I have a page where I\'ll show some customers details. So I created a page called \"customers details\" with all the labels that I need and I set the text of these labels as
You could consider saving references to you GUI fields you need to update in, for example, a dict in your MyApp class. That way you can access them from anywhere in the class regardless of where the actual GUI element happens to be placed.
GUI programming usually produces quite messy classes, using a dict to keep track of the elements reduces the mess. Others like to keep separate class attributes for each element you need to access later.