[Python]属性和property内建函数

     早期的Python版本中，我们一般用__getattr__()和__setattr__()来处理和属性相关的问题。属性的访问会涉及以上的方法(和__getattribute__())，但是如果用property()来处理这些问题，就可以写一个和属性有关的属性来处理实例属性的获取(getting)、赋值(setting)和删除(deleting)操作，就不必在使用那些特殊的方法了。

property()内建函数的四个参数，它们是：

property(fget=None, fset=None, fdel=None, doc=None)

实际上，property()是在它所在的类被创建时调用的，这些传进来的(作为参数的)方法是非绑定的，所以这些方法就是函数！

实例一：

class ProtectAndHideX(object):    def __init__(self,x):        assert isinstance(x,int),\        '"x" must be an integer!'        self.__x = ~x    def get_x(self):        return ~self.__x    x = property(get_x)inst = ProtectAndHideX(10)print "inst.x = ",inst.xinst.x = 20

inst.x =  10

  :

AttributeError: can't set attribute

实例二：

class HideX(object):    def __init__(self,x):        self.x = x    def get_x(self):        return ~self.__x    def set_x(self,x):        assert isinstance(x,int),\        '"x" must be an integer!'        self.__x = ~x    x = property(get_x, set_x)    inst2 = HideX(10)print inst2.xinst2.x = 20print inst2.x

10
20

实例三：

from math import pidef get_pi(dummy):    return piclass PI(object):    pi = property(get_pi,doc = 'Constant "pi"')inst3 = PI()print inst3.piprint PI.pi.__doc__

3.14159265359
Constant "pi"

实例四：

class HideXX(object):    def __init__(self, x):        self.x = x            @property    def x():        def fget(self):            return ~self.__x                def fset(self,x):            assert isinstance(x,int),\            '"x" must be an integer!'            self.__x = ~x                    return locals()inst4 = HideXX(20)print inst4.xinst4.x = 40print inst4.x

  :

AttributeError: can't set attribute(至于为什么，还没搞明白，新式类继承自object反而不可以)

修改上述代码：

class HideXX:    def __init__(self, x):        self.x = x            @property    def x():        def fget(self):            return ~self.__x                def fset(self,x):            assert isinstance(x,int),\            '"x" must be an integer!'            self.__x = ~x                    return locals()inst4 = HideXX(20)print inst4.xinst4.x = 40print inst4.x

20
40

实例五：

class Student(object):    @property    def score(self):        return self._score    @score.setter    def score(self, value):        if not isinstance(value, int):            raise ValueError('score must be an integer!')        if value < 0 or value > 100:            raise ValueError('score must between 0 ~ 100!')        self._score = valuestu = Student()stu.score = 20print stu.score

20

REF:Core Python Programming