How to perform partial inheritance

Question

I have two classes for example:

class Parent(object):

    def hello(self):
        print 'Hello world'

    def goodbye(self):
        print 'Goodbye world'


class Child(Parent):
    pass

class Child must inherit only hello() method from Parent and and there should be no mention of goodbye(). Is it possible ?

ps yes, I read this

Important NOTE: And I can modify only Child class (in the parent class of all possible should be left as is)

Could you elaborate on what is unsatisfactory with the answer given there? — shu zOMG chen, Jun 26 '12 at 09:12
possible duplicate of [Is it possible to do partial inheritance with Python?](http://stackoverflow.com/questions/5647118/is-it-possible-to-do-partial-inheritance-with-python) — Ignacio Vazquez-Abrams, Jun 26 '12 at 09:14
It's technically possible (with a few dirty hacks), but it's a sure design smell. What's your real use case ? — bruno desthuilliers, Jun 26 '12 at 09:17
adding to bruno: check out [How to inherit only a small part of methods from a large class?](https://www.sololearn.com/Discuss/1314620/how-to-inherit-only-a-small-part-of-methods-from-a-large-class-a-into-a-new-class-b-without). Best answer indicates: your class design is messed up, if you want to do that. — PythoNic, Aug 12 '22 at 12:31

score 18 · Accepted Answer · answered Jun 26 '12 at 09:50

The solution depends on why you want to do it. If you want to be safe from future erroneous use of the class, I'd do:

class Parent(object):
    def hello(self):
        print 'Hello world'
    def goodbye(self):
        print 'Goodbye world'

class Child(Parent):
    def goodbye(self):
        raise NotImplementedError

This is explicit and you can include explanation in the exception message.

If you don't want to use a lot of methods from the parent class a better style would be to use composition instead of inheritance:

class Parent(object):
    def hello(self):
        print 'Hello world'
    def goodbye(self):
        print 'Goodbye world'

class Child:
    def __init__(self):
        self.buddy = Parent()
    def hello(self):
        return self.buddy.hello()

score 3 · Answer 2 · answered Jun 26 '12 at 09:49

3

class Child(Parent):
    def __getattribute__(self, attr):
        if attr == 'goodbye':
            raise AttributeError()
        return super(Child, self).__getattribute__(attr)

answered Jun 26 '12 at 09:49

Aleksei astynax Pirogov

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I dont need raise exception I just need that this method is missing – Denis Jun 26 '12 at 09:53
@Denis: please try to call an inexistant method on any object and see what happens (yes, an AttributeError is raised). – bruno desthuilliers Jun 26 '12 at 10:03

score 1 · Answer 3 · edited Jul 14 '12 at 22:12

1

This Python example shows how to design classes to achieve child class inheritance:

class HelloParent(object):

    def hello(self):
        print 'Hello world'

class Parent(HelloParent):
    def goodbye(self):
        print 'Goodbye world'


class Child(HelloParent):
    pass

edited Jul 14 '12 at 22:12

octopusgrabbus

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answered Jun 26 '12 at 09:30

yedpodtrzitko

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This is a good solve but I cant change composition or use Mixin classes. Anyway +1 – Denis Jun 26 '12 at 09:33
This is a good answer on design level, thanks for pointing it out. – PythoNic Aug 12 '22 at 12:22

How to perform partial inheritance

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