Python AsyncIO 这个任务第二次 await 什么时候发生

发布于08月04日

我有一个可以异步发出http请求的python脚本，提供了一系列URL，下面是示例代码.

#!/usr/local/bin/python3
import httpx
import asyncio

async def httpx_get(client, url):
    resp1 = await client.get(url, timeout=5, allow_redirects=True) 
    # ... other computation ...
    resp2 = await client.get(url, timeout=5, allow_redirects=True) # what happens during this second await?

async def fetch_pages(urls):
    async with httpx.AsyncClient(verify=False) as client:
        # create task for all URLs
        coros = []
        for url in urls:
            coros.append(asyncio.create_task(httpx_get(client, url)))

        # await all tasks
        for coro in asyncio.as_completed(coros):
            resp = await coro 

def main():
    urls = [ "https://google.com", "https://yahoo.com", "https://youtube.com" ] 
    asyncio.run(fetch_pages(urls))

if __name__ == "__main__":
    main()

我意识到我对Asyncio何时处理我httpx_get函数中的第二个等待，resp2 = await client.get(..，缺乏理解.

因为for coro in asyncio.as_completed(coros): resp = await coro只 for each 协程解析第一个等待resp1 = await client.get，所以第二个等待resp2 = await client.get什么时候得到解析？

第二个等待/请求是否同时执行和等待？还是发生了其他事情？如有任何澄清，我们将不胜感激，谢谢！

import asyncio,random,time async def httpx_get(client, url): print(f'{time.time()} task:{client} resp1 will be called') resp1 = await asyncio.sleep(random.randrange(1,10)) # ... other computation ... print(f'{time.time()} task:{client} resp1 returned') print(f'{time.time()} task:{client} executing') print(f'{time.time()} task:{client} executing') print(f'{time.time()} task:{client} executing') print(f'{time.time()} task:{client} executing') print(f'{time.time()} task:{client} resp2 will be called') resp2 = await asyncio.sleep(random.randrange(1,10)) print(f'{time.time()} task:{client} resp2 returned') return f'{time.time()} task:{client} finished - url' async def fetch_pages(urls): # create task for all URLs coros = [] for n,url in enumerate(urls): coros.append(asyncio.create_task(httpx_get(n, url))) # await all tasks for coro in asyncio.as_completed(coros): resp = await coro print(f'{time.time()} {resp}') def main(): urls = [ "https://google.com", "https://yahoo.com", "https://youtube.com" ] asyncio.run(fetch_pages(urls)) if __name__ == "__main__": main()

1659744155.1480112 task:0 resp1 will be called and awaited 1659744155.1480112 task:1 resp1 will be called and awaited 1659744155.1480112 task:2 resp1 will be called and awaited 1659744161.152556 task:2 resp1 returned 1659744161.152556 task:2 executing 1659744161.152556 task:2 executing 1659744161.152556 task:2 executing 1659744161.154198 task:2 executing 1659744161.154198 task:2 resp2 will be called and awaited 1659744163.1660972 task:1 resp1 returned 1659744163.1660972 task:1 executing 1659744163.1660972 task:1 executing 1659744163.1660972 task:1 executing 1659744163.1660972 task:1 executing 1659744163.1675234 task:1 resp2 will be called and awaited 1659744164.1542242 task:0 resp1 returned 1659744164.1542242 task:0 executing 1659744164.1542242 task:0 executing 1659744164.1542242 task:0 executing 1659744164.155838 task:0 executing 1659744164.155838 task:0 resp2 will be called and awaited 1659744166.167943 task:2 resp2 returned 1659744166.167943 1659744166.167943 task:2 finished - https://youtube.com 1659744168.1679864 task:1 resp2 returned 1659744168.1685212 1659744168.1685212 task:1 finished - https://yahoo.com 1659744169.1565957 task:0 resp2 returned 1659744169.1565957 1659744169.1565957 task:0 finished - https://google.com

Python AsyncIO 这个任务第二次 await 什么时候发生

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