erroneous complaint during tree walk #18608
Description
Bug Report
@hauntsaninja suggested I raise this.
To Reproduce
from dataclasses import dataclass
from typing import TypeVar, Generic, Any
T = TypeVar('T')
@dataclass()
class Element(Generic[T]):
value: T
parent: "Element[Any] | None" = None
def walk(self) -> None:
current: Element[Any] | None = self
while current := current.parent:
print(current.value)Expected Behavior
$ pyright --version
pyright 1.1.393
$ pyright type_bug.py
0 errors, 0 warnings, 0 informations Actual Behavior
$ mypy --version
mypy 1.14.1 (compiled: yes)
$ mypy type_bug.py
type_bug.py:14: error: Item "None" of "Element[Any] | None" has no attribute "parent" [union-attr]
Found 1 error in 1 file (checked 1 source file)Your Environment
- Mypy version used: 1.14.1
- Python version used: Python 3.12.1
Activity
hauntsaninja commentedon Feb 5, 2025
Thanks for filing. Looking at this, I think it's just a (slightly confusing) duplicate of #2008. Old issue, but we've recently made progress towards it. Last I checked the primer for the fix was starting to look not too bad (see hauntsaninja#4)
One way to work around is to move the assignment to a separate line from the annotation:
See also:
ilevkivskyi commentedon Feb 5, 2025
Yes, a duplicate of #2008