keyboard teleop but publish a same message at a fixed rate?

edit

Hi everyone, I tried to modify the source of package keyboard_teleop_twist to be able to send a same twist message at a fixed rate, because I want to keep the same twist message instead of keeping pushing down the button. I tried to used rospy.Rate but it did not work. Here is my code:

 
import rospy 
from geometry_msgs.msg import Twist 
import roslib; roslib.load_manifest('teleop_twist_keyboard')
import rospy
import tty
import sys
import termios
import select
moveBindings = {
        'i':(1,0,0,0),
        'o':(1,0,0,-1),
        'j':(0,0,0,1),
        'l':(0,0,0,-1),
        'u':(1,0,0,1),
        ',':(-1,0,0,0),
        '.':(-1,0,0,1),
        'm':(-1,0,0,-1),
        'O':(1,-1,0,0),
        'I':(1,0,0,0),
        'J':(0,1,0,0),
        'L':(0,-1,0,0),
        'U':(1,1,0,0),
        '<':(-1,0,0,0),
        '>':(-1,-1,0,0),
        'M':(-1,1,0,0),
        't':(0,0,1,0),
        'b':(0,0,-1,0),
    }
class teleop():
 
def __init__(self):

    rospy.init_node('teleop', anonymous=False)

    rospy.loginfo(" Press CtrL+c to stop ")

    rospy.on_shutdown(self.shutdown)

    self.cmd_vel = rospy.Publisher('cmd_vel_mux/input/navi',
    Twist, queue_size=10)
    orig_settings = termios.tcgetattr(sys.stdin)

    tty.setcbreak(sys.stdin)

    rate = rospy.Rate(30);


    while not rospy.is_shutdown():
        key =sys.stdin.read(1)[0]
        if key in moveBindings.keys():
            x = moveBindings[key][0]
            y = moveBindings[key][1]
            z = moveBindings[key][2]
            th = moveBindings[key][3]
        twist = Twist()
        twist.linear.x = x; twist.linear.y = y; twist.linear.z = z
        twist.angular.x = 0; twist.angular.y = 0; twist.angular.z = th
        self.cmd_vel.publish(twist)
        rate.sleep()

    termios.tcsetattr(sys.stdin, termios.TCSADRAIN, orig_settings)  
def shutdown(self):

    rospy.loginfo("Stopping")
    self.cmd_vel.publish(Twist())

    rospy.sleep(1)
 
if __name__ == '__main__':
    try:
        teleop()
    except: 
        rospy.loginfo("end")