http://cxc.harvard.edu/contrib/pyyaks/index.html

https://github.com/sot/eng_archive/blob/master/Ska/engarchive/file_defs.py
https://github.com/sot/eng_archive/blob/master/Ska/engarchive/fetch.py#L125

The point of the `pyyaks.context` is that you can define package-wide file names as templates.  So it's really useful if there are interpolated values like `{{obsid}}` or whatever.  In this case you set the context (e.g. obsid=15304) and then something like ``files['ACEN1'].abs`` will point there.  In this case a simple `FILES` dict will probably suffice.