Writing a Simple Publisher and Subscriber

Writing the Publisher Node

Change directory into the techx2019 package

roscd techx2019

The Code

mkdir scripts
cd scripts
touch talker.py
chmod +x talker.py

Open the editor

gedit talker.py

Copy the following Python Code into talker.py:

#!/usr/bin/env python

import rospy
from geometry_msgs.msg import Twist

def talker():
    pub = rospy.Publisher('turtle1/cmd_vel', Twist, queue_size=10)
    rospy.init_node('publisher')
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
        msg = Twist()
        msg.linear.x = 1.0
        msg.angular.z = 1.0
        pub.publish(msg)
        rate.sleep()

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

Build the code

cd ~/catkin_ws
catkin_make

Test Using TurtleSim

Open roscore

roscore

Open Another Terminal to run TurtleSim

打开另一个终端（命令行）来运行TurtleSim

rosrun turtlesim turtlesim_node

Open Another Terminal to run the code

再打开一个终端（命令行）来运行代码

Run the code

cd ~/catkin_ws/src/techx2019/scripts/
python talker.py

You should keep every programs running and move on!!

到这里，一定不要暂停任何代码，之后会用到！！

Open a Terminal!!

打开一个新的命令行！！

Writing the Subscriber Node

The Code

roscd techx2019/scripts/
touch listener.py
chmod +x listener.py

Open the editor

gedit listener.py

Copy the following Python Code into listener.py.

#!/usr/bin/env python

import rospy
from turtlesim.msg import Pose

def printMessage(msg):

    print msg.x
    print msg.y
    print msg.theta

def listener():

    rospy.init_node('listener')

    rospy.Subscriber('turtle1/pose', Pose, printMessage)

    # spin() simply keeps python from exiting until this node is stopped
    rospy.spin()

if __name__ == '__main__':
    listener()

Building your nodes

cd ~/catkin_ws
catkin_make

Save and run the code:

roscd techx2019/scripts
python listener.py