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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def read_data(archive, arc_type, day, stachans, length=86400):
 """ Function to read the appropriate data from an archive for a day. :type archive: str :param archive: The archive source - if arc_type is seishub, this should be a url, if the arc_type is FDSN then this can be either a url or a known obspy client. If arc_type is day_vols, then this is the path to the top directory. :type arc_type: str :param arc_type: The type of archive, can be: seishub, FDSN, day_volumes :type day: datetime.date :param day: Date to retrieve data for :type stachans: list :param stachans: List of tuples of Stations and channels to try and get, will not fail if stations are not available, but will warn. :type length: float :param length: Data length to extract in seconds, defaults to 1 day. :returns: Stream of data :rtype: obspy.core.stream.Stream .. note:: A note on arc_types, if arc_type is day_vols, then this will \ look for directories labelled in the IRIS DMC conventions of \ Data within these files directories should be stored as day-long, \ single-channel files. This is not implemented in the fasted way \ possible to allow for a more general situation. If you require more \ speed you will need to re-write this. .. rubric:: Example 1 Trace(s) in Stream: BP.JCNB.40.SP1 | 2012-03-26T00:00:00.000000Z - 2012-03-26T23:59:59.\ 950000Z | 20.0 Hz, 1728000 samples .. rubric:: Example, missing data 1 Trace(s) in Stream: BP.JCNB.40.SP1 | 2012-03-26T00:00:00.000000Z - 2012-03-26T23:59:59.\ 950000Z | 20.0 Hz, 1728000 samples .. rubric:: Example, local day-volumes 2 Trace(s) in Stream: AF.WHYM..SHZ | 2012-03-26T00:00:00.000000Z - 2012-03-26T23:59:59.000000Z \ | 1.0 Hz, 86400 samples AF.EORO..SHZ | 2012-03-26T00:00:00.000000Z - 2012-03-26T23:59:59.000000Z \ | 1.0 Hz, 86400 samples """

    st = []
    available_stations = _check_available_data(archive, arc_type, day)
    for station in stachans:
        if len(station[1]) == 2:
            # Cope with two char channel naming in seisan
            station_map = (station[0], station[1][0] + '*' + station[1][1])
            available_stations_map = [(sta[0], sta[1][0] + '*' + sta[1][-1])
                                      for sta in available_stations]
        else:
            station_map = station
            available_stations_map = available_stations
        if station_map not in available_stations_map:
            msg = ' '.join([station[0], station_map[1], 'is not available for',
                            day.strftime('%Y/%m/%d')])
            warnings.warn(msg)
            continue
        if arc_type.lower() == 'seishub':
            client = SeishubClient(archive)
            st += client.get_waveforms(
                    network='*', station=station_map[0], location='*',
                    channel=station_map[1], starttime=UTCDateTime(day),
                    endtime=UTCDateTime(day) + length)
        elif arc_type.upper() == "FDSN":
            client = FDSNClient(archive)
            try:
                st += client.get_waveforms(
                    network='*', station=station_map[0], location='*',
                    channel=station_map[1], starttime=UTCDateTime(day),
                    endtime=UTCDateTime(day) + length)
            except FDSNException:
                warnings.warn('No data on server despite station being ' +
                              'available...')
                continue
        elif arc_type.lower() == 'day_vols':
            wavfiles = _get_station_file(os.path.join(
                archive, day.strftime('Y%Y' + os.sep + 'R%j.01')),
                station_map[0], station_map[1])
            for wavfile in wavfiles:
                st += read(wavfile, starttime=day, endtime=day + length)
    st = Stream(st)
    return st