@data_factory(
    label='FITS file',
    identifier=is_fits,
    priority=100,
)
def fits_reader(source, auto_merge=False, exclude_exts=None, label=None):
    """
    Read in all extensions from a FITS file.

    Parameters
    ----------
    source: str or HDUList
        The pathname to the FITS file.
        If an HDUList is passed in, simply use that.

    auto_merge: bool
        Merge extensions that have the same shape
        and only one has a defined WCS.

    exclude_exts: [hdu, ] or [index, ]
        List of HDU's to exclude from reading.
        This can be a list of HDU's or a list
        of HDU indexes.
    """

    from astropy.io import fits
    from astropy.table import Table

    exclude_exts = exclude_exts or []
    if not isinstance(source, fits.hdu.hdulist.HDUList):
        hdulist = fits.open(source, ignore_missing_end=True)
        hdulist.verify('fix')
    else:
        hdulist = source
    groups = OrderedDict()
    extension_by_shape = OrderedDict()

    if label is not None:

        label_base = label

    else:

        hdulist_name = hdulist.filename()
        if hdulist_name is None:
            hdulist_name = "HDUList"

        label_base = basename(hdulist_name).rpartition('.')[0]

        if not label_base:
            label_base = basename(hdulist_name)

    # Create a new image Data.
    def new_data():
        label = '{0}[{1}]'.format(
            label_base,
            hdu_name
        )
        data = Data(label=label)
        data.coords = coords
        groups[hdu_name] = data
        extension_by_shape[shape] = hdu_name
        return data

    for extnum, hdu in enumerate(hdulist):
        hdu_name = hdu.name if hdu.name else "HDU{0}".format(extnum)
        if (hdu.data is not None and
                hdu.data.size > 0 and
                hdu_name not in exclude_exts and
                extnum not in exclude_exts):
            if is_image_hdu(hdu):
                shape = hdu.data.shape
                coords = coordinates_from_header(hdu.header)
                if not auto_merge or has_wcs(coords):
                    data = new_data()
                else:
                    try:
                        data = groups[extension_by_shape[shape]]
                    except __HOLE__:
                        data = new_data()
                data.add_component(component=hdu.data,
                                   label=hdu_name)
            elif is_table_hdu(hdu):
                # Loop through columns and make component list
                table = Table(hdu.data)
                label = '{0}[{1}]'.format(
                    label_base,
                    hdu_name
                )
                data = Data(label=label)
                groups[hdu_name] = data
                for column_name in table.columns:
                    column = table[column_name]
                    if column.ndim != 1:
                        warnings.warn("Dropping column '{0}' since it is not 1-dimensional".format(column_name))
                        continue
                    component = Component.autotyped(column, units=column.unit)
                    data.add_component(component=component,
                                       label=column_name)
    return [groups[idx] for idx in groups]


# Utilities
dataset/ETHPy150Open glue-viz/glue/glue/core/data_factories/fits.py/fits_reader