old_contents: import logging
  from tornado.ioloop import IOLoop
  from tornado import gen
  from tornado.iostream import StreamClosedError
  from tornado.tcpserver import TCPServer
  from tornado.options import options, define
  
  define("port", default=9888, help="TCP port to listen on")
  clients = set()
  logger = logging.getLogger(__name__)
  
  
  class EchoServer(TCPServer):
      @gen.coroutine
      def handle_stream(self, stream, address):
          clients.add(address)
          while True:
              try:
                  data = yield stream.read_until(b"\n")
                  logger.info("Received bytes: %s", data)
                  if not data.endswith(b"\n"):
                      data = data + b"\n"
                  yield stream.write(data)
              except StreamClosedError:
                  clients.remove(address)
                  logger.warning("Lost client at host %s", address[0])
                  break
              except Exception as e:
                  print(e)
  
  
  if __name__ == "__main__":
      options.parse_command_line()
      server = EchoServer()
      server.listen(options.port)
      logger.info("Listening on TCP port %d", options.port)
      IOLoop.current().start()
  
new_contents: import logging
  from tornado.ioloop import IOLoop
  from tornado import gen
  from tornado.iostream import StreamClosedError
  from tornado.tcpserver import TCPServer
  from tornado.options import options, define
  
  define("port", default=9888, help="TCP port to listen on")
  logger = logging.getLogger(__name__)
  
  
  class EchoServer(TCPServer):
      @gen.coroutine
      def handle_stream(self, stream, address):
          while True:
              try:
                  data = yield stream.read_until(b"\n")
                  logger.info("Received bytes: %s", data)
                  if not data.endswith(b"\n"):
                      data = data + b"\n"
                  yield stream.write(data)
              except StreamClosedError:
                  logger.warning("Lost client at host %s", address[0])
                  break
              except Exception as e:
                  print(e)
  
  
  if __name__ == "__main__":
      options.parse_command_line()
      server = EchoServer()
      server.listen(options.port)
      logger.info("Listening on TCP port %d", options.port)
      IOLoop.current().start()
  
subject: Remove unused clients set