【Python】正则表达式-判断输入字符串为字母、数字、长度大于8

代码：

# -*- coding: utf8 -*-
import re  
while True:
    line = raw_input("input:")
    if len(line) == 0:
        print "NO"
    else:
        if re.search("^(?![A-Z]+$)(?![a-z]+$)(?!d+$)(?![W_]+$)S{8,}$", line):
            print "YES"
        else:
            print "NO"