用python生成指定位数的密码

#!/usr/bin/env python
#coding:utf8
#随机生成8位、20位、10位密码

import random
import string
all_chs = string.letters + string.digits

def gen_pass(num=8):
    pwd = ''
#    num = int(raw_input('numer: '))
    for i in range(num):
        mima = random.choice(all_chs)
        pwd += mima
    return pwd
if __name__  == '__main__' :
    print gen_pass()
    print gen_pass(20)
    print gen_pass(10)