from abc import ABC, abstractmethod

class Foo(ABC):
    @classmethod
    @property
    @abstractmethod
    def x(cls):
        pass

class Bar(Foo):
    x = 1

# This works (but is hacky, and possibly shouldn't work).
Bar()


class FooToo(ABC):
    @property
    @abstractmethod
    def x(self):
        pass

class BarToo(FooToo):
    def __init__(self):
        self.x = 1

# This does not work.
BarToo()