Python 2.3.3 super() behaviour

[Peter Otten]

Nicolas Lehuen wrote:

> Hi,
> 
> I hope this is not a FAQ, but I have trouble understanding the behaviour
> of the super() built-in function. I've read the excellent book 'Python in
> a Nutshell' which explains this built-in function on pages 89-90. Based on
> the example on page 90, I wrote this test code :
> 
> class A(object):
>     def test(self):
>         print 'A'
> 
> class B(object):
>     def test(self):
>         print 'B'
> 
> class C(A,B):
>     def test(self):
>         super(C,self).test()
>         print 'C'
> 
> print C.__mro__
> c=C()
> c.test()
> 
> The output is :
> (<class '__main__.C'>, <class '__main__.A'>, <class '__main__.B'>, <type
> 'object'>)
> A
> C
> 
> Whereas I was expecting :
> (<class '__main__.C'>, <class '__main__.A'>, <class '__main__.B'>, <type
> 'object'>)
> A
> B
> C
> 
> Was I wrong to expect this (based on what I've read ?)

As soon as a test() method without the super(...).test() is reached, no
further test methods will be invoked. Only the first in the list of base
classes will be invoked. If I'm getting it right you have to do something
like:

class Base(object):
    def test(self):
        print "base"

class D1(Base):
    def test(self):
        super(D1, self).test()
        print "derived 1"

class D2(Base):
    def test(self):
        super(D2, self).test()
        print "derived 2"

class All(D1, D2):
    pass

All().test()

Here all cooperating methods have a super() call, and the base class acts as
a showstopper to prevent that Python tries to invoke the non-existent
object.test().

Peter