File not closed on exception

arve.knudsen at gmail.com arve.knudsen at gmail.com
Tue Oct 20 08:13:30 CEST 2009


On Oct 19, 3:48 pm, Ethan Furman <et... at stoneleaf.us> wrote:
> arve.knud... at gmail.com wrote:
> > Hi
>
> > I thought that file objects were supposed to be garbage-collected and
> > automatically closed once they go out of scope, at least that's what
> > I've been told by more merited Python programmers. I'm also quite sure
> > that this is quite a common assumption in various programs, at least
> > given what opensource code I've seen in my time. However, the
> > following script doesn't work on Windows, since the file is still open
> > when I try to remove it:
>
> > import os.path
>
> > def create():
> >     f = file("tmp", "w")
> >     raise Exception
>
> > try: create()
> > finally:
> >     os.remove("tmp")
>
> > So, what's the deal exactly, is the file supposed to be garbage-
> > collected (and closed) at the end of create?
>
> > Thanks!
> > Arve
>
> When an exception is raised, the entire stack frame at that location
> (which includes local vars) is saved in the exception traceback.  Since
> the objects are still alive, they are not GC'ed.  That is why this is
> better:
>
> def create():
>      f = file("tmp", "w")
>      try:
>          do_stuff_that_raises_exception
>      finally:
>          os.remove("tmp")
>
> ~Ethan~

Why should this work? If I replace "do_stuff_that_raises_exception"
with "raise Exception", it fails in the same way, since the file is
open. Maybe you forgot "f.close()"? In any case, thanks for explaining
that the traceback keeps the object alive, that explains the issue.

Arve



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