Python多线程抓取Google搜索链接网页

1）urllib2+BeautifulSoup抓取Goolge搜索链接

近期，参与的项目需要对Google搜索结果进行处理，之前学习了Python处理网页相关的工具。实际应用中，使用了urllib2和beautifulsoup来进行网页的抓取，但是在抓取google搜索结果的时候，发现如果是直接对google搜索结果页面的源代码进行处理，会得到很多“脏”链接。

看下图为搜索“titanic  james”的结果：

图中红色标记的是不需要的，蓝色标记的是需要抓取处理的。

这种“脏链接”当然可以通过规则过滤的方法来过滤掉，但是这样程序的复杂度就高了。正当自己愁眉苦脸的正在写过滤规则时。同学提醒说google应该提供相关的api，才恍然大明白。

（2）Google Web Search API+多线程

文档中给出使用Python进行搜索的例子：

import simplejson 
   
# The request also includes the userip parameter which provides the end  
# user's IP address. Doing so will help distinguish this legitimate  
# server-side traffic from traffic which doesn't come from an end-user.  
url = ('https://ajax.googleapis.com/ajax/services/search/web'
       '?v=1.0&q=Paris%20Hilton&userip=USERS-IP-ADDRESS') 
   
request = urllib2.Request( 
    url, None, {'Referer': /* Enter the URL of your site here */}) 
response = urllib2.urlopen(request) 
   
# Process the JSON string.  
results = simplejson.load(response) 
# now have some fun with the results... 
 
import simplejson
  
# The request also includes the userip parameter which provides the end
# user's IP address. Doing so will help distinguish this legitimate
# server-side traffic from traffic which doesn't come from an end-user.
url = ('https://ajax.googleapis.com/ajax/services/search/web'
       '?v=1.0&q=Paris%20Hilton&userip=USERS-IP-ADDRESS')
  
request = urllib2.Request(
    url, None, {'Referer': /* Enter the URL of your site here */})
response = urllib2.urlopen(request)
  
# Process the JSON string.
results = simplejson.load(response)
# now have some fun with the results..

实际应用中可能需要抓取google的很多网页，所以还需要使用多线程来分担抓取任务。使用google web search api的参考详细介绍，请看此处（这里介绍了Standard URL Arguments）。另外要特别注意，url中参数rsz必须是8（包括8）以下的值，若大于8，会报错的！

（3）代码实现

代码实现还存在问题，但是能够运行，鲁棒性差，还需要进行改进，希望各路大神指出错误（初学Python），不胜感激。

#-*-coding:utf-8-*-  
import urllib2,urllib 
import simplejson 
import os, time,threading 
  
import common, html_filter 
#input the keywords  
keywords = raw_input('Enter the keywords: ')                                  
  
#define rnum_perpage, pages  
rnum_perpage=8
pages=8                        
  
#定义线程函数  
def thread_scratch(url, rnum_perpage, page): 
 url_set = []  
 try: 
   request = urllib2.Request(url, None, {'Referer': 'http://www.sina.com'}) 
   response = urllib2.urlopen(request) 
   # Process the JSON string.  
   results = simplejson.load(response) 
   info = results['responseData']['results'] 
 except Exception,e: 
   print 'error occured'
   print e 
 else: 
   for minfo in info: 
      url_set.append(minfo['url']) 
      print minfo['url'] 
  #处理链接  
 i = 0
 for u in url_set: 
   try: 
     request_url = urllib2.Request(u, None, {'Referer': 'http://www.sina.com'}) 
     request_url.add_header( 
     'User-agent', 
     'CSC'
     ) 
     response_data = urllib2.urlopen(request_url).read() 
     #过滤文件  
     #content_data = html_filter.filter_tags(response_data)  
     #写入文件  
     filenum = i+page 
     filename = dir_name+'/related_html_'+str(filenum) 
     print '  write start: related_html_'+str(filenum) 
     f = open(filename, 'w+', -1) 
     f.write(response_data) 
     #print content_data  
     f.close() 
     print '  write down: related_html_'+str(filenum) 
   except Exception, e: 
     print 'error occured 2'
     print e 
   i = i+1
 return 
  
#创建文件夹  
dir_name = 'related_html_'+urllib.quote(keywords) 
if os.path.exists(dir_name): 
   print 'exists  file'
   common.delete_dir_or_file(dir_name) 
os.makedirs(dir_name) 
  
#抓取网页  
print 'start to scratch web pages:'
for x in range(pages): 
  print "page:%s"%(x+1) 
  page = x * rnum_perpage 
  url = ('https://ajax.googleapis.com/ajax/services/search/web'
                  '?v=1.0&q=%s&rsz=%s&start=%s') % (urllib.quote(keywords), rnum_perpage,page) 
  print url 
  t = threading.Thread(target=thread_scratch, args=(url,rnum_perpage, page)) 
  t.start() 
#主线程等待子线程抓取完  
main_thread = threading.currentThread() 
for t in threading.enumerate(): 
  if t is main_thread: 
    continue
  t.join()