2.自定义元类控制类的创建行为

class MyPeople(type):
    def __init__(self, class_name, class_bases, class_dic):
        if not class_name.istitle():
            raise TypeError("类的首字母必须大写")
        if not "__doc__" in class_dic or not class_dic["__doc__"].strip():
            raise TypeError("必须有注释,且注释不能为空")
        super(MyPeople, self).__init__(class_name, class_bases, class_dic)


class People(object, metaclass=MyPeople):
    """
    there must be doc,
    and the doc must be in the first line
    """
    country = "China"
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def tell_info(self):
        print(f"{self.name} is from {self.country}, and he is {self.age} years old")


chen = People("chenjun", 21)
chen.tell_info()