Type narrowing with missing generic argument

[cdce8p]

Came across something like this today

from typing import Generic, TypeVar

_T = TypeVar("_T", bound="DataUpdateCoordinator")

class DataUpdateCoordinator:
    data: str | int

class CoordinatorEntity(Generic[_T]):
    def __init__(self, coordinator: _T) -> None:
        self.coordinator = coordinator

class A(CoordinatorEntity):
    def __init__(self) -> None:
        reveal_type(self.coordinator)
        reveal_type(self.coordinator.data)
        print(self.coordinator.error)  # This should be an error

CoordinatorEntity for class A is (obviously) missing a generic argument. Let's assume for a moment that it's not possible to add one in a legacy codebase. Can self.coordinator still be narrowed to DataUpdateCoordinator?

mypy and pyre just infer it as Any whereas pyright says it's unknown. We do know that _T has an upper bound in DataUpdateCoordinator so every generic argument will need to be a subclass of DataUpdateCoordinator and thus also have a data attribute. error is more complicate. Without a concrete type, I would assume this should be an error though.

Am I missing something? If not, improving the type narrowing here could help with better intellisense suggestions and type checking in partially typed code bases.

[erictraut]

The type of coordinator is _T@CoordinatorEntry (i.e. _T scoped to the class CoordinatorEntry). Outside of the class, its type is dictated by the specialization of CoordinatorEntity. In your particular example, CoordinatorEntity has been specialized implicitly with Any because of the missing type argument. That means the type of self.coordinator is Any. So the behavior of all three type checkers is correct in this case.