How to do Obj-C Categories in Python?

Question

Obj-C (which I have not used for a long time) has something called categories to extend classes. Declaring a category with new methods and compiling it into your program, all in

Answer 1

Why not just add methods dynamically ?

>>> class Foo(object):
>>>     pass
>>> def newmethod(instance):
>>>     print 'Called:', instance
...
>>> Foo.newmethod = newmethod
>>> f = Foo()
>>> f.newmethod()
Called: <__main__.Foo object at 0xb7c54e0c>

I know Objective-C and this looks just like categories. The only drawback is that you can't do that to built-in or extension types.