Python : access to a variable from an other module is only given as a reference

I am working on writing the tests for a project that has a massive technical debt and am running into limitations of my understanding as to how python references variables

Here is the very simplified example :

main.py
src/
  __init__.py
  foo.py
  variables.py
tests/
  __init__.py
  unit_test.py
main.py

the __init__.py and main.py files are empty

foo.py

from src.variables import GLOBAL_VARIABLE


class Foo:
    def bar(self):
        print(f"foo :{id(GLOBAL_VARIABLE)}")
        if GLOBAL_VARIABLE:
            return 1
        return 2

variables.py

GLOBAL_VARIABLE = False
print(f"\norig:{id(GLOBAL_VARIABLE)}")

unit_test.py

import src.variables
from src.foo import Foo


def testFoo():
    src.variables.GLOBAL_VARIABLE = True
    print(f"\ntest:{id(src.variables.GLOBAL_VARIABLE)}")
    foo = Foo()
    assert foo.bar() == 1

I am attempting to change the value of a variable contained in the src/variables.py file in order to run some tests but I can only get a copy rather than the variable itself

The output is as follows ( simply running pytest with no configuration nor arguments ) :

orig:140734094465928
collected 1 item                                                                                                                                                                                                                                                                                            

tests\unit_test.py
test:140734094465896
foo :140734094465928

I cannot seem to get access to the variable itself from the test module, only a copy. I have attempted different imports for the tests but I am consistently getting a variable that does not have the same id and the simply fails

How can I change the value of GLOBAL_VARIABLE ?

There are solutions that I have attempted such as <a href="https://stackoverflow.com/questions/34913078/importing-and-changing-variables-from-another-file">this one</a> but was not able to change the value of my boolean ( the difference seems to be that I am importing from an other module ? )

As a bit of context I cannot change the tested code ( would like to ), only the tests, so I cannot implement better coding practices on the tested code

The module unit_test.py actually modifies the variables.GLOBAL_VARIABLE, but the foo.py has a copy of it.

You could either update the unit_test.py so that it imports the copy from foo.py:

# unit_test.py
import src.foo
def testFoo():
    src.foo.GLOBAL_VARIABLE = True
    print(f"\ntest:{id(src.foo.GLOBAL_VARIABLE)}")
    f = src.foo.Foo()
    assert f.bar() == 1

Or you could update the foo.py so that it also does import variables instead of from variables import GLOBAL_VARIABLE.

# foo.py
import src.variables
class Foo:
    def bar(self):
        print(f"foo:{id(src.variables.GLOBAL_VARIABLE)}")
        if src.variables.GLOBAL_VARIABLE:
            return 1
        return 2

I am not saying that importing and changing global variables from other modules is a good idea for production codes, but for testing, this is probably fine.