code: def event(self, event):
          
          if (event.type() == QEvent.KeyPress) and (event.key() == Qt.Key_Tab):
              self.sig_tab_pressed.emit(True)
              self.numpress += 1
              if self.numpress == 1:
                  self.presstimer = QTimer.singleShot(400, self.handle_keypress)
              return True
          return QComboBox.event(self, event)
docs: Qt Override.
  
          Filter tab keys and process double tab keys.