How to use the spectral.AsterDatabase.create function in spectral

already exists if
                                      ``data_dir`` isn't provided, or will
                                      be generated if ``data_dir`` is provided
            hdr_file (str):           name of the ENVI spectral library to
                                      generate (without the ``.hdr`` or
                                      ``.sli`` extension)
        """
        if not hdr_file:
            raise ValueError(
                "Must provide path for generated ENVI header file.")

        if not db_file:
            raise ValueError("Must provide path for sqlite file.")

        if data_dir:
            spectral.AsterDatabase.create(db_file, data_dir)

        aster_database = spectral.AsterDatabase(db_file)
        spectrum_ids = [x[0] for x in aster_database.query(
            'SELECT SampleID FROM Samples').fetchall()]
        band_min = 0.38315
        band_max = 2.5082
        band_num = 128
        band_info = spectral.BandInfo()
        band_info.centers = numpy.arange(band_min, band_max,
                                         (band_max - band_min) / band_num)
        band_info.band_unit = 'micrometer'
        library = aster_database.create_envi_spectral_library(spectrum_ids,
                                                              band_info)

        library.save(hdr_file)

already exists if
                                      ``data_dir`` isn't provided, or will
                                      be generated if ``data_dir`` is provided
            hdr_file (str):           name of the ENVI spectral library to
                                      generate (without the ``.hdr`` or
                                      ``.sli`` extension)
        """
        if not hdr_file:
            raise ValueError(
                "Must provide path for generated ENVI header file.")

        elif not db_file:
            raise ValueError("Must provide path for sqlite file.")

        if data_dir:
            spectral.AsterDatabase.create(db_file, data_dir)

        aster_database = spectral.AsterDatabase(db_file)
        spectrum_ids = [x[0] for x in aster_database.query(
            'SELECT SampleID FROM Samples').fetchall()]
        band_min = 0.38315
        band_max = 2.5082
        band_num = 128
        band_info = spectral.BandInfo()
        band_info.centers = numpy.arange(band_min, band_max,
                                         (band_max - band_min) / band_num)
        band_info.band_unit = 'micrometer'
        library = aster_database.create_envi_spectral_library(spectrum_ids,
                                                              band_info)

        library.save(hdr_file)