code: def request_client_list(self, req, msg):
          
          # TODO Get list of ClientConnection* instances and implement a standard
          # 'address-print' method in the ClientConnection class
          clients = self._client_conns
          num_clients = len(clients)
          for conn in clients:
              addr = conn.address
              req.inform(addr)
          return req.make_reply('ok', str(num_clients))
docs: Request the list of connected clients.
  
          The list of clients is sent as a sequence of #client-list informs.
  
          Informs
          -------
          addr : str
              The address of the client as host:port with host in dotted quad
              notation. If the address of the client could not be determined
              (because, for example, the client disconnected suddenly) then
              a unique string representing the client is sent instead.
  
          Returns
          -------
          success : {'ok', 'fail'}
              Whether sending the client list succeeded.
          informs : int
              Number of #client-list inform messages sent.
  
          Examples
          --------
          ::
  
              ?client-list
              #client-list 127.0.0.1:53600
              !client-list ok 1