Dictionaries & sets

def group_data(items, key_func):
    """Group items into a dictionary of sets based on a key function."""
    grouped = {}
    for item in items:
        key = key_func(item)
        if key not in grouped:
            grouped[key] = set()
        grouped[key].add(item)
    return grouped


if __name__ == "__main__":
 …