def METHOD_NAME(self, key):
    """
    Return the names of objects defined using a given key.
    :param key: The name of the key whose value lists the objects
            (e.g. 'nics').
    """
    lst = self.get(key, "").split()
    # remove duplicate elements
    objs = list({}.fromkeys(lst).keys())
    # sort list to keep origin order
    objs.sort(key=lst.index)
    del lst
    return objs