Thanks a lot folks for all the help. Its a lot clearer now. If I could summarise my original misunderstanding about inheritance:
I belived that a sub class inherited a *specific instance* of the super class. This is clearly not right - the misunderstanding arose as I was instantiating the super class from within the base class. As people have pointed out it seems strange to instantiate an 'animal' and then only later decide that it is a 'fish' or a 'bird'. Obviously my code is an analogy to the problem I'm tackling. What I'm doing is a bit more abstract: I'm instantiating a 'world' (as a super class) and then various 'worldviews' as sub-classes. The 'worldviews' must know about various aspects of the 'world' from which they are instantiated to be able to do what they need to do (as the 'bird' needs to know about 'weight' and 'colour' to be able to describe itself). Passing these aspects forward to the constructor of the sub class is the solution I've implemented and it works and looks sensible. Thanks again to all, Lorcan. -- http://mail.python.org/mailman/listinfo/python-list
