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Date: Thu, 22 Mar 2012 09:00:50 -0500
From: Tycho Andersen <tycho@tycho.ws>
To: Chris Rebert <clp2@rebertia.com>
Subject: Re: Best way to disconnect from ldap?
References: <jkda88$mrk$1@reader1.panix.com> <CAMZYqRQR0VFweQgN8jb3wkx-opabvVQJy5zRtQQrv7tnnzivwA@mail.gmail.com> <CALvWhxvq-KO0ZxMwo-A7ieLyULHh95LAAiLon3zqBgMixZpFbA@mail.gmail.com> <4F6A4D02.6020403@tim.thechases.com> <20120322131447.GG19657@ccapuser-ubuntu.WICOURTS.GOV> <CAMZYqRRxtQD8g5GQOS1c_P_cFBC9sF1dp+qh1PNkBe0FX34FFw@mail.gmail.com>
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Xref: csiph.com comp.lang.python:22024

On Thu, Mar 22, 2012 at 06:27:45AM -0700, Chris Rebert wrote:
> On Thu, Mar 22, 2012 at 6:14 AM, Tycho Andersen <tycho@tycho.ws> wrote:
> > On Wed, Mar 21, 2012 at 04:49:54PM -0500, Tim Chase wrote:
> >> On 03/21/12 15:54, Chris Kaynor wrote:
> >> >As Chris Rebert pointed out, there is no guarantee as to when the
> >> >__del__ method is called. CPython will generally call it immediately,
> >> >however if there are reference cycles it may never call it
> >>
> >> And more maddeningly, modules/objects used/called from within the
> >> __del__ may have already gone out of scope, producing
> >> head-scratching errors.  I've been bitten by this enough times that
> >> I just stopped using __del__ completely.
> >
> > I've had similar experiences. In fact, in light of all this - why does
> > __del__ exist at all? Novice python users may (reasonably) assume it
> > behaves similarly to a C++ destructor (even though the docs warn
> > otherwise).
> >
> > Given that you can't trust __del__, is there a legitimate use case for
> > it?
> 
> Writing resource classes (like `file`) in C? Their __del__()s
> typically involve little/less Python-level stuff and thus less
> paranoia need be exercised.

Sure, but you still have no guarantee that __del__ will ever be
called, so it's a bad idea to rely on it to clean up anything.

> There is somewhat of a perverse incentive in having such last-ditch
> clean-up mechanisms though. "This code seems to work fine without
> `with`, so why bother changing it?"

Yeah, I guess I can see doing something like:
  __del__ = __exit__
but anything beyond that seems risky...

\t