@classmethod Task -- This works in PyCharm but not for this excercise?

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, input_str):
        pattern = []
        input_str_list = input_str.split("-")
        for blip in input_str_list:
            if blip == 'dash':
                pattern.append('-')
            else:
                pattern.append('.')
        return cls(pattern)

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



# >>> test = Letter.from_string("dot-dot-dot-dash")
# >>> print(test.pattern)
# ['.', '.', '.', '-']