[Tutor] Beginner Question

[Dave Angel]

On 22/10/2013 10:25, Sven Hennig wrote:

>  Hello, I would like to learn a programming language and have decided to use
> Python. I have some programming experience and doing well in Python. What
> really causes me problems is OOP.
> I'm just dont get it... I'm missing a really Practical example. In every
> book I've read are the examples of such Class Dog and the function is bark. Has
> anyone an OOP example for me as it is really used in real code, so I can
> better understand the concept? I do not know why this is so hard for me.
>

What you may not realize is you're already doing OOP, just by using the
standard library.  When you open a file (or many other things that can
produce a stream of bytes), you get an instance of class file.  When you
use that instance, you're calling methods of that instance.  So when you
say:

infile = open("myfile.txt,"r")
data = infile.readline()

you're doing object oriented programming.  You don't have to know what
kind of thing "infile" is, you just have to know it has methods read(),
readline(), close(), etc.

When you want to write your own classes, or when you want to make a new
class that's related but different from one of the thousands that are
standard, that's when it gets interesting.  As Alan says, GUI is one
place where you'll be wrting your own classes, usually by deriving from
one of the GUI library classes.

At its most fundamental, a class is a description of how to create and
how to manipulate instances.  An instance has methods (functions), and
attributes (data).  When one class is derived from another, it can share
some or most of the attributes and behavior of the parent class, but
make changes.  This helps avoid duplicating code when two things are
similar.

You're familiar with list and tuple.  Those are built-in
collection classes, supported explicitly by the language. But if you
want your own collection, you may want to make a class for it.  The Dog
bark() example may seem silly, but a Dog has lots of other methods
besides that one, and has lots of attributes (color, breed, health
state, owner, etc.).  In a sense those attributes are like a list within
the Dog, but you want them to have nice names, instead of remembering
that the 3rd one is owner.


-- 
DaveA