python - Override module method where from...import is used

Question

I have a problem overriding the method where from...import statement is used. Some example to illustrate the problem:

# a.py module
def print_message(msg):
    print(msg)

# b.py module
from a import print_message
def execute():
    print_message("Hello")

# c.py module which will be executed
import b
b.execute()

I'd like to override print_message(msg) method without changing code in a or b module. I tried in many ways but from...import imports the original method. When I changed the code to

import a
a.print_message

then I see my change.

Could you suggest how to solve this problem?

------------------ Update ------------------

I tried to do that like below e.g.:

# c.py module
import b
import a
import sys
def new_print_message(msg):
    print("New content")
module = sys.modules["a"]
module.print_message = new_print_message
sys.module["a"] = module

But this is not working where I'm using for...import statement. Is working only for import a but as I wrote I don't want change code in b.py and a.py modules.

Answer 1

With your a and b modules untouched you could try implementing c as follows:

import a

def _new_print_message(message):
    print "NEW:", message

a.print_message = _new_print_message

import b
b.execute()

You have to first import a, then override the function and then import b so that it would use the a module that is already imported (and changed).