Question

Hi! I'm very confused... I failed to follow the instructions from http://library.isr.ist.utl.pt/docs/roswiki/wiki(3a)ROSNodeTutorialPython.html

1 #!/usr/bin/env python
   2 # license removed for brevity
   3 import rospy
   4 from std_msgs.msg import String
   5 
   6 def publisher():
   7     pub = rospy.Publisher('chatter', String, queue_size=10)

.........

I have a file name publisher.py and it has

float32 a
float32 b
float32 c

Should I do the following? But it doesn't work. What should I do so it pulls the data from publisher.py?

 1 #!/usr/bin/env python
   2 # license removed for brevity
   3 import rospy
   4 from std_msgs.msg import Float32
   5 
   6 def publisher():
   7     pub = rospy.Publisher('topicName', Float32, queue_size=10)

Asked by notSoTechnical on 2019-09-26 00:12:34 UTC

Answer 1

I usually program in C++ when working with ROS. By the way, what you first define as publisher.py is not a python file, it is a message file and it must be a *.msg file. Once you've written the code of your *.msg file, you must compile it in order to let ROS create the header file for that message.

To use that message, lets imagine you've called your message my_msg, so you must write in python something like this:

import rospy
from your_ros_package_name import my_msg

def publisher():
  pub = rospy.Publisher('topicName',my_msg, queue_size=10)

Try with something like this. It could be some python spelling mistake because as I've already told you I am used to work with C++ nodes.

Asked by drodgu on 2019-09-26 02:03:50 UTC

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I thought : "The std_msgs.msg import is so that we can reuse the std_msgs/String message type (a simple string container) for publishing."

Asked by notSoTechnical on 2019-09-26 11:55:47 UTC

If you want to use a String type msgs you can import String from std_msgs.msg. But I understood that you want to use a msg to broadcast 3 float32 numbers. This second way is better because you do not have to filter the String msg once is received.

Asked by drodgu on 2019-09-30 02:04:39 UTC

How to write the publisher in Python correctly?

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