I must be missing something obvious. OOP Morse Challenge.

I must be missing something obvious about classes and methods here. When I run the code below as a classless function in the work-space (with some obvious substitutions - as seen below), it checks out. I try to run it in the code chellenge and I get an error.

Here's the code in work-space: def morse(pattern): converted = [] for item in pattern: if item == ".": converted.append("dot") elif item == "_": converted.append("dash") print('-'.join(converted))

morse(trial)

More than just showing me how to pass the challenge, WHAT am I missing about classes?

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

    def __str__(self):
        converted = []
        for item in self.pattern:
            if item == ".":
                converted.append("dot")
            elif item == "_":
                converted.append("dash")
        return '-'.join(converted)

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