from tkinter import *
from tkinter.ttk import *

class MyButtonGUI:
    '''A tkinter program using classes rather than global
    variables.'''

    def __init__(self, window):
        self.button_text = StringVar()
        self.button_text.set('Hello')
        button = Button(window,
                        textvariable=self.button_text,
                        command=self.my_button_behavior)
        button.grid(row=0, column=0)
        button.configure(padding=50)        

    def my_button_behavior(self):
        '''executes when the 'hello' button is clicked'''
        self.button_text.set('You clicked me!')

def main():
    window = Tk()   # create the main program window
    MyButtonGUI(window) # create the button
    window.mainloop() # enter the GUI main loop
    
main()