code: def update(self, signals):
          
          if self._sfd < 0:
              _err_closed()
          mask = sigset_t()
          sigemptyset(mask)
          if signals is not None:
              for signal in signals:
                  sigaddset(mask, signal)
          # flags are ignored when sfd is not -1
          _signalfd(self._sfd, mask, 0)
          self._signals = frozenset(signals)
docs: Update the mask of signals this signalfd reacts to
  
          :param signals:
              A replacement set of signal numbers to monitor
          :raises ValueError:
              If :meth:`closed()` is True