參考资料
http://www.ibm.com/developerworks/library/os-pythondescriptors/
顾名思义，property用于生成一个属性。通过操作这个属性。能够映射为对某些函数的操作，类似于C#。
形式为
pvar = propery(get_func, set_func, del_fun, doc_func);
在get。set，del，doc的时候分别调用对应的函数；
尝试这样定义
>>> aa = property(lambda: "hello", lambda x: print(x))
>>> aa
<property object at 0x7fdcd9ecf9a8>
>>> aa = 1
看来property仅仅有在class中才有意义（看后文）
>>> class Test:
... aa = property(lambda self: "hello", lambda self,x: print(x))
...
>>> t = Test()
>>> t.aa
'hello'
>>> t.aa = (1,2,2)
(1, 2, 2)
property的神奇面纱
事实上propery并非一个真正的函数，而是一个类
>>> type(property)
<class 'type'>
而普通的函数为
>>> def f():
... pass
...
>>> type(f)
<class 'function'>
property类实现了__get__, __set__, __delete__方法，这3个方法合在一起，就定义了描写叙述符规则，实现了当中不论什么一个方法的对象就叫描写叙述符（descriptor）。描写叙述符的特殊之处在于它使怎样被訪问的。比方，程序读取一个属性时。假设该属性被绑定到实现了__get__方法的对象上。那么就会调用__get__方法（返回其结果），而不是简单的返回该对象。
class Something:
... def __get__(self, instance, owner):
... print(instance)
... print(owner)
... return "__get__"
... def __set__(self, instance, name):
... print(instance)
... print(name)
... print("__set__")
>>> class Holder:
... s = Something()
...
>>> h = Holder()
>>> h.s
<__main__.Holder object at 0x7fdcd9ed8518>
<class '__main__.Holder'>
'__get__'
>>> h.s = 3
<__main__.Holder object at 0x7fdcd9ed8518>
3
__set__
Something的__get__ 和 __set__方法的參数instance，相应了Something对象所所绑定的对象；能够想象。Property是通过instance调用传入当中的get, set, del, doc。
须要注意的是：描写叙述符必须被赋值给类属性，而不是对象实例属性，才有效；
>>> class Something:
... pass
>>> setattr(Something, 'aa', property(lambda self: "hello", lambda self, x: print(x)))
>>> t.aa
'hello'
>>> t.aa = 3
3
而设置在对象实例上，则无效果：
>>> setattr(t, 'aa', property(lambda self: "hello", lambda self, x: print(x)))
>>> setattr(Something, 'aa', None)
>>> t.aa
<property object at 0x7fdcd9edf4f8>
>>> t.aa = 3
另外，还能够通过注解（Annotation）的方式定义property
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
http://www.ibm.com/developerworks/library/os-pythondescriptors/给了一种动态创建Property的方法
|
class Person(object):
def addProperty(self, attribute): # create local setter and getter with a particular attribute name getter = lambda self: self._getProperty(attribute) setter = lambda self, value: self._setProperty(attribute, value)
# construct property attribute and add it to the class setattr(self.__class__, attribute, property(fget=getter, fset=setter, doc="Auto-generated method"))
def _setProperty(self, attribute, value): print "Setting: %s = %s" %(attribute, value) setattr(self, '_' + attribute, value.title())
def _getProperty(self, attribute): print "Getting: %s" %attribute return getattr(self, '_' + attribute) |