TypedDict doesn't respect subtypes or promoted types.

[rowillia]

Repro:

test_typed_dict_return_value.py

from mypy_extensions import TypedDict

TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': float, 'y': float})

def create_tagged_point():
    # type: () -> TaggedPoint
    return TaggedPoint(type='2d', x=42, y=1337)

$ mypy test_typed_dict_return_value.py
test_typed_dict_return_value.py:9: error: Incompatible return value type (got "TypedDict(type=str, x=int, y=int)", expected "TaggedPoint")

As an aside, the error message above is fairly hard to decode. It took me a few hours to realize what was going on.

The problem also exists with Any types:

from mypy_extensions import TypedDict

TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': int, 'y': int})

def create_tagged_point(some_value):
    # type: (Any) -> TaggedPoint
    return TaggedPoint(type=some_value.type, x=some_value.x, y=some_value.y)

[gvanrossum]

It took me some time to understand the bug report too... It seems that the failure (with --py2 only) is due to str not being an exact match for Text?

(I wouldn't call that duck typing (mypy makes special allowances for str -> Text and int -> float called "type promotions"), so the subject didn't help me.)

[rowillia]

@gvanrossum Sorry for the obtuse bug report...it took me a bit to figure out what was going on. I changed the example to not rely on the --py2 flag. The core of the issue is SubtypeVisitor.visit_typeddict_type was checking for type equivalence rather than a subtype - https://github.com/python/mypy/blob/master/mypy/subtypes.py#L214. I have a PR that fixes this - #2621

[JukkaL]

#2621 (comment) describes an alternative way to fix this.