Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #27335

Re: set and dict iteration

Date 2012-08-18 23:14 +0100
From MRAB <python@mrabarnett.plus.com>
Subject Re: set and dict iteration
References (3 earlier) <mailman.3404.1345158704.4697.python-list@python.org> <502dab6c$0$29978$c3e8da3$5496439d@news.astraweb.com> <fe95c29c-2289-4e9c-870e-e3c475f13459@googlegroups.com> <mailman.3435.1345240665.4697.python-list@python.org> <d4708687-2925-421a-b755-969d6dac731a@googlegroups.com>
Newsgroups comp.lang.python
Message-ID <mailman.3476.1345328046.4697.python-list@python.org> (permalink)

Show all headers | View raw

On 18/08/2012 21:29, Aaron Brady wrote:
> 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:
>>
>> > Is there a problem with hacking on the Beta?
>>
>>
>>
>> Nope. Hack on the beta, then when the release arrives, rebase your
>>
>> work onto it. I doubt that anything of this nature will be changed
>>
>> between now and then.
>>
>>
>>
>> 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’s possible to prove that no reference cycle can be composed entirely of tuples.
> '''
>
> I didn't follow the reasoning in the proof; the premise is necessary but IMHO not obviously sufficient.  Nevertheless, the earlier diagram contains an overt homogeneous reference cycle.
>
> Reposting: http://home.comcast.net/~castironpi-misc/clpy-0062%20set%20iterators.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 don'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?
>
In simple terms, when you create an immutable object it can contain
only references to pre-existing objects, but in order to create a cycle
you need to make an object refer to another which is created later, so
it's not possible to create a cycle out of immutable objects.

However, using Python's C API it _is_ possible to create such a cycle,
by mutating an otherwise-immutable tuple (see PyTuple_SetItem and
PyTuple_SET_ITEM).

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-16 11:00 -0700
  Re: set and dict iteration Dave Angel <d@davea.name> - 2012-08-16 15:49 -0400
    Re: set and dict iteration Paul Rubin <no.email@nospam.invalid> - 2012-08-16 14:26 -0700
      Re: set and dict iteration Dave Angel <davea@dejaviewphoto.com> - 2012-08-16 19:11 -0400
        Re: set and dict iteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-17 02:24 +0000
          Re: set and dict iteration Paul Rubin <no.email@nospam.invalid> - 2012-08-16 19:30 -0700
            Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-17 11:11 -0700
          Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-17 11:37 -0700
            Re: set and dict iteration Chris Angelico <rosuav@gmail.com> - 2012-08-18 07:57 +1000
              Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-18 13:29 -0700
              Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-18 13:29 -0700
                Re: set and dict iteration MRAB <python@mrabarnett.plus.com> - 2012-08-18 23:14 +0100
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-18 19:28 -0700
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-23 09:49 -0700
                Re: set and dict iteration Ian Kelly <ian.g.kelly@gmail.com> - 2012-08-27 13:17 -0600
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-02 10:43 -0700
                Re: set and dict iteration Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-03 13:29 -0600
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-03 13:04 -0700
                Re: set and dict iteration Dave Angel <d@davea.name> - 2012-09-03 16:27 -0400
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-03 17:24 -0700
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-03 17:24 -0700
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-03 13:04 -0700
                Re: set and dict iteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-04 01:26 +0000
                Re: set and dict iteration Dave Angel <d@davea.name> - 2012-09-03 21:50 -0400
                Re: set and dict iteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-04 01:59 +0000
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-08 08:42 -0700
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-02 10:43 -0700
                Re: set and dict iteration Serhiy Storchaka <storchaka@gmail.com> - 2012-09-04 00:46 +0300
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-23 09:49 -0700
                Re: set and dict iteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-23 18:11 +0000
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-27 11:10 -0700
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-09-08 15:07 -0700
                Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-18 19:28 -0700
                Re: set and dict iteration Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2012-09-08 22:06 +0200
                Re: set and dict iteration Hans Mulder <hansmu@xs4all.nl> - 2012-09-08 23:18 +0200
                Re: set and dict iteration MRAB <python@mrabarnett.plus.com> - 2012-09-08 22:22 +0100
      Re: set and dict iteration Ian Kelly <ian.g.kelly@gmail.com> - 2012-08-16 17:43 -0600
        Re: set and dict iteration Paul Rubin <no.email@nospam.invalid> - 2012-08-16 18:01 -0700
          Re: set and dict iteration Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-08-17 13:16 +0200
          Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-17 11:03 -0700
          Re: set and dict iteration 88888 Dihedral <dihedral88888@googlemail.com> - 2012-09-10 13:14 -0700
  Re: set and dict iteration Ian Kelly <ian.g.kelly@gmail.com> - 2012-08-16 16:55 -0600
  Re: set and dict iteration Ian Kelly <ian.g.kelly@gmail.com> - 2012-08-16 17:07 -0600
    Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-17 10:47 -0700
    Re: set and dict iteration Aaron Brady <castironpi@gmail.com> - 2012-08-17 10:47 -0700

csiph-web