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python爬虫实例详解

时间:2021-03-06 00:29     来源/作者:孙华强

本篇博文主要讲解python爬虫实例,重点包括爬虫技术架构,组成爬虫的关键模块:url管理器、html下载器和html解析器。

爬虫简单架构

python爬虫实例详解

程序入口函数(爬虫调度段)

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#coding:utf8
import time, datetime
 
from maya_spider import url_manager, html_downloader, html_parser, html_outputer
 
 
class spider_main(object):
 #初始化操作
 def __init__(self):
  #设置url管理器
  self.urls = url_manager.urlmanager()
  #设置html下载器
  self.downloader = html_downloader.htmldownloader()
  #设置html解析器
  self.parser = html_parser.htmlparser()
  #设置html输出器
  self.outputer = html_outputer.htmloutputer()
 
 #爬虫调度程序
 def craw(self, root_url):
  count = 1
  self.urls.add_new_url(root_url)
  while self.urls.has_new_url():
   try:
    new_url = self.urls.get_new_url()
    print('craw %d : %s' % (count, new_url))
    html_content = self.downloader.download(new_url)
    new_urls, new_data = self.parser.parse(new_url, html_content)
    self.urls.add_new_urls(new_urls)
    self.outputer.collect_data(new_data)
 
    if count == 10:
     break
 
    count = count + 1
   except:
    print('craw failed')
 
  self.outputer.output_html()
 
if __name__ == '__main__':
 #设置爬虫入口
 root_url = 'http://baike.baidu.com/view/21087.htm'
 #开始时间
 print('开始计时..............')
 start_time = datetime.datetime.now()
 obj_spider = spider_main()
 obj_spider.craw(root_url)
 #结束时间
 end_time = datetime.datetime.now()
 print('总用时:%ds'% (end_time - start_time).seconds)

url管理器

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class urlmanager(object):
 def __init__(self):
  self.new_urls = set()
  self.old_urls = set()
 
 def add_new_url(self, url):
  if url is none:
   return
  if url not in self.new_urls and url not in self.old_urls:
   self.new_urls.add(url)
 
 def add_new_urls(self, urls):
  if urls is none or len(urls) == 0:
   return
  for url in urls:
   self.add_new_url(url)
 
 def has_new_url(self):
  return len(self.new_urls) != 0
 
 def get_new_url(self):
  new_url = self.new_urls.pop()
  self.old_urls.add(new_url)
  return new_url

网页下载器

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import urllib
import urllib.request
 
class htmldownloader(object):
 
 def download(self, url):
  if url is none:
   return none
 
  #伪装成浏览器访问,直接访问的话csdn会拒绝
  user_agent = 'mozilla/4.0 (compatible; msie 5.5; windows nt)'
  headers = {'user-agent':user_agent}
  #构造请求
  req = urllib.request.request(url,headers=headers)
  #访问页面
  response = urllib.request.urlopen(req)
  #python3中urllib.read返回的是bytes对象,不是string,得把它转换成string对象,用bytes.decode方法
  return response.read().decode()

网页解析器

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import re
import urllib
from urllib.parse import urlparse
 
from bs4 import beautifulsoup
 
class htmlparser(object):
 
 def _get_new_urls(self, page_url, soup):
  new_urls = set()
  #/view/123.htm
  links = soup.find_all('a', href=re.compile(r'/item/.*?'))
  for link in links:
   new_url = link['href']
   new_full_url = urllib.parse.urljoin(page_url, new_url)
   new_urls.add(new_full_url)
  return new_urls
 
 #获取标题、摘要
 def _get_new_data(self, page_url, soup):
  #新建字典
  res_data = {}
  #url
  res_data['url'] = page_url
  #<dd class="lemmawgt-lemmatitle-title"><h1>python</h1>获得标题标签
  title_node = soup.find('dd', class_="lemmawgt-lemmatitle-title").find('h1')
  print(str(title_node.get_text()))
  res_data['title'] = str(title_node.get_text())
  #<div class="lemma-summary" label-module="lemmasummary">
  summary_node = soup.find('div', class_="lemma-summary")
  res_data['summary'] = summary_node.get_text()
 
  return res_data
 
 def parse(self, page_url, html_content):
  if page_url is none or html_content is none:
   return none
 
  soup = beautifulsoup(html_content, 'html.parser', from_encoding='utf-8')
  new_urls = self._get_new_urls(page_url, soup)
  new_data = self._get_new_data(page_url, soup)
  return new_urls, new_data

网页输出器

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class htmloutputer(object):
 
 def __init__(self):
  self.datas = []
 
 def collect_data(self, data):
  if data is none:
   return
  self.datas.append(data )
 
 def output_html(self):
  fout = open('maya.html', 'w', encoding='utf-8')
  fout.write("<head><meta http-equiv='content-type' content='text/html;charset=utf-8'></head>")
  fout.write('<html>')
  fout.write('<body>')
  fout.write('<table border="1">')
  # <th width="5%">url</th>
  fout.write('''<tr style="color:red" width="90%">
     <th>theme</th>
     <th width="80%">content</th>
     </tr>''')
  for data in self.datas:
   fout.write('<tr>\n')
   # fout.write('\t<td>%s</td>' % data['url'])
   fout.write('\t<td align="center"><a href=\'%s\'>%s</td>' % (data['url'], data['title']))
   fout.write('\t<td>%s</td>\n' % data['summary'])
   fout.write('</tr>\n')
  fout.write('</table>')
  fout.write('</body>')
  fout.write('</html>')
  fout.close()

运行结果

python爬虫实例详解

附:完整代码

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。

原文链接:https://blog.csdn.net/sunhuaqiang1/article/details/66472363

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