What is the purpose of the '&' in the string in this line?
exitAction = QtGui.QAction(QtGui.QIcon('exit.png'), '&Exit', self)
fileMenu = menubar.addMenu('&File')
& character has a special purpose if you use it in the text of a
QAction object: If the QAction object is used in a tool button, the character directly after the
& symbol can be used as a keyboard shortcut for that button (in combination with the alt-key).