class_extension

A mechanism for extending python classes.

Code for adding methods to classes outside of class definitions. For reference: another version of the same idea was found, proposed by GVR himself: https://mail.python.org/pipermail/python-dev/2008-January/076194.html I'm providing this version as a slightly safer alternative. It has various extra checks that avoid issues.

Pros:

• Promotes functional cohesion; Cross-class inter-dependant code can stay together, easing understanding (only need to refer to one file to see how something works or make changes).
• Actually safer than python's class definition mechanism due to the existing-name-check assertion. i.e. we can't define something twice with extensions, but we can with ordinary classes.
• Provides a way to avoid circular imports when adding methods. This can be a huge benefit for a large project.
• Provides a good way to extend classes from external libraries. This can also be a nice benefit, as sometimes it's not possible to use your subclass inside an external library.

Cons:

• Methods don't appear to metaclasses at class instantiation time. This shouldn't be a problem, as the metaclasses shouldn't be concerned with methods added in this way anyway.
• Surprises developers who expect all methods to be inside a class definition.

Notes: Monkey-patching is expressly disallowed. This means you can't replace an attribute on an existing class. However, you can override a superclass method, like an ordinary class can and you can always create a subclass and extend that.