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While loop and time.sleep function

Brian Kelley bkelley at wi.mit.edu
Fri Feb 22 09:44:41 EST 2002 
Alves, Carlos Alberto - Coelce wrote:

> Hi all,
> I tray to make a simple clock program ( see the code below ).
> Can someone explain to me why code 01 works while code 02 doesn't
> 


You almost never want to use things like time.sleep in Tkinter apps 
since Tkinter is single threaded.  This means while time.sleep is 
sleeping, the gui window will not be updated.

It is much safer to use things like

root.after(milliseconds, function)

to set up timers like you want.  You might want to read Lundh's 
introduction to Tkinter at:

http://www.pythonware.com/library/tkinter/introduction/index.htm


Here is a Clock class that uses the .after timer

import time

class Clock:
     def __init__(self,root):
         self.root = root
         self.lb=Label(root,padx=5,pady=5,
                       fg='blue',font=('Times',20))
         self.lb.pack()
         self.root.after(1000, self.ck)
         self.ck()


     def ck(self):
         self.lb.configure(text=time.asctime()[11:19])
         # set up the next callback
         self.root.after(1000, self.ck)

if __name__ == "__main__":
     from Tkinter import *
     root = Tk()
     root.title('Clock')
     Clock(root)
     mainloop()


Brian Kelley
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