alternative publisher for Joy_node

edit

Hi everyone,

I'm trying to publish to modify the Publisher tutorial (Python)) and simplify this tutorial in order to read some values from the joy_node, do some operations and publish the new values in another topic in the foo array. This is my file talker2.py in Python under ROS Indigo. I know there are errors (probably in the foo variable), but I don't know what is really wrong. Someone can help me?

#!/usr/bin/env python
import rospy
from std_msgs.msg import Float32MultiArray
from sensor_msgs.msg import Joy

def joyread(data):
    foo[0] = 4*data.axes[1]
    foo[1] = 4*data.axes[0]
    foo[2] = 15*data.buttons[14]
    pub.publish(foo)

def talker2():
    global pub
    pub = rospy.Publisher('chatter', Float32MultiArray,queue_size=10)
    rospy.Subscriber("joy", Joy, joyread)
    rospy.init_node('talker2', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
      rospy.sleep(1.0)



if __name__ == '__main__':
    try:
        talker2()
    except rospy.ROSInterruptException:
        pass

And this is the error (declaring public foo does not solve anything)

[ERROR] [WallTime: 1479037245.575886] bad callback: <function joyread at 0x7f5b6f923c08>
Traceback (most recent call last):
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rospy/topics.py", line 720, in _invoke_callback
    cb(msg)
  File "/home/marcor/catkin_ws/src/beginner_tutorials/scripts/talker2.py", line 44, in joyread
    foo[0] = 4*data.axes[1]
NameError: global name 'foo' is not defined

Thank you all. (PS Joy_node "alone" works fine)

UPDATE After NEngelhard answer, here the solution. I modified the first function as follows and it works!

def joyread(data):

foo = Float32MultiArray()
foo.data.append(255*data.axes[1])
foo.data.append(255*data.buttons[14])
pub.publish(foo)