super() and automatic method combination

[Laszlo Zsolt Nagy]

>
>I have the impression that this is supposed to call the f method
>in both A and B, so it should print
>  
>
Not really true. The first parameter of 'super' should be a type, not an 
instance.

>   A
>   B
>   C
>or maybe
>  B
>  A
>  C
>depending on the resolution order.  However, it only calls A.f and not B.f.
>
>I also notice that if I say
>
>
>    class B(object):
>        def f(self):
>            super(B,self).f()
>            print 'b'
>
>then 
>  test(B)
>raises an exception since B has no superclass with an f method.  
>
Correct. When you use super(B,self) it accesses the current instance as 
the class B. If it has no method named 'f' then this will end up in an 
exception.

>That doesn't seem like such a good thing necessarily.
>  
>
But yes, it is. When you try to call a nonexistent method, it should 
raise an exception.

>Anyway, is there a preferred way of writing this example so that C.f
>automatically calls both A.f and B.f?
>  
>
I do not know a preferred way. However, I made this example for you, I 
hope it helps.


class CallSupersMixin(object):
    def callsupers(self,fname,*args,**kwargs):
        l = self.__class__.__bases__
        for cls in l:
            if hasattr(cls,fname):
                getattr(cls,fname)(self,*args,**kwargs)
            elif cls == CallSupersMixin:
                pass
            else:
                raise AttributeError("Base class %s does not have a 
method named %s " % ( str(cls),fname ) )
                   
       
class A(object):
    def f(self):
        print 'A.f called'
   
class B(object):
    def f(self):
        print 'B.f called'
       
class AB(A,B,CallSupersMixin):
    def f(self,*args,**kwargs):
        self.callsupers('f',*args,**kwargs)
   
ab = AB()
ab.f()


Of course you can remove the "raise AttributeError" part. Then it will 
call only the classes that have the given method.
I know it is not a very good example but you can go from here.
Best,

   Laci 2.0

-- 
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  Laszlo Nagy		      web: http://designasign.biz
  IT Consultant		      mail: gandalf at geochemsource.com

     		Python forever!