code: def _objective_bestscore(self, old, new):
          
          (oldscore, oldthing) = old
          (newscore, newthing) = new
          if oldscore is None:
              return True
          if newscore is None:
              return False
          return oldscore < newscore
docs: An objective function that returns True if new has a better score
          than old, and ``False`` otherwise.
  
          INPUTS:
              old (tuple): a tuple (score, embedding)
  
              new (tuple): a tuple (score, embedding)