How should I type my validators? #524
Description
I'm trying to add some types to some attrs-using code that uses validators.
Here's a minimal example of such:
from typing import Any, TypeVar from attr import Attribute T = TypeVar("T") def my_validator(instance: Any, attribute: Attribute[T], value: T) -> Any: passThe type is derived by looking at attr/validators.pyi and attr/__init__.pyi.
The code type-checks fine, but fails to execute:
jml@hope:~ $ mypy --strict attribute.py jml@hope:~ $ python attribute.py Traceback (most recent call last): File "attribute.py", line 8, in <module> def my_validator(instance: Any, attribute: Attribute[T], value: T) -> Any: TypeError: 'type' object is not subscriptableIf I remove the [T], the opposite happens:
jml@hope:~ $ mypy --strict attribute.py attribute.py:8: error: Missing type parameters for generic type jml@hope:~ $ python attribute.pyWhat type should my validators have?