super() and automatic method combination

[Scott David Daniels]

Laszlo Zsolt Nagy wrote:
> 
>> The trick is that C.f only calls A.f, but A.f needs to end up calling 
>> B.f when it is used in a C.
>>  
>>
> I believe your response only applies to single inheritance. For classes 
> with muliple bases classes, you need to call the base methods one by one.
> 
> BTW I prefer to call the base methods in this form:
> 
> class AB(A,B):
>    def f(self):
>       A.f(self)
>       B.f(self)
> 
> This arises the question: is there a difference between these:
> 
> super(A,self).f()  # I do not use to use this....
> A.f(self)
> 
The difference is when you have a diamond inheritance diagram.
Here is a simple example:

class Bottom(object):
     def f(self):
         print 'Bottom'

class A(Bottom):
     def f(self):
         print 'A',
         super(A, self).f()

class B(Bottom):
     def f(self):
         print 'B',
         super(B, self).f()

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

C().f()

C A B Bottom

-------
Versus:
-------

class Bottom(object):
     def f(self):
         print 'Bottom'

class A(Bottom):
     def f(self):
         print 'A',
         Bottom.f(self)

class B(Bottom):
     def f(self):
         print 'B',
         Bottom.f(self)

class C(A, B):
     def f(self):
         print 'C',
         A.f(self)
         B.f(self)

C().f()

C A Bottom
B Bottom

--Scott David Daniels
Scott.Daniels at Acm.Org