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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def from_string(cls, s):
 """ Decode from the YY token lattice format. """

        def _qstrip(s):
            return s[1:-1]  # remove assumed quote characters
        tokens = []
        for match in _yy_re.finditer(s):
            d = match.groupdict()
            lnk, pos = None, []
            if d['lnkfrom'] is not None:
                lnk = Lnk.charspan(d['lnkfrom'], d['lnkto'])
            if d['pos'] is not None:
                ps = d['pos'].strip().split()
                pos = list(zip(map(_qstrip, ps[::2]), map(float, ps[1::2])))
            tokens.append(
                YyToken(
                    int(d['id']),
                    int(d['start']),
                    int(d['end']),
                    lnk,
                    list(map(int, d['paths'].strip().split())),
                    _qstrip(d['form']),
                    None if d['surface'] is None else _qstrip(d['surface']),
                    int(d['ipos']),
                    list(map(_qstrip, d['lrules'].strip().split())),
                    pos
                )
            )
        return cls(tokens)