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Date: Sat, 18 Aug 2012 13:29:13 -0700 (PDT)
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Subject: Re: set and dict iteration
From: Aaron Brady <castironpi@gmail.com>
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Xref: csiph.com comp.lang.python:27332

On Friday, August 17, 2012 4:57:41 PM UTC-5, Chris Angelico wrote:
> On Sat, Aug 18, 2012 at 4:37 AM, Aaron Brady <castironpi@gmail.com> wrote=
:
>=20
> > Is there a problem with hacking on the Beta?
>=20
>=20
>=20
> Nope. Hack on the beta, then when the release arrives, rebase your
>=20
> work onto it. I doubt that anything of this nature will be changed
>=20
> between now and then.
>=20
>=20
>=20
> ChrisA

Thanks Chris, your post was encouraging.

I have a question about involving the 'tp_clear' field of the types.

http://docs.python.org/dev/c-api/typeobj.html#PyTypeObject.tp_clear

'''
...The tuple type does not implement a tp_clear function, because it=92s po=
ssible to prove that no reference cycle can be composed entirely of tuples.=
=20
'''

I didn't follow the reasoning in the proof; the premise is necessary but IM=
HO not obviously sufficient.  Nevertheless, the earlier diagram contains an=
 overt homogeneous reference cycle.

Reposting: http://home.comcast.net/~castironpi-misc/clpy-0062%20set%20itera=
tors.png

In my estimate, the 'tp_traverse' and 'tp_clear' fields of the set doesn't =
need to visit the auxiliary collection; the same fields of the iterators do=
n't need to visit the primary set or other iterators; and references in the=
 linked list don't need to be included in the iterators' reference counts.

Can someone who is more familiar with the cycle detector and cycle breaker,=
 help prove or disprove the above?