code: def set_handler(self, handler):
          
          with self._lock:
              if self._handler_ctx is not None:
                  return self._handler_ctx.set_handler(handler)
          return RET_ERROR
docs: 设置异步回调处理对象
  
          :param handler: 回调处理对象，必须是以下类的子类实例
  
                      ===============================    =========================
                       类名                                 说明
                      ===============================    =========================
                      StockQuoteHandlerBase               报价处理基类
                      OrderBookHandlerBase                摆盘处理基类
                      CurKlineHandlerBase                 实时k线处理基类
                      TickerHandlerBase                   逐笔处理基类
                      RTDataHandlerBase                   分时数据处理基类
                      BrokerHandlerBase                   经济队列处理基类
                      ===============================    =========================
  
          :return: RET_OK: 设置成功
  
                  RET_ERROR: 设置失败