Why not use a normal method? I'm struggling with understanding the value of this, why would you use a classmethod?

class Letter:
    def __init__(self, pattern=None):
        self.pattern = pattern

    def __iter__(self):
        yield from self.pattern

    def __str__(self):
        output = []
        for blip in self:
            if blip == '.':
                output.append('dot')
            else:
                output.append('dash')
        return '-'.join(output)

    @classmethod
    def from_string(cls, yourstring):
        splitstring = yourstring.split("-")
        newstring = []
        for i in splitstring:
            if i == "dash":
                newstring.append("-")
            else:
                newstring.append(".")
        return cls(newstring)

class S(Letter):
    def __init__(self):
         pattern = ['.', '.', '.']
         super().__init__(pattern)