Python爬虫初识

本文章是对网易云课堂中的Python网络爬虫实战课程进行总结。感兴趣的朋友可以观看视频课程。课程地址

爬虫简介

一段自动抓取互联网信息的程序

非结构化数据

没有固定的数据格式，如网页资料。
必须通过ETL(Extract,Transformation,Loading)工具将数据转化为结构化数据才能使用。

工具安装

Anaconda

pip install requests
pip install BeautifulSoup4
pip install jupyter

打开jupyter

jupyter notebook

requests 网络资源截取插件

取得页面

import requests
url = ''
res = requests.get(url)
res.encoding = 'utf-8'
print (res.text)

将网页读进BeautifulSoup中

from bs4 import BeautifulSoup
soup  = BeautifulSoup(res.text, 'html.parser')
print (soup.text)

使用select方法找找出特定标签的HTML元素，可取标签名或id，class返回的值是一个list

select('h1')   select('a')
id = 'thehead' select('#thehead')

alink = soup.select('a')
for link in alink:
    print (link['href'])

例子

• 1、取得新浪陕西的新闻时间标题和连接

  import requests
  from bs4 import BeautifulSoup
  res = requests.get('http://sx.sina.com.cn/')
  res.encoding = 'utf-8'
  soup = BeautifulSoup(res.text, 'html.parser')
  
  for newslist in soup.select('.news-list.cur'):
      for news in newslist:
          for li in news.select('li'):
              title = li.select('h2')[0].text
              href = li.select('a')[0]['href']
              time = li.select('.fl')[0].text
              print (time, title, href)
  

• 2、获取文章的标题，来源，时间和正文

  import requests
  from bs4 import BeautifulSoup
  from datetime import datetime
  res = requests.get('http://sx.sina.com.cn/news/b/2018-06-02/detail-ihcikcew5095240.shtml')
  res.encoding = 'utf-8'
  soup = BeautifulSoup(res.text, 'html.parser')
  
  h1 = soup.select('h1')[0].text
  source = soup.select('.source-time span span')[0].text
  timesource = soup.select('.source-time')[0].contents[0].text
  date = datetime.strptime(timesource, '%Y-%m-%d %H:%M')
  
  article = []
  for p in soup.select('.article-body p')[:-1]:
      article.append(p.text.strip())
  
  ' '.join(article)
  

  简写为：

  ' '.join([p.text.strip() for p in soup.select('.article-body p')[:-1]])
  

  说明：

  datatime 包用来格式化时间
  [:-1]去除最后一个元素
  strip() 移除字符串头尾指定的字符（默认为空格或换行符）
  ' '.join(article) 将列表以空格连接
  

• 3、获取文章的评论数，评论数是通过js写入，不能通过上面的方法获取到，在js下，找到文章评论的js

  import requests
  import json
  
  comments = requests.get('http://comment5.news.sina.com.cn/cmnt/count?format=js&newslist=sx:comos-hcikcew5095240:0')
  jd = json.loads(comments.text.strip('var data ='))
  
  jd['result']['count']['sx:comos-hcikcew5095240:0']['total']
  

• 4、将获得评论的方法总结成一个函数

  import re 
  import json
  
  commenturl = 'http://comment5.news.sina.com.cn/cmnt/count?format=js&newslist=sx:comos-{}:0'
  
  def getCommentCounts(url):
      m = re.search('detail-i(.+).shtml' ,url)
      newsid = m.group(1)
      comments = requests.get(commenturl.format(newsid))
      jd = json.loads(comments.text.strip('var data ='))
      return jd['result']['count']['sx:comos-'+newsid+':0']['total']
  
  news = 'http://sx.sina.com.cn/news/b/2018-06-01/detail-ihcikcev8756673.shtml'
  getCommentCounts(news)
  

• 5、输入地址得到文章的所有信息（标题、时间、来源、正文等）的函数（完整版）

  import requests
  import json
  import re
  from bs4 import BeautifulSoup
  from datetime import datetime
  
  commenturl = 'http://comment5.news.sina.com.cn/cmnt/count?format=js&newslist=sx:comos-{}:0'
  
  def getCommentCounts(url):
      m = re.search('detail-i(.+).shtml' ,url)
      newsid = m.group(1)
      comments = requests.get(commenturl.format(newsid))
      jd = json.loads(comments.text.strip('var data ='))
      return jd['result']['count']['sx:comos-'+newsid+':0']['total']
  
  def getNewsDetail(newsurl):
      result = {}
      res = requests.get(newsurl)
      res.encoding = 'utf-8'
      soup = BeautifulSoup(res.text, 'html.parser')
      result['title'] = soup.select('h1')[0].text
      result['newssource'] = soup.select('.source-time span span')[0].text
      timesource = soup.select('.source-time')[0].contents[0].text
      result['date'] = datetime.strptime(timesource, '%Y-%m-%d %H:%M')
      result['article'] = ' '.join([p.text.strip() for p in soup.select('.article-body p')[:-1]])
      result['comments'] = getCommentCounts(newsurl)
      return result
      
  news = 'http://sx.sina.com.cn/news/b/2018-06-02/detail-ihcikcew8995238.shtml'
  getNewsDetail(news)