def unique_list(nonunique_list):
    """ Returns a list where each element of nonunique_list occurs exactly once.
    The last occurence of an element defines its position in the returned list.
    """
    unique_list = []
    for attr in reversed(nonunique_list):
        if attr not in unique_list:
            unique_list.insert(0, attr)
    return unique_list
