Combine Subscriber and Publisher in Python, ROS

This article will describe an example of Combining Subscriber and Publisher in Python in ROS programming.

This is very useful in ROS development.

We will also discuss briefly how to build and modify a catkin package which is written by Python.

• Create a catkin package with the command: catkin_create_pkg, under the path: ~/catkin_ws/src
• Build it with the command: catkin_make, under the path: ~/catkin_ws/
• Source the catkin setup file under devel folder:
  

  $ source ~/catkin_ws/devel/setup.bash

• modify the Python scripts file under the path: ~/catkin_ws/src/<pkg_name>/scripts/nodexxx.py
• chmod +x nodexxx.py
• Run this package by Command:  rosrun package_name nodexxx.py
• Modify the CMakefile.txt for Python: Writing a ROS Python Makefile
  

More about Create and Build catkin ROS package: This blog

The sourcecode for this Combining Subscriber and Publisher in Python is here:

#!/usr/bin/env python
# License removed for brevity
"""
	learn to write Subscriber and Listener in one python script.
	Function Style
	Author: Sonic http://blog.csdn.net/sonictl
	Date: Feb 29, 2016	
"""
import rospy
from std_msgs.msg import String
def callback(data):
rospy.loginfo(rospy.get_caller_id() + "callback:I heard %s", data.data)
#resp_str = "resp_str: I heard: " + data.data
talker(data)
def listener():
# In ROS, nodes are uniquely named. If two nodes with the same
# node are launched, the previous one is kicked off. The
# anonymous=True flag means that rospy will choose a unique
# name for our 'listener' node so that multiple listeners can
# run simultaneously. http://blog.csdn.net/sonictl
rospy.init_node('responsor', anonymous=True)

rospy.Subscriber("uc0Response", String, callback)

# spin() simply keeps python from exiting until this node is stopped
rospy.spin()
def talker(data):
pub = rospy.Publisher('uc0Command', String, queue_size=10)
rospy.loginfo("talker:I heard %s", data.data)
#while not rospy.is_shutdown():
resp_str = "resp_str: I heard: " + data.data
rospy.loginfo(resp_str)
if data.data == "cigit-pc\n" :
    pub.publish(resp_str)
else:
    rospy.loginfo("invalid seri data:" + data.data)
if name == 'main':
#listener()
try:
listener()
#talker()
except rospy.ROSInterruptException:
pass

20160614: I have to paste the next code for an other instance because this should be very good for learners:

#!/usr/bin/env python
""" odom_ekf.py - Version 0.1 2012-07-08
Republish the /robot_pose_ekf/odom_combined topic which is of type
geometry_msgs/PoseWithCovarianceStamped as an equivalent message of
type nav_msgs/Odometry so we can view it in RViz.
Created for the Pi Robot Project: http://www.pirobot.org
Copyright (c) 2012 Patrick Goebel.  All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.5
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details at:

http://www.gnu.org/licenses/gpl.html
"""
import roslib; roslib.load_manifest('rbx1_nav')
import rospy
from geometry_msgs.msg import PoseWithCovarianceStamped
from nav_msgs.msg import Odometry
class OdomEKF():
def init(self):
# Give the node a name
rospy.init_node('odom_ekf', anonymous=False)
    # Publisher of type nav_msgs/Odometry
    self.ekf_pub = rospy.Publisher('output', Odometry)
    
    # Wait for the /odom topic to become available
    rospy.wait_for_message('input', PoseWithCovarianceStamped)
    
    # Subscribe to the /robot_pose_ekf/odom_combined topic
    rospy.Subscriber('input', PoseWithCovarianceStamped, self.pub_ekf_odom)
    
    rospy.loginfo("Publishing combined odometry on /odom_ekf")
    
def pub_ekf_odom(self, msg):
    odom = Odometry()
    odom.header = msg.header
    odom.child_frame_id = 'base_footprint'
    odom.pose = msg.pose
    
    self.ekf_pub.publish(odom)
if name == 'main':
try:
OdomEKF()
rospy.spin()
except:
pass