Keeps returning "Bummer!" Here's my code: Try it out, it works, I tested it on IDLE.

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(string):
        pattern = []
        current_wrd = ''
        for letter in string:
            current_wrd += letter
            if current_wrd == 'dash':
                pattern.append('_')
                current_wrd = ''
            elif current_wrd == 'dot':
                pattern.append('.')
                current_wrd = ''
            elif current_wrd == '-':
                current_wrd = ''
        return pattern


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