Google App EngineとCloud SQLの接続

INSTANCE_CONNECTION_NAME = cnfbox-dev:us-central1:cnfbox-dev-store

import pymysql.cursors

connection = pymysql.connect(
    host=os.getenv('DB_HOST'),
    user=os.getenv('DB_USER'),
    password=os.getenv('DB_PASSWD'),
    db=os.getenv('DB_NAME'),
    unix_socket=os.getenv('UNIX_SOCKET') if os.getenv('UNIX_SOCKET') else None,
    charset='utf8mb4',
    cursorclass=pymysql.cursors.DictCursor)