code: def _prepare_sample_data(self, submission_type):
      
      # write images
      images = np.random.randint(0, 256,
                                 size=[BATCH_SIZE, 299, 299, 3], dtype=np.uint8)
      for i in range(BATCH_SIZE):
        Image.fromarray(images[i, :, :, :]).save(
            os.path.join(self._sample_input_dir, IMAGE_NAME_PATTERN.format(i)))
      # write target class for targeted attacks
      if submission_type == 'targeted_attack':
        target_classes = np.random.randint(1, 1001, size=[BATCH_SIZE])
        target_class_filename = os.path.join(self._sample_input_dir,
                                             'target_class.csv')
        with open(target_class_filename, 'w') as f:
          for i in range(BATCH_SIZE):
            f.write((IMAGE_NAME_PATTERN + ',{1}\n').format(i, target_classes[i]))
docs: Prepares sample data for the submission.
  
      Args:
        submission_type: type of the submission.