How do I extend a python module? Adding new functionality to the `python-twitter` package

Question

What are the best practices for extending an existing Python module – in this case, I want to extend the python-twitter package by adding new methods to the bas

Answer 1

Define a new class, and instead of inherit it from the class you want to extend from the original module, add an instance of the original class as an attribute to your new class. And here comes the trick: intercept all non-existing method calls on your new class and try to call it on the instance of the old class. In your NewClass just define new or overridden methods as you like:

import originalmodule

class NewClass:
    def __init__(self, *args, **kwargs):
        self.old_class_instance = originalmodule.create_oldclass_instance(*args, **kwargs)

    def __getattr__(self, methodname):
        """This is a wrapper for the original OldClass class.

        If the called method is not part of this NewClass class,
        the call will be intercepted and replaced by the method
        in the original OldClass instance.
        """
        def wrapper(*args, **kwargs):
            return getattr(self.old_class_instance, methodname)(*args, **kwargs)
        return wrapper

    def new_method(self, arg1):
        """Does stuff with the OldClass instance"""
        thing = self.old_class_instance.get_somelist(arg1)
        # returns the first element only
        return thing[0]

    def overridden_method(self):
        """Overrides an existing method, if OldClass has a method with the same name"""
        print("This message is coming from the NewClass and not from the OldClass")

In my case I used this solution when simple inheritance from the old class was not possible, because an instance had to be created not by its constructor, but with an init script from an other class/module. (It is the originalmodule.create_oldclass_instance in the example above.)