驗證碼的實現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("請輸入驗證碼:")
    if var == yan:
        print('驗證成功')
        break
    else:
        print("驗證失敗")
        if try_ == 3:
            print("輸入次數超3過次,請過會兒再試...")
            break
憋了好久了，知識這種東西久了不用會生鏽的....