code: def next(self):
          
          if self.is_train:
              data, labels = self.sample_train_batch()
          else:
              if self.test_count * self.batch_size < len(self.test_image_files):
                  data, labels = self.get_test_batch()
                  self.test_count += 1
              else:
                  self.test_count = 0
                  raise StopIteration
          return mx.io.DataBatch(data=[data], label=[labels])
docs: Return a batch.