<class 'struct.error'>: 'required argument is not a float' when writing 'data: [x, y]'

asked 2019-11-20 05:31:00 -0600

Redhwan gravatar image

updated 2019-11-20 18:59:40 -0600

I think that the issue is silly.

I'd like to run the code on two computers and I need to use a list. I followed this Tutorials here

I used my PC as a talker and computer of the robot as a listener.

when running the code on my PC, the output is good as I needed.

[INFO] [1574230834.705510]: [3.0, 2.1]
[INFO] [1574230834.805443]: [3.0, 2.1]

but once running the code on the computer of the robot, the output is:

Traceback (most recent call last):
  File "/home/redhwan/learn.py", line 28, in <module>
    talker()
  File "/home/redhwan/learn.py", line 23, in talker
    pub.publish(position.data)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/topics.py", line 886, in publish
    raise ROSSerializationException(str(e))
rospy.exceptions.ROSSerializationException: <class 'struct.error'>: 'required argument is not a float' when writing 'data: [3.0, 2.1]'

full code on PC:

#!/usr/bin/env python
import rospy
from std_msgs.msg import Float32
x = 3.0
y = 2.1

def talker():
    # if a == None:
    pub = rospy.Publisher('position', Float32, queue_size=10)
    rospy.init_node('talker', anonymous=True)
    # rospy.init_node('talker')
    rate = rospy.Rate(10) # 10hz

    while not rospy.is_shutdown():
        position = Float32()
        a = [x,y]
        # a = x
        position.data = list(a)
        # position.data = a
        # hello_str = [5.0 , 6.1]
        rospy.loginfo(position.data)

        pub.publish(position.data)
        rate.sleep()

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

full code on the computer of the robot:

#!/usr/bin/env python
import rospy
from std_msgs.msg import Float32


def callback(data):
    # a = list(data)
    a = data.data
    print a

def listener():

    rospy.init_node('listener', anonymous=True)

    rospy.Subscriber("position", Float32, callback)

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


if __name__ == '__main__':
    listener()

Updated:

picture to the output with full code

when using one number as float everything is OK.

I understand how to publish and subscribe to them separately as the float but I'd like to do it as list

Any ideas or suggestion, it would be appreciated.

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Comments

Float32 is a message that contains only a single field data, which is a single float32. You cannot assign it a list.

when running the code on my PC, the output is good as I needed.

I won't accuse you of lying, but that would seem to be impossible.

You'll have to create a custom message which contains a field of type float32[] (or use std_msgs/Float32MultiArray, but that may be a bit involved).

gvdhoorn gravatar imagegvdhoorn ( 2019-11-20 06:17:17 -0600 )edit

I don't know why you wrote this sentence !!!!!! "I won't accuse you of lying, but that would seem to be impossible".

did you run the code??? did you get another output?

I put the full code here.

I took it to copy and paste after reading your comment to ensure from its output. for that, I updated my question by adding the picture.

Redhwan gravatar imageRedhwan ( 2019-11-20 19:06:54 -0600 )edit

@Redhwan please calm down. @gvdhoorn was simply suggesting that your statement

when running the code on my PC, the output is good as I needed.

is, at least, not accurately describing what you've been doing.

did you run the code??

As a matter of fact, I just did. And yes, the output from loginfo is actually appearing in the terminal. I guess that is what you tried to prove with your screenshot. But the talker node crashes the instant you open any subscriber to the /postion topic (try with rostopic echo on your PC). It has nothing to do with the robot and the

output is good as I needed.

can be doubted because it seems you haven't tried the listener (or rostopic echo, for that matter) on your PC.

That being said: I'm not familiar enough with the inner plumbing of rospy to explain why this ...(more)

mgruhler gravatar imagemgruhler ( 2019-11-21 03:02:50 -0600 )edit

@mgruhler no problem brother, it fixed by using Float32MultiArray

Redhwan gravatar imageRedhwan ( 2019-11-21 04:56:50 -0600 )edit