self.parse,
endpoint = 'execute',
args = {'lua_source': lua_script, 'ua':
    'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36'
    }
Adding a wait-for-element while performing a SplashRequest in python Scrapy