General programming question. When to use OOP?

Question

My program needs to do 2 things.

1. Extract stuff from a webpage.

2. Do stuff with a webpage.

However, there are many webpages, su

Answer 1

It's up to you. I personally try to stay away from Java-style classes when programming in python. Instead, I use dicts and/or simple objects.

For instance, after defining these functions (the ones you defined in the question), I'd create a simple dict, maybe like this:

{ 'facebook' : { 'process' : facebookProcess, 'extract': facebookExtract }, 
 ..... 
}

or, better yet, use introspection to get the process/extract function automatically:

def processor(sitename):
    return getattr(module, sitename + 'Process')

def extractor(sitename):
    return getattr(module, sitename + 'Extractor')

Where module is the current module (or the module that has these functions).

To get this module as an object:

import sys
module = sys.modules[__name__]

Assuming of course, that the generic main function does something like this:

    figure out sitename based on input.
    get the extractor function for the site
    get processor function for the site
    call the extractor then the processor

Answer 2

"My program needs to do 2 things."

When you start out like that, the objects cannot be seen. You're perspective isn't right.

Change your thinking.

"My program works with stuff"

That's OO thinking. What "stuff" does your program work with? Define the stuff. Those are your basic classes. There's a class for each kind of stuff.

"My program gets the stuff from various sources"

There's a class for each source.

"My program displays the stuff"

This is usually a combination of accessor methods of the stuff plus some "reporting" classes that gather parts of the stuff to display it.

When you start out defining the "stuff" not the "do", you're doing OO programming. OO applies to everything, since every single program involves "doing" and "stuff". You can chose the "doing" POV (which is can be procedural or functional), or you can chose the "stuff" POV (which is object-oriented.)

Answer 3

Put as much of the common stuff together in a single function. Once you've factored as much out as possible, build a mechanism for branching to the appropriate function for each website.

One possible way to do this is with python's if/else clauses, but if you have many such functions, you may want something more elegant such as

F = __import__('yourproject.facebookmodule')

This lets you put the code that's specific for facebook in it's own area. Since you pass __import__() a string, you can modify that at runtime based on which site you're accessing, and then just call function F in your generic worker code.

More on that here: http://effbot.org/zone/import-confusion.htm

Answer 4

You use OOP when it makes sense, when it makes developing the solution quicker and when it makes the end result easier to read, understand and maintain.

In this case it might make sense to create a generic Extractor interface/class and then have subclasses for Twitter, MySpace, Facebook, etc but this really depends on how site-specific the extraction is. The idea of this kind of abstraction is to hide such details. If you can do it, it makes sense. If you can't you probably need a different approach.

It may also be that similar benefits can be obtained from good decomposition of a procedural solution.

Remember at the end of the day that all these things are just tools. Pick the best one for that particular job rather than picking the hammer and then trying to turn everything into a nail.

Answer 5

I regularly define classes for solving problems for a few reasons, I'll model an example of my thinking below. I have no compunctions about mixing OO models and procedural styles, that's often more a reflection of your work society than personal religion. It often works to have a procedural facade for a class hierarchy if that's what other maintainers expect. (Please excuse the PHP syntax.)