描述符
描述符就是一个类，一个至少拥有get(self,instance,owner),set(self,instance,value),delete(self,instance) 三个方法的任意一个或几个
-
get(self,instance,owner)
用于访问属性，它返回属性的值 -
set(self,instance,value)
属性被赋值中调用，不返回任何值 -
delete(self,instance)
控制删除操作，不返回任何内容
>>> 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('deleting',self,instance)
>>> class Test():
x = MyDecriptor()
>>> text = Test()
>>> text.x
getting <__main__.MyDecriptor object at 0x000001B84F911E80> <__main__.Test object at 0x000001B84F8989E8> <class '__main__.Test'>
>>> text.x = 'love'
setting <__main__.MyDecriptor object at 0x000001B84F911E80> <__main__.Test object at 0x000001B84F8989E8> love
>>> del text.x
deleting <__main__.MyDecriptor object at 0x000001B84F911E80> <__main__.Test object at 0x000001B84F8989E8>
>>> text
<__main__.Test object at 0x000001B84F8989E8>
>>> Test
<class '__main__.Test'>
注意instance(拥有者的实例对象） 是Test()的实例化对象test, owner 是Test
自己定义一个 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=1
print(c._x)
1
先定义一个温度类，然后定义两个描述符类用于描述摄氏度和华氏度两个属性
class Celsius:
def __init__(self,value = 26.0):
self.value = value
def __get__(self, instance, owner):
return self.value
def __set__(self, instance, value):
self.value = value
class Fahrenheit:
def __get__(self, instance, owner):
return instance.cel*1.8+32
def __set__(self, instance, value):
instance.cel = (float(value)-32)/1.8
class Temperature:
cel = Celsius()
fah = Fahrenheit()
temp = Temperature()
print(temp.cel)
temp.cel = 100
print(temp.cel)
temp.fah = 70
print(temp.cel)
print(temp.fah)
26.0
100
21.11111111111111
70.0
