python xpath介绍和新闻内容爬虫

二十、python xpath介绍和新闻内容爬虫

Xpath介绍

用xpath提取感兴趣的内容

一个网页文档是一个半结构化的数据，其实html文档就是一个树形结构。根节点是html

用正则表达式也可以提取，但是不如xpath方便

 

1、路径表示法

//定位根节点

/text(): 提取文本的内容

/@attr:提取属性的内容

 

2、筛选条件

/div[@id]

/div[@id="content_id"]

/book[price>100] #按照节点的值

 

问题：先再windows中安装lxml
？？？

前提是先装好：pip

C:\Users\lyd>pip install lxml

 

Xpath使用

#获取新闻列表

import requests

from lxml import etree

import datetime

 

#根据跟url获取该文档中的新闻列表的信息

def getNewsUrlList(baseUrl):

    x = requests.get(baseUrl)

    html = x.content.decode('gbk')

 

    selector = etree.HTML(html)

 

    contents = selector.xpath('//div[@id="content_right"]/div[@class="content_list"]/ul/li[div]')

    for eachLink in contents:

        url = eachLink.xpath('div/a/@href')[0]

        title = eachLink.xpath('div/a/text()')[0]

        ptime = eachLink.xpath('div[@class="dd_time"]/text()')[0]

        yield(title, url, ptime)

 

#根据具体的新闻的url获取该新闻的内容

def getNewsContent(newsUrlList):

    for title, url, ptime in newUrlList:

        x = requests.get(url)

        html = x.content.decode('gbk')  #整个页面的编码为gbk2312

        selector = etree.HTML(html)

        constants = selector.xpath('//div[@class="left_zw"]/p/text()')

        news = '\r\n'.join(constants) #在每一个p标签都回车换行。
\r\n: linux中的换行，就相当于wind中的\n

        yield title, url, ptime, news

 

# 获取昨天的日期

def getYesterday(i):

    today = datetime.date.today()

    oneday = datetime.timedelta(days=i)

    yesterday = today - oneday

    return yesterday.strftime("%m%d")

 

if __name__ == "__main__":

    urlTemplate = 'http://www.chinanews.com/scroll-news/mil/{0}/{1}{2}/news.shtml'

    #http://www.chinanews.com/scroll-news/2017/0719/news.shtml

    #http://www.chinanews.com/scroll-news/mil/2017/0717/news.shtml

    testurl = urlTemplate.format('2017', '7', '20')

    #print testurl

 

    # newUrlList = getNewsUrlList(testurl)

    # for title, url, ptime in newUrlList:

    #      print title, url, ptime

 

 

    # newsConstant = getNewsContent(newUrlList)

    # f = open('news.txt','w') #以写的方式打开一个文件

    # w = lambda x: f.write((x+u'\r\n').encode('utf-8'))

    # for title, url, ptime, news in newsConstant:

    #     w(u'~'*100)

    #     w(title)

    #     w(url)

    #     w(news)

    # f.close()

#########################如下是作业：####################################

#爬去今天以前n多天的新闻数据

    for i in range(0, 10):

        yesterday = getYesterday(i)

        urls = '%s%s%s' % ("http://www.chinanews.com/scroll-news/mil/2017/", yesterday, '/news.shtml')

 

        newUrlList = getNewsUrlList(urls)

        for title, url, ptime in newUrlList:

              print title, url, ptime

            # newsConstant = getNewsContent(newUrlList)

            # f = open('news.txt','w') #以写的方式打开一个文件

            # w = lambda x: f.write((x+u'\r\n').encode('utf-8'))

            # for title, url, ptime, news in newsConstant:

            #     w(u'~'*100)

            #     w(title)

            #     w(url)

            #     w(news)

            # f.close()

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