code: def persist_upstream_structure(self):
          
          persist_dir = os.path.join(self.experiment_directory, '{}_upstream_structure.json'.format(self.name))
          logger.info('Step {}, saving upstream pipeline structure to {}'.format(self.name, persist_dir))
          joblib.dump(self.upstream_structure, persist_dir)
docs: Persist json file with the upstream steps structure, that is step names and their connections.