mypy is unable to narrow a union type that includes a `StrEnum` subclass and a `Literal`
Open
Nobody has claimed this yet.
bug
topic-enum
topic-type-narrowing
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
Bug Report
As per the title, see the gist for an example. The issue does not occur when using Enum instead of StrEnum.
To Reproduce
https://mypy-play.net/?gist=cf9926c276e8fe0f48d7d20b7ebf2b6e
Expected Behavior
The output should be
main.py:12: note: Revealed type is "Literal['none']"
main.py:14: note: Revealed type is "__main__.Color"
Actual Behavior
The output is
main.py:12: note: Revealed type is "__main__.Color | Literal['none']"
main.py:14: note: Revealed type is "__main__.Color | Literal['none']"
Your Environment
- Mypy version used: 1.19.1
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 linked mypy-play.net reproduction and compare its revealed types with the expected and actual output for main.py lines 12 and 14. Trace the union narrowing behavior for a StrEnum subclass combined with Literal, then add or update coverage for this case and verify the revealed types using the project’s test suite.
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
- 45/100