-2
class A(object):
    def show(self):
        print 'A'

class B(A):
    def show(self):
        super(B,self).show()
        print 'B'

class C(A):
    def show(self):
        #A.__init__(self)
        super(C,self).show()
        print 'C'

class D(B,C):
    def show(self):
        super(D,self).show()

d=D()
print d.show()

Why is the result: 

A
C
B

instead of:

A
B
C
Thierry Lathuille
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Jack1222
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1 Answers1

1

Because this is exactly what you have asked) Reed more info on c3 linearization. Short hint - super does not call parents method, instead it calls method, that corresponds to next class in linearized inheritance graph.

More specifically:

>>> D.mro()
0: [<class '__main__.D'>,
    <class '__main__.B'>,
    <class '__main__.C'>,
    <class '__main__.A'>,
    <class 'object'>
   ]

This mro thing is a list, through witch any method of class D that delegates its behavior to parents (sort of speak) would be pushed any time you call it. So you call D().show() - first it calls implementation of show in D, it does nothing but delegating this call further - to class B. Class B fist delegates this call to C (see the mro list) which delegates it further to A, which prints "A", then C prints "C" and then B prints "B".

You might ask - why B delegates to C instead of A (since B extends A, not C). This actually done on purpose, for more info have a look on this great talk

hello world
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