_user = "tom"

_passwd = "abc123"

counter = 0

while counter < 3:  　　#当条件为假时，跳出循环

    username = input("Username:")

    password = input("Password:")

    if username == _user and password == _passwd:

        print("welcome %s login...." % _user)

        break           # 跳出循环

    else:

        print("Invalid username or password!")

    counter += 1

    if counter == 3:

        keeping_going = input("还想继续吗？[Y/N]")

        if keeping_going == "Y":

            counter = 0

else:

    print("已经错三次了，双双小可爱") 

exit_flag = False

for n in range(10):

    if n < 5:

        continue

    print(n)

    for N in range(10):

        print("layer2", N)

        if N == 6:

            exit_flag = True

            break

    if exit_flag:

 　　　　break