How to use the pylsl.IRREGULAR_RATE function in pylsl

n = stream.name()
                stream_params = copy.deepcopy(self.def_stream_parms)
                stream_params['metadata'].update({
                    "name": n,
                    "ch_count": stream.channel_count(),
                    "ch_format": stream.channel_format(),
                    "srate": stream.nominal_srate()
                })
                # ch = stream.desc().child("channels").child("channel")
                # for ch_ix in range(stream.channel_count()):
                #     print("  " + ch.child_value("label"))
                #     ch = ch.next_sibling()

                stream_params['inlet'] = pylsl.StreamInlet(stream)
                stream_params['is_marker'] = stream.channel_format() in ["String", pylsl.cf_string]\
                                             and stream.nominal_srate() == pylsl.IRREGULAR_RATE
                if not stream_params['is_marker']:
                    if self.sig_strm_idx < 0:
                        self.sig_strm_idx = k
                    srate = stream.nominal_srate()
                    stream_params['downSampling'] = srate > 1000
                    stream_params['chunkSize'] = round(srate / self.chunksPerScreen * self.seconds_per_screen)
                    if stream_params['downSampling']:
                        stream_params['downSamplingFactor'] = round(srate / 1000)
                        n_buff = round(stream_params['chunkSize'] / stream_params['downSamplingFactor'])
                        stream_params['downSamplingBuffer'] = [[0] * int(stream.channel_count())] * n_buff
                self.stream_params.append(stream_params)

            self.updateStreamNames.emit([_['metadata'] for _ in self.stream_params], self.sig_strm_idx)
            self.start()

def start_server(server_name, n_channels=1, channel_format='string', nominal_srate=pylsl.IRREGULAR_RATE, stype='EEG',
                 source_id=None):
    """
    Start a new LSL server

    Params
    ------
    server_name:
        Name of the server
    n_channels:
        Number of channels
    channel_format:
        pylsl.cf_string (or 'string')
        pylsl.cf_float32 (or 'float32')
        pylsl.cf_double64 (or 'double64')
        pylsl.cf_int8 (or 'int8')
        pylsl.cf_int16 (or 'int16')