Error using Python GetModelResponse

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This code works in cpp.

 ros::ServiceClient client = n.serviceClient<gazebo_msgs::GetModelState>("/gazebo/get_model_state");
 gazebo_msgs::GetModelState getmodelstate;
 getmodelstate.request.model_name ="rrbot";
 client.call(getmodelstate);

But in python ...

 # Take pose from gazebo: ignore rviz pose: 
 rospy.wait_for_service("/gazebo/get_model_state")
 client = rospy.ServiceProxy("/gazebo/get_model_state", GetModelState)
 getmodelstate = client(model_name="rrbot")

 # Set starting data x,y and theta for odometry used in handelerJointControllerState
 self.theta = getmodelstate.response.pose.orientation.z

I get the following error:

 self.theta = getmodelstate.response.pose.orientation.z
AttributeError: 'GetModelStateResponse' object has no attribute 'response'

Any thoughts on the nature of this error.