next

        It generates tuple of data.

        For example,
        if :py:meth:`self._variables == ('x', 'y')`
        This method returns :py:meth:` ( [[X] * batch_size], [[Y] * batch_size] )`

        Returns:
            tuple: tuple of data for mini-batch in numpy.ndarray.

def next(self):
        '''next

        It generates tuple of data.

        For example,
        if :py:meth:`self._variables == ('x', 'y')`
        This method returns :py:meth:` ( [[X] * batch_size], [[Y] * batch_size] )`

        Returns:
            tuple: tuple of data for mini-batch in numpy.ndarray.
        '''
        if self._use_thread:
            # Wait for finish previous thread.
            self._next_thread.join()

            if self._current_data is None:
                logger.log(99, 'next() got None retrying.')
                self._next_thread = threading.Thread(target=self._next)
                self._next_thread.start()
                self._next_thread.join()
            self._current_epoch, data = self._current_data
            # Start next thread.
            self._next_thread = threading.Thread(target=self._next)
            self._next_thread.start()
        else:
            self._next()
            self._current_epoch, data = self._current_data

        return data