GenericAlias is not compatible with type?

[shcheklein]

Trying to understand if this is a bug or not:

a: type = list[int]

works fine, but:

a: type = list[type(1)]

gives:

test.py:2:11: error: Type expected within [...]  [misc]
    a: type = list[type(1)]
              ^
test.py:2:11: error: Incompatible types in assignment (expression has type "GenericAlias", variable has type "type")  [assignment]
    a: type = list[type(1)]
              ^~~~~~~~~~~~~
Found 2 errors in 1 file (checked 1 source file)

[sobolevn]

Yes, it is expected. MyPy does not evaluate type() call in this case.

[shcheklein]

Why does it have to evaluate it though? type returns Type I assume? (we don't need to know the exact type int in this case, no?).

Also, why do we have the second error? list[int] is also has type of GenericAlias AFAIU, and it assigns it fine to a: type.

[erictraut]

I would consider this a bug in mypy. This is a value expression, not a type expression, so mypy should not be applying rules that apply to type expressions. By comparison, pyright does not generate an error here.

In mypy's defense, the typing spec is silent on this topic. Draft PEP 747 may help provide additional clarity about this matter.

[Aalian123]

Using type in type hints confusing the type checker. It expects a different type or generic type not type evaluations inside type annotations.