Return an array and missing value suitable for factorization.

        Returns
        -------
        values : ndarray

            An array suitable for factorization. This should maintain order
            and be a supported dtype (Float64, Int64, UInt64, String, Object).
            By default, the extension array is cast to object dtype.
        na_value : object
            The value in `values` to consider missing. This will be treated
            as NA in the factorization routines, so it will be coded as
            `na_sentinal` and not included in `uniques`. By default,
            ``np.nan`` is used.

        Notes
        -----
        The values returned by this method are also used in
        :func:`pandas.util.hash_pandas_object`.

def _values_for_factorize(self) -> Tuple[np.ndarray, Any]:
        """
        Return an array and missing value suitable for factorization.

        Returns
        -------
        values : ndarray

            An array suitable for factorization. This should maintain order
            and be a supported dtype (Float64, Int64, UInt64, String, Object).
            By default, the extension array is cast to object dtype.
        na_value : object
            The value in `values` to consider missing. This will be treated
            as NA in the factorization routines, so it will be coded as
            `na_sentinal` and not included in `uniques`. By default,
            ``np.nan`` is used.

        Notes
        -----
        The values returned by this method are also used in
        :func:`pandas.util.hash_pandas_object`.
        """
        return self.astype(object), np.nan