[Py] Update label's content

I am writing a simple program in Python with Tkinter, and got troubles when I wanted to update the text showed in the label. I have a variable which has been changed in certain function and I want to show its latest value on a label of the root window.

Before I find the solutions, I think all I need are Label.config() and time.sleep(). However, they didn't make the program run as what I expected.

Finally, I found the key is the update() function. There are two ways to do what I want, but I don't know the differences between them. Let me just show the test programs I've written.

[label_test1.py]

from Tkinter import *
import time

class App:
     def __init__(self, master):

             frame = Frame(master).pack()
             master.geometry("200x100")

             var_text = StringVar()
             counter = Label(frame)
             counter.config(textvariable=var_text, font=("arial",60,"bold"), bg="green")
             counter.pack(expand=YES, fill=BOTH)

             for i in range(10):
                     time.sleep(1)
                     var_text.set(i)
                     master.update()

def main():
     root = Tk()
     app = App(root)
     root.mainloop()

if __name__ == "__main__":
     main()

[label_test2.py]

from Tkinter import *
import time

class App:
     def __init__(self, master):

             frame = Frame(master).pack()
             master.geometry("200x100")

             counter = Label(frame)
             counter.config(font=("arial",60,"bold"), bg="green")
             counter.pack(expand=YES, fill=BOTH)

             for i in range(10):
                     time.sleep(1)
                     counter.config(text=i)
                     master.update()

def main():
     root = Tk()
     app = App(root)
     root.mainloop()

if __name__ == "__main__":
     main()

---
Ref:

• Tkinter Countdown by bumsfeld
• Tkinter: How can I update an image display?
• The Tkinter Label Widget
• The Variable Classes (BooleanVar, DoubleVar, IntVar, StringVar)