The problem is that there's a severe hole in the ABCs: there is no distinction between "container whose elements are mutable" and "container whose elements and size are mutable".

(related, there's no distinction for supporting slice operations or not, e.g. deque)

If you don't need to reuse the collection or access its items out of order, you can also use Iterable which accepts even more inputs like generators.

Good point, and Łukasz Langa mentioned this in his talk (check it out). He names it the robustness principle, in his words (around 22:20 mark:

"Vague in what you accept, concrete in what you return"

But he also mentions some gotchas like how Iterable[str] can backfire, because str is also an Iterable[str] and it might be better to use list[str].

Sequence now lives at collections.abc. BTW, float is not a supertype of int (issubclass(int, float) == False). Normaly, It is acceptable to use int instead of float, but speaking of variance, it is more precise to use numbers.Real:

issubclass(Integral, Real) == True
issubclass(int, Real) == True
issubclass(float, Real) == True
issubclass(complex, Real) == False