title: python tornado websocket server send message to specific client
body: <p>Is it possible, if multiple socket clients are connected to a tornado websocket server, to send a message to a specific one? 
  I don't know if there is a possibility of getting a client's id and then send a message to that id.</p>
  
  <p>My client code is:</p>
  
  <pre><code>from tornado.ioloop import IOLoop, PeriodicCallback
  from tornado import gen
  from tornado.websocket import websocket_connect
  
  
  class Client(object):
      def __init__(self, url, timeout):
          self.url = url
          self.timeout = timeout
          self.ioloop = IOLoop.instance()
          self.ws = None
          self.connect()
          PeriodicCallback(self.keep_alive, 20000, io_loop=self.ioloop).start()
          self.ioloop.start()
  
  
      @gen.coroutine
      def connect(self):
          print "trying to connect"
          try:
              self.ws = yield websocket_connect(self.url)
          except Exception, e:
              print "connection error"
          else:
              print "connected"
  
              self.run()
  
      @gen.coroutine
      def run(self):
  
  
          while True:
              msg = yield self.ws.read_message()
              print msg
              if msg is None:
                  print "connection closed"
                  self.ws = None
                  break
  
      def keep_alive(self):
          if self.ws is None:
              self.connect()
          else:
              self.ws.write_message("keep alive")
  
  if __name__ == "__main__":
      client = Client("ws://xxx", 5 )
  </code></pre>