This lecture provides a step by a step guide to subscribe to a topic.

Summary

Start a new CCS and source the workspace setup files.

Use the template and start editing it. We will first create a new file, and copy the contents of the example file into it.
$ roscd hrwros_week1/scripts
$ touch sensor_info_subscriber.py
$ cp template_subscriber_script.py sensor_info_subscriber.py

Next, we will take a look inside our new file. Open it in your favourite editor, and follow along with the lines we indicate. #L16 means line 16.

Import sensor information
#L36: from hrwros_msgs.msg import SensorInformation

Then give a meaningful names and log message (#L41,42,49)
#L51: rospy.init_node('sensor_info_subscriber', anonymous=False)
#L53: rospy.Subscriber('sensor_info', SensorInformation, sensorInfoCallback)
#L59: sensorInfoListener()

Make the subscriber script executable
chmod +x sensor_info_subscriber.py

To run our new subscriber node:
Run roscore in a new course command shell. Remember you need to source your workspace in every new shell!
$ source $HOME/hrwros_ws/devel/setup.bash
$ roscore
Then, in a separate CCS:
$ source $HOME/hrwros_ws/devel/setup.bash
$ rosrun hrwros_week1 sensor_info_subscriber.py

Check with rostopic list:
$ rostopic info /sensor_info

Note: Inspect the topic with the rostopic info when debugging your ROS problems.

To actually see the contents of the topic, you will need to publish it from a new CCS.
$ rosrun hwros_week1 sensor_info_publisher.py