新手上路，求大佬指点

class Dog():
    """模拟"""

    def__init__(self, name, age):
        """初始"""
        self.name = name
        self.age = age

    def sit(self):
        """action_1"""
        print(self.name .title() + ' is now sitting.')

    def roll_over(self):
        """action_2"""
        print(self.name.title() + ' rolled over!')
为什么会显示无效语法？