code: def transmit(self):
          
          if not self.queue:
              return
  
          deliverable = []
  
          for src, dst, msg in self.queue:
              _assert_valid_addr(src)
              _assert_valid_addr(dst)
  
              # assert (src, dst) in self.connections, "Hubs should only send messages to addresses they have previously connected to"
  
              if random.random() <= self._packet_loss.get((src, dst), 0.0):
                  dbg("packet lost: %r  %s → %s" % (msg, src, dst))
                  continue
  
              if dst not in self.listeners:
                  pass  # dbg(u"%r ⇝ ↴" % (_dumpmsg(msg),))
              else:
                  # dbg(u"%r → %s" % (_dumpmsg(msg), dst))
                  sock = self.listeners[dst]
                  deliverable.append((msg, src, sock))
  
          del self.queue[:]
  
          for msg, src, sock in deliverable:
              sock.gotMultipart(msg)
docs: Puts all currently pending sent messages to the insock buffer of the recipient of the message.
  
          This is more useful than immediate "delivery" because it allows full flexibility of the order in which tests
          set up nodes and mock actors on those nodes, and of the order in which messages are sent out from a node.