day1 if 判断

_username = "mask"
_password = "a111"

username = input("username:")
password = input("password:")


if _username == username and _password == password: #如果 _username 等于username 并且 _password 等于 password 执行下面缩进代码
    print('Hello {name}'.format(name=username))
else:                                               #否则执行下面的缩进代码
    print('Invalid username or password !')