LoggerAdapter is typed as a generic but using it as such raises an error at runtime

[babolivier]

With the following code:

class ContextLoggingAdapter(logging.LoggerAdapter):
    def process(self, msg: str, kwargs: Any) -> Tuple[str, Any]:
        ...

mypy raises the following type-arg error : error: Missing type parameters for generic type "LoggerAdapter"

According to this type stub it's typed as a generic and should be passed the type of the logger it's an adapter for. However, changing the code into this:

class ContextLoggingAdapter(logging.LoggerAdapter[logging.Logger]):
    def process(self, msg: str, kwargs: Any) -> Tuple[str, Any]:
        ...

makes mypy happy but raises an error at runtime: TypeError: 'type' object is not subscriptable

I'm not sure if this is an issue with the stubs or with mypy (and I'm not fully sure how they interact), so apologies if this issue should have been created on https://github.com/python/mypy instead (feel free to transfer it there if that's the case).

[AlexWaygood]

You created the issue in the right place :) and, this is a problem we're aware of.

LoggerAdapter will actually be generic at runtime on 3.11, because of this very issue: python/cpython#92129

In the meantime, however, @Akuli's advice here is probably the best way around this issue: #5954 (comment):

import logging
from typing import TYPE_CHECKING, Tuple, Any

if TYPE_CHECKING:
    _LoggerAdapter = logging.LoggerAdapter[logging.Logger]
else:
    _LoggerAdapter = logging.LoggerAdapter

class ContextLoggingAdapter(_LoggerAdapter):
    def process(self, msg: str, kwargs: Any) -> Tuple[str, Any]:
        ...

There's also some great mypy docs on this problem here: https://mypy.readthedocs.io/en/stable/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime

[babolivier]

That makes sense, thanks a lot for the details and references :)