dynamically adding a function to existing imported module

Question

This maybe a very naive question and perhaps it's best asked with an example:

module1.py

import module2

def new_func():
    print(var_string)
module2.new_func = new_func

module2.func()
module2.new_func()

module2.py

var_string = "i'm the global string!"

def func():
    print(var_string)

result

> python module1.py
i'm the global string!
Traceback (most recent call last):
  File "module1.py", line 8, in <module>
    module2.new_func()
  File "module1.py", line 4, in new_func
    print(var_string)
NameError: name 'var_string' is not defined

So my question is this: Is it possible to insert a function into a module and have it's global namespace update accordingly?

Related: global variable defined in main script can't be accessed by a function defined in a different module Note that I am aware that sharing global variables is a bad idea and I'm also aware that a configuration module would be a good compromise to that but also please note that this is not what I am trying to achieve.

Answer 1

You may think it is useful, but very little python code is written this way and I think most python programmers would be confused with code that does this. Modifying a module after it's been imported (monkeypatching) is usually looked down upon because it's very easy to do the wrong thing and cause strange bugs.

You made an analogy comparing it to overriding / extending methods on a class, but if this is really what you want to do, why not just use a class? The features of classes make it much safer and easier to do this kind of thing.

Your code will work if you do this:

from module2 import var_string
#or..
from module2 import *

But I'm not sure if that's the solution you're looking for. Either way, I personally wouldn't try to make this code work, it's fighting against the way python code is normally written. If you have a practical example of code that you think would be improved by dynamically modifying modules, I would like to see it. It's a little hard to see the benefit with the example code you gave.