python 之魔法方法

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

例如下面的示例

class MyDecriptor():

def get(self,instance,owner):

print("getting...",self,instance,owner)

def __set__(self,instance,value):
    print("setting...",self,instance,value)

def __delete__(self,instance):
    print("delete...",self,instance)

class Test():

x = MyDecriptor()//就是把MyDecriptor的实例指派给了Test类的属性x

porperty 的原理

class MyPorperty():

def init(self,fget,fset,fdel):#fget,fset,fdel都是函数

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 __deleted__(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 = MyPorperty(getX,setX,delX)//getX对应的函数是fget，setX对应的函数是fset，delX对应的函是fdel

例子 摄氏温度和华氏温度的转变

class Celsius():

def init(self,value = 26.0):

self.value = float(value)

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

def __set__(self,instance,value):
    self.value = float(value)

class Fahrenheit():

def get(self,instance,owner):#摄氏度转换成华氏度

return instance.cel * 1.8 + 32

def __set__(self,instance,value):#华氏度转换成摄氏度
    instance.cel = (float(value) - 32) / 1.8

class Temperature():

cel = Celsius()

fah = Fahrenheit()