The topic pub instruction of ros2 appears: failed to populate field: 'vector3' object has no attribute 'x:1' error

1 Instructions ros2 topic pub The hidden rules of

         stay yaml In the instruction of format input , There are some details in its format that need attention ; such as , A small space can affect , This article is about the author when executing such commands , Discovered yaml In the format “ Hidden rules ”.

When testing the movement of little turtles , Using instructions ：

ros2 topic pub /turtle1/cmd_vel geometry_msgs/msg/Twist "{linear:{x=5,y=5,z:0},angular:{x=0,y=0,z=3.14}}"

The following prompt appears ：

Failed to populate field: 'Vector3' object has no attribute 'x:5'

What's the reason for this ？ Because

2 The correct input format is as follows ：

ros2 topic pub --once /turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 1.8}}"

3 Corresponding Python Program realization

         Such as ： I'm trying to use RosAria towards Pioneer P3-AT（ edit ：3-AT or P3-AT, Use both names ） dispatch orders . That's true. RosAria Can work , Because when I'm at the terminal , I can use the following commands to move the robot ：

import rclpy
from geometry_msgs.msg import Twist

topic = rospy.Publisher('/RosAria/cmd_vel', Twist, queue_size=10)
linear = [ 0, 0, 0 ]
angular = [ 0, 0, 0 ]
rospy.sleep(1) # waiting for subscribers
test = topic.publish(linear, angular)

Similar error prompt occurs again ,

Traceback (most recent call last):
File "robotControl.py", line 32, in startServer
  test = topic.publish(linear, angular)
packages/geometry_msgs/msg/_Twist.py", line 71, in serialize
buff.write(_get_struct_6d().pack(_x.linear.x, _x.linear.y, _x.linear.z, _x.angular.x, _x.angular.y, _x.angular.z))

AttributeError: 'list' object has no attribute 'x'

        When I use sets or numpy Array time , There will be the same mistake . If I try another format （ Not two lists ） Release value , An unexpected format error will be given . Adding or removing entries from any list does not solve this error .

Please try the above code yourself , Let's see if we can tune .