Solution to Exercise 6.2 solution missing global

Course Support ROS Basics In 5 Days (Python)
1

The proposed solution should mean:

def my_callback(request):
    global move_circle
    global my_pub
    rospy.loginfo("The Service move_bb8_in_circle has been called")
    move_circle.linear.x = 0.2
    move_circle.angular.z = 0.2
    my_pub.publish(move_circle)
    rospy.loginfo("Finished service move_bb8_in_circle")
    return EmptyResponse()

without the global reference, it doesn’t work.

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2

Hi, if you are referring to the file bb8_move_in_circle_service_server.py, then it works as it should. I’ve used it and the bb8 moves as expected:

customer_support
customer_support1386×893 2.36 MB

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3

@ruediger

It actually works, as the global keyword is not needed for those variables:

  1. There’s no need to use the global keyword to access a global variable (it’s required when you are modifying it). Regarding my_pub, we are merely accessing one of it’s methods.
  2. We also don’t need to use the global keyword to modify properties of a global object. In this case, move_circle. This is a special case for objects, vs “plain” variables, I understand that this is quite surprising and interesting!
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4

Hi,
could u check why my code doesn’t work.
I think it’s basically the same, but the robot doesn’t move at all, and only the loginfo outseide the fcun is printed
thank u!

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5

Hi,

You are showing in your screenshot that you have launched the service server, now you have to call that service from a different terminal in order for the robot to move.

1 Like
6

yes, i forgot to call it.
thank u so much!

1 Like