Incorrect resolution of `type[TypeVar]` returning `TypeVar` with `numpy`
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bug
topic-pep-696
topic-type-variables
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
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Description
Bug Report
This came up with pandas-stubs, but can reproduce with just numpy
To Reproduce
from typing import TypeVar
import numpy as np
NDArrayT = TypeVar("NDArrayT", bound=np.ndarray)
def foo(x: type[NDArrayT]) -> NDArrayT:
return x([1, 2])
reveal_type(foo(np.ndarray))
Expected Behavior
Revealed type should be ndarray[tuple[Any, ...], dtype[Any]], which is what pyright reports.
Actual Behavior
mypy reports numpy.ndarray[Any, Any]
Your Environment
- Mypy version used: 1.19.0
- Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.11
- numpy version: 2.3.5
- pyright version: 1.1.407
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 provided Python reproduction with mypy 1.19.0 and compare its revealed type with pyright's result. Trace the type inference for type[TypeVar] and ndarray, then add a regression test showing that foo(np.ndarray) reveals the expected ndarray type.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- numpy, python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100