text: #!/usr/bin/python3.7
  from std_msgs.msg import String
  from basic_example.srv import *
  import rospy
  import sys
  import os
  
  def get_error_handler(req):
  	goal_pos = 0.5
  	error = goal_pos - req.current_pos
  	print("%s %s"%(req.time, error))
  	return GetErrorResponse(error)
  
  def get_error():
  	rospy.init_node("get_error")
  	s = rospy.Service("get_error", GetError, get_error_handler)
  	rospy.spin()
  
  
  if __name__ == "__main__":
  	get_error()
  