src/transformers/convert_slow_tokenizer.py/PegasusConverter/post_processor
class PegasusConverter:    def post_processor(self):
        eos = self.original_tokenizer.eos_token
        special_tokens = [
            (eos, self.original_tokenizer.eos_token_id),
        ]
        return processors.TemplateProcessing(single=["$A", eos], pair=["$A", "$B", eos], special_tokens=special_tokens)