pythonマルチスレッド処理繰返しタスク10000回

#!/usr/bin/python
import threading
import urllib2
#f = open("/root/wget.txt","a")
x = [ i.strip() for i in open("/root/ceshi/abc.txt","r") ]
#f1 = open("/root/abc.txt","r")
def wget(x):
    response = urllib2.urlopen("http://abc.abc.com/organize/domain/allupdate?domainname=%s"%x)
    if  response.read() == '{"code": "0", "data": "ok"}':
        f.write('%s {"code": "0", "data": "ok"}
'%x)
    else:
        f.write('%s {"code": "0", "data": "fail"}
'%x)
def main():
    n = 0
    while len(x) - n >= 20:
        f = open("/root/ceshi/wget.txt","a")
        threads = []
        for i in range(n+0,n+20):
            t = threading.Thread(target=wget,args=(x[i],))
            threads.append(t)
        for i in range(20):
            threads[i].start()
        for i in range(20):
            threads[i].join()
        n+=20
        f.close()
    f = open("/root/ceshi/wget.txt","a")
    for i in range(n,len(x)):
        threads = []
        t = threading.Thread(target=wget,args=(x[i]))
        threads.append(t)
    for i in range(len(x)-n):
        threads[i].start()
    for i in range(len(x)-n):
        threads[i].join()
    f.close()
if __name__ == '__main__':
    main()