Problems with `get` on a TypedDict

Bug Report

This bug is a bit hard to describe, so you should take a look at the test code. Feel free to edit the title.

As you can see in the test code, a expects dict[Literal["exclude"], list[str]]. test_dict, which is passed to b has a opional key named key with this type. As this type is optional, we use get here. Get returns {"exclude": []}) in case key does not exists in test_dict. {"exclude": []}) fits the type dict[Literal["exclude"], list[str]] but Mypy think it does not fit.

This bug does not exists in Mypy 1.17.

To Reproduce

https://mypy-play.net/?mypy=1.18.2&python=3.12&gist=932063170e6ad2c3ab798153870b82d4

Expected Behavior

Mypy should not find any errors

Actual Behavior

main.py:13: error: Argument 1 to "a" has incompatible type "dict[Literal['exclude'], list[str]] | dict[str, list[Never]]"; expected "dict[Literal['exclude'], list[str]]"  [arg-type]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 1.18.2
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.13.7

Commencez par la reproduction mypy-play liée dans main.py, en l’exécutant avec mypy 1.17 et 1.18.2 afin d’isoler la régression. Suivez la manière dont les expressions get de clés facultatives de TypedDict infèrent leur type de repli ; c’est terminé lorsque la reproduction ne produit aucune erreur tout en conservant une vérification de type correcte.