Repository navigation
AbstractContextManager.__enter__ not properly annotated #13950
Description
Per the Python docs, AbstractContextManager provides a default __enter__ implementation which just returns self. But this does not appear to be properly type annotated (using Self):
from typing import reveal_type, Optional, Self
from types import TracebackType
from contextlib import AbstractContextManager
class A1(AbstractContextManager):
def __exit__( # pylint: disable=useless-return
self, exc_type: Optional[type[BaseException]],
exc_val: Optional[BaseException],
exc_tb: Optional[TracebackType]) -> Optional[bool]:
return None
class A2(AbstractContextManager):
def __exit__( # pylint: disable=useless-return
self, exc_type: Optional[type[BaseException]],
exc_val: Optional[BaseException],
exc_tb: Optional[TracebackType]) -> Optional[bool]:
return None
def __enter__(self) -> Self:
return self
class B1(A1):
pass
class B2(A2):
pass
with B1() as d1:
reveal_type(d1)
with B2() as d2:
reveal_type(d2)Running this with mypy, only the second case properly reveals the type as B2. The first one just says Any.
At runtime, the behavior of both is identical.
I have recreated this on both Python 3.12 and Python 3.13.
Activity
srittau commentedon May 6, 2025
This is due to the duality of
AbstractContextManagerbeing both an ABC and a protocol. As a protocol it makes sense that it is generic over the return type of__enter__. Ideally we'd give the type variable a default ofSelf, but I'm not sure that that's possible.srittau commentedon May 6, 2025
I've opened #13951 as a example. I've also opened a discussion on discuss.python.org.
mharding-hpe commentedon May 6, 2025
Yeah, I tried using
AbstractContextManager[Self], but that gave an error sayingSelfcould only be used inside the class body itself.If it isn't possible to have it default to
Self, at least the "workaround" I used inA2isn't too painful.srittau commentedon May 11, 2025
Considering that
Selfcan't be used as a default, and the discussion doesn't look encouraging, I'm going to close this as "can't fix" for now.