Fix string/bytes problem && lint

examples/python/auth/_credentials.py

@@ -22,8 +22,8 @@ import os
 
 def _load_credential_from_file(filepath):
     real_path = os.path.join(os.path.dirname(__file__), filepath)
-    with open(real_path, 'r') as f:
-        return bytes(f.read())
+    with open(real_path, 'rb') as f:
+        return f.read()
 
 
 SERVER_CERTIFICATE = _load_credential_from_file('credentials/localhost.crt')

examples/python/auth/customized_auth_client.py

@@ -20,7 +20,6 @@ from __future__ import print_function
 import argparse
 import contextlib
 import logging
-import os
 
 import grpc
 from examples import helloworld_pb2
@@ -57,12 +56,6 @@ class AuthGateway(grpc.AuthMetadataPlugin):
         callback(((_SIGNATURE_HEADER_KEY, signature),), None)
 
 
-def _load_credential_from_file(filepath):
-    real_path = os.path.join(os.path.dirname(__file__), filepath)
-    with open(real_path, 'r') as f:
-        return f.read()
-
-
 @contextlib.contextmanager
 def create_client_channel(addr):
     # Call credential object will be invoked for every single RPC

examples/python/auth/customized_auth_server.py

@@ -20,7 +20,6 @@ from __future__ import print_function
 import argparse
 import contextlib
 import logging
-import os
 import time
 from concurrent import futures
 
@@ -66,12 +65,6 @@ class SimpleGreeter(helloworld_pb2_grpc.GreeterServicer):
         return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)
 
 
-def _load_credential_from_file(filepath):
-    real_path = os.path.join(os.path.dirname(__file__), filepath)
-    with open(real_path, 'r') as f:
-        return f.read()
-
-
 @contextlib.contextmanager
 def run_server(port):
     # Bind interceptor to server