[Tutor] Dumb question

[alan.gauld@bt.com]

> I'm not a programmer, so this is a kinda dumb question. 

Its not dumb at all. In fact its something experienced 
programmers often find harder to understand than beginners!

> What exactly is a class? 

When programming it often helps to build a kind of 
model of the "real world problem". Classes are descriptions 
of the real world 'objects' that we are modelling. 

This is similar to the techniquie of drawing a scale 
diagram to measure somethjing, or building a scale model 
for windtunnel testing used in other engineering disciplines.

Classes are the blueprints for our "scale model" objects.

> Why would use one? 

To try to keep the solution as much like the problem as 
possible - it helps us focus on the important bits of 
the problem without getting bogged down in details
(which are hidden inside the class!)

> How do you define one? 

class Pen:
   # define properties of the class here
   ink = 'black'
   # also define operations on the objects here
   # just like normal functions but inside the class
   def draw(self, x,y):  # ignore self for now but we need it...
      # code to draw here

Now we can create an instance of a Pen:

p = Pen()

Draw with it

p.draw(5,9)

Describe it

print "Ink color is ", p.ink

and so forth. We can forget about the details of how to 
draw(I dodn't show them anyhow!) and just think about 
using pens.

> alot of reading on Python and this whole concept escapes me.

I dunno if it included my tutor but i have a topic on 
Object orientation and examples of its use in both the 
Event Driven chapter and the GUI chapter plus the Case Study

Alan g.
Author of the 'Learning to Program' web site
http://www.freenetpages.co.uk/hp/alan.gauld