src/transformers/tokenization_utils_base.py/BatchEncoding/n_sequences
class BatchEncoding:    def n_sequences(self) -> Optional[int]:
        """
        :obj:`Optional[int]`: The number of sequences used to generate each sample from the batch encoded in this
        :class:`~transformers.BatchEncoding`. Currently can be one of :obj:`None` (unknown), :obj:`1` (a single
        sentence) or :obj:`2` (a pair of sentences)
        """
        return self._n_sequences