python property

在2.6版本中，添加了一种新的类成员函数的访问方式--property。

原型

class property([fget[, fset[, fdel[, doc]]]])

fget：获取属性

fset：设置属性

fdel：删除属性

doc：属性含义

用法

1.让成员函数通过属性方式调用

class C(object):    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 = property(getx, setx, delx, "I'm the 'x' property.")

a = C()print C.x.__doc__ #打印docprint a.x #调用a.getx()a.x = 100 #调用a.setx()print a.xtry:    del a.x #调用a.delx()    print a.x #已被删除，报错except Exception, e:    print e

输出结果：

I'm the 'x' property. None100'C' object has no attribute '_x'

2.利用property装饰器，让成员函数称为只读的

class Parrot(object):    def __init__(self):        self._voltage = 100000    @property    def voltage(self):        """Get the current voltage."""        return self._voltagea = Parrot()print a.voltage #通过属性调用voltage函数try:    print a.voltage() #不允许调用函数，为只读的except Exception as e:    print e

输出结果：

100000'int' object is not callable

3.利用property装饰器实现property函数的功能

class C(object):    def __init__(self):        self._x = None    @property    def x(self):        """I'm the 'x' property."""        return self._x    @x.setter    def x(self, value):        self._x = value    @x.deleter    def x(self):        del self._x

其他应用

1.bottle源码中的应用

class Request(threading.local):    """ Represents a single request using thread-local namespace. """    ...    @property    def method(self):        ''' Returns the request method (GET,POST,PUT,DELETE,...) '''        return self._environ.get('REQUEST_METHOD', 'GET').upper()    @property    def query_string(self):        ''' Content of QUERY_STRING '''        return self._environ.get('QUERY_STRING', '')    @property    def input_length(self):        ''' Content of CONTENT_LENGTH '''        try:            return int(self._environ.get('CONTENT_LENGTH', '0'))        except ValueError:            return 0    @property    def COOKIES(self):        """Returns a dict with COOKIES."""        if self._COOKIES is None:            raw_dict = Cookie.SimpleCookie(self._environ.get('HTTP_COOKIE',''))            self._COOKIES = {}            for cookie in raw_dict.values():                self._COOKIES[cookie.key] = cookie.value        return self._COOKIES

2.在django model中的应用，实现连表查询

from django.db import modelsclass Person(models.Model):     name = models.CharField(max_length=30)     tel = models.CharField(max_length=30)class Score(models.Model):      pid = models.IntegerField()      score = models.IntegerField()            def get_person_name():            return Person.objects.get(id=pid)       name = property(get_person_name) #name称为Score表的属性，通过与Person表联合查询获取name