class decorators that change the type don't work

[DetachHead]

def deco(value) -> int:
    ...
    
@deco
class Class:
    ...
    
reveal_type(Class) # note: Revealed type is "def () -> __main__.Class"

@deco
def function(): ...

reveal_type(function) # note: Revealed type is "builtins.int"

https://mypy-play.net/?mypy=latest&python=3.10&gist=705baa296d3181f0b670416a405978b4

[CyanoKobalamyne]

Are there any plans for fixing this? I'm using a class decorator that is a class itself (thereby transforming the original class into an instance of the decorator), and running into issues where mypy is inferring the wrong type.

Here is a simplified example:

from typing import Generic, Type, TypeVar

T = TypeVar("T")

class Deco(Generic[T]):
    def __init__(self, cls: Type[T]):
        self._cls = cls

    def get(self) -> T:
        return self._cls()

@Deco
class Klass:
    ...

reveal_type(Deco)  # note: Revealed type is 'def [T] (cls: Type[T`1]) -> __main__.Deco[T`1]'
reveal_type(Deco.get)  # note: Revealed type is 'def [T] (self: __main__.Deco[T`1]) -> T`1'
reveal_type(Klass)  # note: Revealed type is 'def () -> __main__.Klass'
reveal_type(Klass.get)  # error: "Type[Klass]" has no attribute "get" 

[JelleZijlstra]

Duplicate of #3135

[DetachHead]

@JelleZijlstra that looks like a different issue that's since been fixed, since mypy now shows an error on invalid class decorators:

decorator: int = 3

@decorator  # error: "int" not callable  [operator]
class A:
    pass

playground

my issue is that class decorators aren't able to change the type of the class they're decorating:

def decorator(cls: type[object]) -> int: ...


@decorator  
class A:
    pass


reveal_type(A) # `def () -> __main__.A`, should be `int`

so i suggest either closing the original issue and re-opening this one, or updating the original issue with a new example (and maybe change its title)

[SeeFrenchDev]

same issue, does someone knows how to fix it?