def build_mappings(self):
        """
        Uses CSV files of field names and positions for
        different filing types to load mappings into memory,
        for use in parsing different types of rows.
        """
        self.mappings = {}
        for record_type in ('sa', 'sb', 'F8872'):
            path = os.path.join(
                os.path.dirname(
                    os.path.dirname(
                        os.path.dirname(__file__))),
                'mappings',
                '{}.csv'.format(record_type))
            mapping = {}
            with open(path, 'r') as csvfile:
                reader = csv.DictReader(csvfile)
                for row in reader:
                    mapping[row['position']] = (
                        row['model_name'],
                        row['field_type'])

            self.mappings[record_type] = mapping
Uses CSV files of field names and positions for
        different filing types to load mappings into memory,
        for use in parsing different types of rows.