Python使用asyncio+aiohttp异步爬取猫眼电影专业版

asyncio是从pytohn3.4开始添加到标准库中的一个强大的异步并发库，可以很好地解决python中高并发的问题，入门学习可以参考官方文档

并发访问能极大的提高爬虫的性能，但是requests访问网页是阻塞的，无法并发，所以我们需要一个更牛逼的库 aiohttp ，它的用法与requests相似，可以看成是异步版的requests，下面通过实战爬取猫眼电影专业版来熟悉它们的使用：

1. 分析

分析网页源代码发现猫眼专业版是一个动态网页，其中的数据都是后台传送的，打开F12调试工具，再刷新网页选择XHR后发现第一条就是后台发来的电影数据，由此得到接口 https://box.maoyan.com/promovie/api/box/second.json?beginDate=日期

2. 异步爬取

创建20个任务来并发爬取20天的电影信息并写入csv文件，同时计算一下耗费的时间：

import asyncio
from aiohttp import ClientSession
import time
import csv


headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) '
                             'AppleWebKit/537.36 (KHTML, like Gecko) '
                             'Chrome/67.0.3396.99 Safari/537.36'}

# 协程函数，完成一个无阻塞的任务
async def get_one_page(url):
    try:
        async with ClientSession() as session:
            async with session.get(url, headers=headers) as r:
                # 返回解析为字典的电影数据
                return await r.json()
    except Exception as e:
        print('请求异常： ' + str(e))
        return {}


# 解析函数，提取每一条内容并写入csv文件
def parse_one_page(movie_dict, writer):
    try:
        movie_list = movie_dict['data']['list']
        for movie in movie_list:
            movie_name = movie['movieName']
            release = movie['releaseInfo']
            sum_box = movie['sumBoxInfo']
            box_info = movie['boxInfo']
            box_rate = movie['boxRate']
            show_info = movie['showInfo']
            show_rate = movie['showRate']
            avg_show_view = movie['avgShowView']
            avg_seat_view = movie['avgSeatView']
            writer.writerow([movie_name, release, sum_box, box_info, box_rate,
                            show_info, show_rate, avg_show_view, avg_seat_view])
        return '写入成功'
    except Exception as e:
        return '解析异常： ' + str(e)


# 并发爬取
async def main():

    # 待访问的20个URL链接
    urls = ['https://box.maoyan.com/promovie/api/box/second.json?beginDate=201904{}{}'.format(i, j) for i in range(1, 3) for j in range(10)]
    # 任务列表
    tasks = [get_one_page(url) for url in urls]
    # 并发执行并保存每一个任务的返回结果
    results = await asyncio.gather(*tasks)

    # 处理每一个结果
    with open('out/pro_info.csv', 'w') as f:
        writer = csv.writer(f)
        for result in results:
            print(parse_one_page(result, writer))


if __name__ == "__main__":
    start = time.time()

    asyncio.run(main())
    # python3.7之前的写法
    # loop = asyncio.get_event_loop()
    # loop.run_until_complete(main())
    # loop.close()

    print(time.time()-start)

用时0.15秒！

3. 对比同步爬取

import requests
import csv
import time


headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) '
                             'AppleWebKit/537.36 (KHTML, like Gecko) '
                             'Chrome/67.0.3396.99 Safari/537.36'}


def get_one_page(url):

    try:
        r = requests.get(url, headers=headers)
        r.raise_for_status()
        r.encoding = r.apparent_encoding
        return r.json()
    except Exception as e:
        print('请求异常： ' + e)
        return {}


def parse_one_page(movie_dict, writer):
    try:
        movie_list = movie_dict['data']['list']
        for movie in movie_list:
            movie_name = movie['movieName']
            release = movie['releaseInfo']
            sum_box = movie['sumBoxInfo']
            box_info = movie['boxInfo']
            box_rate = movie['boxRate']
            show_info = movie['showInfo']
            show_rate = movie['showRate']
            avg_show_view = movie['avgShowView']
            avg_seat_view = movie['avgSeatView']
            writer.writerow([movie_name, release, sum_box, box_info, box_rate,
                            show_info, show_rate, avg_show_view, avg_seat_view])
        print('写入成功')
    except Exception as e:
        print('解析异常： ' + e)


def main():

	# 待访问的20个URL链接
    urls = ['https://box.maoyan.com/promovie/api/box/second.json?beginDate=201903{}{}'.format(i, j) for i in range(1, 3) for j in  range(10)]
    with open('out/pro_info.csv', 'w') as f:
        writer = csv.writer(f)
        for url in urls:
        	# 逐一处理
            movie_dict = get_one_page(url)
            parse_one_page(movie_dict, writer)


if __name__ == '__main__':
    a = time.time()
    main()
    print(time.time() - a)

可以看到使用asyncio+aiohttp的异步爬取方式要比简单的requests同步爬取快上不少，尤其是爬取大量网页的时候，这种差距会非常明显。