AsdfInFits

stdatamodels.asdf_in_fits contains functions to help migrate code that uses the AsdfInFits format (ASDF data stored in a FITS file) from ASDF (which dropped support for AsdfInFits in ASDF version 3.0) to stdatamodels.

Opening AsdfInFits files

AsdfInFits files can be opened with stdatamodels.asdf_in_fits.open(). This function aims to replace previous calls to asdf.open() or the no-longer-supported asdf.AsdfInFits.open and can similarly be used in a with statement.

with stdatamodels.asdf_in_fits.open('some_file.fits') as af:
    # access the contents of `af` as a normal `asdf.AsdfFile`
    pass

It is recommended that a with statement is used to ensure the resulting asdf.AsdfFile and astropy.io.fits.HDUList are closed properly.

If a with statement cannot be used, stdatamodels.asdf_in_fits.open() can be used as a regular function (be sure to close the file when done).

af = stdatamodels.asdf_in_fits.open('some_file.fits')
# access the contents of `af` as a normal `asdf.AsdfFile`
af.close()

Writing AsdfInFits files

stdatamodels.asdf_in_fits.write() can be used to write ASDF data within a FITS file.

tree = {'sci': [1, 2, 3]}   # data to be stored in ASDF format
stdatamodels.asdf_in_fits.write('some_file.fits', tree)

This functions is meant to replace calls to asdf.AsdfInFits.write_to, which was removed as of ASDF version 3.0. Please see the stdatamodels.asdf_in_fits.write() documentation for all available arguments.

stdatamodels.asdf_in_fits.write() supports references to array data within the astropy.io.fits.HDUList. This can be accomplished by first creating a astropy.io.fits.HDUList and populating it with data

from astropy.io import fits

hdulist = fits.HDUList()
hdulist.append(fits.ImageHDU(np.arange(512, dtype=float), name='SCI'))
hdulist.append(fits.ImageHDU(np.arange(512, dtype=float), name='DQ'))

Then constructing a tree with references to the same data.

tree = {
    'model': {
        'sci': {
            'data': hdulist['SCI'].data,
        },
        'dq': {
            'data': hdulist['DQ'].data,
        }
    }
}

Finally providing the tree and hdulist to stdatamodels.asdf_in_fits.write().

stdatamodels.asdf_in_fits.write('some_file.fits', tree, hdulist)

When read back with stdatamodels.asdf_in_fits.open() the data for sci and dq will be read from the HDUList instead of from the ASDF data embedded in the HDUList.