class LLN:
    def __init__(self, val=None, *subnodes):
        self._subnodes = list(subnodes)
        self.val = val

    def append(val):
        subnode = LLN(val)
        self._subnodes.append(subnode)
        return subnode

    def get():
        """depth-first recursive get"""
        ret = []

        for val in self.val:
            if isinstance(val, LLN):
                ret.extend(val.getDF())
            else:
                ret.append(val)

        return ret