在 python 中等待之前，不会在异步函数中调用 print 函数

Posted 2023-03-13

【中文标题】在 python 中等待之前，不会在异步函数中调用 print 函数

【英文标题】：print function does not get called in an async function before await in python

【发布时间】：2016-09-26 16:44:02

【问题描述】：

我想获得一些请求和异步的链接。我有一个示例程序，但我认为有一个问题，因为打印函数只有在我使用 await 时才会被调用。

那么为什么在我调用实际函数的地方不调用 print 呢？我所理解的，如果使用 await 关键字，该函数会中断，直到未来可以呈现。在我的情况下，应该在 await 关键字之前调用 print 函数，所以在 print 语句之前：doing stuff in between 或者我错了吗？

import asyncio
import requests
import bs4

urls = ["http://www.google.com", "http://www.google.co.uk"]

async def getContent(url):
    loop = asyncio.get_event_loop()
    print("getting content for: " + url) # print should be called here
    # execute a non async function async
    future = loop.run_in_executor(None, requests.get, url)

    # doing stuff with bs4
    soup = bs4.BeautifulSoup((await future).text, "html.parser") # should now interrupt

    return soup 

async def main():
    loop = asyncio.get_event_loop()

    print("starting gathering...")
    # creating a list of futures
    futures = [getContent(url) for url in urls]
    # packing futures into a awaitable list future
    responses_future = asyncio.gather(*futures)

    print("doing stuff in between...")
    # waiting for all futures
    responses = await responses_future

    print("Done")

    for response in responses:
        print(response)

loop = asyncio.get_event_loop()
loop.run_until_complete(main())

输出：

starting gathering...
doing stuff in between...
getting content for: http://www.google.com
getting content for: http://www.google.co.uk
Done

HTML CODE HERE!

问候

【参考方案1】：

协程在等待之前不会被执行，这就是它发生的原因

【讨论】：

好的，谢谢。我在文档中找到了这句话，它总结了我必须做的事情：Calling a coroutine does not start its code running – the coroutine object returned by the call doesn’t do anything until you schedule its execution. There are two basic ways to start it running: call await coroutine or yield from coroutine from another coroutine (assuming the other coroutine is already running!), or schedule its execution using the ensure_future() function or the BaseEventLoop.create_task() method.