type not narrowed within function when it's `Final`
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bug
topic-final
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
from typing import Final
foo: Final[int | None] = 1
if foo is not None:
def bar() -> None:
reveal_type(foo) # note: Revealed type is "Union[builtins.int, None]"
this is actually safe because the type is Final
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the provided example in the linked mypy-play case and inspect how narrowing is handled across the nested function definition. The issue is done when reveal_type(foo) reports only int inside bar while preserving correct behavior for non-Final values.
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
- Clearly specified
- Newbie friendliness
- 35/100