Inheritance and Design Question

[Scott David Daniels]

imageguy wrote:
> I have an object the I would like to use as a base class.  Some of the
> methods I would like to override completely, but others I would simply
> like to call the base class method and use the return value in the
> child method.  The purpose here is to eliminate the duplication of
> valuable code in the parent, when I really just need the child to
> operate of a results of the parent.
> 
> Consider the following two classes;
> 
> class Parent(object):
>     def process(self, value):
>         retval = "Parent.result('%s')" % value
>         return retval
> 
> class Child(Parent):
>     def __init__(self):
>         Parent.__init__(self)
> 
>     def process(self, value):
>         retval = "Child.result('%s')" % super(Child, self).process
> (value)
>         return retval
> 
> So ....
> 
> foo = Child()
> print foo.process('the value')
>>> Child.result('Parent.result('the value')')
> 
> IS there another pattern or idiom that would accomplish this?
> This seems a bit 'smelly' to me.  Also seems almost the inverse of
> decorators, but I am not sure decorators would be appropriate in this
> case.
> 
> Any help suggestions would be appreciated.
> 
> g.
Just don't replace the methods you want to use from the superclass
-- it really is that simple.  Notice how str is changed below,
but not repr:

     class GroupedInt(int):
         def __str__(self):
             old = super(GroupedInt, self).__str__()
             first = old[: len(old) % 3 or 3]
             if first == '-':
                 first = old[: 4]
             parts = [first]
             parts.extend(old[n : n + 3] for n in
                               range(len(first), len(old), 3))
             return '_'.join(parts)

     for n in 1, 12, 123, 1234, 12345, 123456, 1234567:
	print '%s\t%s=%r\t%s=%r' % (n, GroupedInt(n),  GroupedInt(n),
                                        GroupedInt(-n), GroupedInt(-n))

1	1=1	-1=-1
12	12=12	-12=-12
123	123=123	-123=-123
1234	1_234=1234	-1_234=-1234
12345	12_345=12345	-12_345=-12345
123456	123_456=123456	-123_456=-123456
1234567	1_234_567=1234567	-1_234_567=-1234567

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