While循环

import sys
user="houzhiqing"
while True:
       for i in range(0,3):
       username = raw_input("please input your name:").strip()
       if len(username) == 0:
               print "your input in empty,please input again"
               continue
       elif username == user:
               pass
       else:
               print"%s is not a valid user" % username
               continue
       break
       else:
       print "exceeded 3 times"
       sys.exit()      
       break
print "welcome"

其中.strip()是取消空格，continue是继续while循环，pass是向下执行的意思