[Tutor] super() and inherited attributes?

[Brian van den Broek]

Marcus Goldfish said unto the world upon 28/06/2005 00:58:
> Hi,
> 
> The following example doesn't work as I would like-- the child
> instance doesn't expose the attribute set in the parent.  Can someone
> point out what I am missing?
> 
> Thanks,
> Marcus
> 
> 
> class Parent(object):
>    def __init__(self, name="I am a parent"):
>       self.name = name
> 
> class Child(Parent):
>    def __init__(self, number):
>       super(Parent, self).__init__("I am a child")
>       self.number = number
> 
> # I would like it to produce the following:
> 
>>>c = Child(23)
>>>c.number
> 
> 23
> 
>>>c.name
> 
> "I am a child"
> 
> # but I 'AttributeError: 'Child' object has no attribute 'name''

Hi Marcus,

Try it this way:

 >>> class Parent(object):
         def __init__(self, name="I am a parent"):
             self.name = name


 >>> class Child(Parent):
         def __init__(self, number):
             # Note change here in super()
             super(Child, self).__init__("Finally, I'm a child!")
             self.number = number


 >>> c = Child(42)
 >>> c.number
42
 >>> c.name
"Finally, I'm a child!"


Take a look at these classes, and perhaps they will help clear up any 
residual puzzlement.

 >>> class A(object):
         def do_it(self):
             print "From A"

		
 >>> class B(A):
         def do_it(self):
             print "From B"

		
 >>> class C(B):
         def do_it(self):
            # look for do_it in B's superclass (i.e. A)
            super(B, self).do_it()

            # look for do_it in C's superclass (i.e. B)
            super(C, self).do_it()

		
 >>> c = C()
 >>> c.do_it()
 From A
 From B
 >>>

HTH,

Brian vdB