code: def poller(self, item, handler, arg):
          
          return lib.zloop_poller(self._as_parameter_, item, handler, arg)
docs: Register low-level libzmq pollitem with the reactor. When the pollitem
  is ready, will call the handler, passing the arg. Returns 0 if OK, -1
  if there was an error. If you register the pollitem more than once, each
  instance will invoke its corresponding handler. A pollitem with
  socket=NULL and fd=0 means 'poll on FD zero'.