text: def get_class_id(class_str, classes):
      if class_str in classes:
          class_id = classes.index(class_str)
      else:
          if class_str == '':
              raise ValueError("No class name found")
          else:
              class_id = -1000
              # print("class {} not recognized.".format(class_str))
      return class_id
  
  
  def get_class_name(class_id, classes):
      n_class = len(classes)
      if 0 <= class_id < n_class:
          class_name = classes[class_id]
      elif class_id == -1000:
          class_name = '__background'
      else:
          raise ValueError("Class ID is not defined")
      return class_name
  