diff --git a/predictionio/__init__.py b/predictionio/__init__.py
index b76338e..cea9547 100644
--- a/predictionio/__init__.py
+++ b/predictionio/__init__.py
@@ -104,7 +104,7 @@
 RATE_API = "rate"
 
 
-class Client:
+class Client(object):
 
     """PredictionIO client object.
 
diff --git a/predictionio/connection.py b/predictionio/connection.py
index 0ce02dc..4e2abfc 100644
--- a/predictionio/connection.py
+++ b/predictionio/connection.py
@@ -63,7 +63,7 @@
     pass
 
 
-class AsyncRequest:
+class AsyncRequest(object):
 
     """AsyncRequest object
 
@@ -106,7 +106,7 @@
         return self._response
 
 
-class AsyncResponse:
+class AsyncResponse(object):
 
     """AsyncResponse object.
 
@@ -155,7 +155,7 @@
         self.request = request
 
 
-class PredictionIOHttpConnection():
+class PredictionIOHttpConnection(object):
 
     def __init__(self, host, https=True):
         if https:  # https connection
@@ -300,7 +300,7 @@
     connect.close()
 
 
-class Connection:
+class Connection(object):
 
     """abstract object for connection with server