Abstract class properties that are classes incorrectly reported in assignments

• Are you reporting a bug, or opening a feature request?
  I believe this is a bug.

• Please insert below the code you are checking with mypy

from abc import ABC, abstractmethod
from typing import Type


class ISolution(ABC):
    @abstractmethod
    def __init__(self, b: int):
        pass

    @abstractmethod
    def func1(self, a: int) -> int:
        pass


class MySolution(ISolution):
    def __init__(self, b: int):
        self._b = b

    def func1(self, a: int) -> int:
        return a + self._b


class IHolder(ABC):
    @property
    @classmethod
    @abstractmethod
    def SolutionClass(cls) -> Type[ISolution]:
        pass

    # SolutionClass: Type[ISolution]

    @abstractmethod
    def __init__(self, c: int):
        pass

    @abstractmethod
    def cval(self) -> int:
        pass


class Main(IHolder):
    SolutionClass = MySolution

    def __init__(self, c: int):
        self._c = c

    def cval(self) -> int:
        return self._c


def check(holderclass: Type[IHolder], a: int, b: int, c: int) -> bool:
    holder = holderclass(c)
    solclass: Type[ISolution] = holderclass.SolutionClass
    return solclass(b).func1(a) == holder.cval()


print("should be true ", check(Main, 5, 5, 10))
print("should be false ", check(Main, 3, 4, 10))

• What is the actual behavior/output?

classprop.py:53: error: Incompatible types in assignment (expression has type "Callable[[], Type[ISolution]]", variable has type "Type[ISolution]")

This is referring to the line:

    solclass: Type[ISolution] = holderclass.SolutionClass

• What is the behavior/output you expect?
  No error to be reported.

Note. If you comment out

    @property
    @classmethod
    @abstractmethod
    def SolutionClass(cls) -> Type[ISolution]:
        pass

and then uncomment

    SolutionClass: Type[ISolution]

then mypy says the code is fine.

• What are the versions of mypy and Python you are using?
  mypy 0.770
  python 3.7.6

• Do you see the same issue after installing mypy from Git master?
  I'm trying to avoid dealing with that!

• What are the mypy flags you are using? (For example --strict-optional)
  None

首先，使用提供的抽象类、property 和 classmethod 示例重现该诊断。将 holderclass.SolutionClass 的类型推断与带注解的类属性版本进行比较，然后验证对 solclass 的赋值不再报告不兼容的类型。