[Numpy-discussion] proposal: smaller representation of string arrays

[Anne Archibald]

On Tue, Apr 25, 2017 at 7:52 PM Phil Hodge <hodge at stsci.edu> wrote:

> On 04/25/2017 01:34 PM, Anne Archibald wrote:
> > I know they're not numpy-compatible, but FITS header values are
> > space-padded; does that occur elsewhere?
>
> Strings in FITS headers are delimited by single quotes.  Some keywords
> (only a handful) are required to have values that are blank-padded (in
> the FITS file) if the value is less than eight characters.  Whether you
> get trailing blanks when you read the header depends on the FITS
> reader.  I use astropy.io.fits to read/write FITS files, and that
> interface strips trailing blanks from character strings:
>
> TARGPROP= 'UNKNOWN '           / Proposer's name for the target
>
>  >>> fd = fits.open("test.fits")
>  >>> s = fd[0].header['targprop']
>  >>> len(s)
> 7
>

Actually, for what it's worth, the FITS spec says that in such values
trailing spaces are not significant, see page 7:
https://fits.gsfc.nasa.gov/standard40/fits_standard40draft1.pdf
But they're not really relevant to numpy's situation, because as here you
need to do elaborate de-quoting before they can go into a data structure.
What I was wondering was whether people have data lying around with
fixed-width fields where the strings are space-padded, so that numpy needs
to support that.

Anne
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