Repository navigation
False negative involving overload and walrus #22264
Description
from typing import overload
@overload
def first(a: int, b: int) -> int: ...
@overload
def first(a: str, b: int) -> str: ...
def first(a: int | str, b: int) -> int | str:
return a
def f() -> int:
x: int | str = "hello"
return first(x, (x := 1))
Found by Codex
Activity
rathodfalguni52-oss commentedon Nov 10, 2026
Hi maintainers!
I would like to work on this issue. I understand that the problem involves incorrect overload resolution when using the walrus operator, resulting in a false negative during type checking.
My approach would be to first reproduce the issue with a test case, investigate how mypy handles argument evaluation, type narrowing, and overload resolution, and then identify the cause of the incorrect behaviour. Based on my findings, I would work on implementing a fix and adding regression tests to ensure the issue is resolved without affecting existing functionality.
Could you please let me know if I can take this issue up and whether you have any suggestions regarding the implementation approach?
Thank you!