diff --git a/examples/python/data_transmission/client.py b/examples/python/data_transmission/client.py
index 262e366665f..cc4a68e3435 100644
--- a/examples/python/data_transmission/client.py
+++ b/examples/python/data_transmission/client.py
@@ -19,6 +19,11 @@ import grpc
 import demo_pb2_grpc
 import demo_pb2
 
+__all__ = [
+    'simple_method', 'client_streaming_method', 'server_streaming_method',
+    'bidirectional_streaming_method'
+]
+
 SERVER_ADDRESS = "localhost:23333"
 CLIENT_ID = 1
 
diff --git a/examples/python/data_transmission/server.py b/examples/python/data_transmission/server.py
index 0a659281261..3c990945ece 100644
--- a/examples/python/data_transmission/server.py
+++ b/examples/python/data_transmission/server.py
@@ -20,6 +20,7 @@ import grpc
 import demo_pb2_grpc
 import demo_pb2
 
+__all__ = 'DemoServer'
 SERVER_ADDRESS = 'localhost:23333'
 SERVER_ID = 1