Support Unpack with dict for keyword arguments: **kwargs: Unpack[dict[Literal["test"], ...]]

[intgr]

Bug Report

Mypy has support for declaring kwargs as **kwargs: Unpack[SomeTypedDict].

However, sometimes for dicts with uniform value types, it's more convenient to declare them in terms of dict[Literal["key", "another"], ...]. Other times it's a pragmatic work-around to the lack of support for @final declaration for TypedDict (#7981).

To Reproduce

This should pass mypy checking:

from typing import Literal, Unpack

def example(**kwargs: Unpack[dict[Literal["test"], int]]):
    #                        ^^^^
    pass

example(test=123)

Playground link

Actual Behavior

Rejected by mypy with the following error:

error: Unpack item in ** argument must be a TypedDict [misc]

Your Environment

• Mypy version used: 1.10.0
• Python version used: 3.12.3

[intgr]

FWIW, Pyright also rejects this: https://pyright-play.net/?pyrightVersion=1.1.353&pythonVersion=3.12&pythonPlatform=Linux&strict=true&locale=en&code=GYJw9gtgBALgngBwJYDsDmUkQWEMoAySMApiAIYA2ANFAKooLkDGA1gFDsAmJwUJAD3LZKJABQAqCawDu5EGgDOALnqMWrANpckzGJqKkKlTQCJSimKYC6tVDGvWAlMvZR3UJosWdBwhKJiFjAAvACMAEwAzE7sQA

[intgr]

Also when implementing this, it might be useful to allow Mapping/MutableMapping in these contexts as well:

from collections.abc import Mapping
from typing import Literal, Unpack

def example(**kwargs: Unpack[Mapping[Literal["test"], int]]):
    #                        ^^^^^^^
    pass

example(test=123)

[AlexWaygood]

I think you'd probably need to write a PEP if you want to expand the use of Unpack in this way

[erictraut]

What you're proposing here is not allowed by the typing spec currently. If you want to see something like this, you would need to extend the typing spec, probably through a new PEP as @AlexWaygood suggests. If you're interested in pursuing this, I recommend starting a discussion in the Python typing forum to see if you can gain support and consensus for such an idea.

[intgr]

Posted to typing forum: https://discuss.python.org/t/proposal-support-unpack-dict-for-typing-keyword-arguments/53380