code: def extract_means_or_values(cls, observation, prediction, key=None):
          
  
          obs_mv = cls.extract_mean_or_value(observation, key)
          pred_mv = cls.extract_mean_or_value(prediction, key)
          return obs_mv, pred_mv
docs: Extracts the mean, value, or user-provided key from the observation
          and prediction dictionaries.