[Python-Dev] PEP 442: Safe object finalization (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Sat May 18 17:22:02 CEST 2013

On Sat, 18 May 2013 15:52:56 +0100 Richard Oudkerk <shibturn at gmail.com> wrote:

On 18/05/2013 3:18pm, Antoine Pitrou wrote: > 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.

So even more contrived: class Node: def init(self, x): self.x = x self.next = None def del(self): print(self.x, self.next.x) del self.x a = Node(1) b = Node(2) a.next = b b.next = a del a, b gc.collect()

Indeed, there is an exception during destruction (which is ignored as any exception raised from del):

$ ./python sbt.py 1 2 Exception ignored in: <bound method Node.__del__ of <__main__.Node object at 0x7f543cf0bb50>> Traceback (most recent call last): File "sbt.py", line 17, in del print(self.x, self.next.x) AttributeError: 'Node' object has no attribute 'x'

The only reason this currently succeeds is that the objects end up in gc.garbage, of course.

Regards

Antoine.

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