Modules - problem

[A]

Hi,
I would like to access a variable in one module from another module.For example

The main module is like this
#############
#Main modul z1.py
import z3
print "x variable=", z3.x
###########

where z3.py module is like

########
#My module z3.py
global x
x=11
#########
Now if I run z1.py for the first time it prints properly

x variable= 11

but if I do any  change in z3 module , it has no effect
For example If I change in z3
x=12
I still get
 x variable= 11
Why?
Thank you for help.
Is it possible to name module with a different extension from py? For example is it possible 
to import z3.cod file?
Ladislav