Python mock patch a function within another function

Question

def f1():
    return 10, True

def f2():
    num, stat = f1()
    return 2*num, stat

How do I use python\'s mock library to patch f1()

Answer 1

Assuming that you're using this mock libary:

def f1():
    return 10, True

def f2():
    num, stat = f1()
    return 2*num, stat

import mock

print f2()   # Unchanged f1 -> prints (20, True)

with mock.patch('__main__.f1') as MockClass:       # replace f1 with MockClass 
    MockClass.return_value = (30, True)     # Change the return value

    print f2()     # f2 with changed f1 -> prints (60, True)

If your code is divided into modules you would probably need to replace __main__.f1 with the path to your module/function.