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hasattr(v, "__iter__") does not narrow int | Iterable[int] #5582
Description
Describe the Bug
Looks related to #684, I haven't checked what was done there but "In the negative case we do nothing, because the attribute could be present but set to None/empty string, etc." may be related, as with hasattr() we actually know that the attribute is not present.
from collections.abc import Iterable
def f(v: int | Iterable[int]) -> int:
if hasattr(v, "__iter__"):
return 0
return v # bad-return: Iterable[int] | int
def g(v: int | Iterable[int]) -> Iterable[int]:
if hasattr(v, "__iter__"):
return v # bad-return: Iterable[int] | int
return [v] # bad-return: list[Iterable[int] | int]Sandbox Link
(Only applicable for extension issues) IDE Information
No response
Activity
rchen152 commentedon Nov 9, 2026
Hmm, this is a little tricky. To handle this correctly, Pyrefly needs to be able to represent the narrowed type after
hasattr(v, "__iter__"). In this specific example, we can use(int & Iterable[int]) | Iterable[int], but this doesn't easily generalize to a protocol with several abstract methods and severalhasattrchecks. Perhaps we can start with a simple partial fix that only handles protocols likeIterablewith only a single abstract method.