Python进阶之协程详解

import asyncio
from pathlib import Path
import logging
from urllib.request import urlopen, Request
import os
from time import time
import aiohttp
logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(name)s - %(levelname)s - %(message)s')
logger = logging.getLogger(__name__)
CODEFLEX_IMAGES_URLS = ['https://codeflex.co/wp-content/uploads/2021/01/pandas-dataframe-python-1024x512.png',
                        'https://codeflex.co/wp-content/uploads/2021/02/github-actions-deployment-to-eks-with-kustomize-1024x536.jpg',
                        'https://codeflex.co/wp-content/uploads/2021/02/boto3-s3-multipart-upload-1024x536.jpg',
                        'https://codeflex.co/wp-content/uploads/2018/02/kafka-cluster-architecture.jpg',
                        'https://codeflex.co/wp-content/uploads/2016/09/redis-cluster-topology.png']
async def download_image_async(session, dir, img_url):
    download_path = dir / os.path.basename(img_url)
    async with session.get(img_url) as response:
        with download_path.open('wb') as f:
            while True:
                # 在 async 函数中使用 await 关键字表示等待 task 执行完成，也就是等待 yeild 让出控制权。
                # 同时，asyncio 使用事件循环 event_loop 来实现整个过程。
                chunk = await response.content.read(512)
                if not chunk:
                    break
                f.write(chunk)
    logger.info('Downloaded: ' + img_url)
# 使用 async 关键字声明一个异步/协程函数。
# 调用该函数时，并不会立即运行，而是返回一个协程对象，后续在 event_loop 中执行。
async def main():
    images_dir = Path("codeflex_images")
    Path("codeflex_images").mkdir(parents=False, exist_ok=True)
    async with aiohttp.ClientSession() as session:
        tasks = [(download_image_async(session, images_dir, img_url)) for img_url in CODEFLEX_IMAGES_URLS]
        await asyncio.gather(*tasks, return_exceptions=True)
if __name__ == '__main__':
    start = time()
    # event_loop 事件循环充当管理者的角色，将控制权在几个协程函数之间切换。
    event_loop = asyncio.get_event_loop()
    try:
        event_loop.run_until_complete(main())
    finally:
        event_loop.close()
    logger.info('Download time: %s seconds', time() - start)