Casting NamedTuple with __call__ to Callable
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bug
topic-named-tuple
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
- PR merge metrics
- PR metrics pending
Description
I think this should be valid:
from typing import Callable, NamedTuple
class Foo(NamedTuple):
x: int
def __call__(self) -> int:
return self.x
foo: Callable[[], int] = Foo(42)
but mypy fails with:
error: Incompatible types in assignment (expression has type "Foo", variable has type "Callable[[], int]")
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 on the NamedTuple and Callable example in the issue to reproduce the incompatible-assignment error. Trace the callable compatibility check for a NamedTuple defining call; done means the example is accepted and the behavior is covered by a regression test.
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
- 38/100