listener_subscribe_notify.py

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#!/usr/bin/env python
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# Revision $Id$

## talker that receives notification of new subscriptions

NAME = 'talker_callback'

import sys

import rospy
from std_msgs.msg import String

class ChatterListener(rospy.SubscribeListener):
    def peer_subscribe(self, topic_name, topic_publish, peer_publish):
        print("a peer subscribed to topic [%s]" % topic_name)
        
        str = "Hey everyone, we have a new friend!"
        print(str)
        topic_publish(String(str))
        str = "greetings. welcome to topic "+topic_name
        print(str)
        peer_publish(String(str))
        
    def peer_unsubscribe(self, topic_name, numPeers):
        print("a peer unsubscribed from topic [%s]" % topic_name)
        if numPeers == 0:
            print("I have no friends")
    
def talker_callback():
    pub = rospy.Publisher("chatter", String, subscriber_listener=ChatterListener(), queue_size=10)
    rospy.init_node(NAME, anonymous=True)
    count = 0
    while not rospy.is_shutdown():
        str = "hello world %d"%count
        print(str)
        pub.publish(String(str))
        count += 1
        rospy.sleep(0.1)
        
if __name__ == '__main__':
    try:
        talker_callback()
    except rospy.ROSInterruptException: pass