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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 index_natsorted(seq, key=None, reverse=False, alg=ns.DEFAULT):
 """ Determine the list of the indexes used to sort the input sequence. Sorts a sequence naturally, but returns a list of sorted the indexes and not the sorted list itself. This list of indexes can be used to sort multiple lists by the sorted order of the given sequence. Parameters seq : iterable The input to sort. key : callable, optional A key used to determine how to sort each element of the sequence. It is **not** applied recursively. It should accept a single argument and return a single value. reverse : {{True, False}}, optional Return the list in reversed sorted order. The default is `False`. alg : ns enum, optional This option is used to control which algorithm `natsort` uses when sorting. For details into these options, please see the :class:`ns` class documentation. The default is `ns.INT`. Returns ------- out : tuple The ordered indexes of the input. See Also -------- natsorted order_by_index Examples -------- Use index_natsorted if you want to sort multiple lists by the sorted order of one list:: [2, 0, 1] [{u}'num2', {u}'num3', {u}'num5'] [{u}'baz', {u}'foo', {u}'bar'] """

    if key is None:
        newkey = itemgetter(1)
    else:

        def newkey(x):
            return key(itemgetter(1)(x))

    # Pair the index and sequence together, then sort by element
    index_seq_pair = [[x, y] for x, y in enumerate(seq)]
    index_seq_pair.sort(reverse=reverse, key=natsort_keygen(newkey, alg))
    return [x for x, _ in index_seq_pair]