code: def save_checkpoint(self, checkpoint_dir):
      pass
  
file_path: ray/doc/source/tune/doc_code/key_concepts.py
imports: from ray import train
  from ray import tune
  from ray.tune.search.bayesopt import BayesOptSearch
  from ray import train
  from ray.tune.schedulers import HyperBandScheduler
label_desc: Use image node_id 3 for calling the Trainable obj's underlying member method code with example usage: obj.save_checkpoint(checkpoint_dir) without return types