Dict, List and Set are imported by default

[gvanrossum]

This code (no import from typing) complains, as expected:

a = None  # type: Any

However, this code passes:

a = None  # type: Dict

Similar with List, Set.

[JukkaL]

Ah, seems like a problem with how mypy handles generic type aliases, such as Dict -> dict. Not sure exactly why this happens, but my guess is that they leak from builtins.pyi somehow.

[gvanrossum]

FWIW the same thing happens to Set. I don't believe there are other types that have this issue; those three (List, Dict, Set) are treated special by mypy. See https://github.com/python/mypy/blob/master/mypy/nodes.py#L74

[gvanrossum]

This is a bit thorny to fix, because Dict/List/Set are currently implemented as aliases to dict/list/set, and all the genericity is specified in typeshed/*/builtins.pyi.

I propose not to worry too much about it for 0.3.2.

[JukkaL]

Agreed. Maybe move this to 0.3.3?

[gvanrossum]

Moved to 0.3.3.