newbie needs help with tkinter

[Sacchi]

I've just learned the main rules of python(I already knew both java and 
C). Now I'm trying to get something out of Tkinter, but while running 
this sample program (made by myself) I encountered a problem. I wanted 
that by clicking on the "configura" command under the "File" menu the 
frame would get yellow and that a label would appear on it. The 
function works(the line "print "hello!"" gets executed) but the gui 
window doesn't change. I even tried to use the widget redraw methods 
but with no success... anyone can help me please?

Thanks in advance
Marco

--------- Program Code ----------------------

from Tkinter import *

class Application(Frame):

        def __init__(self,master=None):
                Frame.__init__(self,master)
                menubar=self.addmenubar()
                master.config(menu=menubar)
                menubar.mainloop()

        def addmenubar(self):
                menubar=Menu()
                filemenu=Menu(menubar)
                menubar.add_cascade(menu=filemenu,label="File")
#these lines got shifted by the newsreader program, but all belong to
#the addmenubar function                
filemenu.add_command(label="Configura"command=self.configframe)         
        filemenu.add_command(label="Lavora")
                return menubar

        def configframe(self):
                self.set(bg="yellow")
                w=Label(self,fg="blue",text="prova")
                w.grid()
                self.update_idletasks()
                print "hello!"

#main

root=Tk()
applicazione=Application(root)
root.mainloop()
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