A smallish Tkinter question

[mediocre_person at hotmail.com]

"""
What I want: A little window to open with a 0 in it. Every second, the
0 should increment by 1.
What I get: A one second delay, see the window with a 1 in it, and then
nothing appears to happen. Never see the 0, never see a 2.  Any quick
clues? Thanks. Nick. (Python 2.4, Win98).
"""

from Tkinter import *
from time import sleep

class Clock:
    def __init__(self, parent):
        self.time = 0
        self.display = Label(parent)
        self.display["font"] = "Arial 16"
        self.display["text"] = str(self.time)
        self.display.pack()

    def run(self): #also tried self,parent
        sleep(1.0)
        self.time = self.time + 1
        self.display["text"] = str(self.time)

win = Tk()
app = Clock(win)
app.run() #also tried run(win) with self,parent above
win.mainloop()