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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 _group_dict_set(iterator):
 """Make a dict that accumulates the values for each key in an iterator of doubles. :param iter[tuple[A,B]] iterator: An iterator :rtype: dict[A,set[B]] """

    d = defaultdict(set)
    for key, value in iterator:
        d[key].add(value)
    return dict(d)