def __as_key(k1, k2):
    """
    Creates a key (tuple) out of the two specified. The key is always ordered.
    If k2 < k1, then (k2, k1), else, (k1, k2).

    :param k1: Key (string).
    :param k2: Key (string).
    :return: (k1, k2) or (k2, k1).
    """
    keys = sorted([k1, k2])
    return keys[0], keys[1]