En Sat, 06 Jun 2009 03:03:34 -0300, <s0s...@gmail.com> escribió:
On Jun 5, 8:56 pm, Robert Dailey <rcdai...@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
afterwards.)
No, that's not how it works in Python (and I think you're mistaken for C++
too).
See http://docs.python.org/reference/datamodel.html and specially
http://docs.python.org/reference/datamodel.html#object.__del__
"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
cycles.)
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...
...
f()
Simple.__init__()
f()
Simple.__del__()
This behaviour isn't guaranteed and you should not rely on it. Also, try
again with:
def f():
s = Simple()
t = Simple()
s.x = t
t.x = s
sys.stdout.write("f()\n")
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
