Walrus narrowing not propagated from inside expression
Open
Nobody has claimed this yet.
bug
good-second-issue
topic-pep-572
topic-type-narrowing
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
def main(cond: bool) -> None:
woo = None
if cond and (woo := 5) in range(10):
reveal_type(woo) # should reveal int, reveals int | None
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 with the provided reproducer and run it through mypy, comparing the actual reveal_type output with the expected int. Trace type narrowing for the walrus assignment inside the and expression; done when the example reveals int and regression coverage verifies the behavior.
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
- 42/100