Question: How do I share global variables across modules?

The canonical way to share information across modules within a single program is to create a special module (often called config or cfg).

Just import the config module in all modules of your application; the module then becomes available as a global name. Because there is only one instance of each module, any changes made to the module object get reflected everywhere.

For example:

config.py: 
x = 0 # Default value of the 'x' configuration setting

mod.py: 
import config
config.x = 1

main.py:
import config
import mod
print config.x

 
Note that using a module is also the basis for implementing the Singleton design pattern, for the same reason.