Ros timing issue

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We did a simple code to subscribe to laser ranges and velocity of a robot in ros stage. But the order of execution of the functions seems to be different. Is this a problem in timing? The python code and output is given below.

CODE:

 #!/usr/bin/env python

import rospy                           
import sensor_msgs.msg
from geometry_msgs.msg import Twist

ranges = []

def start():
    rospy.init_node('robot_values', anonymous = True)

def laser_scanner():
    rospy.Subscriber('base_scan', sensor_msgs.msg.LaserScan,laser_processor)

def laser_processor(data):
    global ranges
    ranges = data.ranges
    print "ranges[0] = ",ranges[0]
    print "ranges[1] = ",ranges[1]

def robot_mon():
    rospy.Subscriber('cmd_vel', Twist, robot_velocity)

def robot_velocity(data):
    all_velocities = data
    linear_velocity = all_velocities.linear.x
    angular_velocity = all_velocities.angular.z
    print "linear_velocity = ",linear_velocity 
    print "\n"

if __name__ == '__main__':
    start()
    laser_scanner()
    robot_mon()
    rospy.spin()

OUTPUT:

ranges[0] =  5.0
ranges[1] =  5.0
ranges[0] =  5.0
ranges[1] =  5.0
linear_velocity =  0.044


ranges[0] =  5.0
ranges[1] =  5.0
linear_velocity =  0.044


linear_velocity =  0.044


ranges[0] =  5.0
ranges[1] =  5.0
linear_velocity =  0.044


ranges[0] =  5.0
ranges[1] =  5.0
ranges[0] =  5.0
ranges[1] =  5.0
linear_velocity =  0.044