[Tutor] How to load a dict into a dict subclass?

[Wayne]

On Tue, Oct 27, 2009 at 10:20 AM, John <jfabiani at yolo.com> wrote:

>
> Hey guru's could one of you explain why such a subclass is needed.  How
> would
> it be used.  I'm not sure but does not the deepcopy() work as above?


A subclass is useful for when you want to do pretty much what another class
does, only with some modifications.

My favorite example (and the easiest to understand) deals with shapes:

class Shape:
     def __init__(self):
        self.sides = 0
        self.area = 0

class Triangle(Shape):
     Shape.__init__(self)
     def __init__(self, base=0, height=0):
         self.sides = 3
         self.area = base/2*height

class Circle(Shape):
      Shape.__init__(self)
      def __init__(self, radius):
          self.sides = 1
          self.area = 2*3.14*radius


There are many other times when subclasses are useful, but that's a nice
simple example. The "is-a" relationship can tell you when it's useful to
have a superclass. "This collection is a list of (un)ordered elements" would
tell you it should be a list. Though, TBH most python objects are so
"batteries" included that I have little (no) reason to subclass - my only
real exception is GUI programming.

Here's something Google pulled up on the subject:
http://www.gidnetwork.com/b-137.html

HTH,
Wayne
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