I am trying to split my code in different layers: GUI, reading the GUI, creating input, calculating the model, interpreting data, creating view, sending the view to the GUI. I got the idea of the MVC and would like to try to build my program that way. But I'm a little confused about how to exchange information between those modules. I'm running into problems with undefined global names and so forth. Example code how I'm trying to get out of this can be found here: http://stackoverflow.com/questions/17385373/setup-a-mvc-mvw-system-in-python-with-tkinter