def _get_value(self, evt):
        """Internal usage only"""
        if evt.err:
            e = evt.errors[0]
            return "[%s] %s" % (e.reason, e.desc)

        if isinstance(evt, EventData):
            return "[%s] %s" % (
                evt.attr_value.quality, str(evt.attr_value.value))
        elif isinstance(evt, AttrConfEventData):
            cfg = evt.attr_conf
            return "label='%s'; unit='%s'" % (cfg.label, cfg.unit)
        elif isinstance(evt, DataReadyEventData):
            return ""
        elif isinstance(evt, PipeEventData):
            return evt.pipe_value
        elif isinstance(evt, DevIntrChangeEventData):
            print("utils::_get_value()")
            return