code: def are_you_sure(flag_changed, evt, parent=None, title="File has been changed",
                   msg="Are you sure you want to exit?"):
      
      if flag_changed:
          r = QMessageBox.question(parent, title, msg,
               QMessageBox.Yes|QMessageBox.No, QMessageBox.Yes)
          if r != QMessageBox.Yes:
              evt.ignore()
docs: "Are you sure you want to exit" question dialog.
  
      If flag_changed, shows question dialog. If answer is not yes, calls evt.ignore()
  
      Arguments:
        flag_changed
        evt -- QCloseEvent instance
        parent=None -- parent form, used to centralize the question dialog at
        title -- title for question dialog
        msg -- text of question dialog
  
      Returns True or False. True means: "yes, I want to exit"