Initializes data necessary to execute attacks.

    This method could be called multiple times, only first call does
    initialization, subsequent calls are noop.

def fetch_attacks_data(self):
    """Initializes data necessary to execute attacks.

    This method could be called multiple times, only first call does
    initialization, subsequent calls are noop.
    """
    if self.attacks_data_initialized:
      return
    # init data from datastore
    self.submissions.init_from_datastore()
    self.dataset_batches.init_from_datastore()
    self.adv_batches.init_from_datastore()
    # copy dataset locally
    if not os.path.exists(LOCAL_DATASET_DIR):
      os.makedirs(LOCAL_DATASET_DIR)
    eval_lib.download_dataset(self.storage_client, self.dataset_batches,
                              LOCAL_DATASET_DIR,
                              os.path.join(LOCAL_DATASET_COPY,
                                           self.dataset_name, 'images'))
    # download dataset metadata
    self.read_dataset_metadata()
    # mark as initialized
    self.attacks_data_initialized = True