Return type of dict.get is wrong when using strict optional checking

[JukkaL]

The revealed type in the following program is int though it should be Optional[int] when using --strict-optional:

d = {'x': 1}
a = d.get('y')
reveal_type(a)

This also needs a typeshed change, but I think that there was a mypy issue with overloaded functions that is related. It's worth having a separate issue to track this here.

[gvanrossum]

I think this is relevant: python/typeshed#223 (comment)

[ambv]

Currently landed PR for this feature in typeshed: python/typeshed#822. Contains a Union[] return type so might have to be fixed to simple @overload.

[ilevkivskyi]

It looks like this is fixed on master, I get:

Revealed type is 'Union[builtins.int*, builtins.None]'

[gvanrossum]

(Also, if you pass an explicit default of a different type, it becomes a union of int and that type, regardless of the --strict-optional setting. IIRC that was a problem in the past too.)