Python 进阶 (二十)Python 爬虫实例讲解

2022-10-14
江苏
本文字数：2784 字
阅读完需：约 9 分钟

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:utf8import 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)

复制代码

四、URL 管理器

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

复制代码

五、网页下载器

import urllibimport 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()

复制代码

六、网页解析器

import reimport urllibfrom 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

复制代码

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()