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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 unique(iterable, key=identity):
 """Yields all the unique values in an iterable maintaining order"""

    seen = set()
    for item in iterable:
        item_key = key(item)
        if item_key not in seen:
            seen.add(item_key)
            yield item