For 循环

_user = "Alex"
_pwd = "123"
flag = False
for i in range(3):
    user_input = input("Enter your login user:")
    pwd_input = input("Enter your login password：")
    if user_input == _user and pwd_input == _pwd:
        print("Hi , %s , Wellcome login you CSDN." % user_input)
        flag = True
        break
    else:
        print("Your user or password not right!")
if not flag:
    print("小婊砸，你已经试了 %d" % (i+1),"次了！别玩了，程序已经停下来了")

_user = "Alex"
_pwd = "123"
counter = 0
while counter < 3:
    username = input("Enter your login user:")
    pwssword = input("Enter your login password：")
    if username == _user and pwssword == _pwd:
        print("Hi , %s , Wellcome login you CSDN." % username)
        break # break for 后，就不会执行最下面的else语句
    else:
        print("Your user or password not right!")
        counter += 1
else:#只要上面的for循环正常执行完毕，中间没有被打断，就会执行else语句
    print("小婊砸，你已经试了 %d" % (counter),"次了！别玩了，程序已经停下来了")

重点

_user = "Alex"
_pwd = "123"
for i in range(3):
    username = input("Enter your login user:")
    pwssword = input("Enter your login password：")
    if username == _user and pwssword == _pwd:
        print("Hi , %s , Wellcome login you 博客园." % username)
        break # break for 后，就不会执行最下面的else语句
    else:
        print("Your user or password not right!")
else:#只要上面的for循环正常执行完毕，中间没有被打断，就会执行else语句
    print("大兄弟，你已经试了 %d" % (i+1),"次了！别玩了，程序已经停下来了")