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Newbie Newbie, we are all Newbie to something

Gregoire Welraeds greg at perceval.be
Fri Feb 25 09:28:06 EST 2000 
In reply to the message of Gordon McMillan sent on Feb 25 (see below) :

> If you code a __del__, it's to release some resource 
> that won't be automatically reclaimed.

Can someone give me an example of resource that won't be automatically
reclaimed. 


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Gregoire Welraeds
greg at perceval.be
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On Fri, 25 Feb 2000, Gordon McMillan wrote:

> Date: Fri, 25 Feb 2000 09:01:34 -0500
> From: Gordon McMillan <gmcm at hypernet.com>
> To: Gregoire Welraeds <greg at perceval.be>, python-list at python.org
> Subject: Re: Newbie Newbie, we are all Newbie to something
> 
> Gregoire Welraeds wrote:
> 
> > I'm currently reading the Python Reference Manual and I got a small
> > question regarding the __del__() statement in a class definition.
> > I understand his utility when you don't have a garbage collector and
> > memory management. In this case, it is important to have del statement to
> > free object properly. 
> 
> No, the __del__ method (if it exists) is called when Python is 
> about to dealloc the object because the refcount has dropped 
> to zero. If you code a __del__, it's to release some resource 
> that won't be automatically reclaimed.
> 
> But what if you have ?
> > In the same topic, do we have to explicitly close an open file before
> > exiting:  
> 
> No. File objects close themselves when dealloc'ed. So this is 
> a common idiom in Python:
> 
>  text = open(filenm, 'r').read()
> 
> With both GC (at least, most implementations) and refounting 
> you have problems with circular references. In (most) GC, 
> when a unreachable cycle of objects is reclaimed, the 
> finalizers are not called, but the memory is reclaimed. With 
> refcounting, unreachable cycles live forever.
> 
> But, with refcounting, when a refcount reaches 0, the object is 
> deallocated then and there, so it is safe to release resources 
> in the dealloc (or __del__). In GC, there are any number of 
> factors that can influence when the finalizer is run, so you 
> normally code an explicit close method if you need the 
> resource released in a timely manner.
> 
> - Gordon
> 
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>
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