python并行爬虫

Python并行化

并行化介绍
Map的使用

1)并行化介绍

[x] 多个线程同时处理任务
[x] 高效
[x] 快速

2)Map的使用

map函数一手包办了序列的操作，参数传递和结果保存等一系列的操作。
from multiprocessing.dummy import Pool
pool = Pool(计算机核数)
results = pool.map(爬取函数，网址列表)

# -*-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)

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(2)
time3 = time.time()
results = pool.map(getsource, urls)
pool.close()
pool.join()
time4 = time.time()
print u'并行耗时：' + str(time4-time3)

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5.实战–百度贴吧爬虫

目标网站：http://tieba.baidu.com/p/3522395718
目标内容：前20页的跟帖用户名，跟帖内容，跟帖时间
涉及知识：Requests获取网页，XPath提取内容，map实现多线程爬虫
tiebaspider.py

# -*- coding: utf-8 -*-
from lxml import etree
from multiprocessing.dummy import Pool as ThreadPool
import requests
import json  #转义json格式的内容

import sys      #将编码转义为utf-8
reload(sys)
sys.setfaultencoding('utf-8')

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：' +str(contentdict['user_time']) + '\n\n')

def spider(url):
html = requests.get(url)
selector = etree.HTML(html.text)
content_field = selector.xpath('//div[@class="l_post l_post_bright "]')
item = {}
for each in content_field:
reply_info = json.loads(each.xpath('@data-field')[0].replace('"',''))       #因为获取的是xpath后的内容所以直接@
author = reply_info['author']['user_name']
content = each.xpath('div[@class="d_post_content_main"]/div/cc/div[@class="d_post_content j_d_post_content "]/text()')[0]
reply_time = reply_info['content']['date']
print content
print reply_time
print author
item['user_name'] = author
item['topic_reply_content'] = content
item['topic_reply_time'] = reply_time
towrite(item)

if __name__ == "__main__":
pool = ThreadPool(2)
f = open('content.txt', 'a')
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()