How to properly shutdown a node from command coded in the script of the same node

edit

I have a simple ros application that is used to create a .world file. Everything is working as expected unless the shutdown process. When the script ends the following message is retrieved:

================================================================================REQUIRED process [world_creation-2] has died!
process has finished cleanly
log file: /home/nut/.ros/log/452cd878-dd8f-11e7-9623-e02a82110940/world_creation-2*.log
Initiating shutdown!
================================================================================
[world_creation-2] killing on exit
[rosout-1] killing on exit
[master] killing on exit
shutting down processing monitor...
... shutting down processing monitor complete

I am unsatisfied with the fist part of the message which is appearing in the red color e may pass the felling the some thing is wrong. So, here is my question: How can I finish in a way clean way, from a command codded in the node script, this node. The node script is:

#!/usr/bin/env python    
import sys
import rospy
import numpy as np
import road_generation_gazebo.roads as roads
import road_generation_gazebo.worlds as worlds
import road_generation_gazebo.utils as utils
import road_generation_gazebo.generates as generates

def main(road_pts, road_close, offset, offset_npts, offset_var, doplot ,model, file_name):
   pass #there is some code here

if __name__ == '__main__':

  # Initialize the node and name it.
  rospy.init_node('world_creation', anonymous=True, disable_signals=True)

  # Getting parameters
  metadata = rospy.get_param('~metadata')
  road_close=metadata['close']
  if metadata['mode'] == 'function':
    if metadata['geometry'] == 'ellipse':
      road_pts = generates.ellipse(metadata['radius']
                                  ,metadata['RADIUS']
      )
  elif metadata['mode'] == 'waypoints':
      road_pts = metadata['points']
  else:
    raise ValueError('Not expected mode...')

  main(road_pts=road_pts
      ,road_close=road_close
      ,offset=rospy.get_param('~offset')
      ,offset_npts=rospy.get_param('~offset_npts')
      ,offset_var=rospy.get_param('~offset_var')
      ,doplot=rospy.get_param('~doplot')
      ,model=rospy.get_param('~model')
      ,file_name =rospy.get_param('~file_name')
  )

and the launch file used is;

<launch>
<node name="world_creation" pkg="road_generation_gazebo" type="road_gazebo.py" required="true" output='screen'>
<!--node name="world_creation" pkg="road_generation_gazebo" type="road_gazebo.py"-->
  <rosparam command="load" file="$(find road_generation_gazebo)/yaml/metadata.yaml" />
  <param name="doplot" value="true" />
  <param name="offset_road_add_noise" value="true" />
  <param name="offset" value="5.0" />
  <param name="offset_npts" value="100.0" />
  <param name="offset_var" value="1.5" />
  <param name="model" value="bush" />
  <!--param name="model" value="cylinder"/-->
  <param name="file_name" value="custom.world" />
</node>
</launch>

I tried the command rospy.signal_shutdown(reason), but the red message was not suppressed.