def next(self) -> mx.io.DataBatch:
        """
        Returns the next batch from the data iterator.
        """
        if not self.iter_next():
            raise StopIteration

        i, j = self.batch_indices[self.curr_batch_index]
        self.curr_batch_index += 1

        batch_size = self.bucket_batch_sizes[i].batch_size
        source = self.data.source[i][j:j + batch_size]
        target = self.data.target[i][j:j + batch_size]
        data = [source, target]
        label = [self.data.label[i][j:j + batch_size]]

        provide_data = [mx.io.DataDesc(name=n, shape=x.shape, layout=C.BATCH_MAJOR) for n, x in
                        zip(self.data_names, data)]
        provide_label = [mx.io.DataDesc(name=n, shape=x.shape, layout=C.BATCH_MAJOR) for n, x in
                         zip(self.label_names, label)]

        # TODO: num pad examples is not set here if fillup policy would be padding
        return mx.io.DataBatch(data, label,
                               pad=0, index=None, bucket_key=self.buckets[i],
                               provide_data=provide_data, provide_label=provide_label)
Returns the next batch from the data iterator.