After looking through many posts of class variables and instance variables I am not understanding how to share variables among classes.

#!/usr/bin/python3
from PyQt5.QtWidgets import (QApplication)
import sys
class One():
    def __init__(self, myTextString, parent=None):
        self.mytext = myTextString
        self.printtxt()
        Main.txt = 'another string'
        self.txt2 = 'a third string'
    def printtxt(self):
        print('One',self.mytext)

class Two():
    def __init__(self, parent=None):
        self.printtxt()

    def printtxt(self):
       print('Two',One.txt) # Attribute Error
       print('Two',One.txt2) # Attribute Error

class Main():
    def __init__(self, parent = None):
       self.txt = 'a string of text'
       self.w = One(self.txt)
       self.w1 = Two()
       print(self.txt) # not changed by One

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = Main()
    sys.exit(app.exec_())

In the above code the Main class initiates class One and class Two. While I can send the value of self.txt to the initiated class One, there are two problems I am having.

1. When I try to print One’s variables in class Two’s printtxt I get attribute errors:

AttributeError: type object ‘One’ has no attribute ‘mytext’

AttributeError: type object ‘One’ has no attribute ‘txt2’

2. When I try and change Main’s txt variable in One, it is not changed

I would like to share a value created in any particular class with all the other classes that are created (in other words ‘global’ variables up to a point).

The controller concept in Bryan Oakley’s Tkinter example (see Switch between two frames in tkinter? and How to get variable data from a class?) is close I think, but if anyone can answer or point me to posts that explain this simply, I’d be grateful.
Thank you for any help.