keyboard key teleop not registering movement: Getting started

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I'm trying to get a keyboard controller working (teleop I think its called):

code:

#!/usr/bin/env python

import rospy
from std_msgs.msg import String
from geometry_msgs.msg import Twist

key_mapping = { 'w': [0, 1], 'x': [0, -1],
            'a': [-1, 0], 'd': [1, 0],
            's': [0, 0] }
#g_last_twist = None
g_vels_scales = [0.1, 0.1]

def keys_cb(msg, twist_pub):
    global g_last_twist
    if len(msg.data) == 0 or not key_mapping.has_key(msg.data[0]):
        return #unknown key
    vels = key_mapping[msg.data[0]]
    g_last_twist.angular.z = vels[0] * g_vels_scales[0]
    g_last_twist.linear.x = vels[1] * g_vels_scales[1]
    twist_pub.publish(g_last_twist)

if __name__ == '__main__':
    rospy.init_node('keys_to_twist')
    twist_pub = rospy.Publisher('cmd_vel', Twist, queue_size=1)
    rospy.Subscriber('keys', String, keys_cb, twist_pub)
    g_last_twist= Twist()
    if rospy.has_param('~linear_scale'):
        g_vels_scales[1] = rospy.get_param('~linear_scale')
     else:
         rospy.logwarn("linear scale not provided; usint %.1f" %g_vels_scales[1])
if rospy.has_param('~angualr_scale'):
    g_vels_scales[0] = rospy.get_param('~angular_scale')
else: 
    rospy.logwarn("angular scale not provided; using %.1f" %g_vels_scales[0])
rate = rospy.Rate(10)
while not rospy.is_shutdown():
    twist_pub.publish(g_last_twist)
    rate.sleep()

I can't seem to get the keys to work and publish the right twist. all of my dependencies are in the package.xml and the make file. Everything compiles and runs, but there is no "key event"

I want to expand on this exaple i got from a text book, but cant get it to do what it advertises.

any help would be appreciated.