用python编写简单爬虫

需求：抓取百度百科python词条相关词条网页的标题和简介，并将数据输出在一个html表格中

 入口页:python的百度词条页 https://baike.baidu.com/item/Python/407313

 词条页面URL：'/item/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%A8%8B%E5%BA%8F%E8%AE%BE%E8%AE%A1%E8%AF%AD%E8%A8%80' 注意:这不是一个完整的url,需要对之进行拼接

 数据格式：

 -标题：<dd class="lemmaWgt-lemmaTitle-title"><h1>***</h1></dd>
 -简介：<div class='lemma-summary'>***</div> 
 页面编码：UTF-8

实例代码：
文件目录结构如图 

入口文件（spider_main.py）：

# coding:utf-8
import url_manager
import html_parser
import html_downloader
import html_outputer


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():  # 如果有待爬取的url
            try:
                new_url = self.urls.get_new_url()  # 取一个待爬取的url
                print 'craw %d:%s' % (count, new_url)
                html_cont = self.downloader.download(new_url)  # 下载页面
                new_urls, new_data = self.parser.parse(new_url, html_cont)  # 解析页面得到新的url和一些数据
                self.urls.add_new_urls(new_urls)  # 将新得到的url添加到url管理器
                self.outputer.collect_data(new_data)  # 将获取到的数据添加到output文件中
                if count == 10:
                    break
                count += 1
            except Exception as e:
                print e
        self.outputer.output_html()


if __name__ == '__main__':
    obj_spider = SpiderMain()
    obj_spider.craw('https://baike.baidu.com/item/Python/407313')

url管理文件（url_manager.py）:

# coding:utf-8

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()  # 从列表中获取一个并且移除
        self.old_urls.add(new_url)
        return new_url

页面源码下载（html_downloader.py）:

# coding:utf-8
import urllib2


class 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()

源码解析（html_parser.py）:

# coding:utf-8
from bs4 import BeautifulSoup
import urlparse
import re


class HtmlParser(object):
    def _get_new_urls(self, page_url, soup):
        new_urls = set()
        # 页面中的链接格式：/item/xxx
        links = soup.find_all('a', href=re.compile(r"/item/(.*)"))  # 得到所有的url的标签
        for link in links:
            new_url = link['href']  # 获取所有的链接
            new_full_url = urlparse.urljoin(page_url, new_url)  # 让new_url按照page_url的格式拼接成一个完整的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></dd>
        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">    简介的html
        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

将爬取到的数据输出（html_output.py）:

# coding:utf-8


class HtmlOutputer(object):
    def __init__(self):
        self.datas = []

    def collect_data(self, data):  # 收集数据
        if data is None:
            return
        self.datas.append(data)

    def output_html(self):  # 将数据输出为html
        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>%s</td>' % data['url'])
            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>')