code: def disconnect(self, callback=None):
          
          ret = EventEmitter.disconnect(self, callback)
          if len(self._callbacks) == 0:
              self._connect_emitters(False)
          return ret
docs: Disconnect the callback from this group. See
          :func:`connect() <vispy.event.EmitterGroup.connect>` and
          :func:`EventEmitter.connect() <vispy.event.EventEmitter.connect>` for
          more information.