homepage

In the documentation on weakrefs there is the following quote
 Note: Weak references to an object are cleared before the object’s
 __del__() is called, to ensure that the weak reference callback 
 (if any) finds the object still alive.
But I think the weakref is always dead by the time the callback is invoked. The first paragraph from the documentation for weakref.ref(object[, callback]) contains the following:
 If callback is provided and not None, and the returned weakref 
 object is still alive, the callback will be called when the object 
 is about to be finalized; the weak reference object will be passed 
 as the only parameter to the callback; **the referent will no longer 
 be available**.
Which does prompt a question: what use is there for the weakref argument to the callback if it already dead?
(Compare http://bugs.python.org/issue14933)