def METHOD_NAME(self, tokens):
    """Converts a sequence of tokens (string) in a single string."""
    current_sub_tokens = []
    out_string = ""
    prev_is_special = False
    for i, token in enumerate(tokens):
        # make sure that special tokens are not decoded using sentencepiece model
        if token in self.all_special_tokens:
            if not prev_is_special and i != 0:
                out_string += " "
            out_string += self.sp_model.decode(current_sub_tokens) + token
            prev_is_special = True
            current_sub_tokens = []
        else:
            current_sub_tokens.append(token)
            prev_is_special = False
    out_string += self.sp_model.decode(current_sub_tokens)
    return out_string