`any` breaks the type checking of its argument
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bug
topic-type-context
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
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Description
Bug Report
Mypy cannot determine the type of the declared field inside a protocol method.
To Reproduce
Invoke mypy on the following Python file
# bug.py
from typing import List
x: List[str] = []
any(filter(lambda x : x.startswith(''), x))
Mypy complains: Argument 1 to "filter" has incompatible type "Callable[[Any], Any]"; expected "Callable[[str], TypeGuard[object]]".
Expected Behavior
No such error.
My Environment
- Mypy version used: https://github.com/python/mypy@e3827a1b950f83332656ad9c51ca8eea06ea2234
- Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.10.4
- Operating system and version: Ubuntu 20.04.4
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 mypy with no command-line flags on the reported bug.py example and compare the diagnostic with the expected behavior. Trace how the lambda passed to filter is inferred when its result is consumed by any; done means the example no longer produces the incompatible Callable error.
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
- 35/100