为什么Python中的@ foo.setter对我不起作用？ [英] Why does @foo.setter in Python not work for me?

问题描述

因此，我正在使用Python 2.6中的装饰器，但在使它们工作时遇到了一些麻烦。这是我的课程文件：

So, I'm playing with decorators in Python 2.6, and I'm having some trouble getting them to work. Here is my class file:

class testDec:

    @property
    def x(self): 
        print 'called getter'
        return self._x

    @x.setter
    def x(self, value): 
        print 'called setter'
        self._x = value

我认为这意味着要治疗 x 就像一个属性，但是在get和set上调用这些函数。因此，我启动了IDLE并进行了检查：

What I thought this meant is to treat x like a property, but call these functions on get and set. So, I fired up IDLE and checked it:

>>> from testDec import testDec
from testDec import testDec
>>> t = testDec()
t = testDec()
>>> t.x
t.x
called getter
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "testDec.py", line 18, in x
    return self._x
AttributeError: testDec instance has no attribute '_x'
>>> t.x = 5
t.x = 5
>>> t.x
t.x
5

由于我调用getter，并且没有默认值，并且它将失败。好，很好，我了解。但是，调用 tx = 5 的调用似乎会创建一个新属性 x ，而现在的getter并没有

Clearly the first call works as expected, since I call the getter, and there is no default value, and it fails. OK, good, I understand. However, the call to assign t.x = 5 seems to create a new property x, and now the getter doesn't work!

我缺少什么？

推荐答案

您似乎使用经典的老式类在python 2中。为了获得属性要正常工作，您需要使用新型类（在python 2中，您必须继承自 object ）。只需将您的类声明为 MyClass（object）：

You seem to be using classic old-style classes in python 2. In order for properties to work correctly you need to use new-style classes instead (in python 2 you must inherit from object). Just declare your class as MyClass(object):

class testDec(object):

    @property
    def x(self): 
        print 'called getter'
        return self._x

    @x.setter
    def x(self, value): 
        print 'called setter'
        self._x = value

它起作用：

>>> k = testDec()
>>> k.x
called getter
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/devel/class_test.py", line 6, in x
    return self._x
AttributeError: 'testDec' object has no attribute '_x'
>>> k.x = 5
called setter
>>> k.x
called getter
5
>>> 

另一个可能引起问题的细节是，这两种方法都需要使用相同的名称才能使该属性起作用。 如果您使用这样的其他名称来定义设置器，则将无法使用：

Another detail that might cause problems is that both methods need the same name for the property to work. If you define the setter with a different name like this it won't work:

@x.setter
def x_setter(self, value):
    ...

首先，还不容易发现的另一件事是顺序：吸气剂必须首先定义。如果您先定义设置器，则会出现未定义名称 x的情况错误。

And one more thing that is not completely easy to spot at first, is the order: The getter must be defined first. If you define the setter first, you get name 'x' is not defined error.

这篇关于为什么Python中的@ foo.setter对我不起作用？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！