code: def doc_modified_prompt(self, ):
          
          msgbox = QtGui.QMessageBox()
          msgbox.setWindowTitle("Discard changes?")
          msgbox.setText("Documents have been modified.")
          msgbox.setInformativeText("Do you really want to exit? Changes will be lost!")
          msgbox.setStandardButtons(msgbox.Yes | msgbox.Cancel)
          msgbox.setDefaultButton(msgbox.Cancel)
          msgbox.exec_()
          return msgbox.result()
docs: Create a message box, that asks the user to continue although files have been modified
  
          :returns: value of the standard button of qmessagebox that has been pressed. Either Yes or Cancel.
          :rtype: QtGui.QMessageBox.StandardButton
          :raises: None