On Sat, Nov 1, 2014 at 8:40 AM, Rob Gaddi <rgaddi@technologyhighland.invalid> wrote: > For this specific exercise, a Square is a subclass of Rectangle because > the point of Rectangle is to demonstrate that extraneous get/set > functions are completely unnecessary in Python. The point of > Square is to demonstrate that get/set functions can be useful in > certain circumstances where you need to implement non-trivial behaviors, > such as making the "width" property into an alias for the "length" true > data member.
As the Wikipedia article explains, this has its own consequences. A reasonable test suite for Rectangle would quite probably fail if given a Square. Hence my belief that this makes for a less-than-ideal example. But I can't think of *any* good example of @property for a tutorial. ANY. > As a learning tool for thinking about inheritance hierarchies it's kind > of rubbish. But then again, most inheritance hierarchies are ambigious > at best, which is why "has a" is often a better choice than "is a". Agreed. There certainly are times when "is a" is the right choice, but there are a lot more times when "has a" is the better choice. Usually, when I subclass, it's because I want to tweak the behaviour of an existing type (for instance, subclass int and change its repr() to return hex(self)), so it really truly is a <superclass>, in every way except that one tiny change. Otherwise, new type with a member. Much simpler. Much safer. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
