python 装饰器 @property

@property

• 将类方法转换为只读属性
• 重新实现一个属性的setter和getter方法

例子：

1）只读属性：

class Person(object):

    """"""



    #----------------------------------------------------------------------

    def __init__(self, first_name, last_name):

        """Constructor"""

        self.first_name = first_name

        self.last_name = last_name



    #----------------------------------------------------------------------

    @property

    def full_name(self):

        """

        Return the full name

        """

        return "%s %s" % (self.first_name, self.last_name)

>>> person = Person("Mike", "Driscoll")

>>> person.full_name

'Mike Driscoll'

>>> person.first_name

'Mike'

>>> person.full_name = "Jackalope"

Traceback (most recent call last):

  File "<string>", line 1, in <fragment>

AttributeError: can't set attribute

 

2）重写 set、get方法

from decimal import Decimal



########################################################################

class Fees(object):

    """"""



    #----------------------------------------------------------------------

    def __init__(self):

        """Constructor"""

        self._fee = None



    #----------------------------------------------------------------------

    def get_fee(self):

        """

        Return the current fee

        """

        return self._fee



    #----------------------------------------------------------------------

    def set_fee(self, value):

        """

        Set the fee

        """

        if isinstance(value, str):

            self._fee = Decimal(value)

        elif isinstance(value, Decimal):

            self._fee = value

>>> f = Fees()

>>> f.set_fee("1")

>>> f.get_fee()

Decimal('1')

如果你想添加可以使用正常点符号访问的属性，而不破坏所有依赖于这段代码的应用程序，你可以通过添加一个属性函数非常简单地改变它

class最后增加一行

fee = property(get_fee, set_fee)

后面我们可以这样调用了

>>> f = Fees()

>>> f.set_fee("1")

>>> f.fee

Decimal('1')

>>> f.fee = "2"

>>> f.get_fee()

Decimal('2')

当我们以这种方式使用属性函数时，它允许fee属性设置并获取值本身而不破坏原有代码。让我们使用属性装饰器来重写这段代码，看看我们是否能得到一个允许设置的属性值。

from decimal import Decimal



########################################################################

class Fees(object):

    """"""



    #----------------------------------------------------------------------

    def __init__(self):

        """Constructor"""

        self._fee = None



    #----------------------------------------------------------------------

    @property

    def fee(self):

        """

        The fee property - the getter

        """

        return self._fee



    #----------------------------------------------------------------------

    @fee.setter

    def fee(self, value):

        """

        The setter of the fee property

        """

        if isinstance(value, str):

            self._fee = Decimal(value)

        elif isinstance(value, Decimal):

            self._fee = value



#----------------------------------------------------------------------

if __name__ == "__main__":

    f = Fees()

上面的代码演示了如何为fee属性创建一个setter方法。你可以用一个名为@fee.setter的装饰器装饰第二个方法名也为fee的方法来实现这个。当你如下所做时，setter被调用：

>>> f = Fees()

>>> f.fee = "1"