Re: Inner workings of this Python feature: Can a Python data structure reference itself?

Path	csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!1.eu.feeder.erje.net!ecngs!feeder2.ecngs.de!217.188.199.168.MISMATCH!takemy.news.telefonica.de!storethat.news.telefonica.de!telefonica.de!news.panservice.it!feed.xsnews.nl!border01.ams.xsnews.nl!feeder01.ams.xsnews.nl!abp001.ams.xsnews.nl!frontend-F10-10.ams.news.kpn.nl
From	Cecil Westerhof <Cecil@decebal.nl>
Newsgroups	comp.lang.python
Subject	Re: Inner workings of this Python feature: Can a Python data structure reference itself?
Organization	Decebal Computing
References	<387ac520-9da3-411a-a3b8-b326e1e8a2c0@googlegroups.com> <mailman.26.1430597813.12865.python-list@python.org>
X-Face	"(y8cC@tg_12{">GF'UXTW]FHI2wMiZNrnf'1EFQ&O#$m:f#O7+7}kR<J%a^F2lh4[N~Yz4 nSp#c+aQo1b5=?HcNEkQ7QzF<])O3X4MDL/AYjys&*mt>,v+Pti8=Vi/Z"g^?b"E
X-Homepage	http://www.decebal.nl/
Date	Sat, 02 May 2015 23:06:38 +0200
Message-ID	<87a8xmn0yp.fsf@Equus.decebal.nl> (permalink)
User-Agent	Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)
Cancel-Lock	sha1:dd9VJgBHk5tw+uEdfWiTX+mbeGU=
MIME-Version	1.0
Content-Type	text/plain
Lines	41
NNTP-Posting-Host	81.207.62.244
X-Trace	1430602130 news.kpn.nl 21092 81.207.62.244@kpn/81.207.62.244:41941
Xref	csiph.com comp.lang.python:89806

Show key headers only | View raw

Op Saturday 2 May 2015 22:17 CEST schreef Tim Chase:

> [dangit, had Control down when I hit <enter> and it sent
> prematurely]
>
> On 2015-05-02 13:02, vasudevram wrote:
>> http://jugad2.blogspot.in/2015/05/can-python-data-structure-reference.html
>>
>> https://docs.python.org/2/reference/datamodel.html
>>
>> and saw this excerpt:
>>
>> [ CPython implementation detail: CPython currently uses a
>> reference-counting scheme with (optional) delayed
>> detection of cyclically linked garbage, which collects
>> most objects as soon as they become unreachable, but is
>> not guaranteed to collect garbage containing circular
>> references. ]
>>
>> Not sure whether it is relevant to the topic at hand,
>> since, on the one hand, it uses the words "cyclically
>> linked", but on the other, it says "garbage collection".
>
> The gotcha happens in a case where you do something like this:
>
> lst = []
> lst.append(lst)  # create a cycle
> del lst
>
> This creates a cycle, then makes it unreachable, but the list is
> still referenced by itself, so the reference count never drops to
> zero (where it would get GC'd), and thus that item lingers around in
> memory.

Maybe look at Java? If my memory is correct, the JVM gc reclaims those
kind of things also.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof

Thread

csiph-web