We're back after a server migration that caused effbot.org to fall over a bit harder than expected. Expect some glitches.

ReferenceError

This exception is raised when a weak reference proxy, created by the weakref.proxy function, is used to access an attribute of the referent after it has been garbage collected. For more information on weak references, see the weakref module. New in version 2.2: Previously known as the weakref.ReferenceError exception.