python之元类

python之元类

1.类可以由默认的type来创建

class People:
    def __init__(self,name):
        self.name = name
    def play(self,s):
        print(self.name,"在玩",s)

p = People("xxx")
p.play("yyy")
// **********和下面等价***************
def init(self,name):
    self.name = name
def play(self, name):
    print(self.name,"在玩",name)
People = type("People",(),{"name":"lqw","__init__":init,"play":play})
// type 创建类  type("类名",(继承的类),{属性和方法,参照上方})
p1 = People("xxx") 
p1.play("y")

2.类由metaclass元类来创建

class Mytype(type):   # 原类
    _instance = None
    def __init__(self, class_name, super_name, name_space):  # 定制类的时候
        print("类名", class_name,"类型",type(class_name))
        print("继承类的名字", super_name,type(super_name))
        print("名称空间:", name_space,type(name_space))
        self._name = "lqw666"
    def __new__(cls, *args, **kwargs):   # 定制类
        print("cls是啥:", cls)
        print("args有啥:", args)
        print("kwargs有啥:", kwargs)
        print("我执行了?")
        print("*****************************************")
        s = super().__new__(cls, *args, **kwargs)
        return s
    def __call__(self, *args, **kwargs):    # 定制对象  下面是单例
        if not self._instance:
            self._instance = self.__new__(self,*args,**kwargs)
        self.__init__(self._instance,*args,**kwargs)
        return self._instance
class People(object, metaclass=Mytype):

    def __init__(self,name):
        self.name = name

    def play(self, play):
        print(play, "被玩了")
p = People("xxx")
//	Peoples是原类的对象，也就是元类加()调用，先执行元类的__new__，在执行元类的__init__初始化People这个类，p是People的对象，就是People加()，对象加()，调用类的__call__，也就是调用元类的__call__，完成实例化对象

元类可以定制类,下面几个小题目尝试一下

1.类名必须大写，否则报错

2.类有play方法，如果没有，给他添加一个

3.类必须继承object,否则报错

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