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
# 自由软件
title_node = soup.find('dd', class_='lemmaWgt-lemmaTitle-title').find('h1')
res_data['title'] = title_node.get_text()
# <div>
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）<pre class="brush:php;toolbar:false;"># 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('')
fout.write('')
fout.write('<meta>')
fout.write('')
fout.write('')
fout.write('
| %s | ' % (data['url'].encode('utf-8'), data['title'].encode('utf-8'))) fout.write('%s | ' % data['summary'].encode('utf-8')) fout.write('
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