您不能创建对方法对象的弱引用。方法对象是 短暂的 ; 它们是在您访问实例上的名称时动态创建的。请参阅描述符howto的工作原理。
当您访问方法名称时，将为您创建一个 新的 方法对象，然后将该方法添加到中WeakSet，不再有对其的其他引用，因此垃圾回收很高兴再次对其进行清理。
您将不得不存储一些不太瞬变的东西。存储实例对象本身可以工作，然后在已注册的回调中调用预定义方法：
def __del__(self):
for f in self.destroyCallback:
f.destroyedObjectListener(self)
并注册：
a1.destroyCallback.add(b)
您还可以通过给它一个方法使b 自己 成为可调用的__call__：
class ClassB:
def __call__(self,obj):
print('ClassB object %d is called because obj %d '
'is being destroyed' % (id(self), id(obj)))
import weakref
class ClassA:
def __init__(self):
self._callbacks = []
def registerCallback(self, callback):
try:
# methods
callback_ref = weakref.ref(callback.__func__), weakref.ref(callback.__self__)
except AttributeError:
callback_ref = weakref.ref(callback), None
self._callbacks.append(callback_ref)
def __del__(self):
for callback_ref in self._callbacks:
callback, arg = callback_ref[0](), callback_ref[1]
if arg is not None:
# method
arg = arg()
if arg is None:
# instance is gone
continue
callback(arg, self)
continue
else:
if callback is None:
# callback has been deleted already
continue
callback(self)
演示：
>>> class ClassB:
... def listener(self, deleted):
... print('ClassA {} was deleted, notified ClassB {}'.format(id(deleted), id(self)))
...
>>> def listener1(deleted):
... print('ClassA {} was deleted, notified listener1'.format(id(deleted)))
...
>>> def listener2(deleted):
... print('ClassA {} was deleted, notified listener2'.format(id(deleted)))
...
>>> # setup, one ClassA and 4 listeners (2 methods, 2 functions)
...
>>> a = ClassA()
>>> b1 = ClassB()
>>> b2 = ClassB()
>>> a.registerCallback(b1.listener)
>>> a.registerCallback(b2.listener)
>>> a.registerCallback(listener1)
>>> a.registerCallback(listener2)
>>>
>>> # deletion, we delete one instance of ClassB, and one function
...
>>> del b1
>>> del listener1
>>>
>>> # Deleting the ClassA instance will only notify the listeners still remaining
...
>>> del a
ClassA 4435440336 was deleted, notified ClassB 4435541648
ClassA 4435440336 was deleted, notified listener2
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