Sample ROS Service Server and Client

sos_service.py

#! /usr/bin/env python
# remember to make this file executable (`chmod +x`) before trying to run it

import rospy
from std_srvs.srv import Trigger, TriggerResponse

def trigger_response(request):
    return TriggerResponse(
        success=True,
        message="Hey, roger that; we'll be right there!"
    )

rospy.init_node('sos_service') 
my_service = rospy.Service('/fake_911', Trigger, trigger_response)
rospy.spin()

sos_service_client.py

#! /usr/bin/env python
# remember to make this file executable (`chmod +x`) before trying to run it

import rospy
from std_srvs.srv import Trigger, TriggerRequest

# init a node as usual
rospy.init_node('sos_service_client')

# wait for this service to be running
# Ideally, this service should run 24/7, but remember it's fake :) 
rospy.wait_for_service('/fake_911')

# Create the connection to the service. Remeber it's a Trigger service
sos_service = rospy.ServiceProxy('/fake_911', Trigger)

# Create an object of type TriggerRequest. We need a TriggerRequest for a Trigger service
# We don't need to pass any argument because it doesn't take any
sos = TriggerRequest()

# Now send the request through the connection
result = sos_service(sos)

# Done, let's see the result!
print result