[Tkinter] Defining a self made module's function to interact with the main .py variables?

[Gribouillis]

I don't know how it works for you, but from my point of vue, it is not correct to launch a different thread which updates the text window as you are doing with the read_file method. Such things are not normally supported by tkinter. If you want to wait 4 seconds before reading the file, instead of using a thread, simply do

self.after(4000, self.read_file)

It won't freeze the GUI (but remove the time.sleep() from read_file)

Have you tried running the code I posted above?