二十一. 多进程爬虫

1.多进程的使用方法如下：

from multiprocessing import Pool         #引入进程池模块
pool = Pool(processes=4)                 #创建进程池
pool.map(func,iterable[,chunksize])  #map()函数运行进程，func为需运行的函数，iterable为迭代参数。

2.多进程的性能对比：
爬取网址：https://www.qiushibaike.com/text/
爬取内容：用户ID、发表段子文字信息、好笑数量、评价数量
爬取方式：正则表达式
性能对比：（单线程，2进程，4进程）比较运行时间

import requests
import re
from multiprocessing import Pool
import time

'''解析内容，并创建多线程执行，存入CSV文档中'''
hds = {'User-Agent': 'ozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36'}
def scraper(url):
    r = requests.get(url,headers = hds)
    ids = re.findall("<h2>(.*?)</h2>",r.text,re.S)       
    contents = re.findall('<div class="content">.*?<span>(.*?)</span>',r.text,re.S)
    laughs = re.findall('<span class="stats-vote">.*?<i class="number">(.*?)</i>',r.text,re.S)
    comments = re.findall('<span class="stats-comments">.*?<i class="number">(.*?)</i>',r.text,re.S)
    for id,content,laugh,comment in zip(ids,contents,laughs,comments):
        info = {
            'id':id,
            'content':content,
            'laugh':laugh,
            'comment':comment
            }
        return info



if __name__ == '__main__':    #多进程必须使用此语句，否则报错   
    
    '''构建网页列表并将其入队'''
    url_list = ["https://www.qiushibaike.com/text/page/{}/".format(i) for i in range(1,14)]
    hds = {'user-agent':'Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3294.6 Safari/537.36'}    

    start1 = time.time()
    for url in url_list:
        scraper(url)
    stop1 = time.time()
    
    print("单线程耗时", stop1 - start1)

    start2 = time.time()
    pool = Pool(processes=2)
    pool.map(scraper,url_list)
    stop2 = time.time()
    print("2个进程耗时", stop2 - start2)

    start3 = time.time()
    pool = Pool(processes=2)
    pool.map(scraper,url_list)
    stop3 = time.time()
    print("4个进程耗时", stop3 - start3)

结果为：

单线程耗时 2.73215651512146
2个进程耗时 2.477141857147217
4个进程耗时 2.3501341342926025