Fix List[T] not inheriting list/List methods

[brettcannon]

microsoft/vscode-python#2446

E.g.

from typing import List

def func(a: List[str]):
    pass

Currently a has no completions instead of having completions for a list.

See generics from PEP 484 for some details.

[MikhailArkhipov]

[jakebailey]

Yeah, this works for both of those two cases:

[jakebailey]

Actually, reading through that vscode-python bug, the user is expecting to see list functions on a, not just __getitem__ and __iter__. I'm not sure if that's exactly correct, though, since I don't think the generic type assumes anything other than "I can be indexed" and "I can be iterated over".

[jakebailey]

Reading through that thread also shows that def func(a: List) will show completions for a as though it were list, but def func(a: List[str]) will not, which seems to indicate that there's something else going on here.

[jakebailey]

typing.py says:

class List(list, MutableSequence[T], extra=list):

Which to me implies that it should be inheriting everything from list.

[brettcannon]

I have updated my comment to drop the a[0] case as that case works as demonstrated, but as @jakebailey realized the a case is not working as it should be showing all completions that list would show.