f = open("username.txt","r")
y = f.read()
#print(y)
f.close()

p = open("password.txt","r")
p1 = p.read()
#print(p1)
p.close()



a = 0
while True:

    c = open("cuo.txt","r")
    c1 = c.read()
    #print(c1)
    c.close()

    username = input("請輸入用戶名：")
    password = input("請輸入密碼：")
    if username == c1:
        print("用戶被鎖定。。")
        break

    elif username == y and password == p1 :
        print("輸入正確")
        break

    elif a == 2 :
        c = open("cuo.txt","w")
        c.write(username)
        c.close()

    else:
        print("輸入錯誤-----")

    a += 1

第一次寫作業。 一定寫的不好，但我會努力改進。