Re: when should I explicitly close a file?
In message , Adam Tauno Williams wrote: > On Fri, 2010-04-23 at 16:29 +1200, Lawrence D'Oliveiro wrote: > >> Any implementation that doesn’t do reference-counting is brain-damaged. > > Why? Because a) it uses extra memory needlessly, and b) waiting until an object has dropped out of cache before touching it again just slows things down. > There are much better ways to do memory management / garbage > collection; especially when dealing with large applications. Especially with large applications, the above considerations apply even more so. If you don’t agree, you might as well stick to Java. -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
* Steven D'Aprano: 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. The documentation for Jython specifies the same for 'sys.getrefcount'. However, testing: *sys-package-mgr*: processing new jar, 'C:\Program Files\jython2.5.1\jython.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\resources.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\rt.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\jsse.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\jce.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\charsets.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\dnsns.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\localedata.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\sunjce_provider.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\sunmscapi.jar' *sys-package-mgr*: processing new jar, 'C:\Program Files\Java\jre6\lib\ext\sunpkcs11.jar' A created Traceback (most recent call last): File "c:\test\refcount.py", line 17, in writeln( str( sys.getrefcount( a ) - 1 ) ) AttributeError: 'systemstate' object has no attribute 'getrefcount' However, a Python implementation that always returned 0 for sys.getrefcount would technically satisfy the word of the documentation, if not the spirit. Yes. OK, learned something new: I though Jython actually implemented getrefcount. The Jython docs says it does... Cheers, - Alf -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
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 -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
* Adam Tauno Williams: On Fri, 2010-04-23 at 16:29 +1200, Lawrence D'Oliveiro wrote: In message , Chris Rebert wrote: On Wed, Apr 21, 2010 at 5:53 PM, Lawrence D'Oliveiro wrote: In message <4bc9aad...@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. Why? Depends on what the statement was meant to mean. 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. Whether it uses reference counting to destroy objects at earliest opportunity is another matter. There are much better ways to do memory management / garbage collection; especially when dealing with large applications. Depends on whether you're talking about Python implementations or as a matter of general principle, and depends on how you define "better", "large" and so on. On its own it's a pretty meaningless statement. But although a small flame war erupted the last time I mentioned this, I think a case can be made that Python is not designed for programming-in-the-large. And that the current CPython scheme is eminently suitable for small scripts. But it has its drawbacks, especially considering the various ways that stack frames can be retained, and considering the documentation of 'gc.garbage', ... "Objects that have __del__() methods and are part of a reference cycle cause the entire reference cycle to be uncollectable, including objects not necessarily in the cycle but reachable only from it." ... which means that a programming style assuming current CPython semantics and employing RAII can be detrimental in a sufficiently large system. Cheers & hth., - Alf -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
On Fri, 2010-04-23 at 16:29 +1200, Lawrence D'Oliveiro wrote: > In message , Chris > Rebert wrote: > > On Wed, Apr 21, 2010 at 5:53 PM, Lawrence D'Oliveiro wrote: > >> In message <4bc9aad...@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. Why? There are much better ways to do memory management / garbage collection; especially when dealing with large applications. -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
On Fri, Apr 23, 2010 at 12:29 AM, Lawrence D'Oliveiro wrote: > In message , Chris > Rebert wrote: > > > On Wed, Apr 21, 2010 at 5:53 PM, Lawrence D'Oliveiro wrote: > > > >> In message <4bc9aad...@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. > -- > Why? Nothing in the Python spec calls for reference-counting. And (AFAIK) everything that runs on the JVM or CLR uses garabage collection and not reference counting. Have you heard of those things before? They're rather popular. -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
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 -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
In message , Chris Rebert wrote: > On Wed, Apr 21, 2010 at 5:53 PM, Lawrence D'Oliveiro wrote: > >> In message <4bc9aad...@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. -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
On Thu, 2010-04-22 at 12:53 +1200, Lawrence D'Oliveiro wrote: > In message <4bc9aad...@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. -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
* Lawrence D'Oliveiro: In message <4bc9aad...@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 -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
On Thu, 22 Apr 2010 12:53:51 +1200, Lawrence D'Oliveiro wrote: > In message <4bc9aad...@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. Not all Python implementations have reference counts at all, e.g. Jython and IronPython. Neither of those close files immediately. > In my experiments, this happens immediately. Are your experiments done under PyPy, CLPython, or Pynie? -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
On Wed, Apr 21, 2010 at 5:53 PM, Lawrence D'Oliveiro wrote: > In message <4bc9aad...@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. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
In message <4bc9aad...@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. -- http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
On 04/17/10 21:23, Lawrence D'Oliveiro wrote:
> In message
> , gelonida
> wrote:
>
>> I've been told, that following code snippet is not good.
>>
>> open("myfile","w").write(astring) ...
>
> I do that for reads, but never for writes.
>
> For writes, you want to give a chance for write errors to raise an exception
> and alert the user, instead of failing silently, to avoid inadvertent data
> loss. Hence the explicit close.
In short, in case of doubt, just be explicit.
Since in python nothing is guaranteed about implicit file close, you
must always explicitly close it.
--
http://mail.python.org/mailman/listinfo/python-list
Re: when should I explicitly close a file?
In message
, gelonida
wrote:
> I've been told, that following code snippet is not good.
>
> open("myfile","w").write(astring) ...
I do that for reads, but never for writes.
For writes, you want to give a chance for write errors to raise an exception
and alert the user, instead of failing silently, to avoid inadvertent data
loss. Hence the explicit close.
--
http://mail.python.org/mailman/listinfo/python-list
