Tkinter optionmenu functions

Question

Using the Tkinter module, I am try to elicit an action based on the certain selection of an option menu and cancel that action if the option menu is not on the designated selection. The problem is that the program will compile except when both option menus = "treble clef" it somewhat stops working. I have tried using an if statement which works fine except I'm not sure how to get rid of the label it calls.

originalKey = Label(window, text = "Original Key Signature", bg = 'black', fg = 'white')
originalKey.pack()

oKey = StringVar(window)
oKey.set("Select") # initial value
optionold = OptionMenu(window, oKey, "treble clef", "bass clef", "alto clef")
optionold.config(bg = 'black', fg = 'white')
optionold.pack()

#new key selections option menu
def displayKey(str):
while nKey.get() == "treble clef" and oKey.get() == "treble clef":
    testpic = Label(window, image = logoimage, bg = 'black')
    testpic.pack()
    break

newKey = Label(window, text = "New Key Signature", bg = 'black', fg = 'white')
newKey.pack()

nKey = StringVar(window)
nKey.set("select") # initial value
optionnew = OptionMenu(window, nKey, "treble clef", "bass clef", "alto clef",             
command = displayKey)
optionnew.config(bg = 'black', fg = 'white')
optionnew.pack()