一个关于Event loop is closed的问题

Question

代码如下：

import asyncio
import aiohttp
from lxml import etree
import requests
headers = {
    'user-agent': 'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.198 Safari/537.36'
}
#/html/body/div[13]/div[1]/div[2]/dl/dd/a/img
async def download(url):
    name = url.rsplit('/',1)[1]
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as res:
            with open(f'彼岸桌面壁纸下载/{name}','wb') as f:
                f.write(await res.content.read())
async def main():
    tasks=[]
    for url in urls:
        tasks.append(download(url))
    await asyncio.wait(tasks)
if __name__ == '__main__':
    url0 = 'https://www.enterdesk.com/zhuomianbizhi/'
    text = requests.get(url0).text
    tree = etree.HTML(text)
    urls = tree.xpath('/html/body/div[13]/div[1]/div/dl/dd/a/img/@src')
    asyncio.run(main())

报错如下：
D:\MyPcharmProject\venv\Scripts\python.exe D:/MyPcharmProject/爬虫/Umei.py
Exception ignored in: <function _ProactorBasePipeTransport.__del__ at 0x0000023AD6F1C670>
Traceback (most recent call last):
File "C:\Users\lenovo\AppData\Local\Programs\Python\Python38\lib\asyncio\proactor_events.py", line 116, in del
self.close()
File "C:\Users\lenovo\AppData\Local\Programs\Python\Python38\lib\asyncio\proactor_events.py", line 108, in close
self._loop.call_soon(self._call_connection_lost, None)
File "C:\Users\lenovo\AppData\Local\Programs\Python\Python38\lib\asyncio\base_events.py", line 711, in call_soon
self._check_closed()
File "C:\Users\lenovo\AppData\Local\Programs\Python\Python38\lib\asyncio\base_events.py", line 504, in _check_closed
raise RuntimeError('Event loop is closed')
RuntimeError: Event loop is closed
Process finished with exit code 0

Answer 1

在系统python3.7.6，vscode中运行测试，代码可以正常运行下载图片。
在stackoverflow看到解释说可能与系统的EventLoopPolicy有关，解决办法：在代码最后一句前面加上一行：
asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())，这样试试看可否解决你的问题。
参考一下：

python - "Asyncio Event Loop is Closed" when getting loop - Stack Overflow When trying to run the asyncio hello world code example given in the docs: import asyncio async def hello_world(): print("Hello World!") loop = asyncio.get_event_loop() # Blocking call which https://stackoverflow.com/questions/45600579/asyncio-event-loop-is-closed-when-getting-loop

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