I'm rewriting a design application for a science fiction game. in it you design your own starships. Each component has a mass and cost, but the mass can either be fixed or it can be expressed as a percentage of the tonnage of the overall ship.
Orriginaly I thought I'd need to have a hull object which contains component objects, but the component objects need access to members of the hull object (e.g. the hull size) so that looks messy to implement. I have defined a base class Component with a class member variable 'hull_size' so that all components can see the hull size. I've then got two child classes called Fixed_Component and Percent _Component that implement their mass, mass_percent and cost properties appropriately for their type. I've also defined a Hull class which also inherits from Component and provides methods for access to the hull_size class variable. I'm not sure where to go from here. One possibility is to have a Ship object containing a list of components, but I'd need to have a way to ensure there's only ever one hull object so maybe that shouldn't go in the list? I think the fact that the hull_size is a class member also means I can't ever have an application that loads two designs at the same time, because they'd share the same hull_size class variable. Is that so, and is there a way round that? I suspect the inheritance model will work fine at first, but is too rigid in the long run. Is there a way to cleanly implement a parent-child relationship between objects that gives child objects limited access to members of the parent? Simon Hibbs -- http://mail.python.org/mailman/listinfo/python-list
