How to make a cross-module variable?

Question

The __debug__ variable is handy in part because it affects every module. If I want to create another variable that works the same way, how would I do it?

The variable (let's be original and call it 'foo') doesn't have to be truly global, in the sense that if I change foo in one module, it is updated in others. I'd be fine if I could set foo before importing other modules and then they would see the same value for it.

Answer 1

If you need a global cross-module variable maybe just simple global module-level variable will suffice.

a.py:

var = 1

b.py:

import a
print a.var
import c
print a.var

c.py:

import a
a.var = 2

Test:

$ python b.py
# -> 1 2

Real-world example: Django's global_settings.py (though in Django apps settings are used by importing the object django.conf.settings).