class Dog():                      #一般来说类的首字母大写
    """一次模拟小狗的简单测试"""

    def __init__(self, name, age):
        """初始化属性name和age"""
        self.name = name
        self.age = age

    def sit(self):
        """模拟小狗被命令蹲下"""
        print(self.name.title() + " is now sitting.")

    def roll_over(self):
        """模拟小狗被命令打滚"""
        print(self.name.title() + " is rolled over")

my_dog = Dog('willie',6)
print("My dog's name is " + my_dog.name.title() + ".")
print("My dog is " + str(my_dog.age) + " years old.")
my_dog.sit()
my_dog.roll_over()
