How to use timer callback in ROS?

edit

I am working with ROS Kinetic. Like in ROS2, we can use a create_timer() function as described here.

Similarly I would want to use a similar functionality in rospy in ROS. Something that is mentioned here in point 3.

Can anyone give an example how to use it ?

I am trying something like this in my class constructor but it never enters the callback function :

class DemoNode():
    def __init__(self):
        print("entering constructor")
        #super().__init__('custom_talker')
        self.pub = rospy.Publisher('topic',customMessage, queue_size=10)
        self.counter = 1
        print("creating a publisher")
        self.timer = rospy.Timer(rospy.Duration(1), self.demo_callback)
        print("timer called")

    def demo_callback(self):
        print("entering callback")
        msg = DetectedObject()
        print("Reading the message correctly")
        msg.id = self.counter
        counter += 1
        rospy.loginfo("Publishing message {}".format(msg.id))
        pub.publish(msg)

if __name__ == '__main__':

    print("entering main")
    rospy.init_node('custom_talker')
    try:
        DemoNode()
        print("entering Try")
    except rospy.ROSInterruptException:
        print("exception thrown")
        pass

Is it correct ? The node is running but it never enters the callback function

Also, it is mentioned that this Timer is supported in ROS 1.5+ . What is exactly that ? Does Kinetic already fulfill this condition ?