`possibly-undefined` false positive when assigning variable for every case in match statement for all possible values
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bug
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
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Description
# mypy: enable-error-code=possibly-undefined
from typing import Literal
value: Literal[1, 2]
match value:
case 1:
result = 1
case 2:
result = 2
result # error: possibly-undefined
similar issue: #15958 (seems it was only fixed when using assert_never at the end)
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 running the minimal Python example in the issue, using the linked mypy playground, and compare the behavior with similar issue #15958. Trace how mypy handles the possibly-undefined check after the exhaustive Literal match; done means the reported error is no longer produced for this example.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100