Generic subclass. ABCMeta object is not subscriptable

[cburgdorf]

Please provide more information to help us understand the issue:

I'm trying to write the following

class ServiceContext(UserList[BaseService]):
...

However, that leaves me with

TypeError: 'ABCMeta' object is not subscriptable

I know that for simple type annotations I can simply define the type in strings in cases like this. However, that clearly doesn't apply in the inheritance case.

The only solution that I found to that seems very hacky.

Since I want to enable --disallow-any-generics I need to specify the type parameter for UserList.

I'm wondering if there's any other alternative to that?

[ilevkivskyi]

This is a known limitation of Python standard library classes. There is a slightly less hacky solution:

if TYPE_CHECKING:
    QueueBase = queue.Queue
else
    class _Queue:
        def __getitem__(*args):
            return queue.Queue
    QueueBase = _Queue()

In addition, for your particular use case (non-generic subclass) you can simply write:

if TYPE_CHECKING:
    Base = UserList[BaseService]
else:
    Base = UserList

But the latter solution will work only if you don't have type variables.

[cburgdorf]

Ah, that's it! Thanks for clarifying. I think this should be part of the docs (or maybe at least reference to this answer or something).

Closing the issue.

[sultaniman]

I ended up doing sth similar to what @ilevkivskyi did, found this in mypy docs

T = TypeVar("T")

if TYPE_CHECKING:
    class _Queue(Queue[T]):
        pass
else:
    class _Queue(Generic[T], Queue):
        pass


class BaseQueue(_Queue[T]):
    pass