Error when refering to class defined in 'main' in an imported module

[HeRo]

Yes create it in one module and import it from that module into anywhere you want to use it.

Thank you for your reply! But it turns out that this is not really necessary...
The problem I was trying to solve can be solved in another way.

I am using the Kivy framework, so my 'main.py' file "imports" a file written in the Kivy language:

Builder.load_file('MyTabbedPanel.kv')

The real problem was that this was placed AFTER:

from sharebox_ios_etc import ShareBox

So I just had to put them in this order:

Builder.load_file('MyTabbedPanel.kv')

from sharebox_ios_etc import ShareBox