验证码的实现py3

import random
flag = 1
try_=0
while (flag):
    try_ +=1
    yan = ""
    for i in range(0,4):
        cun=random.randrange(1,4)
        if cun==i:
            tmp=chr(random.randint(65,90))
        else:
            tmp=random.randrange(0,9)
        yan+=str(tmp)
    print(yan)
    var=input("请输入验证码:")
    if var == yan:
        print('验证成功')
        break
    else:
        print("验证失败")
        if try_ == 3:
            print("输入次数超3过次,请过会儿再试...")
            break
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