def get_last_tid(self):
        try:
            spec = {'tid': {'$gt': 0}}
            sort = [('tid', -1)]
            row = self.db.docs.find_one(spec, sort=sort)
        except Exception as e:
            raise DatabaseException(e)
        if row:
            return row['tid']
        return 0
def usage_iter(root):
    root = os.path.abspath(root)
    root_size = get_folder_size(root)
    root_string = "{0}\n{1}".format(root, root_size)
    yield [root_string, None, root_size]