Proper syntax for adding methods to a class instance dynamically?

[Fernando Pérez]

I'd like to know what the proper way to do this is. I've been using the new 
module with new.instancemethod(), but the docstring for new isn't very 
confidence inducing:

Docstring:
    Functions to create new objects used by the interpreter.

    You need to know a great deal about the interpreter to use this!


Is there a simpler, perhaps 'safer' way to achieve the same result? What I 
want is to have code which runs after an instance of a certain class has been 
created and which can add new methods to the class instance. I'd also like to 
know how to add them to the whole class. I have some solutions in store but I 
feel they're kind of kludgy.

Thanks for any help,

f.