How to use the cltk.prosody.latin.StringUtils.mark_list function in cltk

def correct_invalid_start(self, scansion: str) -> str:
        """If a hexameter, hendecasyllables, or pentameter scansion starts with spondee,
        an unstressed syllable in the third position must actually be stressed,
        so we will convert it: - - | U    ->  - - | -
        :param scansion:
        :return:
        >>> print(VerseScanner().correct_invalid_start(
        ... " -   - U   U -  -  U U U U  U U  - -").strip())
        -   - -   - -  -  U U U U  U U  - -
        """
        mark_list = StringUtils.mark_list(scansion)
        raw_scansion = scansion.replace(" ", "")
        if raw_scansion.startswith(self.constants.SPONDEE + self.constants.UNSTRESSED):
            new_scansion = list(self.constants.SPONDEE + self.constants.SPONDEE + raw_scansion[4:])
            corrected = "".join(new_scansion)
            new_sequence = list(" " * len(scansion))
            for idx, car in enumerate(corrected):
                new_sequence[mark_list[idx]] = car
            return "".join(new_sequence)
        return scansion

def correct_penultimate_dactyl_chain(self, scansion: str) -> str:
        """For pentameter the last two feet of the verse are predictable dactyls,
        and do not regularly allow substitutions.
        :param scansion: scansion line thus far
        :return: corrected line of scansion

        >>> print(PentameterScanner().correct_penultimate_dactyl_chain(
        ... "U  U  U  U  U  U  U  U  U  U  U  U  U  U"))
        U  U  U  U  U  U  U  -  U  U  -  U  U  U
        """
        mark_list = StringUtils.mark_list(scansion)
        vals = list(scansion.replace(" ", ""))
        n_vals = vals[:-7] + [self.constants.DACTYL + self.constants.DACTYL] + [vals[-1]]
        corrected = "".join(n_vals)
        new_line = list(" " * len(scansion))
        for idx, car in enumerate(corrected):
            new_line[mark_list[idx]] = car
        return "".join(new_line)

def make_dactyls(self, scansion: str) -> str:
        """If a pentameter line has 14 syllables, it starts and ends with double dactyls.

        >>> print(PentameterScanner().make_dactyls("U  U  U  U  U  U  U  U  U  U  U  U  U  U"))
        -  U  U  -  U  U  -  -  U  U  -  U  U  U
        """
        mark_list = StringUtils.mark_list(scansion)
        vals = list(scansion.replace(" ", ""))
        new_vals = self.DACTYLIC_PENTAMETER[:-1] + vals[-1]
        corrected = "".join(new_vals)
        new_line = list(" " * len(scansion))
        for idx, car in enumerate(corrected):
            new_line[mark_list[idx]] = car
        return "".join(new_line)

Since this method takes a Procrustean approach to modifying the scansion pattern,
         it is not used by default in the scan method; however, it is available as an optional
         keyword parameter, and users looking to further automate the generation of scansion
         candidates should consider using this as a fall back.
        :param scansion: scansion with broken dactyl chain; inverted amphibrachs not allowed
        :return: corrected line of scansion

        >>> print(HexameterScanner().correct_dactyl_chain(
        ... "-   U U  -  - U U -  - - U U  - x"))
        -   - -  -  - U U -  - - U U  - x
        >>> print(HexameterScanner().correct_dactyl_chain(
        ... "-   U  U U  U -     -   -   -  -   U  U -   U")) # doctest: +NORMALIZE_WHITESPACE
        -   -  - U  U -     -   -   -  -   U  U -   U
        """
        mark_list = StringUtils.mark_list(scansion)
        vals = list(scansion.replace(" ", ""))
        #  ignore last two positions, save them
        feet = [vals.pop(), vals.pop()]
        length = len(vals)
        idx = length - 1
        while idx > 0:
            one = vals[idx]
            two = vals[idx - 1]
            if idx > 1:
                three = vals[idx - 2]
            else:
                three = ""
            # Dactyl foot is okay, no corrections
            if one == self.constants.UNSTRESSED and \
                            two == self.constants.UNSTRESSED and \
                            three == self.constants.STRESSED:

def correct_invalid_start(self, scansion: str) -> str:
        """The third syllable of a hendecasyllabic line is long, so we will convert it

        :param scansion:
        :return: scansion string with corrected start
        >>> print(HendecasyllableScanner().correct_invalid_start(
        ... "- U U  U U  - U   -  U - U").strip())
        - U -  U U  - U   -  U - U
        """
        mark_list = StringUtils.mark_list(scansion)
        vals = list(scansion.replace(" ", ""))
        corrected = vals[:2] + [self.constants.STRESSED] + vals[3:]
        new_line = list(" " * len(scansion))
        for idx, car in enumerate(corrected):
            new_line[mark_list[idx]] = car
        return "".join(new_line)

def correct_antepenult_chain(self, scansion: str) -> str:
        """For hendecasyllables the last three feet of the verse are predictable
        and do not regularly allow substitutions.

        :param scansion: scansion line thus far
        :return: corrected line of scansion

        >>> print(HendecasyllableScanner().correct_antepenult_chain(
        ... "-U -UU UU UU UX").strip())
        -U -UU -U -U -X
        """
        mark_list = StringUtils.mark_list(scansion)
        vals = list(scansion.replace(" ", ""))
        new_vals = vals[:len(vals) - 6] + [self.constants.TROCHEE +
                                           self.constants.TROCHEE +
                                           self.constants.STRESSED] + vals[-1:]
        corrected = "".join(new_vals)
        new_line = list(" " * len(scansion))
        for idx, car in enumerate(corrected):
            new_line[mark_list[idx]] = car
        return "".join(new_line)