Question

如何将call_back函数传递给这些字典？因此，如果有任何对象被垃圾回收，则会调用该函数。

import weakref

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

we_dict_demo = weakref.WeakKeyDictionary()

或

we_dict_demo = weakref.WeakValDictionary()

Answer 1

我认为它没有实际意义，但是尝试尝试很有趣：

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 []

如何添加具有回调功能的WeakValueDictionary？

1 个答案: