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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def next(self):
 """Return a batch."""

        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])