One caveat, as I recently discovered, to dynamically adding methods is that it doesn't work for __foo__ methods. For example, you can't make an object into an iterator by dynamically assigning bound methods to obj.__iter__ and obj.next. Same thing with __getitem__, __setitem__, etc; adding them directly to the instance doesn't get you a subscriptable object. This is because the interpreter looks at the methods defined by the class, rather than the instance's attributes.
Just a word of caution. Collin Winter -- http://mail.python.org/mailman/listinfo/python-list
