描述符类

# 描述符就是将某种特殊类型的类的实例指派给另一个类的属性
class MyDescriptor:  # 某种特殊类型的类就是下面方法中至少要实现一个
    def __get__(self, instance, owner):  # __get__用于访问属性，它返回属性的值
        print('getting...', self, instance, owner)

    def __set__(self, instance, value):  # __set__赋值时被调用，不返回任何内容
        print('setting...', self, instance, value)

    def __delete__(self, instance):  # __delete__控制删除操作，不返回任何内容
        print('deleting...', self, instance)


class Test:
    x = MyDescriptor()  # MyDescriptor类的实例x，作为Test类的属性


test = Test()
test.x  # 调用__get__方法，打印出getting... self的值，instance的值和owner的值
print(test)  # 打印出<__main__.Test object at 0x00000233F57555C8>，就是instance的值
print(Test)  # 打印出<class '__main__.Test'>，就是owner的值
test.x = 'X-man'  # 调用__set__方法，打印出setting... self的值，instance的值和value的值，value就是X-man
del test.x  # 调用__delete__方法，打印出deleting... self的值和instance的值

# property
class MyProperty:
    def __init__(self, fget=None, fset=None, fdel=None):
        self.fget = fget
        self.fset = fset
        self.fdel = fdel

    def __get__(self, instance, owner):
        return self.fget(instance)

    def __set__(self, instance, value):
        self.fset(instance, value)

    def __delete__(self, instance):
        self.fdel(instance)


class C:
    def __init__(self):
        self._x = None

    def getX(self):
        return self._x

    def setX(self, value):
        self._x = value

    def delX(self):
        del self._x

    x = MyProperty(getX, setX, delX)


c = C()
c.x = 'hello'
print(c.x)  # c.x赋值打印hello
print(c._x)  # c._x也是hello
del c.x  # __delete__控制删除操作，不返回任何内容