python简单实现随机验证码

这是自己在学习pyton时写的一个随机验证码,有不对的地方欢迎指出

代码

import random
def verification():
    lis = ''
    for i in range(4):
        Suiji = random.randint(1,3)
        if Suiji == 1:
            ra = random.randint(97,122)
            yzm = chr(ra)
            lis += yzm
        elif Suiji == 2:
            ra = random.randint(65, 90)
            yzm = chr(ra)
            lis += yzm
        else:
            ra = random.randint(0,9)
            yzm = ra
            lis += str(yzm)
    return lis

Yanzhengma = verification()
print(Yanzhengma)