src/transformers/models/perceiver/tokenization_perceiver.py/PerceiverTokenizer/_convert_id_to_token
class PerceiverTokenizer:    def _convert_id_to_token(self, index):
        """Converts an index (integer) in a token (str) using the vocab."""
        if index in self.special_tokens_decoder:
            token = self.special_tokens_decoder[index]
        elif index in self.added_tokens_decoder:
            token = self.added_tokens_decoder[index]
        else:
            token = chr(index - self._num_special_tokens)
        return token