的属性设置为一个单独的列表元素

问题描述：

class Device: 

    def __init__(self): 
    self._channels = [None]*6 
    self._outputs = [None]*4 

    @property 
    def channels(self): 
    return self._channels 

    @channels.setter 
    def channels(self,value): 
    print("inside:",self.channels, value) 
    self._channels = value

这里奇怪的是，在调用device.channels[1] = 'try'作品，但似乎并没有为'通过@ setter.channels函数。从下面的输出显示古怪：

device = Device() 
print("before:",device.channels) 
device.channels[1] = "try" 
print("after:",frmdeviced.channels) 
device.channels = "try2" 
print("check:",frm4d.channels)

并且输出是：


before: [None, None, None, None, None, None] 
 
after: [None, 'try', None, None, None, None] # accessing single element is achieved
            # , but not through @channels.setter!
 
inside: [None, 'try', None, None, None, None] try # only here we're
 
check: try2         # at least the setter works..

由于我需要逻辑时的channels单个元件被设置为运行，这种行为是有问题的。我想知道导致这种行为的基础python机制是什么，它是如何被覆盖？是否有更多pythonic方式来实现设置/获取特定列表元素的目标？

您需要在'channels'引用的对象上实现'__setitem__'，在'Device'上执行它是没有意义的。 – jonrsharpe

设置列表的一个元素是列表的一个操作，而不是交给列表的'Device'的操作。 – user2357112

答

device.channels[1] = "try"首先要访问"@property" getter方法，它返回一个列表，然后索引操作将在不在设备上的列表上执行。下面的例子证明它 -

>>> class Device: 

    def __init__(self): 
    self._channels = [None]*6 
    self._outputs = [None]*4 

    @property 
    def channels(self): 
    print("inside @property") 
    return self._channels 

    @channels.setter 
    def channels(self,value): 
    print("inside:",self.channels, value) 
    self._channels = value 


>>> device = Device() 
>>> device.channels[1] = "try" 
inside @property

@ user2357112，我以前看不到python3.x标记，现在我已经修改了我的答案。感谢您指出它 – AlokThakur

答

要仪器列表，创建一个仪表列表类。 Jupyter会话示例：

In [23]: class MonitoredList(list): 
      def __setitem__(self, index, value): 
       # run special logic here 
       print("setting index {} to {}".format(index, value)) 
       super(MonitoredList, self).__setitem__(index, value) 

In [24]: zz = MonitoredList([None]*6) 

In [25]: zz 
Out[25]: [None, None, None, None, None, None] 

In [26]: zz[3] = 42 
     setting index 3 to 42 

In [27]: zz 
Out[27]: [None, None, None, 42, None, None]

的属性设置为一个单独的列表元素

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