Mypy tries to instantiate an abstract class

[tal-zvon]

mypy version 0.942

With test.py like this:

from abc import ABC, abstractmethod

class AbstractClass(ABC):
    @abstractmethod
    def method(self):
        pass

class ConcreteClass1(AbstractClass):
    def method(self):
        print("hello")

class ConcreteClass2(AbstractClass):
    def method(self):
        print("hello")

class ConcreteClass3(AbstractClass):
    def method(self):
        print("hello")

classes = [
    ConcreteClass1,
    ConcreteClass2,
    ConcreteClass3,
]

for c in classes:
    c().method()

Mypy shows:

test.py:27: error: Cannot instantiate abstract class "AbstractClass" with abstract attribute "method"

Some weird behavior I've noticed:

If, instead of a loop, I do this:

...
ConcreteClass1().method()
ConcreteClass2().method()
ConcreteClass3().method()

mypy is happy.

Also, if, instead of 3 classes in the loop, I do 2:

classes = [
    ConcreteClass1,
    ConcreteClass2,
    #ConcreteClass3,
]

for c in classes:
    c().method()

mypy is happy with that as well.
I posted this on stackoverflow, and this seems to be a bug.

This can be worked around by explicitly defining the type of list:

classes: List[Type[AbstractClass]] = [
    ConcreteClass1,
    ConcreteClass2,
    ConcreteClass3,
]

[AlexWaygood]

Duplicate of #3115