src/transformers/models/t5/tokenization_t5.py/T5Tokenizer/_convert_id_to_token
class T5Tokenizer:    def _convert_id_to_token(self, index):
        """Converts an index (integer) in a token (str) using the vocab."""
        if index < self.sp_model.get_piece_size():
            token = self.sp_model.IdToPiece(index)
        else:
            token = f"<extra_id_{self.vocab_size - 1 - index}>"
        return token