Python initializing a global varriable from a Mocked global varriable does not work?

Question

When mocking a global variable, if I initialize another global from the mocked global, the other global does not pick up the mocked value. I hope the code makes it clearer.

myglobal.py:

    ROOT="/"

    #When we mock ROOT to "/tmp/", DIR below
    #still gets "/etc". Assignments from the global, in the module 
    #that contains/creates the global, don't pick up the mocked value.
    DIR=ROOT+"etc"

---

mytest.py:

    import unittest  
    import myglobal
    from unittest.mock import patch   

    my_root=""
    my_dir=""

    class TestGlobal(unittest.TestCase):

        def setUp(self):
            # Mock ROOT global in myglobal
            self.mock_ROOT_patcher = patch.object(myglobal, 'ROOT', "/tmp/")
            self.mock_ROOT = self.mock_ROOT_patcher.start()

        def tearDown(self):
            self.mock_ROOT_patcher.stop()

        def test_root(self):
            # Local Globals do get the mocked global value.
            # The print Bellow prints:
            # 
            # myglobal.ROOT=/tmp/, myglobal.DIR=/etc
            # my_root:/tmp/, my_dir:/tmp/etc
            #
            my_root=myglobal.ROOT
            my_dir=my_root+"etc"
            print(f"\n myglobal.ROOT={myglobal.ROOT}, myglobal.DIR={myglobal.DIR}")
            print(f"my_root:{my_root}, my_dir:{my_dir}")

What I see printed: myglobal.ROOT=/tmp/, myglobal.DIR=/etc my_root:/tmp/, my_dir:/tmp/etc

What I want to see printed: myglobal.ROOT=/tmp/, myglobal.DIR=/tmp/etc my_root:/tmp/, my_dir:/tmp/etc