getting robot location members to update all the time.

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Hello, I'm new to ROS and I'm working on indigo and gazebo with python 2.7. I have a task to implement robotic navigation where the map is known in advance. I'm having difficulties to make my robot object update its x,y, and yaw (2D world, I only care about x location, y location and orientation).

Here is the code that suppose to get me the most accurate values, but for some reason when it does not seem to work:

def get_robot_location():
    listener = tf.TransformListener()
    listener.waitForTransform("/map", "/base_footprint", rospy.Time(0), rospy.Duration(10.0))

    (trans, rot) = listener.lookupTransform("/map", "/base_footprint", rospy.Time(0))
    robot_x = trans[0]
    robot_y = trans[1]
    (roll, pitch, yaw) = euler_from_quaternion(rot)
    rospy.loginfo("current position (%f,%f)" % (robot_x, robot_y))
    rospy.loginfo("yaw is: %f", yaw)
    return robot_x, robot_y, yaw

I would appreciate very much if someone can help me to insert the x,y and yaw as members of my robot object, that keeps updating through time. Thanks!