human
Write me a the Python program you requested given the following:
Complete the below
def import_tabbed_readings(folder, start_station, end_station, suffix, prefix, fields, clear_existing_data, separator, missing_data_marker):

    ''''Expects a folder containing files with name rtXXXX.txt
    each file contains lines of the form e.g.:
    1978    1       1       0       -99.9   -99.9
    representing year, month, day, rainfall(mm), minimum and maximum temperature'
    '''
assistant
#Here is the Python program you requested.
    import os
    assert os.path.isdir(folder), ('%s    is    not    a    folder!' % folder)
    from decimal import Decimal
    import datetime
    field_order = []
    def readings_lambda(sample_table):
        return (lambda missing_data_marker, converter, place_id: Readings(sample_table, place_id, missing_data_marker=missing_data_marker, converter=Decimal, year_month_to_month_number=ClimateDataPortal.year_month_to_month_number, maximum=None, minimum=None))
    date_format = {}
    field_positions = []
    for (field, position) in zip(fields, range(len(fields))):
        sys.stderr.write(field)
        if (field != 'UNUSED'):
            if (field in ('year', 'month', 'day')):
                date_format[(field + '_pos')] = position
            else:
                try:
                    sample_table = ClimateDataPortal.SampleTable.matching(field, 'O')
                except KeyError:
                    raise Exception(("'%s'    not    recognised,    available    options    are:    %s\nYou    can    add    new    tables    using    add_table.py" % (field, ',    '.join(map('"%s"'.__mod__, available_tables.keys())))))
                else:
                    if clear_existing_data:
                        sys.stderr.write((('Clearing    ' + sample_table._tablename) + '\n'))
                        db((sample_table.id > 0)).delete()
                    field_positions.append((readings_lambda(sample_table), position))
    for field in ('year', 'month', 'day'):
        assert ((field + '_pos') in date_format), ('%s    is    not    specified    in    --fields' % field)
    query_terms = []
    if (start_station is not None):
        query_terms.append((climate_station_id.station_id >= start_station))
    if (end_station is not None):
        query_terms.append((climate_station_id.station_id <= end_station))
    if (not query_terms):
        query = climate_station_id
    else:
        import operator
        query = reduce(operator.and_, query_terms)
    stations = list(db(query).select())
    if stations:
...