python ros 回充调用demo

#!/usr/bin/env python
#coding=utf-

import rospy
from std_msgs.msg import String
def talker():
    pub = rospy.Publisher('nav_goal',String, queue_size=)
    rospy.init_node('talker',anonymous=True)
    #rate = rospy.Rate() # 10hz
    while not rospy.is_shutdown():
        rospy.loginfo("pub")
        pub.publish("touch_charge")
        rospy.signal_shutdown("closed!")
        #rate.sleep()

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