I tested this in my terminal and it worked? Why won't it pass?

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):
        newList = string.rsplit('-')
        newStrList = []
        for item in newList:
            if item == 'dot':
                newStrList.append('.')
            elif item == 'dash':
                newStrList.append('-')
        return (Letter(newStrList))



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