为什么弱引用不适用于此绑定方法? [英] Why doesn't the weakref work on this bound method?

问题描述

我有一个项目，我试图在回调中使用弱引用，但我不明白我做错了什么.我创建了简化的测试，显示了我混淆的确切行为.

I have a project where i'm trying to use weakrefs with callbacks, and I don't understand what I'm doing wrong. I have created simplified test that shows the exact behavior i'm confused with.

为什么在这个测试中 test_a 按预期工作，但是 self.MyCallbackB 的弱引用在类初始化和调用 test_b 之间消失了?我想只要实例 (a) 存在，对 self.MyCallbackB 的引用就应该存在，但它不存在.

Why is it that in this test test_a works as expected, but the weakref for self.MyCallbackB disappears between the class initialization and calling test_b? I thought like as long as the instance (a) exists, the reference to self.MyCallbackB should exist, but it doesn't.

import weakref

class A(object):
    def __init__(self):

        def MyCallbackA():
            print 'MyCallbackA'
        self.MyCallbackA = MyCallbackA

        self._testA = weakref.proxy(self.MyCallbackA)
        self._testB = weakref.proxy(self.MyCallbackB)

    def MyCallbackB(self):
        print 'MyCallbackB'

    def test_a(self):
        self._testA()

    def test_b(self):
        self._testB()

if __name__ == '__main__':
    a = A()    
    a.test_a()
    a.test_b()

推荐答案

你想要一个 WeakMethod.

您的解决方案为何不起作用的解释可以在对配方的讨论中找到:

An explanation why your solution doesn't work can be found in the discussion of the recipe:

绑定方法的普通weakref.refs并不像人们期望的那样工作，因为绑定方法是一等对象；对绑定方法的弱引用在到达时无效，除非存在对同一绑定方法的其他强引用.

Normal weakref.refs to bound methods don't quite work the way one expects, because bound methods are first-class objects; weakrefs to bound methods are dead-on-arrival unless some other strong reference to the same bound method exists.

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