diff --git a/shards/mishards/service_handler.py b/shards/mishards/service_handler.py
index e64f1f1fb0..6b9422e832 100644
--- a/shards/mishards/service_handler.py
+++ b/shards/mishards/service_handler.py
@@ -27,7 +27,8 @@ class ServiceHandler(milvus_pb2_grpc.MilvusServiceServicer):
         self.max_workers = max_workers
 
     def _reduce(self, source_ids, ids, source_diss, diss, k, reverse):
-        sort_f = lambda x, y: x >= y if reverse else lambda x, y: x <= y
+        sort_f = (lambda x, y: x >= y) if reverse else (lambda x, y: x <= y)
+
         if sort_f(source_diss[k - 1], diss[0]):
             return source_ids, source_diss
         if sort_f(diss[k - 1], source_diss[0]):