python method resolution order and diamond inheritance

Question

Here is an example model of what I have in my python code

class BasicActivity:
    def run(self):
        print "basic run"

    def jump(self):
        print "basic jump"

class ChickenStyleActivity(BasicActivity):
    def run(self):
        print "run like chicken"

class BunnyStyleActivity(BasicActivity):
    def jump(self):
        print "jump like bunny"

class ExtraordinaryActivity(ChickenStyleActivity,BunnyStyleActivity):
    pass

d = ExtraordinaryActivity()
d.run()
d.jump()

I was expecting to have both chicken and bunny styles in one class, but surprisingly for me it was chicken run but basic jump. I started reading about method resolution order and now I can see that changing order of classes in multiple inheritance will bring the opposite effect.

The question is - how can I have both Chicken and Bunny styles in one class?

More generally: how to properly inherit several classes which have common base class when method overriding comes into play?

score 4 · Accepted Answer · edited May 23 '17 at 10:34

4

I think you're using Python 2.x, not Python 3.x.

Therefore BasicActivity needs to inherit from object:

class BasicActivity(object):
    pass

Alex Martelli describes it here: Method Resolution Order (MRO) in new style Python classes

In Python 3 all classes inherit from object

edited May 23 '17 at 10:34

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answered Sep 06 '12 at 09:47

Dave Halter

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for the sake of completeness: old-style classes (ones that don't inherit from object) use depth-first left-to-right method resolution order. – soulcheck Sep 06 '12 at 09:55
no, I'm using python2.7, but your solution works - I kept methods in Base class, just modified it to inherit from `object` and now I have both overridden versions in my top class. Thanks! – pavel_kazlou Sep 06 '12 at 09:56
I didn't mean python2.0, I meant 2.x. – Dave Halter Sep 06 '12 at 09:58
so in python 3 my sample would work without inheriting from `object`? – pavel_kazlou Sep 06 '12 at 10:00
Exactly. Basically you shouldn't use old style classes in 2.7, because they are not forward-compatible. – Dave Halter Sep 06 '12 at 10:05

python method resolution order and diamond inheritance

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