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special-case NotImplementedType in binop signatures to match runtime semantics #1129
Description
Describe the Bug
from types import NotImplementedType
class A:
def __add__(self, i: object) -> NotImplementedType: ...
class B:
def __radd__(self, i: A) -> int: ...
_ = A() + B() # _NotImplementedTypebinops can Never return NotImplementedType by cause of runtime semantics, i would expect this to result in Never or int
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stroxler commentedon Sep 23, 2025
Thanks for the issue!
I think we may have partial support for not implemented, but this seems like a gap in our support
yangdanny97 commentedon Jul 13, 2026
For future implementors: one tricky thing to consider
If we have an argument
A | B, andAreturns something for__add__whileBreturnsNotImplemented, we should only call__radd__withBfix special-case NotImplementedType in binop signatures to match runt…