Multiple Publishers and subscribers in ROS | ROS Noetic Tutorial 5

Multiple Publishers and subscribers in ROS Noetic 

Already we have tried publisher subscriber in Python script and multiple sub/pub also we have tried. 

Here is an experiment that does the following.

1. A packet publisher publishes the name of the packet (string format)

2. A security publisher (string) converts the above packet into an encrypted packet (usually the ceaser cipher, VITCC is equivalent to YLWFF).

3. A third publisher is an Int32 publisher, which publishes an integer number with the number of packets. 

4. There is only one subscriber, that tells the "Number of packets encrypted" after all the publishers publishes. 

i.e P1 AND P2 AND P3 => Subscribers

SOURCE CODE: Publisher1.py

#!/usr/bin/env python3

import rospy

from std_msgs.msg import String

def talker():

rospy.init_node('publisher_node1', anonymous=True)

pub = rospy.Publisher('P1', String, queue_size=10)

rate = rospy.Rate(1) 

while not rospy.is_shutdown():

_string = "ABCDEF"

rospy.loginfo(_string)

pub.publish(_string)

rate.sleep()

if __name__ == '__main__':

try:

    talker()

    except rospy.ROSInterruptException:

    pass

Publisher2.py

#!/usr/bin/env python3

from cryptography.fernet import Fernet

import rospy

from std_msgs.msg import String

def cipher(s):

s1 = ""

for x in s:

s1 += s + 'X'

return s1

def talker():

rospy.init_node('publisher_node2', anonymous=True)

pub = rospy.Publisher('P2', String, queue_size=10)

rate = rospy.Rate(1) 

while not rospy.is_shutdown():

_string = cipher("ABCDEF")

rospy.loginfo(_string)

pub.publish(_string)

rate.sleep()

if __name__ == '__main__':

try:

    talker()

    except rospy.ROSInterruptException:

    pass

Publisher3.py

#!/usr/bin/env python3

import rospy

from std_msgs.msg import String

def talker():

rospy.init_node('publisher_node3', anonymous=True)

pub = rospy.Publisher('P3', String, queue_size=10)

rate = rospy.Rate(1) 

while not rospy.is_shutdown():

_string = str(len("ABCDEF"))

rospy.loginfo(_string)

pub.publish(_string)

rate.sleep()

if __name__ == '__main__':

try:

talker()

except rospy.ROSInterruptException:

pass

Subscriber1.py

#!/usr/bin/env python3

import rospy

from std_msgs.msg import String

def course(data: str):

rospy.loginfo("I took %s", data.data)

def listener():

rospy.init_node('subscriber_node', anonymous=True)

rospy.Subscriber("P1", String, course)

rospy.Subscriber("P2", String, course)

rospy.Subscriber("P3", String, course)

rospy.spin()

if __name__ == '__main__':

listener()

OUTPUTS:

ROS  Publisher 1

ROS  Publisher 2

ROS  Publisher 3

ROS  Subscriber