Type not narrowed with keyboard in and list

[edaqa-uncountable]

In the following code I was expecting the type of item to be narrowed inside the conditional. Instead I get an error message about an incompatible return type. The code following the conditional shows that two separated checks do narrow the type.

from typing import TypeVar

VariantResult = dict | None
MISSING: VariantResult = {}
T = TypeVar("T")


def get_something(key: int, default: T) -> int | T:
    """ Trying to mimic the type of the "dict.get" method """
    return default


def check() -> VariantResult:
    item = get_something(123, MISSING)

    if item in [None, MISSING]:
        return item  # Error here*

    if item == None:
        return None
    if item == MISSING:
        return MISSING

    return {}

*Error: mypy :return-value Incompatible return value type (got "Union[int, Dict[Any, Any], None]", expected "Optional[Dict[Any, Any]]")

The error is unexpected since item can only be one of None or INVALID_SPEC, which are both valid for the result of VariantResult. If they weren't, then the following returns would also fail, but they do not.

[edaqa-uncountable]

Additionally, the code following the if ... in does not narrow the type either. While there is no way to exlclude the MISSING type, the None type should be excluded. But the item is still marked as | None after the if statement, this fails:

...
def require_int(value: int) -> None:
   pass

require_int(item)  # Type error, may not be None

[A5rocks]

Yes, this is a good idea.

Duplicate of #10977 though

[AlexWaygood]

Duplicate of #10977 though

Indeed