Fix the pylint complain

examples/python/data_transmission/alts_client.py

@@ -17,8 +17,9 @@ The example would only successfully run in GCP environment."""
 
 import grpc
 
-import client
 import demo_pb2_grpc
+from client import (bidirectional_streaming_method, client_streaming_method,
+                    server_streaming_method, simple_method)
 
 SERVER_ADDRESS = "localhost:23333"
 
@@ -28,10 +29,10 @@ def main():
             SERVER_ADDRESS,
             credentials=grpc.alts_channel_credentials()) as channel:
         stub = demo_pb2_grpc.GRPCDemoStub(channel)
-        client.simple_method(stub)
-        client.client_streaming_method(stub)
-        client.server_streaming_method(stub)
-        client.bidirectional_streaming_method(stub)
+        simple_method(stub)
+        client_streaming_method(stub)
+        server_streaming_method(stub)
+        bidirectional_streaming_method(stub)
 
 
 if __name__ == '__main__':

examples/python/data_transmission/alts_server.py

@@ -18,15 +18,16 @@ The example would only successfully run in GCP environment."""
 from concurrent import futures
 
 import grpc
+
 import demo_pb2_grpc
-import server
+from server import DemoServer
 
 SERVER_ADDRESS = 'localhost:23333'
 
 
 def main():
     svr = grpc.server(futures.ThreadPoolExecutor())
-    demo_pb2_grpc.add_GRPCDemoServicer_to_server(server.DemoServer(), svr)
+    demo_pb2_grpc.add_GRPCDemoServicer_to_server(DemoServer(), svr)
     svr.add_secure_port(SERVER_ADDRESS,
                         server_credentials=grpc.alts_server_credentials())
     print("------------------start Python GRPC server with ALTS encryption")

src/python/grpcio/grpc/__init__.py

@@ -1833,7 +1833,7 @@ def local_server_credentials(local_connect_type=LocalConnectionType.LOCAL_TCP):
         _cygrpc.server_credentials_local(local_connect_type.value))
 
 
-def alts_channel_credentials(service_accounts=[]):
+def alts_channel_credentials(service_accounts=None):
     """Creates a ChannelCredentials for use with an ALTS-enabled Channel.
 
     This is an EXPERIMENTAL API.
@@ -1851,7 +1851,7 @@ def alts_channel_credentials(service_accounts=[]):
       A ChannelCredentials for use with an ALTS-enabled Channel
     """
     return ChannelCredentials(
-        _cygrpc.channel_credentials_alts(service_accounts))
+        _cygrpc.channel_credentials_alts(service_accounts or []))
 
 
 def alts_server_credentials():