Python class design - Splitting up big classes into multiple ones to group functionality

Question

OK I've got 2 really big classes > 1k lines each that I currently have split up into multiple ones. They then get recombined using multiple inheritance. Now I'm wondering, if there is any cleaner/better more pythonic way of doing this. Completely factoring them out would result in endless amounts of self.otherself.do_something calls, which I don't think is the way it should be done.

To make things clear here's what it currently looks like:

from gui_events import GUIEvents # event handlers
from gui_helpers import GUIHelpers # helper methods that don't directly modify the GUI

# GUI.py
class GUI(gtk.Window, GUIEvents, GUIHelpers):
    # general stuff here stuff here

One problem that is result of this is Pylint complaining giving me trillions of "init not called" / "undefined attribute" / "attribute accessed before definition" warnings.

EDIT:
You may want to take a look at the code, to make yourself a picture about what the whole thing actually is.
http://github.com/BonsaiDen/Atarashii/tree/next/atarashii/usr/share/pyshared/atarashii/

Please note, I'm really trying anything to keep this thing as DRY as possible, I'm using pylint to detect code duplication, the only thing it complains about are the imports.

Answer 1

I think this is more of a general OO-design problem than Python problem. Python pretty much gives you all the classic OOP tools, conveniently packaged. You'd have to describe the problem in more detail (e.g. what do the GUIEvents and GUIHelpers classes contain?)

One Python-specific aspect to consider is the following: Python supports multiple programming paradigms, and often the best solution is not OOP. This may be the case here. But again, you'll have to throw in more details to get a meaningful answer.

Answer 2

Your code may be substantially improved by implementing a Model-View-Controller design. Depending on how your GUI and tool are setup, you may also benefit from "widgetizing" portions of your GUI, so that rather than having one giant Model-View-Controller, you have a main Model-View-Controller that manages a bunch of smaller Model-View-Controllers, each for distinct portions of your GUI. This would allow you to break up your tool and GUI into many classes, and you may be able to reuse portions of it, reducing the total amount of code you need to maintain.

While python does support multiple programming paradigms, for GUI tools, the best solution will nearly always be an Object-Oriented design.

Answer 3

Start by finding classes that model real world concepts that your application needs to work with. Those are natural candidates for classes.

Try to avoid multiple inheritance as much as possible; it's rarely useful and always somewhat confusing. Instead, look to use functional composition ("HAS-A" relationships) to give rich attributes to your objects made of other objects.

Remember to make each method do one small, specific thing; this necessarily entails breaking up methods that do too many things into smaller pieces.

Refactor cases where you find many such methods are duplicating each other's functionality; this is another way to find natural collections of functionality that deserve to be in a distinct class.

Answer 4

If you want to use multiple inheritance to combine everything into one big class (it might make sense to do this), then you can refactor each of the parent classes so that every method and property is either private (starts with '__') or has a short 2-3 character prefix unique to that class. For example, all the methods and properties in your GUIEvents class could start with ge_, everything in GUIHelpers could start with gh_. By doing this, you'll get achieve some of the clarity of using separate sub-class instances (self.ge.doSomething() vs self.ge_doSomething()) and you'll avoid conflicting member names, which is the main risk when combining such large classes into one.