code structure with several callbacks

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Hello,

I am working on a small 4WD rover. I use ultrasonic sensors, and a RPlidar for autonomous navigation and a joy for manual teleoperation. My aim is quite simple, but i am asking some questions about the right python script architecture.

The main idea is to have a loop which check joy inputs, and update both sonar and laser data Joy input decide the current mode ('AUTO' or 'MANUAL')

Thus I write this code :

#!/usr/bin/env python

import rospy
import time
from geometry_msgs.msg import Twist
from sensor_msgs.msg import Joy
from rospy_tutorials.msg import Floats
from sensor_msgs.msg import LaserScan 

## MODE

def auto_mode():
    print( sonar_array[0] + sonar_array[1])
    print( laser_array[0] + laser_array[1])
    # detect obstacle
    # compute path

## CALLBACKS    

def callback_joy(data):

    if data.buttons[0]<0.5 :
        switchMode = 'AUTO'
    else:
        switchMode = 'MANUAL'
        twist.linear.x = 4*data.axes[1]
        twist.angular.z = 4*data.axes[0]

def callback_sonar(data):

    sonar_array = data.data
    #some data filtering and processing

def callback_laser(scan):

    laser_array = scan.ranges
    #some data filtering and processing

if __name__ == '__main__':

    # initialisation
    print("initialization ")

    pub = rospy.Publisher('/cmd_vel',Twist,queue_size=5)
    twist = Twist() 
    rospy.init_node('viva_node', anonymous=True)
    rospy.Subscriber('joy', Joy, callback_joy)
    rospy.Subscriber('sonar', Floats, callback_sonar)
    rospy.Subscriber('/scan', LaserScan, callback_laser)

    # loop
    print('loop')
    while True:
        print('spin')
        rospy.spin()
        print 'Current Mode is : ',  switch_mode

        if switch_mode == 'AUTO':
            auto_mode()

But, when i run, this script nothing append except :

pi@rasberrypi:~ $ rosrun perso_package viva_node_rev3.py

initialization

loop

spin

Then script get stuck and nothing append. I don't know why, any idea would are welcome.

Matt