how to supply the left, right tick and delta tick info to ros node?

edit

I m quite new to ROS. I wrote the first program that pub the odometry information and subscribe it. For each update of the odometry, the robot will receive the following left tick, right tick and delta time. I am wondering who will update this information? Do I need to add something in the Python program subscribe to do that?

This is my below code.

import rospy
from nav_msgs.msg import Odometry

def callback(msg):
    print (msg.pose.pose)

rospy.init_node('check_odometry')
odom_sub = rospy.Subscriber('/odom', Odometry, callback)
rospy.spin()