plz help can't understand what to do to pass tihs question?

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

    @from_string
    def create_dash(cls,string):
        string_list = []
        str = string.split("-")
        for element in string_list:
            if element == "dash":
                string_list.append("-")
            else:
                string_list.append(".")





    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)


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