instance check with generic `type` causes narrowing to `<nothing>`
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bug
topic-type-narrowing
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Extremely similar to #10605
from typing import TypeVar
T = TypeVar("T")
def foo(t: type[T], data: str) -> None:
if isinstance(data, t):
print(data.__str__) # error: <nothing> has no attribute "__str__"
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Research direction
Start by running the Python example from this issue and compare its behavior with issue #10605. Trace the generic type narrowing used by isinstance; done means the valid isinstance branch no longer narrows data to and the reported str error is resolved.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100