assuring class 'clean up' actions are carried out

Terry Reedy tjreedy at udel.edu
Mon Jun 23 19:26:23 CEST 2003


"gyro" <gyromagnetic at excite.com> wrote in message
news:3ef70710 at news.ColoState.EDU...
> Hi,
> I have a class which manages file- and directory-related things for
an
> application. A simplified example is shown by class 'C2' below.
>
> I would like to use an object of this class in another class ('C1'
below).
> My objective is to make sure that the '_cleanup' method of object C2
is
> called when C1 is destroyed or garbage collected.

To 'make sure', you must be explicit.

> I tried the solution below, but I get the following error when I
execute
> file c1.py:
> "Exception exceptions.ImportError: 'No module named shutil' in
<bound
> method C1.__del__ of <__main__.C1 object at 0x811561c>> ignored"
>
> Moreover, the temp directory is not deleted.

When Python exits, it attempts to do some version-dependent,
source-code-documented cleanup in some arbitrary order.  It appears
that shutil gets deleted first.

> If I put an explicit 'del c1' below 'c1 = C1()', the cleanup seems
to
> work fine. However, if possible, I would rather not have to
explicitly
> delete the C1 instance.

You get what you pay for.

> Is there a way to assure that the _cleanup is
> done when an object of C1 is eliminated by Python's garbage
collector?

gc can and should only collect unreachable objects -- refcount 0 or
part of detached cycle.  As long as global name c1 is bound to C1
instance, neither is true, and the instance will continue to exist,

Terry J. Reedy







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