Python 3 爬虫｜第9章：使用 asyncio + aiohttp 并发下载

1. aiohttp

asynciosocketTCPUDPHTTPaiohttp

1.1 安装

# pip install aiohttp

1.2 基本使用

import aiohttp
import asyncio

async def fetch(session, url):
    async with session.get(url) as response:
        return await response.text()

async def main():
    async with aiohttp.ClientSession() as session:
        html = await fetch(session, 'http://www.madmalls.com')
        print(html)

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

2. asyncio + aiohttp

aiohttp.ClientSession()

async with aiohttp.ClientSession() as sessionasync with session.get('http://httpbin.org/') as responseawait response.read()read()text()

# 请使用Python 3.7
import os
import time
import asyncio
import aiohttp
from logger import logger

basepath = os.path.abspath(os.path.dirname(__file__))  # 当前模块文件的根目录

def setup_down_path():
    '''设置图片下载后的保存位置，所有图片放在同一个目录下'''
    down_path = os.path.join(basepath, 'downloads')
    if not os.path.isdir(down_path):
        os.mkdir(down_path)
        logger.info('Create download path {}'.format(down_path))
    return down_path

def get_links():
    '''获取所有图片的下载链接'''
    with open(os.path.join(basepath, 'flags.txt')) as f:  # 图片名都保存在这个文件中，每行一个图片名
        return ['http://192.168.40.121/flags/' + flag.strip() for flag in f.readlines()]

async def download_one(session, image):
    logger.info('Downloading No.{} [{}]'.format(image['linkno'], image['link']))
    t0 = time.time()

    async with session.get(image['link']) as response:
        image_content = await response.read()  # Binary Response Content: access the response body as bytes, for non-text requests

    filename = os.path.split(image['link'])[1]
    with open(os.path.join(image['path'], filename), 'wb') as f:
        f.write(image_content)

    t1 = time.time()
    logger.info('Task No.{} [{}] runs {:.2f} seconds.'.format(image['linkno'], image['link'], t1 - t0))

async def download_many():
    down_path = setup_down_path()
    links = get_links()

    tasks = []  # 保存所有任务的列表
    async with aiohttp.ClientSession() as session:  # aiohttp建议整个应用只创建一个session，不能为每个请求创建一个seesion
        for linkno, link in enumerate(links, 1):
            image = {
                'path': down_path,
                'linkno': linkno,  # 图片序号，方便日志输出时，正在下载哪一张
                'link': link
            }
            task = asyncio.create_task(download_one(session, image))  # asyncio.create_task()是Python 3.7新加的，否则使用asyncio.ensure_future()
            tasks.append(task)
        results = await asyncio.gather(*tasks)
        return len(results)

if __name__ == '__main__':
    t0 = time.time()
    count = asyncio.run(download_many())
    msg = '{} flags downloaded in {:.2f} seconds.'
    logger.info(msg.format(count, time.time() - t0))

0.89多线程

3. 使用 uvloop

uvloopasyncio

3.1 安装

# pip install uvloop

3.2 使用 uvloop.EventLoopPolicy()

增加两行：

import uvloop
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

4. aiofiles

f.write(image_content)asyncio

安装: