Python OOP

[Manolo029]

I am working on a GUI app using Tkinter, with the following file/folder structure
PythonGUI
|-BIKEGUI
|--ADDSTOCK
|---add_stock.py
|--RENTBIKE
|---rent_bike.py
|-main.py
|-bike_main_gui.py

"main.py" is where the all main classes and functionality of my program is,
I need to instantiate some classes from main.py and use them in other files(the other are just guis), how can I achieve this?
my aim is to instantiate a bike shop and uses all its values in other files.

PS. everything is written using OOP paradigm