Python进阶(二十)Python爬虫实例讲解「建议收藏」

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一、前言

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。

二、爬虫简单架构

三、程序入口函数(爬虫调度段)

#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)

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四、URL管理器

IT知识分享网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

五、网页下载器

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()

六、网页解析器

IT知识分享网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

七、网页输出器

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()

八、运行结果

九、拓展阅读

• 完整代码