Listbox In Python

I've made a listbox which it is possible to get to using the mouse, or
route jaws to pc cursor, but I can't get to it just using the normal
cursor. When I arrow up and down it just doesn't do anything. I know
the only thing I have in the window right now is the listbox, but
still ...
Can anyone make any suggestions as to how to improve the attached file?
Thanks,
Harmony.

from Tkinter import *
import tkMessageBox
import Tkinter
top = Tk()
Lb1 = Listbox(relief=RAISED)
Lb1.insert(1, "Python")
Lb1.insert(2, "C")
Lb1.insert(3, "PHP")
Lb1.insert(4, "HTML")
Lb1.insert(5, "Ruby")
Lb1.insert(6, "C++")
Lb1.pack()
top.mainloop()

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