CPython's cyclic garbage collector (was [Python-ideas] Automatic context managers)

[Ian Kelly]

On Fri, Apr 26, 2013 at 10:54 AM, Chris Angelico <rosuav at gmail.com> wrote:
> Once it's been proven that there's an unreferenced cycle, why not
> simply dispose of one of the objects, and replace all references to it
> (probably only one - preferably pick an object with the fewest
> references) with a special temporary object? In fact, that could
> probably be done in CPython by wiping out the object in memory and
> replacing it with a special marker of some sort, which would then
> automatically "take over" all references to the old object. Any
> attempt to manipulate this object could simply pop back with a
> DestructedObject exception or something.

I think it still boils down to the same problem -- how should Python
*predictably* choose which object will be disposed of in order to
break the cycle?  I don't see that this question is any different than
asking how should Python choose which __del__ method should be called
first, since the object so disposed of would still need its __del__
method called.