python multiprocessing多线程爬取并解析百度贴吧某贴小trick

preface:看极客学院关于xpath的视频时，偶然看到可以用multiprocessing进行多线程爬取网页，只有小段代码，故先贴出来。mark下。新增xpath提取网页内容，主要分析html文本，然后存为字典写到文件夹中。

参考极客学院的python并行化介绍与演示视频

coding:

#!/usr/bin/env python
# coding=utf-8
from multiprocessing.dummy import Pool as ThreadPool
import requests
import time

def getsource(url):
    html = requests.get(url)

urls = []
for i in range(1,21):
    newpage = "http://tieba.baidu.com/p/3522395718?pn=" + str(i)
    urls.append(newpage)#构造url列表

time1 = time.time()
for i in urls:
    print i
    getsource(i)
time2 = time.time()
print u"单线程耗时："+str(time2-time1)

pool = ThreadPool(4)#机器是多少核便填多少，卤煮实在ubuntu14.04 4核戴尔电脑上跑的程序
time3 = time.time()
results = pool.map(getsource, urls)
pool.close()
pool.join()
time4 = time.time()
print u"并行耗时："+str(time4-time3)

效果：

Figure 1-1: multiprocessing效果明显

可以看出，使用multiprocessing包对爬虫函数进行优化，其效果还是很明显的。另外，用requests包解析url时，未发生重定向问题，也是我比较意外的，以往卤煮写的没注意爬取访问时间被封掉ip。

xpath提取某贴回帖信息

极客学院网站视频：实战——百度贴吧爬虫-xpath与多线程爬虫

coding

#-*-coding:utf8-*-
from lxml import etree
from multiprocessing.dummy import Pool as ThreadPool
import requests
import json
import sys
reload(sys)
sys.setdefaultencoding("utf-8")
'''重新运行之前请删除content.txt，因为文件操作使用追加方式，会导致内容太多。'''

def towrite(contentdict):
    f.writelines(u'回帖时间:' + str(contentdict['topic_reply_time']) + '\n')
    f.writelines(u'回帖内容:' + unicode(contentdict['topic_reply_content']) + '\n')
    f.writelines(u'回帖人:' + contentdict['user_name'] + '\n\n')

def spider(url):
    html = requests.get(url)
    selector = etree.HTML(html.text)
    #主要解析html文件，用xpath表达式提取文本，存到字典中
#    content_field = selector.xpath('//div[@class="l_post l_post_bright  "]')
    content_field = selector.xpath('//div[@class="l_post j_l_post l_post_bright  "]')#先抓大后抓小,这里改了
    item = {}
    print len(content_field)
    for each in content_field:
	#print "=============="
        reply_info = json.loads(each.xpath('@data-field')[0].replace('"',''))
        author = reply_info['author']['user_name']
        reply_time = reply_info['content']['date']
        #print reply_time
        #print author
        content = each.xpath('div[@class="d_post_content_main"]/div/cc/div[@class="d_post_content j_d_post_content  clearfix"]/text()')[0]#还有这里也改了
        #print content
        item['user_name'] = author
        item['topic_reply_content'] = content
        item['topic_reply_time'] = reply_time
        towrite(item)

if __name__ == '__main__':
    pool = ThreadPool(4)	#机器为4核，故4个线程
    f = open('content.txt','a')#主函数中并未直接f.write，而是通过spider函数，f作为全局变量传到towrite函数中实现写入文件
    page = []
    for i in range(1,21):
        newpage = 'http://tieba.baidu.com/p/3522395718?pn=' + str(i)
        page.append(newpage)

    results = pool.map(spider, page)
    pool.close()
    pool.join()
    f.close()

效果：

转载请认证：http://blog.csdn.net/u010454729/article/details/49765929