No method named "from_string"

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, string):
        result = []
        mylist = string.split('-')
        for item in mylist:
            if item == 'dash':
                result.appned('_')
            if item == 'dot':
                result.append('.')
            else:
                continue
        return cls(pattern=result)


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