# 随机4位验证码
def yanzhengma():
strvar = ""
for i in range(4):
# 产生大写字母A~Z
bchr = chr(random.randrange(65,91))
# 产生小写字母a~z
schr = chr(random.randrange(97,123))
# 数字0~9
num = str(random.randrange(0,10))
# 把所有随机值得种类塞到列表里
listvar = [bchr,schr,num]
# 随机选取一个
res = random.choice(listvar)
# 拼接字符串
strvar += res
# 返回字符串
return strvar
res = yanzhengma()
print(res)