简单爬虫——爬取百度百科总结

来源：互联网发布：华西电子盘软件下载编辑：程序博客网时间：2024/05/19 07:07

在慕课网学习简单爬虫来爬取百度百科的总结：

一、逻辑：根据根url: http://baike.baidu.com/item/Python,通过python的第三方插件Beautiful Soup来获取页面的html代码，找到我们需要的信息，这里我们需要的信息是：

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

和

#<div class="lemma-summary" label-module="lemmaSummary">

中的h1标签、类名为lemma-summary的div内的内容。

有一个url管理器，来获取和管理所有需要爬取的链接a，比如在这里我们先获取http://baike.baidu.com/item/Python这个页面的所有a标签，将其存入一个容器（new_urls）中，然后依次爬取这个容器中的所有url，每爬一次，把爬取过的url从这个容器中删去，加入到old_urls容器中, 并且加入到new_urls时要判断这个url是否在new_urls和old_urls已经存在，若存在，不加入，防止重复爬取。然后通过页面下载器利用urllib2下载我们需要的页面代码，页面解析器html_parse利用beautifulsoup获取我们需要的数据。

二、具体代码：

1.主函数 spider_main.py

#_*_coding:utf-8_*_from baike_spider2 import url_manager,html_downloader,html_parser,html_outputerclass SpiderMain(object):    def __init__(self):        self.urls = url_manager.UrlManager()        self.downloader = html_downloader.HtmlDownloader()        self.parser = html_parser.HtmlPsrser()        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 == 100:                    break                count = count + 1            except:                print 'craw fail'        self.outputer.output_html()if __name__=="__main__":    # 爬虫入口页面    root_url = 'http://baike.baidu.com/item/Python'    obj_spider = SpiderMain()    # 启动爬虫    obj_spider.craw(root_url)

2.页面下载器 html_downloader.py

#_*_coding:utf-8_*_import urllib2class HtmlDownloader(object):    def download(self, url):        if url is None:            return None        response = urllib2.urlopen(url)        if response.getcode() != 200:            return None        return response.read()

3.页面输出器 html_outputer.py

#_*_coding:utf-8_*_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')        fout.write("<html>")        fout.write("<body>")        fout.write("<table>")        for data in self.datas:            fout.write("<tr>")            fout.write("<td style='width:400px'>%s</td>" % data['url'].encode('utf-8'))            fout.write("<td>%s</td>" % data['title'].encode('utf-8'))            fout.write("<td>%s</td>" % data['summary'].encode('utf-8'))            fout.write("</tr>")        fout.write("</table>")        fout.write("</body>")        fout.write("</html>")

4.页面解析器 html_parser.py

#_*_coding:utf-8_*_from bs4 import  BeautifulSoupimport urlparseimport reclass HtmlPsrser(object):    def _get_new_urls(self, page_url, soup):        new_urls = set()        # links = soup.find_all('a', href=re.compile(r"/item/\d+\.html"))        links = soup.find_all('a', href=re.compile(r"/item/(.*)"))        for link in links:            new_url = link['href']            new_full_url = urlparse.urljoin(page_url, new_url)            new_urls.add(new_full_url)        return new_urls    def _get_new_data(self, page_url, soup):        res_data = {}        res_data['url'] = page_url        #<dd class="lemmaWgt-lemmaTitle-title"><h1>Python</h1>        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        soup = BeautifulSoup(html_cont, '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

5.url管理器 url_manager.py

#_*_coding:utf-8_*_class UrlManager(object):    def __init__(self):        self.new_urls = set()        self.old_urls = set()    #向管理器中添加新的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)    #向管理器中添加批量的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)    #判断管理器中是否有新的url    def has_new_url(self):        return len(self.new_urls) != 0    #获取新的带爬取的url    def get_new_url(self):        new_url = self.new_urls.pop()        self.old_urls.add(new_url)        return new_url

备注：

1.urljoin是拼接url地址的方法，比如 urljoin("http://www.asite.com/folder/currentpage.html", "anotherpage.html") 会输出'http://www.asite.com/folder/anotherpage.html'

urljoin("http://www.asite.com/folder/currentpage.html", "folder2/anotherpage.html")会输出'http://www.asite.com/folder/folder2/anotherpage.html'

urljoin("http://www.asite.com/folder/currentpage.html", "/folder3/anotherpage.html") 会输出'http://www.asite.com/folder3/anotherpage.html'

urljoin("http://www.asite.com/folder/currentpage.html", "../finalpage.html")会输出'http://www.asite.com/finalpage.html'

2.pop() 函数用于移除列表中的一个元素（默认最后一个元素），并且返回该元素的值

3.页面内容随时可能变化，根据不同情况做不同的分析处理，比如以前a标签的href跟现在的不一样，是类似于：/item/123.htm格式，所以在以前，页面解析器找a的代码为

# links = soup.find_all('a', href=re.compile(r"/item/\d+\.html"))

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