Python 如何添加具有回调功能的WeakValueDictionary？

如何将回调函数传递给这些字典？因此，如果任何对象被垃圾回收，将调用该函数

import weakref

def call_back():
    print("call back function called")

we_dict_demo = weakref.WeakKeyDictionary()

或

---

我认为这没有实际意义，但尝试一下很有趣：

import weakref

def callback(elem):
    print(elem, "gc'ed!")


# After reading lib/weakref.py it's clear what 
# WeakKeyDictionary pushes as callback self._remove, 
# which constructed in __init__, so let's redefine it
class MyWeakKeyDict(weakref.WeakKeyDictionary):
    def __init__(self, cb, dict=None):
        super().__init__(dict)
        self.cb = cb

        def new_remove(el, selfref=weakref.ref(self)):
            self = selfref()
            if self is not None:
                self.cb(el)
                self._old_remove(el)

        self._old_remove = self._remove
        self._remove = new_remove


class C:
    pass

c = C()
#d = weakref.WeakKeyDictionary()
# Use our class instead of WeakKeyDictionary
d = MyWeakKeyDict(callback)

d[c] = 0

print('Before gc', list(d.items()))
del c
print('After gc', list(d.items()))

结果是

Before gc [(<__main__.C object at 0x000002690F53A588>, 0)]
<weakref at 0x000002690F54A728; dead> gc'ed!
After gc []

gc[（0）之前的

gc'ed！
在gc[]之后

您可以在

\uuuu del\uuuu

中放置一些内容，但不能保证它会被调用。谢谢heemayl，但我需要类似的功能，如用于单个对象的功能。r=weakref.ref（obj，回调），但在字典中，对象可以用作键或值。每当垃圾收集器删除对象时，每次回调（）时都应调用该对象

Before gc [(<__main__.C object at 0x000002690F53A588>, 0)]
<weakref at 0x000002690F54A728; dead> gc'ed!
After gc []