I think for the current functionality the current error messages are good enough, but I don't think you're wasting your time at all with better error messages given the functionality you're adding. In particular the "has no attribute 'split'" one (when you pass in an unrelated class) is pretty terrible, and I don't really like the "has no attribute ''" when you pass in the same class, either. So generally I think you're on the right track that those cases could use better error messages.