python-3.x - 为什么 asyncio.create_task 不运行该方法？

Question

代码示例:

async def download_page(session, url):
    print(True)


async def downloader_init(session):
    while True:
        url = await download_queue.get()
        task = asyncio.create_task(download_page(session, url))
        print(task)
        print(f"url: {url}")


async def get_urls(url):
    while True:
        try:
            url = find_somewhere_url
            await download_queue.put(url)
        except NoSuchElementException:
            break
    return True


async def main():
    async with aiohttp.ClientSession(headers=headers) as session:
        get_urls_task = asyncio.create_task(get_urls(url))
        downloader_init_task = asyncio.create_task(downloader_init(session))

        asyncio.gather(get_urls_task, downloader_init_task)


if __name__ == "__main__":
    asyncio.get_event_loop().run_until_complete(main())

输出:

<Task pending coro=<download_page() running at main.py:69>>
url: https://someurl.com/example
<Task pending coro=<download_page() running at main.py:69>>
url: https://someurl.com/example
<Task pending coro=<download_page() running at main.py:69>>
url: https://someurl.com/example

为什么是方法 download_page没有执行？
奇怪的是，脚本刚刚结束它的工作，任何地方都没有错误。 downloader_init应该无休止地工作，但事实并非如此。

在 download_queue , 方法 get_urls在找到链接时添加链接，之后它停止工作。 downloader_init队列中出现新链接时应立即执行，但仅在 get_urls 时才开始工作。已经完成了它的工作。

Answer 1

试试这个:

注意:您的问题不在于任务创建，而是因为asyncio.gather 没有等待部分。

import asyncio
import aiohttp


async def download_page(session, url):
    # Dummy function.
    print(f"session={session}, url={url}")


async def downloader_init(session):
    while True:
        url = await download_queue.get()
        task = asyncio.create_task(download_page(session, url))
        print(f"task={task}, url={url}")


async def get_urls(url):
    while True:
        try:
            url = find_somewhere_url()
            await download_queue.put(url)
        except NoSuchElementException:
            break


async def main():
    async with aiohttp.ClientSession(headers=headers) as session:
        get_urls_task = asyncio.create_task(get_urls(url))
        downloader_init_task = asyncio.create_task(downloader_init(session))

        # Use await here to make it finish the tasks.
        await asyncio.gather(get_urls_task, downloader_init_task)


if __name__ == "__main__":
    # Use this as it deals with the loop creation, shutdown,
    # and other stuff for you.
    asyncio.run(main())  # This is new in Python 3.7