python报错，帮看一下，怎么解决

async def aio_download(url_list):
    tasks = []
    timeout = aiohttp.ClientTimeout(total=600)
    async with aiohttp.ClientSession(timeout=timeout) as session:  
        async for url in url_list:       #（报错处）
            tasks.append(asyncio.create_task(aio_download_pic(session, url)))
        await asyncio.wait(tasks)

错误：
TypeError: 'async for' requires an object with aiter method, got list

报错提示async 后面是要一个函数方法，你要将for url in url_list: 定义一个函数方法才行