from tkinter import *
from tkinter.ttk import *

def my_button_behavior():
    '''Executes when the 'hello' button is pressed'''
    button_text.set(button_text.get() + '!')  # update the StringVar associated with the button


def main():
    window = Tk()

    global button_text   # data is a global variable (OOP is better)

    button_text = StringVar()
    button_text.set('Hello')
    
    my_button = Button(window, textvariable=button_text, command=my_button_behavior)
    my_button.grid(row=0, column=0)
    my_button.configure(padding=50) # add 50 pixels of padding on all sides
    
    window.mainloop() # start the event loop

main()