gagsl-py2 at yahoo.com.ar
Sat Jun 6 05:44:47 EDT 2009
En Sat, 06 Jun 2009 03:03:34 -0300, <s0suk3 at gmail.com> escribió:
> On Jun 5, 8:56 pm, Robert Dailey <rcdai... at gmail.com> wrote:
>> Is it possible to create an object in Python that will clean itself up
>> at function exit? I realize destruction of objects may not occur
>> immediately and can be garbage collected, but this functionality would
>> still be great to have.
> I don't know what you mean by:
> "I realize destruction of objects may not occur immediately and can be
> garbage collected"
> Aren't you just missing ordinary destructors (__del__() methods)?
> These are closest to C++ destructors AFAICS. As far as I know, these
> are guaranteed to be called when an object goes out of scope. (Note
> that destruction and garbage collection are different operations; an
> object may be destructed without being immediately garbage-collected
No, that's not how it works in Python (and I think you're mistaken for C++
See http://docs.python.org/reference/datamodel.html and specially
"Objects are never explicitly destroyed; however, when they become
unreachable they may be garbage-collected. An implementation is allowed to
postpone garbage collection or omit it altogether."
CPython uses a "reference count" scheme - an object is destroyed as soon
as it loses its last reference. Other implementations may choose another
strategy - in fact, Jython relies on garbage collection instead; object
destruction may be delayed an arbitrary amount of time. (CPython has a
garbage collector too, but its purpose is to detect and break object
So the OP is right - you can't rely on object destruction to perform any
cleanup; use try/finally or a with statement instead.
>>>> import sys
>>>> class Simple:
> ... def __init__(self): sys.stdout.write("Simple.__init__()\n")
> ... def __del__(self): sys.stdout.write("Simple.__del__()\n")
>>>> def f():
> ... s = Simple()
> ... sys.stdout.write("f()\n")
> ... # 's' now going out of scope...
This behaviour isn't guaranteed and you should not rely on it. Also, try
s = Simple()
t = Simple()
s.x = t
t.x = s
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