Python实现随机读取文本N行数据

工作中需要判断某个文本中的URL是否能正常访问，并且随机获取其中N行能正常访问的URL数据，我的思路是：读取文本每一行数据，用urlopen访问，将返回状态码为200的URL保存到一个列表，获得列表长度，使用random产生一个随机值作为列表下标，获取该行数据。具体实现如下：

 import urllib2,random
 from sets import Set

 def get_responses(url):
     global good_list
     global bad_list
     if not url.startswith("http:"):
         http_url = "http://" + url
     headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 5.1; rv:10.0.1) Gecko/20100101 Firefox/10.0.1',}
     try:
         request = urllib2.Request(http_url, headers=headers)
         resp = urllib2.urlopen(request)
         print url
     except urllib2.URLError, e:
         print e
         bad_list.append(url)
         return 0

     retcode = resp.getcode()
     if retcode == 200:
         good_list.append(url)
         #return 1
     else:
         bad_list.append(url)
         #return 0

 def readFile():
     try:
         urllist = open(r'C:\Users\888\Desktop\urls.txt','r')
     except IOError:
         print "file does not exist.\n"
     for item in urllist:
         item = item.strip('\n')
         r = get_responses(item)

     urllist.close()
     print "Total URLs: %d, Good URLs:%d, Bad URLs: %d." %((len(good_list)+len(bad_list)),len(good_list),len(bad_list))

 def writeFile(linenum):
     result = []
     linelen = len(good_list)
     while len(result) < int(linenum):
         s = random.randint(0,linelen-1)
         result.append(good_list[s])
         result = list(Set(result))

     # Put the good_url in goodurl.txt file
     try:
         goodurl = open(r'C:\Users\888\Desktop\goodurl.txt','w+')
     except IOError:
         print "file does not exist.\n"

     for item in result:
         goodurl.write(item+'\n')
     goodurl.close()

     print "The mission is done, Please check the goodurl.txt file"

 if __name__ == "__main__":
     good_list = []
     bad_list = []
     readFile()
     writeFile(150)