Python爬虫之requests

python爬虫之requests

在python中使用requests简化了网络请求，在使用requests之前需要

pip install requests

来安装requests,requests中文手册是一个很好的入门资料。

制作爬虫需要对html的结构有一定的了解，同时使用正则表达式原生匹配的爬虫也会随网页结构的改变而失效，所以若使下述代码无效，请分析网页的结构是否发生了改变。

抓取网页：极客学院视频库网页

爬取效果：

# -*-coding:utf-8 -*-
import requests
import re
import sys

'''
1.先获取整个网页
2.获取整个网页中的课程块
3.通过正则表达使获取想要的特定内容
'''

class spider(object):
def __init__(self):
print(u'开始爬取内容...')

# 用于获取网页的源代码
def getsource(self, url):
html = requests.get(url)
html.encoding = 'utf-8'
return html.text

# 改变链接中的页码数
def changepage(self, url, total_page):
now_page = int(re.search('pageNum=(\d+)', url, re.S).group(1))  # 返回页码数
page_group = []
for i in range(now_page, total_page + 1):
link = re.sub('pageNum=\d+', 'pageNum=%s' % i, url, re.S)  # 替换url中的页码数
page_group.append(link)
return page_group

# 抓取每个课程块消息
def geteveryclass(self, source):
everyclass = re.findall('(<li id=".*?</li>)', source, re.S)
return everyclass

# 从课程块中得到我们想要的信息
def getinfo(self, eachclass):
info = {}
info['title'] = re.search('.*>(.*?)</a></h2>', eachclass, re.S).group(1)
info['content'] = re.search('.*>(.*?)</p>', eachclass, re.S).group(1).strip()
timeandlevel = re.findall('<em>(.*?)</em>', eachclass, re.S)
classtime = timeandlevel[0].split()  # 截取字符中的空格
info['classtime'] = classtime[0] + classtime[1]
info['classlevel'] = timeandlevel[1]
info['learnnum'] = re.search('"learn-number">(.*?)</em>', eachclass, re.S).group(1)
return info

def saveinfo(self, classinfo):
f = open('info.txt', 'a', encoding='utf-8')
for each in classinfo:
f.writelines('title:' + each['title'] + '\n')
f.writelines('content:' + each['content'] + '\n')
f.writelines('classtime:' + each['classtime'] + '\n')
f.writelines('classlevel:' + each['classlevel'] + '\n')
f.writelines('learnnum:' + each['learnnum'] + '\n\n')
f.close()

if __name__ == '__main__':
classinfo = []
url = 'http://www.jikexueyuan.com/course/?pageNum=2'
jikespider = spider()
all_links = jikespider.changepage(url, 20)
print(all_links)
for link in all_links:
print(u'正在处理页面：' + link)
html = jikespider.getsource(link)
everyclass = jikespider.geteveryclass(html)
for each in everyclass:
info = jikespider.getinfo(each)
classinfo.append(info)
jikespider.saveinfo(classinfo)