Add a ParentWrapper class

    # end dict like

class ParentWrapper(object):

    def __init__(self, sub_id, type_, parent):

        self.sub_id = sub_id

        self._parent = parent

        self._parent.add_sub_object(self.sub_id, tuple(), type_)

    def __del__(self):

        self._parent.remove_sub_object(self.sub_id)

    def _not_implemented(self, *args, **kwargs):

        raise NotImplementedError

    def add_tags(self, tags):

        for t in tags:

            self.add_tag(t)

    def remove_tags(self, tag_names):

        for n in tag_names:

            self.remove_tag(n)

    def add_tag(self, tag):

        self._parent.add_sub_tag(self.sub_id, tag)

    def remove_tag(self, tag_name):

        self._parent.remove_sub_tag(self.sub_id, tag_name)

    def __getattr__(self, name):

        if name in ('add_sub_tag', 'remove_sub_tag', 'add_sub_object',

                    'remove_sub_object'):

            return self._not_implemented

        return getattr(self._parent, name)

class RootTagDB(TagDB):

    """Root tag database.