Recipe that uses abstract properties and abstract initialization in Python 2

abstract_init.py

#!/usr/bin/env python

from abc import ABCMeta, abstractmethod, abstractproperty

def get_fromcls(cls, num):
    return cls.myinit(num)

class Abs(object):
    __metaclass__ = ABCMeta

    def __init__(self, num):
        self._num = num

    @abstractproperty
    def num(self):
        pass

    @abstractmethod
    def myinit(cls, num):
        pass


class Concr1(Abs):
    # __init__ method has no argument
    # but myinit must be consistent with the interface
    def __init__(self):
        self._num = 42

    @property
    def num(self):
        return self._num

    @classmethod
    def myinit(cls, num):
        return cls()


class Concr2(Abs):
    def __init__(self, num):
        self._num = 3*num

    @property
    def num(self):
        return 7*self._num

    @classmethod
    def myinit(cls, num):
        return cls(2*num)


def main():
    # outputs
    # 42
    # 42
    for cls in [Concr1, Concr2]:
        obj = get_fromcls(cls, 1)
        print('{}'.format(obj.num))

if __name__ == '__main__':
    main()