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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def make_speaker_utters(utterances: List[Utterance]) -> Dict[str, List[Utterance]]: """ Creates a dictionary mapping from speakers to their utterances. """


    speaker_utters = defaultdict(list) # type: DefaultDict[str, List[Utterance]]
    for utter in utterances:
        speaker_utters[utter.speaker].append(utter)

    return speaker_utters