What is the correct way to create a REAL WORLD application in python

I have been learning python for about six months now, and now I am collecting all this and trying to do something useful ...

I completely built my GUI (using wxpython), now I need to create a back-end that I am fully capable of, but I'm a bit confused about how I should bind them ...

what structure do I need to associate with my real GUI program

Suppose you create a background file in a separate file and import all the classes of my internal program into a GUI program and call the functions / methods that I need?

to build all background code in a GUI file?

keep them separate and create a third file that imports the GUI and frontend?

and what if I have functions that need variables from another (the GUI needs an internal variable and vice versa)

Hope this makes sense as I cannot find a better way to describe what logical problem I have