A few days ago I wrote a tutorial about a template for a Publisher node in Python. In the same tutorial, I used the template to write a ROS node to generate a random number.
Today, I continue the series of tutorials that ease the work of beginners in ROS, with a template for Subscriber in Python. In addition, in the article, you will find a template implementation with a ROS node that displays the data generated by the Publisher node from the previous tutorial.
Below you will find the template for a ROS Publisher node in Python. All you have to do is copy the text into a ‘. py’ file, delete the extra text and replace the text with capital letters.
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#The ROS Node Subscriber template
#!/usr/bin/env python
#remove or add the library/libraries for ROS
import rospy, time, math, cv2, sys
#remove or add the message type
from std_msgs.msg import String, Float32, Image, LaserScan, Int32
#define function/functions to provide the required functionality
def name_callback(msg):
    make_something_here_with msg.data
    rospy.loginfo(“I heard %s”, msg.data)
if __name__==‘__main__’:
    #Add here the name of the ROS. In ROS, names are unique named.
    rospy.init_node(‘THE_NAME_OF_THE_NODE’)
    #subscribe to a topic using rospy.Subscriber class
    sub=rospy.Subscriber(‘TOPIC_NAME’, TOPIC_MESSAGE_TYPE, name_callback)
    rospy.spin()
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I used the above template to write a ROS node that will display the random numbers sent by the node created to test the Publisher template.
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#!/usr/bin/env python
import rospy
from std_msgs.msg import Int32
from random import randint
def random_callback(msg):
    rospy.loginfo(“I heard %s”, msg.data)
if __name__==‘__main__’:
    rospy.init_node(‘rand_subscriber’)
 Â
    sub=rospy.Subscriber(‘rand_no’, Int32, random_callback)
    rospy.spin()
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To run the above node, navigate to the .py file and make it executable. The command is:
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chmod u+x my_python_file.py
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After the file is executable, you can run the node.
Step 1: open a new Terminal and run the command:
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roscore
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Step 2: open a new Terminal and run the Publisher node with the following command:
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rosrun your_package your_ros_node_that_generates_random_number.py
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Step 3: open a new Terminal and run the subscriber node with the following command:
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rosrun your_package your_ros_node_for_subscriber.py
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