patching class function in python

Today we had to patch a class function in production. Monkey patching can become tricky if reference are kept at several place like pointer in C and C++.
Here is a simple example on how to make sure all references will use the new definition.
class Foo:
  def f(self):
      print "default f"

def newf(self):
  print "newf"

Foo.f.im_func.func_code = newf.func_code
This is another reason why interpreter language like python are so powerful.