member

   More actions

   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.
10. serhiy-storchaka

    added 2 commits that reference this issue on Nov 13, 2025

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

    b2b68d4

    pythongh-140873: Fix the singledispatchmethod documentation

    a0ff169
11. CuriousLearner

    added 3 commits that reference this issue on Nov 13, 2025

    Merge branch 'main' into fix-issue21914

    b9f473c

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

    c46ecc5

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

    c240289
12. serhiy-storchaka

    added a commit that references this issue on Nov 18, 2025

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

    d89eb2f
13. miss-islington

    added a commit that references this issue on Nov 18, 2025

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

    802dfd9
14. serhiy-storchaka

    closed this as completedon Nov 18, 2025
15. serhiy-storchaka

    added a commit that references this issue on Nov 18, 2025

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

    8f71888
16. StanFromIreland

    added a commit that references this issue on Dec 6, 2025

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

    dfd9a8c

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