# an empty class
class MyClass:
    pass

def greet(self, who): 
    print 'Hello', who

def main():
    obj = MyClass()
    MyClass.greet = greet
    obj.greet('world')





def evil(name):
    exec "%s.greet = greet" % name

def main2():
    obj = MyClass()
    evil("MyClass")
    obj.greet('world')