code: def get_unlabeled_entries(self):
          
          return [
              (idx, entry[0]) for idx, entry in enumerate(self.data)
              if entry[1] is None
          ]
docs: Returns list of unlabeled features, along with their entry_ids
  
          Returns
          -------
          unlabeled_entries : list of (entry_id, feature) tuple
              Labeled entries