human
Complete this python program:
def configure_db():
assistant
#Here is the Python program you requested.

    """Establish the database, create an engine if needed, and
    register the models.
    """
    global _ENGINE
    if (not _ENGINE):
        sql_connection = cfg.CONF.DATABASE.sql_connection
        if (not sql_connection):
            LOG.warn(_(("Option    'sql_connection'    not    specified    in    any    config    file    -    using    default    value    '%s'" % SQL_CONNECTION_DEFAULT)))
            sql_connection = SQL_CONNECTION_DEFAULT
        connection_dict = sql.engine.url.make_url(sql_connection)
        engine_args = {'pool_recycle': 3600, 'echo': False, 'convert_unicode': True}
        if ('mysql' in connection_dict.drivername):
            engine_args['listeners'] = [MySQLPingListener()]
            if ((MySQLdb is not None) and cfg.CONF.DATABASE.sql_dbpool_enable):
                pool_args = {'db': connection_dict.database, 'passwd': (connection_dict.password or ''), 'host': connection_dict.host, 'user': connection_dict.username, 'min_size': cfg.CONF.DATABASE.sql_min_pool_size, 'max_size': cfg.CONF.DATABASE.sql_max_pool_size, 'max_idle': cfg.CONF.DATABASE.sql_idle_timeout}
                pool = db_pool.ConnectionPool(MySQLdb, **pool_args)
                def creator():
                    conn = pool.create()
                    if isinstance(conn, tuple):
                        (_1, _2, conn) = conn
                    return conn
                engine_args['creator'] = creator
            if ((MySQLdb is None) and cfg.CONF.DATABASE.sql_dbpool_enable):
                LOG.warn(_('Eventlet    connection    pooling    will    not    work    without    python-mysqldb!'))
        if ('sqlite' in connection_dict.drivername):
            engine_args['listeners'] = [SqliteForeignKeysListener()]
            if (sql_connection == 'sqlite://'):
                engine_args['connect_args'] = {'check_same_thread': False}
        _ENGINE = create_engine(sql_connection, **engine_args)
        sql.event.listen(_ENGINE, 'checkin', greenthread_yield)
        if (not register_models()):
            if cfg.CONF.DATABASE.reconnect_interval:
                remaining =...