Get next data batch from iterator.

        Returns
        -------
        DataBatch
            The data of next batch.

        Raises
        ------
        StopIteration
            If the end of the data is reached.

def next(self):
        """Get next data batch from iterator.

        Returns
        -------
        DataBatch
            The data of next batch.

        Raises
        ------
        StopIteration
            If the end of the data is reached.
        """
        if self.iter_next():
            return DataBatch(data=self.getdata(), label=self.getlabel(), \
                    pad=self.getpad(), index=self.getindex())
        else:
            raise StopIteration