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redundant-numeric-union (PYI041) --fix incorrect fix for functools.singledispatch registered function #27333

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#27335
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redundant-numeric-union (PYI041) --fix incorrect fix for functools.singledispatch registered function#27333
#27335
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ntBre
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bugAn issue describing something that isn't working, or a PR that fixes a bug

Description

@agalasso
agalasso
opened on Jul 30, 2026

Summary

Applying PYI041 --fix will replace a numeric union annotation like int | float with float, but this is an incorrect fix for a method that is annotated with @func.register for a functools.singledispatch function.
Minimal example code:

import functools

@functools.singledispatch
def int_or_float(value: object) -> str:
    return False

@int_or_float.register
def _(value: int | float):
    return True

assert int_or_float(3)

Repro script:

repro-ruff-redundant-numeric-union-singledispatch.sh

Version

ruff 0.16.0 (did not check any other versions)

Activity

  1. ntBre commented on Jul 30, 2026

    @ntBre
    ntBre
    on Jul 30, 2026
    Contributor

    Thanks for the report! Seems like the rule should not apply to singledispatch functions.

  2. ntBre
    self-assigned this
    on Jul 30, 2026
  3. ntBre
    added
    bugAn issue describing something that isn't working, or a PR that fixes a bug
    on Jul 30, 2026
  4. ntBre
    closed this as completedin #27335on Jul 31, 2026
  5. ntBre
    added a commit that references this issue on Jul 31, 2026

    [`flake8-pyi`] Avoid false positives on `singledispatch` functions (`…

    31cb63a
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