最初的声明方式
在没有@property修饰的情况下,需要分别声明get、set、delete函数,然后初始化property类,将这些方法加载进property中
class C持有property的实例化对象x
对外表现出来C().x时,实际上是调用C()中的x(property类)中设置的fset,fget,fdel,分别对应getx,setx,delx
C真正持有的x,是self._x被隐藏起来了
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class C( object ): def getx( self ): return self ._x def setx( self , value): self ._x = value def delx( self ): del self ._x x = property (getx, setx, delx, "I'm the 'x' property." ) |
property类 结合x = property(getx, setx, delx, "I'm the 'x' property.")
与property的__init__()
可以发现property接受四个参数
fget,用于获取属性值,
fset,用于设置属性值
fdel,用于删除属性
doc,属性的介绍
可以单独设置fget、fset、fdel…
x = property,x.getter(getx),x.setter(setx),x.deleter(delx)
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class property ( object ): def deleter( self , * args, * * kwargs): # real signature unknown """ Descriptor to change the deleter on a property. """ pass def getter( self , * args, * * kwargs): # real signature unknown """ Descriptor to change the getter on a property. """ pass def setter( self , * args, * * kwargs): # real signature unknown """ Descriptor to change the setter on a property. """ pass def __delete__( self , * args, * * kwargs): # real signature unknown """ Delete an attribute of instance. """ pass def __getattribute__( self , * args, * * kwargs): # real signature unknown """ Return getattr(self, name). """ pass def __get__( self , * args, * * kwargs): # real signature unknown """ Return an attribute of instance, which is of type owner. """ pass def __init__( self , fget = None , fset = None , fdel = None , doc = None ): # known special case of pass |
使用装饰器的声明方式
需要注意,装饰器只是一个python的语法糖,可以拆解成普通使用方法,如property(getx)
@property
创建了一个实例x,对于def x(self)
实际上是C类持有x = property(fget=x)
因此,x.setter
方法指向的是property.setter
,也是起到装饰器效果x.setter(x)
(注意,前者x是property实例x,后者x是def x(self, value)
函数),x.deleter
同理
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class C( object ): @property def x( self ): "I am the 'x' property." return self ._x @x .setter def x( self , value): self ._x = value @x .deleter def x( self ): del self ._x |
为什么property实例化后的名字与属性名一致?
换种问法就是为什么x = property(...)
可以认为是
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attributes_and_methods = { x.__name__: property (x), / / 声明C类持有 property 实例 #... } C = type ( 'C' , ( object ,), attributes_and_methods) |
使用装饰器的调用过程
执行C().x时,调用的是C().x(property)绑定的fget方法,用过__get__
唤醒,setter、deleter同理
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class property ( object ): #... def __init__( self , fget = None , fset = None , fdel = None , doc = None ): self .fget = fget self .fset = fset self .fdel = fdel ... def __get__( self , obj, objtype = None ): # real signature unknown if obj is None : return self if self .fget is None : raise AttributeError( "unreadable attribute" ) return self .fget(obj) |
总结
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原文链接:https://blog.csdn.net/ct2020129/article/details/122681130