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