python中五个模块的详细介绍

本次python爬虫百步百科，里面详细分析了爬虫的步骤，对每一步代码都有详细的注释说明，可通过本案例掌握python爬虫的特点：

1、爬虫调度入口（crawler_main.py）

# coding:utf-8
from com.wenhy.crawler_baidu_baike import url_manager, html_downloader, html_parser, html_outputer

print "爬虫百度百科调度入口"

# 创建爬虫类
class SpiderMain(object):

    # 初始化 url管理器 html下载器 解析器 

输出器 def __init__(self): self.urls = url_manager.UrlManager() self.downloader = html_downloader.HtmlDownloader() self.parser = html_parser.HtmlParser() self.output = html_outputer.HtmlOutput() def craw(urls, downloader, parser, output, root_url): # 计数 count = 1 # 添加url到url管理器中 urls.add_new_url(root_url) # 判断是否有新的URL while urls.has_new_url(): try: # 获取新的URL new_url = urls.get_new_url() print 'crawler %d : %s' % (count, new_url) # 下载html页面数据 html_cont = downloader.download(new_url) # 解析页面得到新的url列表，新的数据 new_urls, new_data = parser.parser(new_url, html_cont) # 把解析到的url数组批量添加到url管理器中 urls.add_new_urls(new_urls) # 收集数据 output.collect_data(new_data) # 爬虫1000页面 if count == 500: break count = count + 1 except Exception as e: print 'Crawler Failed ', e output.output_html() if __name__ == '__main__': # 入口URL 百度百科地址 root_url = "http://baike.baidu.com/item/Python" # 创建爬虫 obj_spider = SpiderMain() # 启动爬虫 craw(obj_spider.urls, obj_spider.downloader, obj_spider.parser, obj_spider.output, root_url) 2、封装URL管理器（url_manager.py）

# coding:utf-8

print "URL管理器"


class UrlManager(object):

    # 初始化url容器（set集合）
    def __init__(self):
        self.new_urls = set()
        self.old_urls = set()

    # 添加一个新的待爬取url
    def add_new_url(self, url):

        if url is None:
            return

        # 判断url不在新的url集合中也不再旧的url集合中 说明是一个全新的url
        if url not in self.new_urls and url not in self.old_urls:
            self.new_urls.add(url)

    # 批量添加解析页面的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)

    # 判断是否有新的待爬取的url
    def has_new_url(self):
        # 如果新的url集合里面len不等于0 说明有待爬取的url
        return len(self.new_urls) != 0

    # 获得url地址
    def get_new_url(self):
        # 获取url并移除当前url
        new_url = self.new_urls.pop()
        self.old_urls.add(new_url)
        return new_url

3、HTML下载器（html_downloader.py）

# coding:utf-8

import urllib2
print "下载HTML"


class HtmlDownloader(object):

    def download(self, url):
        # 判断是否为空
        if url is None:
            return None
        # 下载url
        response = urllib2.urlopen(url)
        # 判断返回结果是否为200
        if response.getcode() != 200:
            return None
        # 成功 返回页面内容
        return response.read()

4、HTML 解析器(html_parser.py)

# coding:utf-8

from bs4 import BeautifulSoup
import re
import urlparse

print "HTML 解析器"


class HtmlParser(object):

    def _get_new_urls(self, page_url, soup):

        # 创建一个集合保存页面解析出来的所有url
        new_urls = set()
        # /item/  词条url
        links = soup.find_all('a', href=re.compile(r'/item/'))
        for link in links:
            # 获取连接
            new_url = link['href']
            # url拼接
            new_full_url = urlparse.urljoin(page_url, new_url)
            # print 'new_full_url', new_full_url
            # 添加到集合中url
            new_urls.add(new_full_url)
        return new_urls


    def _get_new_data(self, page_url, soup):
        # 定义一个dict 集合
        res_data = {}

        res_data['url'] = page_url
        # < dd class ="lemmaWgt-lemmaTitle-title" >< h1 > 自由软件 < / 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


    # 解析器
    def parser(self, page_url, html_content):

        if page_url is None or html_content is None:
            return

        # 使用BeautifulSoup 解析html页面
        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

5、HTML 

输出页面（html_outputer.py）

# coding:utf-8

print "HTML 

输出页面" class HtmlOutput(object): def __init__(self): self.datas = [] # 收集数据 def collect_data(self, data): if data is None: return self.datas.append(data) # 展示数据 def output_html(self): fout = open('output.html', 'w') fout.write('<html>') fout.write('<head>') fout.write('<meta http-equiv="Content-Type" content="text/html;charset=utf-8">') fout.write('</head>') fout.write('<body>') fout.write('<table border="1">') for data in self.datas: fout.write('<tr>') fout.write('<td><a href = "%s">%s</a></td>' % (data['url'].encode('utf-8'), 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>') fout.close() 总结：python爬虫主要就是五个模块：爬虫启动入口模块，URL管理器存放已经爬虫的URL和待爬虫URL列表，html下载器，html解析器，html输出器 同时可以掌握到urllib2的使用、bs4（BeautifulSoup）页面解析器、re正则表达式、urlparse、python基础知识回顾（set集合操作）等相关内容。

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