constrained TypeVar and star operator incompatible type
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bug
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- Python
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Description
Bug Report
We can't use TypeVar with star operator, maybe I wrongly used TypeVar.
Thanks
To Reproduce
T = TypeVar("T", str, int)
def test(a: Sequence[T]) -> list[T]:
return [*a]
Expected Behavior
No error
Actual Behavior
cactus.py: note: In function "test":
cactus.py:57:14: error: List item 0 has incompatible type "Sequence[T]"; expected "str" [list-item]
return [*a]
^
cactus.py:57:14: error: List item 0 has incompatible type "Sequence[T]"; expected "int" [list-item]
return [*a]
^
cactus.py:57:14: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-list-item for more info
Your Environment
- Mypy version used: 1.11.1
- Python version used: 3.12.1
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 Python reproducer in the issue using mypy 1.11.1 and Python 3.12.1, confirming the incompatible list-item errors for the constrained TypeVar and star expression. Trace the type-checking path for this expression and make the example pass without errors, then rerun the reproducer to verify the expected behavior.
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
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100