How to avoid parallel class hierarchy in python

Question

I\'ve been running into a weird little smell in my python code lately and I think it has something to do with parallel inheritance. Here is a small example I concoc

Answer 1

This answer assumes that the DogHabits is much more complex than a mere list and is really worth a dedicated class with its own inheritance.

On a design point of view, I can see a first question on whether habits and type should be class or instance members. Here again, this answer assumes that there are reasons to make them instance members.

I would make Habits an inner class of Dogs and state in the class documentation that is can be customized by building a subclass of it in a subclass of Dogs:

 class Dog:
    class Habits:
        """Represents the habits of a Dog.

        It can be customized in a child class by creating in the subclass an
        inner class named Habits that would be a subclass of Dog.Habits
        """

        def __init__(self):
            self.habits = ['lick butt']

    def __init__(self, typ='generic_dog'):
        self.type = typ
        self.my_habits = self.__class__.Habits()

    def do_stuff(self):
        for habit in self.my_habits.habits:
            print(habit)


class GermanShepherd(Dog):

    class Habits(Dog.Habits):

        def __init__(self):
            super().__init__()
            self.habits.extend(['herd sheep'])

    def __init__(self):
        super().__init__('german shepherd')


class Labrador(Dog):

    class Habits(Dog.Habits):
        def __init__(self):
            super().__init__()
            self.habits.extend(['hunt', 'pee on owner'])

    def __init__(self):
        super().__init__('labrador')