9.异步爬虫

异步爬虫可以理解为非只单线程爬虫

我们下面做个例子，之前我们通过单线程爬取过梨视频 https://blog.csdn.net/potato123232/article/details/135672504

在保存视频的时候会慢一些，为了提升效率，我们使用异步爬虫爬取

目录

1  线程池

2  单线程+异步协程

2.1  aiohttp的基本使用

2.2  爬取梨视频

3  单线程，协程，多线程的运行速度比较

---

1  线程池

线程池的基本用法在这里有提到 python并发任务-CSDN博客

多线程应仅用于耗时的部分，如果我们为了省事去将所有部分都封装为一个函数就容易出错

• 走单线程可以成功爬取10个视频，当我将所有过程封装为一个函数时，使用多线程爬取会报错。在JS中的异步也会有这种问题，就像是请求还没请求完，后面加载就加载上了

import requests
from lxml import etree
import random
import re
from multiprocessing.dummy import Pool
 
# 保存根页面
url = 'https://www.pearvideo.com/popular'
headers={'User-Agent':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36'}
response = requests.get(url=url,headers=headers)
response.encoding = response.apparent_encoding
with open('./test.html','w',encoding='utf-8') as f:
    f.write(response.text)
print(response)
 
# 获取所有细节页面url
detail_htmls = []
tree = etree.HTML(response.text)
for i in range(1,len(tree.xpath('//*[@id="popularList"]/li'))+1):
    detail_htmls.append({'url':'https://www.pearvideo.com/' + tree.xpath('//*[@id="popularList"]/li[{}]/a/@href'.format(i))[0],'title':tree.xpath('//*[@id="popularList"]/li['+ str(i) +']/div[2]/a/h2/text()')[0]})
 
# print(detail_htmls)
p = re.compile(r'.*\/(.*?)-\d')
 
video_detail_list = []
for i in detail_htmls:
    contId = i['url'].split('_')[-1]
    mrd = round(random.random(), 16)
    headers['Host'] = 'www.pearvideo.com'
    headers['Referer'] = i['url']
    response = requests.get(url='https://www.pearvideo.com/videoStatus.jsp?contId=' + str(contId) + '&mrd=' + str(mrd),
                            headers=headers).text
 
    srcUrl = eval(response).get('videoInfo').get('videos').get('srcUrl')
 
    need_change_part = p.findall(srcUrl)[0]
    true_video_url = srcUrl.split(need_change_part)[0] + 'cont-' + contId + srcUrl.split(need_change_part)[1]
 
    video_name = re.sub(r'[\\/:*?"<>|]', '', i['title'])
    video_detail_list.append({"name":video_name,"url":true_video_url})
 
print(video_detail_list)
def get_video(item):
    response = requests.get(item['url'])
    with open('./result/' + str(item['name']) + '.mp4', 'wb') as fp:
        fp.write(response.content)
        print(item['url'] + '下载成功')
 
pool = Pool(4)
pool.map(get_video,video_detail_list)

耗时的部分只有保存，所以我们保存的部分剥离出来，这样就能成功爬取10个视频

2  单线程+异步协程

2.1  aiohttp的基本使用

我们先做个简单的服务，这三个服务无论请求哪一个都会等待两秒，然后返回一个字符串

之后我们尝试只用asyncio发起异步请求

从耗时来看这段代码并没有发起异步请求

这个时候我们可以使用aiohttp进行异步请求

• 这个能看懂就行了，如果到了一定要使用的时候，看看别人怎么写的抄一抄就完了
• 如果不加最后打印之前的await，那么就有可能会打印不出来东西，由于请求是异步的，他会跳过请求而执行下面，就像js中的定时器
• response.text()是返回字符串类型的响应，read()是返回二进制类型的响应，json()返回的是json对象类型的响应
• 除了发get请求还可以发post请求，参数与requests.get()，requests.post()基本一致(get用的params一致，post用的data一致，请求头headers一致，aiohttp的代理参数名为proxy,proxy参数值为字符串)

2.2  爬取梨视频

异步保存文件可以借助 aiofiles

import requests
from lxml import etree
import random
import re
import aiohttp
import asyncio
import aiofiles
 
# 保存根页面
url = 'https://www.pearvideo.com/popular'
headers={'User-Agent':'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/116.0.0.0 Safari/537.36'}
response = requests.get(url=url,headers=headers)
response.encoding = response.apparent_encoding
with open('./test.html','w',encoding='utf-8') as f:
    f.write(response.text)
print(response)
 
# 获取所有细节页面url
detail_htmls = []
tree = etree.HTML(response.text)
for i in range(1,len(tree.xpath('//*[@id="popularList"]/li'))+1):
    detail_htmls.append({'url':'https://www.pearvideo.com/' + tree.xpath('//*[@id="popularList"]/li[{}]/a/@href'.format(i))[0],'title':tree.xpath('//*[@id="popularList"]/li['+ str(i) +']/div[2]/a/h2/text()')[0]})
 
# print(detail_htmls)
p = re.compile(r'.*\/(.*?)-\d')
 
video_detail_list = []
for i in detail_htmls:
    contId = i['url'].split('_')[-1]
    mrd = round(random.random(), 16)
    headers['Host'] = 'www.pearvideo.com'
    headers['Referer'] = i['url']
    response = requests.get(url='https://www.pearvideo.com/videoStatus.jsp?contId=' + str(contId) + '&mrd=' + str(mrd),
                            headers=headers).text
 
    srcUrl = eval(response).get('videoInfo').get('videos').get('srcUrl')
 
    need_change_part = p.findall(srcUrl)[0]
    true_video_url = srcUrl.split(need_change_part)[0] + 'cont-' + contId + srcUrl.split(need_change_part)[1]
 
    video_name = re.sub(r'[\\/:*?"<>|]', '', i['title'])
    video_detail_list.append({"name":video_name,"url":true_video_url})
 
print(video_detail_list)
 
async def test(item):
    async with aiohttp.ClientSession() as session:
        async with await session.get(item['url']) as response:
            async with aiofiles.open('./result/' + str(item['name']) + '.mp4', 'wb') as fp:
                await fp.write(await response.read())
                print(item['url'] + '下载成功')
 
future_list = []
for something1 in video_detail_list:
    a = test(something1)
    future = asyncio.ensure_future(a)
    future_list.append(future)
 
loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(future_list))
 

可以爬取成功，每个视频都可以点开看

但是代码在pycharm的返回值并不是0

3  单线程，协程，多线程的运行速度比较

就梨视频的例子来说，单线程最慢，多线程第二(因为我只用4线程，如果10线程应该还会快一些)，感觉上来讲协程最快