python while、continue、break

while循环实现用户登录

_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") 

continue和break：

continue   # 结束本次循环，进行下次循环

Break      # 跳出整个当前循环

实例程序：

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

 输出结果：

5
layer2 0
layer2 1
layer2 2
layer2 3
layer2 4
layer2 5
layer2 6