Multiple Tables saved in the same .fits file

Question

I have multiple tables created with astropy.table.Table, for example:

 from astropy.table import Table
 import numpy as np
 #table 1
 ta=Table()
 ta["test1"]=np.arange(0,100.)
 #table 2
 tb=Table()
 tb["test2"]=np.arange(0,100.)

I can save them individually to .fits files using

ta.write('table1.fits')
tb.write('table2.fits')

But I would like to have them saved to the same .fits file, each of them with a different hdu. How can I do that?

Answer 1

There's an example of how to do this here. So, you could do something like the following:

import numpy as np
from astropy.io import fits

ta = Table()
ta['test1'] = np.arange(0, 100.)
col1 = fits.Column(name=ta.colnames[0], format='E', array=ta)

tb = Table()
tb['test2'] = np.arange(0, 100.)
col2 = fits.Column(name=tb.colnames[0], format='E', array=tb)

cols = fits.ColDefs([col1, col2])

hdu = fits.BinTableHDU.from_columns(cols)
hdu.writeto('table.fits')

which only has one binary table HDU, but with two columns. Alternatively, to add them as separate HDUs, you could do something like

ta = Table()
ta['test1'] = np.arange(0, 100.)
col1 = fits.Column(name=ta.colnames[0], format='E', array=ta)

hdu1 = fits.BinTableHDU.from_columns(fits.ColDefs([col1]))

tb = Table()
tb['test2'] = np.arange(0, 100.)
col2 = fits.Column(name=tb.colnames[0], format='E', array=tb)

hdu2 = fits.BinTableHDU.from_columns(fits.ColDefs([col2]))

# create a header
hdr = fits.Header()
hdr['Author'] = 'Me'
primary_hdu = fits.PrimaryHDU(header=hdr)

# put all the HDUs together
hdul = fits.HDUList([primary_hdu, hdu1, hdu2])

# write it out
hdul.writeto('table.fits')

Answer 2

There's a utility function astropy.io.fits.table_to_hdu.

To continue your example if you have two table objects ta and tb:

from astropy.io import fits
hdu_list = fits.HDUList([
    fits.PrimaryHDU(),
    fits.table_to_hdu(ta),
    fits.table_to_hdu(tb), 
])
hdu_list.writeto('tables.fits')