Is this homework? This same question has been asked at least three times on Stackoverflow over the last month or so. The answer is always the same: you'll need to learn about closed-loop control. It's also best to share your code and ask specific questions about it rather than only describing the task you are given and asking for a solution.

!/usr/bin/env python

import rospy from geometry_msgs.msg import Twist from turtlesim.msg import Pose

def pose_callback(ms): print("msg.theta")

def revolve():

rospy.init_node('turtle_revolve', anonymous=True)
velocity_publisher = rospy.Publisher('/turtle1/cmd_vel', Twist, queue_size=10)
vel_loop_rate = rospy.Rate(10)


while not rospy.is_shutdown():

    rospy.Subscriber("/turtle1/pose", Pose, pose_callback)

    vel_msg = Twist()

    vel_msg.linear.x = 10
    vel_msg.linear.y= 0
    vel_msg.linear.z= 0 
    vel_msg.angular.x= 0
    vel_msg.angular.y= 0
    vel_msg.angular.z= 2

    velocity_publisher.publish(vel_msg)
    vel_loop_rate.sleep()
    rospy.spin()

if __name__ == '__revolve__': try: revolve() except rospy.ROSInterruptException: pass

this is the code i have been working on. i just want write a callback function for this script where the turtlebot stops to its initial position after drawing a circle. i also don't know that my code is working or not because whenever i execute the file it spawns a new command line and no output. It would be really helpful for me, i am a beginner in ROS and in python i feel a bit hard to troubleshoot the problem which i face

Thank You