Set and Dict generalizing the type unnecessarily

Bug Report

See these two example functions:

def f(items: list[str] | list[int]) -> None:
    items_as_set: set[str] | set[int] = set(items)

def g(key_to_count: dict[str, float] | dict[int, float]) -> None:
    key_to_count_2: dict[str, float] | dict[int, float] = {k: v for k, v in key_to_count.items()}

Mypy 1.10.0 complains about the assignment in each of them:

test_mypy_dict.py:2: error: Incompatible types in assignment (expression has type "set[object]", variable has type "set[str] | set[int]")  [assignment]
test_mypy_dict.py:5: error: Incompatible types in assignment (expression has type "dict[str | int, float]", variable has type "dict[str, float] | dict[int, float]")  [assignment]

To Reproduce

Playground gist: https://mypy-play.net/?mypy=latest&python=3.12&gist=83bde5f3f11470e94b6a680158649641

Expected Behavior

The set() or dict() operation applied on a variable that is either a list[str] | list[int] is always either a set[str] or set[int]. The same applies to function g using a dict. Thus the functions should not raise a mypy error.

Workarounds

I tried two workarounds:

• Using a mixed type of list[str | int]. However, I get the type list[str] | list[int] by an external function, thus this is not compatible.
• Using a generic. This is not working either.

See the playground gist: https://mypy-play.net/?mypy=latest&python=3.12&gist=264490179628a0a214a2e5bd947b8ccf

Commencez par exécuter les deux reproductions Python de l’issue, y compris les exemples mypy-play liés, puis comparez les types inférés et les erreurs d’affectation pour set() et la dict comprehension. Suivez le chemin de vérification des types pour ces expressions de constructeur et de comprehension ; le travail est terminé lorsque les deux fonctions sont vérifiées sans erreur tout en préservant l’union de types de conteneurs homogènes.