Might be better / simpler just to make check_fname call _check_fname internally and return the str-ified absolute path, then our code ends up more DRY. It seems like every time we check_fname we probably want to call _check_fname anyway...

Or we could go the other way and make _check_fname accept a ext argument, and have it call check_fname internally. I think I'd rather go that way.

#9613 (comment)