`fits.writeto()` discards header input for non-image data

When I use fits.writeto(filename,data=data, header=header), the header information is not included in the output file’s header.

I make a minimal FITS file:

import numpy as np
from astropy.io import fits
data=np.zeros((5,),dtype=[('x',np.float),('y',np.int)])
h_in = fits.Header()
h_in['ANSWER']=(42.0,'LTU&E')
fname='/tmp/foo.fits'
fits.writeto(fname,data=data,header=h_in,clobber=True)
h_out=fits.getheader(fname,ext=1)
h_in,'------------------------------------------------',h_out

and the output header doesn’t have the ANSWER field that was passed to the writeto():

(ANSWER  =                 42.0 / LTU&E                                          ,
 '------------------------------------------------',
 XTENSION= 'BINTABLE'           / binary table extension
 BITPIX  =                    8 / array data type
 NAXIS   =                    2 / number of array dimensions
 NAXIS1  =                   16 / length of dimension 1
 NAXIS2  =                    5 / length of dimension 2
 PCOUNT  =                    0 / number of group parameters
 GCOUNT  =                    1 / number of groups
 TFIELDS =                    2 / number of table fields
 TTYPE1  = 'x       '
 TFORM1  = 'D       '
 TTYPE2  = 'y       '
 TFORM2  = 'K       '                                                            )

The ANSWER field is also not in extension 0.

On the other hand, if I make an image FITS file, the header data is retained:

image = np.zeros((10,10),dtype=np.float)
fname='/tmp/foo_image.fits'
fits.writeto(fname,data=image,header=h_in,clobber=True)
h_out_image=fits.getheader(fname,ext=0)
h_out_image

which has ANSWER in the ext=0 header:

SIMPLE  =                    T / conforms to FITS standard
BITPIX  =                  -64 / array data type
NAXIS   =                    2 / number of array dimensions
NAXIS1  =                   10
NAXIS2  =                   10
ANSWER  =                 42.0 / LTU&E

This is in astropy 1.3.2 .

Work-around:

hdu = fits.BinTableHDU(data=data, header=h_in)
hdu.writeto(fname, clobber=True)
fits.getheader(fname,ext=1)

gives a file with the ANSWER in the header.

[saimn]

oops 😁

[pllim]

@saimn , did you just pinged yourself? >_>