实例方法中可以修改类的属性值

class Person:

    def __init__(self, name, weight):

        # self.属性 = 形参
        self.name = name
        self.weight = weight

    def __str__(self):

        return "我的名字叫 %s 体重是 %.2f 公斤" % (self.name, self.weight)

    def run(self):
        print("%s 爱跑步，跑步锻炼身体" % self.name)

        self.weight -= 0.5

    def eat(self):
        print("%s 是吃货，吃完这顿再减肥" % self.name)

        self.weight += 1

xiaoming = Person("小明", 75.0)

xiaoming.run() # 调用跑步方法后体重减少0.5
xiaoming.eat() # 调用吃东西方法后体重增加1

print(xiaoming)