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Mypy cannot determine the type of the declared field inside a protocol method
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 Protocol
class Test(Protocol):
k: int
def test(self, i: int):
self.k = self.k
Mypy complains: bug.py:7: error: Cannot determine type of "k". Strange here is if I remove the parameter i, the error would disappear.
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
Strange here is if I remove the parameter
i, the error would disappear.
I think that's just because mypy doesn't check functions that are completely unannotated. You still get the weird error for the following snippet, which doesn't have the i parameter, but does have a return annotation:
from typing import Protocol
class Test(Protocol):
k: int
def test(self) -> None:
self.k = self.k # error: Cannot determine type of "k"
https://mypy-play.net/?mypy=0.971&python=3.10&gist=d7a6bc98b693ad31605c3df9c83906d4
from typing import Protocol class Test(Protocol): k: int def test(self) -> None: self.k = self.k # error: Cannot determine type of "k"
In your case, the test method is annotated (-> None), isn't it? Then why is there still an error?
Mypy (by default) only checks methods that do have annotations.
Thanks for your comment. But still, the program shown by @AlexWaygood through the link can not type check. The same error lies in the latest mypy.
- https://mypy-play.net/?mypy=0.971&python=3.10&gist=d7a6bc98b693ad31605c3df9c83906d4
