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)