判断语句_if else 的使用

Python中最简单的判断语句当属if else 语句了，流程图如下：

Python程序语言指定任何非0和非空（null）值为true，0 或者 null为false，if 语句用于控制程序的执行。

_username = "aaa"
_password = "123456"
username = input("username:")
password = input("password:")
if _username == username and _password == password:
    print("good!!!")
else:
    print("you are wrong")

当出现多种选择时也可直接运用if elif来进行输出程序。

_username = "aaa"
_password = "123456"
username = input("username:")
password = input("password:")
if _username == username and _password == password:
    print("good!!!")
elif _username != username and _password == password:
    print("username is wrong")
elif _username == username and _password != password:
    print("password is wrong")