如何在列表上触发Traits静态事件通知？

Question

我正在学习一个叫做 traits 的东西，这是在2010年PyCon大会上的一个演示。大约在2小时30分钟的时候，演讲者开始讲解 trait事件通知，这让我们可以在某个 trait 发生变化时，自动调用一个子程序。

我在运行他给的例子，但我做了一些修改……这次实验中，我想看看每当我改变 volume 或 volume_inputs 时，是否能触发一个静态事件。

# Filename: spinaltap.py
from traits.api import HasTraits, Range, List, Float
import traits

class Amplifier(HasTraits):
    """
    Define an Amplifier (ref -> Spinal Tap) with Enthought's traits.  Use traits
    to enforce values boundaries on the Amplifier's attributes.  Use events to
    notify via the console when the volume trait is changed and when new volume
    traits are added to inputs.
    """

    # Define a volume trait as a Float between 0.0 and 11.0 (inclusive)
    # see self._volume_changed()
    volume = Range(value=5.0, trait=Float, low=0.0, high=11.0)

    # Define an inputs trait as a List() containing volume traits
    volume_inputs = List(volume) # <-- fire a static trait notification
                             # when another volume element is added
                             # see self._volume_inputs_changed()

    def __init__(self, volume=5.0):
        super(Amplifier, self).__init__()
        self.volume = volume
        self.volume_inputs.append(volume)

    def _volume_changed(self, old, new):
        # This is a static event listener for self.volume
        #                                     ^^^^^^^^^^^
        if not (new in self.inputs):
            self.inputs.append(self.volume)
        if new == 11.0:
            print("This one goes to eleven... so far, we have seen", self.inputs)

    def _volume_inputs_changed(self, old, new):
        # This is a static event listener for self.volume_inputs
        #                                     ^^^^^^^^^^^^^^^^^^
        print("Check it out!!")

if __name__=='__main__':
    spinal_tap = Amplifier()
    candidate_volume = 4.0
    spinal_tap.event_fired = False
    print("- INITIAL_VALUE var volume_inputs = {}".format(spinal_tap.volume_inputs))
    print("- APPEND a new volume of 4.0")
    print("    - volume_inputs = {} # BEGIN".format(spinal_tap.volume_inputs))
    print("    - volume_inputs.append({})".format(candidate_volume))
    spinal_tap.volume_inputs.append(candidate_volume)
    print("    - volume_inputs: {} # END".format(spinal_tap.volume_inputs))
    if spinal_tap.event_fired is False:
        print("    - Test FAILED: Traits did not fire _volume_inputs_changed()")
    else:
        print("    - Test PASSED: Traits fired _volume_inputs_changed()")
    try:
        spinal_tap.event_fired = False
        print("- NEGATIVE Test... try to append 12.0.  This should fail; 12.0 is out of bounds")
        print("    - volume_inputs: {} # BEGIN".format(spinal_tap.volume_inputs))
        candidate_volume = 12.0
        print("    - volume_inputs.append({})".format(candidate_volume))
        spinal_tap.volume_inputs.append(candidate_volume)
        print("    - volume_inputs: {} # END".format(spinal_tap.volume_inputs))
        if spinal_tap.event_fired is False:
            print("    - Test FAILED: Traits did not fire _volume_inputs_changed()")
    except  traits.trait_errors.TraitError:
        print("    - TraitError raised --> HERE <--")
        print("    - volume_inputs: {} # END".format(spinal_tap.volume_inputs))
        print("    - Test PASSED: traits correctly raised TraitError instead of appending {}.".format(candidate_volume))

问题是 -> 我从来没有看到过 _volume_inputs_changed() 这个事件。无论我尝试什么例子，都无法让 List 触发事件。

在下面的输出中，没有任何证据表明 _volume_inputs_changed() 曾经被触发过。

[mpenning@Bucksnort ~]$ python spinaltap.py
- INITIAL_VALUE var volume_inputs = [5.0]
- APPEND a new volume of 4.0
    - volume_inputs = [5.0] # BEGIN
    - volume_inputs.append(4.0)
    - volume_inputs: [5.0, 4.0] # END
    - Test FAILED: Traits did not fire _volume_inputs_changed()
- NEGATIVE Test... try to append 12.0.  This should fail; 12.0 is out of bounds
    - volume_inputs: [5.0, 4.0] # BEGIN
    - volume_inputs.append(12.0)
    - TraitError raised --> HERE <--
    - volume_inputs: [5.0, 4.0] # END
    - Test PASSED: traits correctly raised TraitError instead of appending 12.0.
[mpenning@Bucksnort ~]$

使用traits时，List() 应该能够触发一个静态的 List() 事件（比如 _inputs_changed()）吗？如果可以的话，我是不是做错了什么？

代码示例事件通知 traits 子程序调用实验调试静态事件变化监听 PyCon

如何在列表上触发Traits静态事件通知？

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