new方法、定制属性、描述符、装饰器

一、_new_方法

创建实例时触发_new_方法

_new_方法会创建并返回实例

class Cls:
    instance = 0
    #cls 规范命名 ，表示一个类
    def __new__(cls, *args, **kwargs):
        if cls.instance == 0: #当标志值为0
            cls.instance = super().__new__(cls)
        #调用父类的_new_并传入本类
        #实例化，获取实例
        #将实例赋值给当前类的instance属性
        return cls.instance
        #返回当前类的instance属性
    def __init__(self):
        print("初始化")
c1 = Cls()
c2 = Cls()
# print(id(c1), id(c2))
# print(Cls.mro())

二、定制属性访问

class Cls:
    name = "我"

    def __setattr__(self, key, value):
        print("属性名：%s; 属性值：%s" % (key, value))

    def __delattr__(self, item):
        print("删除%s" % item)

    def __getattribute__(self, item):
        print("获取%s" % item)
        return "111"

    def __getattr__(self, item):
        print("%s不存在" % item)


c = Cls()
# setattr(c, "name", "李坤")
# print(c.name)
# ss = getattr(c, "name")
# print(ss)
attr_bool = hasattr(c, "傻逼")
print(attr_bool)
# c.傻逼

 

三、描述符

#描述符
class A:
    def __get__(self, instance, owner):
        print("获取")
    def __set__(self, instance, value):
        print("修改")
    def __delete__(self, instance):
        print("删除")

class B:
    ins = A()

a = B()

#当属性是一个实例的时候
#对这个属性 查 改 删
# print(a.ins)
a.ins = 23
# del a.ins

四、装饰器

#内置装饰器
class Cls:
    @property
    def test01(self):
        print("调用")
        return "属性形式调用"

    @staticmethod
    def test02(name):
        print("不会自动传入self", name)

    @classmethod
    def test03(cls):
        print("自动传入类")

#类装饰器
class Cls:

    def __init__(self, func):
        print("初始化装饰器")
        self.fun = func

    def __call__(self, *args, **kwargs):
        print("执行被装饰的函数")
        self.fun( *args, **kwargs)

@Cls
def fun(name):
    print(name, "执行函数")

aa = Cls("1111")

fun("李坤")