Astroplan - set issue

Hi,

I am trying to use the astroplan feature to decide when to observe various fields for an all sky H-alpha Survey. I am trying to incorporate the "best_month" feature into my output table which will then be used to decide which fields to schedule when. However, some of the fields are not observable due to only being observable from the Northern Hemisphere or Southern Hemisphere. As a result, I think best months should return an empty list. However, when it tries to write the column to a text file, it throws an error

"TypeError: unhashable type: 'set'"

Happy to share my python notebook if that is helpful. Just can't upload it here.

Best,

David

Start by reproducing the error from the astroplan `best_month` feature when its result is added to an output table and written to a text file; the reporter's notebook may be needed for a complete case. Trace how non-observable fields produce an empty result and verify that the table can be written successfully with those fields included.

Written by the indexing model from the issue text.