The problem is, what do I do if I need a module's functionality but don't want to rewrite it?

Two possibilities spring to mind.

1. Simply write a module which uses the other. This is probably the appropriate way to do it if you are adding functionality to a module anyway. Subclassing, I think, is best when you want to change the functionality, particularly by making it more specific.

2. A tried and true method that doesn't get enough respect these days is to create a copy of the module and modify it. Forking a module's development is a perfectly fine form of code reuse which, like any other, has its advantages and its disadvantages.

-sauoq
"My two cents aren't worth a dime.";