how to create python modal forms

[shaun]

I am brand new to Python and I need some help with modality. I would like to set up an application say codeA.py screen with some buttons that call other python forms codeB.py, codeC.py etc. I need to know how codeA.py would call these (either codeB.py, codeC.py etc.) in a modal state and also how I could pass data back to codeA.py. I have found at the following statements that I loaded into codeA.py

import os 
os.system('python codeB.py'

from subprocess import Popen
Popen('python codeB.py')

from subprocess import call
call(["python", "codeB.py"]) )

which do open the codeB.py form but it needs to be modal and neither of these statements seem to allow for return data.

Can anyone suggest how this could be done with some example coding?

Shaun.