As shortly mentioned in the basic concept part, ROS allows interaction pulisher nodes and subscriber nodes. In this chapter we'll create our first publisher node, which will send a basic message.

Make sure your current path is the previously created package.

touch talker.py

sudo chmod +x talker.py

import rospy
from std_msgs.msg import String

def talker():
    pub = rospy.Publisher('chatter', String, queue_size=10)
    rospy.init_node('talker', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
        hello_str = "hello world %s" % rospy.get_time()
        rospy.loginfo(hello_str)
        pub.publish(hello_str)
        rate.sleep()

if __name__ == '__main__':
    try:
        talker()
    except rospy.ROSInterruptException:
        pass

First we create the publisher node with reference 'chatter' and initialize it.

Then we go through a loop and create a 'hello world' string that we will publish on this 'talker' node.

rospy.loginfo() is used to debug info to the user but doesn't interact with the node itself.

We could now run roscore and rosrun my_awesome_code talker in the console and see the debugger info but we don't have anybody subscribed(listening) to that talker node yet.