Tkinter.Listbox: activate() doesn't work

[Theodore D. Sternberg]

How can I programmatically activate an element in a Tkinter.Listbox?
I've tried activate() but nothing happens.  For example,

import Tkinter
root=Tkinter.Tk()
lb = Tkinter.Listbox(root)
lb.insert( Tkinter.End, 'foo' )
lb.insert( Tkinter.End, 'bar' )
lb.pack()
lb.activate( 1 )

...but I don't see 'bar' now getting highlighted.  What am I doing wrong?

Ted Sternberg
Berkeley, CA