monkey patch example

monkey-patch.py

# import A
class A:

        def say_hello(self):
                print("hi!")

        def say_goodbye(self):
                print("goodbye!")

# apply monkey-patch!
class A(A):

        def say_hello(self):
                print("hello!")


a = A() 
a.say_hello()   # => hello!
a.say_goodbye() # => goodbye!


# import A
class B:

        def say_hello(self):
                print("hi!")

        def say_goodbye(self):
                print("goodbye!")

# re-define B with no inherit
class B:

        def say_hello(self):
                print("hello!")

b = B() 
b.say_hello()   # => hello!
b.say_goodbye() # => error because B doesn't have such a method.