def set_src_lang_special_tokens(self, src_lang) -> None:
        """Reset the special tokens to the source lang setting.
        - In legacy mode: No prefix and suffix=[eos, src_lang_code].
        - In default mode: Prefix=[src_lang_code], suffix = [eos]
        """
        self.cur_lang_code = self.convert_tokens_to_ids(src_lang)

        if self.legacy_behaviour:
            self.prefix_tokens = []
            self.suffix_tokens = [self.eos_token_id, self.cur_lang_code]
        else:
            self.prefix_tokens = [self.cur_lang_code]
            self.suffix_tokens = [self.eos_token_id]

        prefix_tokens_str = self.convert_ids_to_tokens(self.prefix_tokens)
        suffix_tokens_str = self.convert_ids_to_tokens(self.suffix_tokens)

        self._tokenizer.post_processor = processors.TemplateProcessing(
            single=prefix_tokens_str + ["$A"] + suffix_tokens_str,
            pair=prefix_tokens_str + ["$A", "$B"] + suffix_tokens_str,
            special_tokens=list(zip(prefix_tokens_str + suffix_tokens_str, self.prefix_tokens + self.suffix_tokens)),
        )
Reset the special tokens to the source lang setting.
        - In legacy mode: No prefix and suffix=[eos, src_lang_code].
        - In default mode: Prefix=[src_lang_code], suffix = [eos]
        
dpkd/transformers/src/transformers/models/nllb/tokenization_nllb_fast.py