In article <[EMAIL PROTECTED]>, "Paul McGuire" <[EMAIL PROTECTED]> wrote: ... > This reminds me of some maddening O-O discussions I used to > have at a former place of employment, in which one developer cited > similar behavior for not having Square inherit from Rectangle - calling > Square.setWidth() would have to implicitly call setHeight() and vice > versa, in order to maintain its squarishness, and thereby broke Liskov. > I withdrew from the debate, citing lack of context that would have > helped resolve how things should go. At best, you can *probably* say > that both inherit from Shape, and can be drawn, have an area, a > bounding rectangle, etc., but not either inherits from the other.
This Squares and Rectangles issue sounds debatable in a language like C++ or Java, where it's important because of subtype polymorphism. In Python, does it matter? As a user of Square, I'm not supposed to ask about its parentage, I just try to be clear what's expected of it. There's no static typing to notice whether Square is a subclass of Rectangle, and if it gets out that I tried to discover this issubclass() relationship, I'll get a lecture from folks on comp.lang.python who suspect I'm confused about polymorphism in Python. This is a good thing, because as you can see it relieves us of the need to debate abstract principles out of context. It doesn't change the real issues - Square is still a lot like Rectangle, it still has a couple of differences, and the difference could be a problem in some contexts designed for Rectangle - but no one can fix that. If you need Square, you'll implement it, and whether you choose to inherit from Rectangle is left as a matter of implementation convenience. Donn Cave, [EMAIL PROTECTED] -- http://mail.python.org/mailman/listinfo/python-list
