Creating a Subscriber in python

Question

Hi!

I’m trying to create a subscriber using python for this package, following the tutorials that ros provide. The package already contains a subscriber in c++. It uses geometry_msgs/Twist.h

I just want to publish in terminal the values from x, y, width and height. However when I run the code I receive nothing.

This is the code that Im using

 #!/usr/bin/env python
 import rospy
 from geometry_msgs.msg import Twist

 def callback(data):
   rospy.loginfo(rospy.get_caller_id() + "I heard %s", data.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.
    rospy.init_node('listener', anonymous=True)

    rospy.Subscriber("commands", Twist, callback)

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

 if __name__ == '__main__':
      listener()

Hope you could give me a hand thanks

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Originally posted by G212 on ROS Answers with karma: 5 on 2016-01-11

Post score: 0

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Original comments

Comment by nickw on 2016-01-11:
Check the format of the commands topic - is it a Twist message

Answer 1

The Twist message as no field named data. I know that you took this example from the python tutorial on subscribers. That tutorial use a String.msg as you can see this as a field named data. The Twist.msg as two data fields, linear and angular. which are Vector3.msg which contain 3 float64 numbers. So to clear it up to get the 'X' value, you would do the following.

data.linear.x

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Originally posted by ngoldfarb with karma: 127 on 2016-01-11

This answer was ACCEPTED on the original site

Post score: 2

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Original comments

Comment by s.vaichu on 2019-05-14:
thanks a lot, it really helped me