Since Python 3.3 a bug was fixed meaning the property() decorator is now correctly identified as abstract when applied to an abstract method.

Note: Order matters, you have to use @property above @abstractmethod

Python 3.3+: (python docs):

from abc import ABC, abstractmethod

class C(ABC):
    @property
    @abstractmethod
    def my_abstract_property(self):
        ...

Python 2: (python docs)

from abc import ABCMeta, abstractproperty

class C:
    __metaclass__ = ABCMeta

    @abstractproperty
    def my_abstract_property(self):
        ...

After some thought, I think the second code snippet does not use the Factory method as it is not concerned with the creation of objects.

However, the code can be refactored to use the Factory method and better communicate the intent:

class CraneInterface(ABC):

    def __init__(self):
        self.__axis = self._make_axis()

    @property
    def axis(self) -> AxisInterface:
        return self.__axis

    @abstractmethod
    def _make_axis(self) -> AxisInterface:
        """
        Factory method: "Subclasses override to change the class of object that will be created"
        """
        pass

import abc
from typing import ClassVar

from pydantic import BaseModel
from devtools import debug

class Fruit(BaseModel, abc.ABC):
    @property
    @abc.abstractmethod
    def type(self) -> str:
        """The name of the type of fruit."""

class Apple(Fruit):
    type: ClassVar[str] = "apple"
    size: int

a = Apple(size=4)
debug(a, a.type)

Unless you want to allow type to be changed when creating a model instance, in which case just make it a field on Fruit.

Python 3.3+

from abc import ABCMeta, abstractmethod


class A(metaclass=ABCMeta):
    def __init__(self):
        # ...
        pass

    @property
    @abstractmethod
    def a(self):
        pass

    @abstractmethod
    def b(self):
        pass


class B(A):
    a = 1

    def b(self):
        pass

Failure to declare a or b in the derived class B will raise a TypeError such as:

TypeError: Can't instantiate abstract class B with abstract methods a

Python 2.7

There is an @abstractproperty decorator for this:

from abc import ABCMeta, abstractmethod, abstractproperty


class A:
    __metaclass__ = ABCMeta

    def __init__(self):
        # ...
        pass

    @abstractproperty
    def a(self):
        pass

    @abstractmethod
    def b(self):
        pass


class B(A):
    a = 1

    def b(self):
        pass

A possibly a bit better solution compared to the accepted answer:

from better_abc import ABCMeta, abstract_attribute    # see below

class AbstractFoo(metaclass=ABCMeta):

    @abstract_attribute
    def bar(self):
        pass

class Foo(AbstractFoo):
    def __init__(self):
        self.bar = 3

class BadFoo(AbstractFoo):
    def __init__(self):
        pass

It will behave like this:

Foo()     # ok
BadFoo()  # will raise: NotImplementedError: Can't instantiate abstract class BadFoo
# with abstract attributes: bar

This answer uses same approach as the accepted answer, but integrates well with built-in ABC and does not require boilerplate of check_bar() helpers.

Here is the better_abc.py content:

from abc import ABCMeta as NativeABCMeta

class DummyAttribute:
    pass

def abstract_attribute(obj=None):
    if obj is None:
        obj = DummyAttribute()
    obj.__is_abstract_attribute__ = True
    return obj


class ABCMeta(NativeABCMeta):

    def __call__(cls, *args, **kwargs):
        instance = NativeABCMeta.__call__(cls, *args, **kwargs)
        abstract_attributes = {
            name
            for name in dir(instance)
            if hasattr(getattr(instance, name), '__is_abstract_attribute__')
        }
        if abstract_attributes:
            raise NotImplementedError(
                "Can't instantiate abstract class {} with"
                " abstract attributes: {}".format(
                    cls.__name__,
                    ', '.join(abstract_attributes)
                )
            )
        return instance

The nice thing is that you can do:

class AbstractFoo(metaclass=ABCMeta):
    bar = abstract_attribute()

and it will work same as above.

Also one can use:

class ABC(ABCMeta):
    pass

to define custom ABC helper. PS. I consider this code to be CC0.

This could be improved by using AST parser to raise earlier (on class declaration) by scanning the __init__ code, but it seems to be an overkill for now (unless someone is willing to implement).

2021: typing support

You can use:

from typing import cast, Any, Callable, TypeVar


R = TypeVar('R')


def abstract_attribute(obj: Callable[[Any], R] = None) -> R:
    _obj = cast(Any, obj)
    if obj is None:
        _obj = DummyAttribute()
    _obj.__is_abstract_attribute__ = True
    return cast(R, _obj)

which will let mypy highlight some typing issues

class AbstractFooTyped(metaclass=ABCMeta):

    @abstract_attribute
    def bar(self) -> int:
        pass


class FooTyped(AbstractFooTyped):
    def __init__(self):
        # skipping assignment (which is required!) to demonstrate
        # that it works independent of when the assignment is made
        pass


f_typed = FooTyped()
_ = f_typed.bar + 'test'   # Mypy: Unsupported operand types for + ("int" and "str")


FooTyped.bar = 'test'    # Mypy: Incompatible types in assignment (expression has type "str", variable has type "int")
FooTyped.bar + 'test'    # Mypy: Unsupported operand types for + ("int" and "str")

and for the shorthand notation, as suggested by @SMiller in the comments:

class AbstractFooTypedShorthand(metaclass=ABCMeta):
    bar: int = abstract_attribute()


AbstractFooTypedShorthand.bar += 'test'   # Mypy: Unsupported operand types for + ("int" and "str")