As part of ccdproc we're adding a FITS reader/writer, following the instructions in the I/O registry documentation.

We register our reader/writer (and get autodetection of fits files) with:

registry.register_reader('fits', CCDData, fits_ccddata_reader)
registry.register_writer('fits', CCDData, fits_ccddata_writer)
registry.register_identifier('fits', CCDData, fits.connect.is_fits)

(excerpt is from https://github.com/mwcraig/ccdproc/blob/api-implementation-1/ccdproc/ccddata.py )

This works fine when I run python setup.py test in python 2.7.6. In python 3 (all of the versions and travis and 3.3.5 on my machine) running the tests gets me the long traceback at https://gist.github.com/mwcraig/10481015

The errors come up when the config file is being generated. Key lines seem to be:

  File "/Users/mcraig/anaconda/envs/py3k/lib/python3.3/site-packages/astropy-0.4.dev7991-py3.3-macosx-10.5-x86_64.egg/astropy/io/registry.py", line 43, in get_formats
    format_classes = sorted(set(_readers) | set(_writers))
TypeError: unorderable types: type() < type()

Additional information:

• It is the lines registry_reader and registry_writer that generate the error. Commenting both out makes this error go away.
• Changing the name of format from 'fits' to another string (e.g. 'fits2') makes the error go away.