what is the purpose of the global name space?

[Gribouillis]

there are three files.

So you need to change the title of this thread, because there is no global namespace in your sense. There is a global namespace at file scope, but three files define three global namespaces. You can exchange data between the functions by sharing a common object in these namespaces, for example

# haad.py
common = type('Common', (), {})()
common.a = 1
common.b = 2

and

# ien.py
from __main__ import common

def ien():
    common.c = 3
    common.d = 4