def _atomic_partition(self, char: int) -> Tuple[str, str, str]:
        """Partition self.string where `char`'s not in atomic sub-spans."""
        s, e = self._span
        index = self._shadow.find(char)
        if index == -1:
            return self._lststr[0][s:e], '', ''
        lststr0 = self._lststr[0]
        return lststr0[s:s + index], chr(char), lststr0[s + index + 1:e]
Partition self.string where `char`'s not in atomic sub-spans.