File Closing Problem in 2.3 and 2.4, Not in 2.5

[John Machin]

Martin v. Löwis wrote:
> Carroll, Barry schrieb:
> > What I want to know is:
> >
> > * has anyone else encountered a problem like this, * how was the
> > problem corrected, * can the fix be retro-fitted to 2.5 and 2.4?
>
> From your description, I suspect an error in your code. Your description
> indicates that you don't expect to have more than five files open
> simultaneously. Yet, the error message "Too many open files" occurs when
> you open many more files (in the order of hundreds of files).
>
> It is very unlikely that there is a bug in Python where it would fail to
> close a file when .close() is explicitly invoked on it (as your
> description suggests that you do), so if you get that error message, it
> can only mean that you fail to close some files.

I don't understand:  the OP's description suggests nothing of the sort
to me. What he said was:
"""
In this way, a tree of Parser instances is created, each with a single
open file object.  (BTW, recursive and circular references are not
allowed.)  When each Parser instance comes to the end of its table, the
instance is explicitly destroyed, presumably destroying any objects it
holds, AND closing its open file.
"""
which I interpret as: he is doing del parser_instance, and *presuming*
(incorrectly) that attributes of parser_instance (including an open
file object) are magically whisked away instantly, instead of
later/maybe. He later says he explicitly closed the files, which fixed
what he alleges (incorrectly) to be a bug.

To the OP:
(1) The del statement doesn't "destroy" anything. It unbinds the name
from the object in the current namespace, and decrements the object's
reference count. Only if the reference count is then zero will the
janitor be called in.
(2) Check the reference count on the parser_instance just before you
del it. You could be retaining a reference somewhere.
(3) Explicitly close all non-lightweight objects like files (even
read-only ones) and sockets rather than hoping they will go away.

HTH,
John