On Sat, 18 May 2013 14:56:38 +0100 Richard Oudkerk <shibt...@gmail.com> wrote: > On 18/05/2013 9:59am, Antoine Pitrou wrote: > > This PEP proposes to turn CI disposal into the following sequence (new > > steps are in bold): > > > > 1. Weakrefs to CI objects are cleared, and their callbacks called. At > > this point, the objects are still safe to use. > > > > 2. **The finalizers of all CI objects are called.** > > How do you know that one of the finalizers will not do something which > causes another to fail? > > Presumably the following would cause an AttributeError to be printed: > > class Node: > def __init__(self): > self.next = None > def __del__(self): > print(self, self.next) > del self.next # break Node object > > a = Node() > b = Node() > a.next = b > b.next = a > del a, b > gc.collect()
It works fine: $ ./python sbt.py <__main__.Node object at 0x7f3acbf8f400> <__main__.Node object at 0x7f3acbf8f878> <__main__.Node object at 0x7f3acbf8f878> <__main__.Node object at 0x7f3acbf8f400> The reason is that, when you execute "del self.next", this removes the last reference to self.next and destroys it immediately. In essence, you were expecting to see: - enter a.__del__, destroy b - leave a.__del__ - enter b.__del__ oops? But what happens is: - enter a.__del__, destroy b - enter b.__del__ - leave b.__del__ - leave a.__del__ Regards Antoine. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
