hi can someone help please key bind

[Gary]

Hi im trying to use key bind on Tkinter to call this function
def Start():
    for i in range(60,-1,-1):
        ent['text'] = i
      time.sleep(1)
      root.update()
    ent['text'] = 'Time Out!'
    root.update()

i know the function is ok as i have assigned a button and i calls the 
function as i expect
but
root.bind('<a>',Start)
gives the following error

Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1413, in __call__
    return self.func(*args)
TypeError: Start() takes no arguments (1 given)

Thanks
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