Python开发轻量级爬虫

时间:2021-10-11 02:35:27

这两天自学了python写爬虫,总结一下:

开发目的:抓取百度百科python词条页面的1000个网页

设计思路:

1,了解简单的爬虫架构:

Python开发轻量级爬虫

2,动态的执行流程:

Python开发轻量级爬虫

3,各部分的实现:

URL管理器:python内存

网页下载器:python3自带的urllib模块

网页解析器:使用第三方插BeautifulSoup

4,开发思路:

入口页:http://baike.baidu.com/view/21087.htm

URL格式:

词条页面URL:/view/125370.htm

数据格式:

标题:<dd class=”lemma Wgt-lemmaTitle-title”><h1>***</h1></dd>

简介:<div class=”lemma-summary”>***</div>

页面编码:UTF-8

5,开发过程:

①首先建立一个Pydev工程,新建一个web_spider库,新建一个主函数spider_main,在主函数中调用:URL管理器:url_manager,网页下载器:html_downloader,网页解析器:html_paeser.,网页输出:html_outputer来完成相应的功能

②URL管理器的建立:

新建已读取和未读取的URL集合,用来存放相应的URL地址,定义三个函数:get_new_url(self), add_new_urls(self,urls),add_new_url(self,url)来完成相应的功能

③ 网页下载器的建立:

网页下载的方法:

import urllib.request

response=urllib.request.urlopen(url)

if response.getcode()!=200:

return None

return response.read().decode('UTF-8')

④网页解析器的建立:

导入BeautifulSoup模块,

创建BeautifulSoup对象,调用find方法搜索并访问节点

⑤网页输出的实现:

将抓取到的数据写入到一个HTML网页中

6,遇到的问题及解决方案:

准备工作:

一、1,BeautifulSoup下载地址:https://www.crummy.com/software/BeautifulSoup/

2.下载完成之后需要解压缩,假设放到D:/python下。

3.运行cmd,切换到D:/python/beautifulsoup4-4.1.3/目录下(根据自己解压缩后的目录      和下载的版本号修改),

4.运行命令:

setup.py build

setup.py install

5.在IDE下from bs4 import BeautifulSoup,没有报错说明安装成功。

二、在ecplise中安装PyDev插件后却无法建立项目,后来发现是没有配置python3的解释器,具体步骤为:在 Eclipse 菜单栏中,选择 Window > Preferences > Pydev > Interpreter - (Python/Jython),在这里配置 Python/Jython 解释器

实例代码如下

1spider_main.py

# coding:utf8

from baike_spider import url_manager, html_downloader, html_outputer,\

html_parser

class SpiderMain(object):

def __init__(self):

self.urls=url_manager.UrlManager()

self.downloader=html_downloader.HtmlDownloader()

self.parser=html_parser.HtmlParser()

self.outputer=html_outputer.HtmlOutputer()

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_cont=self.downloader.download(new_url)

new_urls,new_data=self.parser.parse(new_url,html_cont)

self.urls.add_new_urls(new_urls)

self.outputer.collect_data(new_data)

if count==1000:

break

count=count+1

except:

print("craw failed")

self.outputer.output_html()

if __name__=="__main__":

root_url="http://baike.baidu.com/view/21087.htm"

obj_spider=SpiderMain()

obj_spider.craw(root_url)

 (2)url_manager.py

# coding:utf8

class UrlManager(object):

def __init__(self):

self.new_urls=set()

self.old_urls=set()

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

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 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)

(3)html_downloader.py

# coding:utf8

import urllib.request

class HtmlDownloader(object):

def download(self,url):

if url is None:

return None

response=urllib.request.urlopen(url)

if response.getcode()!=200:

return None

return response.read().decode('UTF-8')

 (4)html_paeser.py

# coding:utf8

from bs4 import BeautifulSoup

import re

import urllib

class HtmlParser(object):

def _get_new_urls(self, page_url, soup):

new_urls=set()

links=soup.find_all('a',href=re.compile(r"/view/\d+\.htm"))

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

def _get_new_data(self, page_url, soup):

#<dd class="lemmaWgt-lemmaTitle-title"><h1>Python</h1>

res_data={}

res_data['url']=page_url

title_node=soup.find('dd',class_="lemmaWgt-lemmaTitle-title").find("h1")

res_data['title']=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_cont):

if page_url is None or html_cont is None:

return None

soup=BeautifulSoup(html_cont,'html.parser',from_encoding='utf8')

new_urls=self._get_new_urls(page_url,soup)

new_data=self._get_new_data(page_url,soup)

return new_urls,new_data

(5)html_outputer.py

# coding:utf8

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("output.html",'w',encoding='utf8')

fout.write("<html>")

fout.write("<body>")

fout.write("<table>")

for data  in self.datas:

fout.write("<tr>")

fout.write("<td>%s</td>"%str(data['url']))

fout.write("<td>%s</td>"%str(data['title']))

fout.write("<td>%s</td>"%str(data['summary']))

fout.write("</tr>")

fout.write("</table>")

fout.write("</body>")

fout.write("</html>")

fout.close()

运行结果如图:

Python开发轻量级爬虫