# Create a multi-extension FITS (MEF) file from scratch¶

This example demonstrates how to create a multi-extension FITS (MEF) file from scratch using astropy.io.fits.

By: Erik Bray

import os


HDUList objects are used to hold all the HDUs in a FITS file. This HDUList class is a subclass of Python’s builtin list. and can be created from scratch. For example, to create a FITS file with three extensions:

from astropy.io import fits
new_hdul = fits.HDUList()
new_hdul.append(fits.ImageHDU())
new_hdul.append(fits.ImageHDU())


Write out the new file to disk:

new_hdul.writeto('test.fits')


Alternatively, the HDU instances can be created first (or read from an existing FITS file).

Create a multi-extension FITS file with two empty IMAGE extensions (a default PRIMARY HDU is prepended automatically if one is not specified; we use overwrite=True to overwrite the file if it already exists):

hdu1 = fits.PrimaryHDU()
hdu2 = fits.ImageHDU()
new_hdul = fits.HDUList([hdu1, hdu2])
new_hdul.writeto('test.fits', overwrite=True)


Finally, we’ll remove the file we created:

os.remove('test.fits')


Total running time of the script: ( 0 minutes 0.006 seconds)

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