TypedDict.values() always returns object.

[Dreamsorcerer]

from typing import TypedDict

class A(TypedDict):
    a: str

def foo(a: A):
    for v in reveal_type(a.values()):
        v.lower()

This produces:

test.py:7: note: Revealed type is 'typing.ValuesView[builtins.object]'
test.py:8: error: "object" has no attribute "lower"
Found 1 error in 1 file (checked 1 source file)

Expected Behavior

TypedDict.values() to return a different type if all values of a TypedDict are of the same type.

Your Environment

• Mypy version used: 0.910

[JukkaL]

TypedDict types support structural subtyping, so it's always possible that there is a subtype of A that has a value with a non-str type:

class B(TypedDict):
    a: str
    b: int

b: B = {'b': 1, 'a': 'y'}
foo(b)

One way to make this work as proposed could be to support final TypedDict types that don't allow additional keys in subtypes.

[Dreamsorcerer]

I think when I use TypedDict, I'm always thinking about it as not allowing additional keys. So, I guess a final type is probably what I'm missing (though, generally, I'd still like it to be subclassable, just the opposite of total=False).

[JelleZijlstra]

Pyright supports @Final TypedDicts; it would be a useful addition for mypy too. Not sure if there's already an issue about it.

[JukkaL]

Created #12266.