listener_with_user_data.py

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#!/usr/bin/env python
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## Simple listener demo that demonstrates how to register additional
## arguments to be passed to a subscription callback

NAME = 'listener_with_user_data'

import sys

import rospy
from std_msgs.msg import *

def callback(data, args):
    if args == 1:
        print "#1: I heard [%s]"%data.data
    elif args == 2:
        print "#2: I heard [%s]"%data.data
    else:
        print "I heard [%s] with userdata [%s]"%(data.data, str(args)) 
    
def listener_with_user_data():
    # Callback arguments (aka user data) allow you to reuse the same
    # callback for different topics, or they can even allow you to use
    # the same callback for the same topic, but have it do something
    # different based on the arguments.
    rospy.Subscriber("chatter", String, callback, 1)
    rospy.Subscriber("chatter", String, callback, 2)
    rospy.Subscriber("chatter", String, callback, ("chatter1", 4))    
    rospy.Subscriber("chatter2", String, callback, "This is from chatter2")
    rospy.init_node(NAME, anonymous=True)
    rospy.spin()
        
if __name__ == '__main__':
    try:
        listener_with_user_data()
    except KeyboardInterrupt, e:
        pass
    print "exiting"