is there anybody using __del__ correctly??

[Michele Simionato]

The title is provocative, of course ;)

However, I was browsing through our codebase here at work and I
noticed a few
usages of __del__ as a resource finalizer (i.e. __del__ just calls a
close
method).

I consider this practice an error, since with __del__
you are never sure that the resource will be released
(http://docs.python.org/ref/customization.html#l2h-175) and anyway
this
should be done with try .. finally or the 'with' statement.

So I got into thinking: "yes, using __del__ as a resource finalizer is
wrong,
but then what are good use cases for it? Let's look at the standard
library and see what people use __del__ for".

So I did, and to my dismay 95% of the __del__ methods in the standard
library
are just calling a close method!!

In particular this happens in the following modules: (Python 2.5 on
Ubuntu):

 zipfile, wave, urllib, close, tarfile, sunau, shelve, httplib, gzip,
 fileinput, dumbdbm, audiodev, aifc, bsddb.dbshelve, tempfile, socket,
 platform, ... (I got tired after this point)

I see one good use case for __del__ in wsgiref.validate: here __del__
prints a warning if the resource is *not* closed explicitely.
Something
similar happens in subprocess and popen2, where __del__ updates the
list
of active processes.

So I am beginning to  wonder if there exists good use cases for
__del__,
apart for debugging/checking purposes. Can you provide some?
Yes, you may take that as a challenge ;)


  Michele Simionato


P.S. BTW, I should mention that if you search comp.lang.python for
__del__
you will find hundreds of people who were bitten by __del__, so I
usually give
advices such as "you should never __del__ in your code". If I am wrong
in
giving this advice, please let me know!

P.P.S. Here and there I hear rumors about deprecating __del__ and
nothing
happens, are there any news about that? Expecially concerning Py3k?