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builtins.sum: Spurious error for operands having __add__ defined using partialmetho #17734
Description
Bug Report
This is a follow-on from python/typeshed#7739. See there for additional context provided by @srittau and @AlexWaygood.
To Reproduce
from __future__ import annotations
from functools import partialmethod
class A:
def my_add(self, other: A, reverse: bool) -> A:
return self
__add__ = partialmethod(my_add, reverse=False)
a = A()
aa = A()
aaa = A()
result = sum([aa, a], start=aaa)Expected Behavior
The above seems like a legitimate way to define __add__.
Actual Behavior
$ mypy --version mypy 0.950 (compiled: yes) $ mypy --show-error-codes --strict mypy_bug_report.py mypy_bug_report.py:15: error: No overload variant of "sum" matches argument types "List[A]", "A" [call-overload] mypy_bug_report.py:15: note: Possible overload variants: mypy_bug_report.py:15: note: def [_SumT <: _SupportsSum] sum(Iterable[_SumT]) -> Union[_SumT, Literal[0]] mypy_bug_report.py:15: note: def [_SumT <: _SupportsSum, _SumS <: _SupportsSum] sum(Iterable[_SumT], start: _SumS) -> Union[_SumT, _SumS] Found 1 error in 1 file (checked 1 source file)
mypy 1.11.1's output is essentially unchanged.
Your Environment
- Mypy version used: 0.950, 1.11.1
- Mypy command-line flags: none, or as above
- Mypy configuration options from mypy.ini (and other config files): none
- Python version used: 3.12.5, from Debian
cc @kaushikcfd
Activity
erictraut commented on Sep 4, 2024
I think this is because mypy has no special-case logic for functools.partialmethod. If I'm correct, this issue could be considered a duplicate of #8619.
Use checkmember.py to check protocol subtyping (python#18943)
Use checkmember.py to check protocol subtyping (python#18943)