Using Classes

[Alf P. Steinbach /Usenet]

* Mag Gam, on 24.06.2010 13:58:
> I have been using python for about 1 year now and I really like the
> language. Obviously there was a learning curve but I have a programing
> background which made it an easy transition. I picked up some good
> habits such as automatic code indenting :-), and making my programs
> more modular by having functions.
>
> I know that Python is very OOP friendly, but I could not figure out
> why and when to use Classes in it. I mostly use it for simple text
> parsing  I suppose when a program gets "complicated" I should start
> using Classes. Are there any tips or tricks people use to "force" them
> into the OOP mentality? I would like to force myself to learn the
> Python way but so far I could not figure out WHY I would need a class
> for this...

Use whatever paradigm that yields code that you easily understand. <g>

Having said that, the main use of a class is to model some data with an 
associated set of operations.

For this a class is merely a convenience, but sometimes the convenience can be 
so great that any other approach would be impractical in comparision.

In some cases a non-class approach ends up with a number of routines foo, bar, 
zlopf etc. that all take some argument of a "general" type and all internally 
has some "if it's really a BRACHYKLURB, do A, assuming that it has 
BRACHYKLURB-specific data, but if it's really a KNETCHOFICHUS, then do B, 
assuming that it has KNETCHOFICHUS-specific data, and as default, if it's none 
of those, do C".

This is a maintainance nightmare. You have to be sure that every such routine 
discriminates correctly on type, checking all possibilities and doing the right 
thing for each possibility. And you have to be sure of that in the face of 
possible additions of new subtypes, or removal of a subtype (maintainance).

Then the answer is to introduce some classes and OOP stuff.

In essence, instead of letting general routines awkwardly and error-prone choose 
the right type-specific routines depending on the object, let the object specify 
the right type-specific routines directly. :-)


Cheers & hth.,

- Alf

-- 
blog at <url: http://alfps.wordpress.com>