How do I redefine functions in python?

Question

I got a function in a certain module that I want to redefine(mock) at runtime for testing purposes. As far as I understand, function definition is nothing more than an assignment in python(the module definition itself is a kind of function being executed). As I said, I wanna do this in the setup of a test case, so the function to be redefined lives in another module. What is the syntax for doing this? For example, 'module1' is my module and 'func1' is my function, in my testcase I have tried this (no success):

import module1

module1.func1 = lambda x: return True

Answer 1

Use redef: http://github.com/joeheyming/redef

import module1
from redef import redef

rd_f1 = redef(module1, 'func1', lambda x: True)

When rd_f1 goes out of scope or is deleted, func1 will go back to being back to normal

Answer 2

import foo

def bar(x):
    pass

foo.bar = bar