[AstroPy] External packages in astropy

Olе Streicher astropy at liska.ath.cx
Wed Jun 20 15:19:46 EDT 2012

Michael Droettboom <mdroe at stsci.edu> writes:
>>> Mike D (the maintainer of astropy.wcs and pywcs) will know for sure,
>>> but I think his plan is to keep wcslib where it is, because the
>>> python-level wrapper is rather closely tied to the particular
>>> version of wcslib. 
>> I don't see this tight bound to a specific version. pywcs/astropy.wcs
>> uses the official API of wcslib, so it should work with every
>> version. And the shared library contains a SONAME that is going to be
>> changed if binary compability breaks.

> I don't see how this proves that case.  API stability has no
> reflection on correctness.  There are bugfixes to the error handling
> in 4.13 that allow the astropy.wcs unit tests to pass, that do not
> pass with previous versions.

I had rather good communication with the wcslib author in the past, so I
would always prefer a bugfixing there (and, obviously, Mark fixed the
bugs your mentioned). If you find new bugs, I (and probably other
packagers) would probably also happily include fixes into the packages
until upstream incorporates them.

> "extended_ctype.patch" makes wcslib compatible with FITS files that
> contain SIP information.  

Could you explain this a bit more? It would be interesting for the
Debian version of wcslib as well.

> This patch will not be included upstream for political reasons. 
> Without this patch, astropy.wcs can not support SIP and is thus
> effectively broken.

As broken as wcslib itself (I dont't know who of you is right here).  I,
however, see no reason to provide on a system (like Debian, or Gentoo) a
broken wcslib for direct use and a patched version for python use -- so
if your patch is useful it should go to the wcslib author, and/or into
the distribution patches.

Could you explain a bit the advantages and drawbacks of your patch?

> I have been told by the upstream author that MS-Windows compatibility
> is not something he cares about.

This is also not python specific. Also, for distribution packaging
Windows patches are not interesting.

To summarize: pywcs works well with the original wcslib (especially the
latest, bugfixed versions), and it has the same limitations as the used
wcslib. If one wants to use SIP, he needs to use a patched wcslib,
regardless of the programming language (Python or C). Right?

Best regards


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