Python add to a function dynamically

Question

how do i add code to an existing function, either before or after?

for example, i have a class:

 class A(object):      def test(self):          print "here" 

how do i edit the class wit metaprogramming so that i do this

 class A(object):      def test(self):          print "here"           print "and here" 

maybe some way of appending another function to test?

add another function such as

 def test2(self):       print "and here" 

and change the original to

 class A(object):      def test(self):          print "here"          self.test2() 

is there a way to do this?

Answer 1

You can use a decorator to modify the function if you want. However, since it's not a decorator applied at the time of the initial definition of the function, you won't be able to use the @ syntactic sugar to apply it.

>>> class A(object): ...     def test(self): ...         print "orig" ... >>> first_a = A() >>> first_a.test() orig >>> def decorated_test(fn): ...     def new_test(*args, **kwargs): ...         fn(*args, **kwargs) ...         print "new" ...     return new_test ... >>> A.test = decorated_test(A.test) >>> new_a = A() >>> new_a.test() orig new >>> first_a.test() orig new 

Do note that it will modify the method for existing instances as well.

EDIT: modified the args list for the decorator to the better version using args and kwargs