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From: Alf P. Steinbach on 22 Apr 2010 01:48
* Lawrence D'Oliveiro:
> In message <4bc9aadb$1(a)dnews.tpgi.com.au>, Lie Ryan wrote:
>
>> Since in python nothing is guaranteed about implicit file close ...
>
> It is guaranteed that objects with a reference count of zero will be
> disposed.

Only in current CPython.


> In my experiments, this happens immediately.

Depends what you mean, but even in current CPython destruction of a local can be
postponed indefinitely if a reference to the stack frame is kept somewhere.

And that happens, for example, when an exception is raised (until the handler
completes, but it doesn't necessarily complete for a Very Long Time).


Cheers & hth.,

- Alf
From: Adam Tauno Williams on 22 Apr 2010 05:59
On Thu, 2010-04-22 at 12:53 +1200, Lawrence D'Oliveiro wrote:
> In message <4bc9aadb$1(a)dnews.tpgi.com.au>, Lie Ryan wrote:
> > Since in python nothing is guaranteed about implicit file close ...
> It is guaranteed that objects with a reference count of zero will be
> disposed. In my experiments, this happens immediately.

A current implementation specific detail. Always close files.
Otherwise, in the future, or on a different run-time, your code will
break.


From: Lawrence D'Oliveiro on 23 Apr 2010 00:29
In message <mailman.2119.1271898215.23598.python-list(a)python.org>, Chris
Rebert wrote:

> On Wed, Apr 21, 2010 at 5:53 PM, Lawrence D'Oliveiro wrote:
>
>> In message <4bc9aadb$1(a)dnews.tpgi.com.au>, Lie Ryan wrote:
>>
>>> Since in python nothing is guaranteed about implicit file close ...
>>
>> It is guaranteed that objects with a reference count of zero will be
>> disposed.
>
>> In my experiments, this happens immediately.
>
> Experiment with an implementation other than CPython and prepare to be
> surprised.

Any implementation that doesn't do reference-counting is brain-damaged.
From: Steven D'Aprano on 23 Apr 2010 00:49
On Fri, 23 Apr 2010 16:29:46 +1200, Lawrence D'Oliveiro wrote:

> Any implementation that doesn't do reference-counting is brain-damaged.

Funny, that's exactly what other people say about implementations that
*do* use reference counting.

--
Steven

From: Steven D'Aprano on 23 Apr 2010 18:04
On Fri, 23 Apr 2010 13:19:41 +0200, Alf P. Steinbach wrote:

> But for a literal context-free interpretation e.g. the 'sys.getrefcount'
> function is not documented as CPython only and thus an implementation
> that didn't do reference counting would not be a conforming Python
> implementation.

Since Jython and IronPython are conforming Python implementations, and
Guido has started making policy decisions specifically to support these
other implementations (e.g. the language feature moratorium, PEP 3003), I
think we can assume that this is a documentation bug.

However, a Python implementation that always returned 0 for
sys.getrefcount would technically satisfy the word of the documentation,
if not the spirit.



--
Steven
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