A superclass using a child classes' methods

[Michael Torrie]

Kurt Schwehr wrote:
> I'm trying to build an OO system for encoding and decoding
> datapackets.  I'd like the parent class to have an encode function
> that uses each of the child classes' packing methods.  It appears that
> this works for attributes of children accessed by the parent, but not
> for methods.  Is that right?  For attributes I found this example,
> where the alphabet attribute is set in the child, but used in the
> parent.

There is no difference between an attribute and a method.  They are both
attributes.  One happens to be callable and is a method call.

I just tried it and it seemed to work fine.  In my old C++ days, I
believe you would call this scenario virtual classes.  In python, since
everything is dynamic and computed at runtime, I think you can just
refer to any attribute in the instance and as long as someone down the
road provides it, it would work.

For example:

class parent(object):
    def test(self):
        print self.child_attribute
        self.child_method()

class child(parent):
    def __init__(self):
        self.child_attribute = 'child'

    def child_method(self):
        print 'child method is called'


c=child()
c.test()

This should display "child" and "child method is called"