You can write it like this:

T = TypeVar('T')

class MyAbstractGeneric(Generic[T]):
    pass

class MyGeneric(MyAbstractGeneric[T], Generic[T]):
    pass

You have to declare the type variables using a Generic[...] base class, even if another base class is generic. There is an open issue for fixing this (#302).

Would you like to contribute a fix (either a fix to #302 or a documentation update)?

Leaving this open as a missing documentation issue.

@JukkaL thanks for the fast response. I think I can make time for the documentation update, but I'll probably wait until I've answered a few more questions for myself.

Um, PEP 484 is explicit that this should be allowed:

The Generic[T] base class is redundant in simple cases where you
subclass some other generic class and specify type variables for its
parameters

  from typing import TypeVar, Iterator

  T = TypeVar('T')

  class MyIter(Iterator[T]):
      ...

That class definition is equivalent to:

  class MyIter(Iterator[T], Generic[T]):
      ...

So I rather think that we should fix this instead of documenting it. (Though I'm okay with the fix being scheduled for Milestone 0.5 and the docs updated temporarily to explain the issue.)

Yeah, I was aware of this -- #302 that I referred to above is about this.