src/transformers/convert_slow_tokenizer.py/PegasusConverter/vocab
class PegasusConverter:    def vocab(self, proto):
        vocab = [
            (self.original_tokenizer.pad_token, 0.0),
            (self.original_tokenizer.eos_token, 0.0),
        ]

        if self.original_tokenizer.mask_token_sent is not None:
            vocab += [(self.original_tokenizer.mask_token_sent, 0.0)]

        if (
            self.original_tokenizer.mask_token is not None
            and self.original_tokenizer.mask_token_id < self.original_tokenizer.offset
        ):
            vocab += [(self.original_tokenizer.mask_token, 0.0)]

        vocab += [(f"<unk_{i}>", -100.0) for i in range(2, self.original_tokenizer.offset)]
        vocab += [(piece.piece, piece.score) for piece in proto.pieces[2:]]
        return vocab