@final(TypedDict).get() with unknown key returns object instead of None

[Dreamsorcerer]

See: #12143 (comment)

---

Original report:

With:

from typing import TypedDict, final

@final
class A(TypedDict):
    """Empty"""

a: A = {}
reveal_type(a.get("foo", None))

I expect to get None, but instead get object | Any.

Maybe the object should be replaced with None here? https://github.com/python/typeshed/blob/master/stdlib/typing.pyi#L717-L728
I'm not too sure how that works.

[97littleleaf11]

Actually the issue is get("missing_key", foo) cannot infer correct type. #9906 (comment) Jukka explained this before.

[jhance]

Does object | Any not still seem wrong? Going with the spirit of the comment we shouldn't be inferring an Any at all, it seems object | None would make more sense no?

[97littleleaf11]

Does object | Any not still seem wrong?

I can only get object on master branch

[Dreamsorcerer]

Actually the issue is get("missing_key", foo) cannot infer correct type. #9906 (comment) Jukka explained this before.

I think the real issue why this can't be inferred is the allowance of inheritance. I think there was a conversation about this elsewhere, but my example can't work, as you could create a subclass with any other type like:

class A(TypedDict): ...

class B(A):
    foo: str

b: B = {"foo": "bar"}
a: A = b
reveal_type(a.get("foo", None))

In the future, it might be possible to support my example using final types:

@final
class A(TypedDict): ...

At that point, there is no reason it can't be inferred. The key is a literal and it can be checked what type it should return (or no type if not present).

[roganov]

Another example of the issue:

import typing


@typing.final
class Node(typing.TypedDict):
    name: str
    children: list[typing.Union['Node', 'Leaf']]


@typing.final
class Leaf(typing.TypedDict):
    name: str


x: Node | Leaf
reveal_type(x.get('children', []))

The inferred type should be list[Node], not builtins.object.

[ilevkivskyi]

Just to confirm for more visibility: @final decorator on TypedDicts is now soft-deprecated (and is only supported on the best effort basis), for all relevant use cases, please use PEP 728 closed=True.