del behavior 2

Eric Snow esnow at verio.net
Wed Jan 7 21:04:35 CET 2009


On Jan 7, 1:03 pm, Eric Snow <es... at verio.net> wrote:
> On Jan 7, 12:57 pm, "Chris Rebert" <c... at rebertia.com> wrote:
>
>
>
> > On Wed, Jan 7, 2009 at 11:42 AM, Eric Snow <es... at verio.net> wrote:
> > > I was reading in the documentation about __del__ and have a couple of
> > > questions.  Here is what I was looking at:
>
> > >http://docs.python.org/reference/datamodel.html#object.__del__
>
> > > My second question is about the following:
>
> > > "It is not guaranteed that __del__() methods are called for objects
> > > that still exist when the interpreter exits."
>
> > > I understand that and have seen it too.  That's fine.  But how do any
> > > of you deal with things that are left open because you did not get a
> > > chance to close them?  How do you clean up after the fact?  Do you
> > > simply keep track externally the things that need to be cleaned up if
> > > __del__ doesn't get a chance?  Any ideas?  Thanks
>
> > As you point out, __del__ is not a reliable way to free limited
> > resources. Instead, one generally includes logic to explicitly free
> > the resources. This is generally done using try-finally or the `with`
> > statement.
>
> > Example:
>
> > def mess_with_file(f):
> >     try:
> >         #fiddle with the file
> >     finally:
> >         f.close() #guarantee that the file gets closed
>
> > def mess_with_other_file(filename):
> >     with open(filename) as f:
> >         #do stuff with file
> >     x = None #the file has now been closed, and it'll be closed even
> > if an exception gets raised
> >     #the "context handler" (see PEP 343) for the `file` type
> > guarantees this for us
>
> > Cheers,
> > Chris
>
> > --
> > Follow the path of the Iguana...http://rebertia.com
>
> Thanks for the responses.  What I mean is when a python process is
> interrupted and does not get a chance to clean everything up then what
> is a good way to do so?  For instance, I have a script that uses child
> ptys to facilitate ssh connections (I'm using pxssh).  When I ^C the
> python process I am left with the child processes running and the ssh
> connections open.  Naturally I run out of ttys if this happens too
> much, which I have had happen.  So if python does not get a chance to
> take care of those, what is a good way to do so?  Does a try/finally
> or a with statement address that?  Thanks!
>
> -eric

pxssh uses pexpect which uses pty.fork



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