gc.garbage

[Chris Mellon]

On 8/30/07, 7stud <bbxx789_05ss at yahoo.com> wrote:
> On Aug 30, 3:50 am, "Martin v. Löwis" <mar... at v.loewis.de> wrote:
> > > gc.set_debug(gc.DEBUG_LEAK)
> > > print gc.garbage
> >
> > > --output:--
> > > []
> > > gc: uncollectable <Dog 0x56e10>
> > > gc: uncollectable <Cat 0x56e30>
> > > gc: uncollectable <dict 0x58270>
> > > gc: uncollectable <dict 0x43e40>
> >
> > gc.garbage is filled only after these messages
> > are printed, not before. You need to add an explicit
> > call to gc.collect() if you want to see what
> > uncollectable garbage you have.
> >
> > Regards,
> > Martin
>
> Hi,
>
> Thanks for the response.  I had a cut and paste error in my reply, so
> here it is again with the corrections...
>
> Now, if I run the code:
>
> ------------
> import gc
>
> class Cat(object):
>     def __del__():
>         pass
>
> class Dog(object):
>     def __del__():
>         pass
>
> def some_func():
>     the_dog = Dog()
>     the_cat = Cat()
>     the_dog.cat = the_cat
>     the_cat.dog = the_dog
>
> some_func()
>
> gc.set_debug(gc.DEBUG_LEAK)
> gc.collect()
> print gc.garbage
> -----------
>
> I get this output:
>
> ----------
> gc: uncollectable <Dog 0x56e10>
> gc: uncollectable <Cat 0x56e30>
> gc: uncollectable <dict 0x58300>
> gc: uncollectable <dict 0x43e40>
> [<__main__.Dog object at 0x56e10>, <__main__.Cat object at 0x56e30>,
> {'cat': <__main__.Cat object at 0x56e30>}, {'dog': <__main__.Dog
> object at 0x56e10>}]
> -----------
>
> Why are there two entries in the list for each uncollectable
> object(same addresses)?  Also, I haven't bound the names "cat" or
> "dog" anywhere in my program.  What do those names mean in the list?
>
Read your output carefully!

gc.garbage is a list of objects. The objects are printed just as they
would be anywhere else in Python. You've got the dog object, the cat
object, and the __dict__ of each instance.

> Doing some further testing, if I eliminate the __del__ methods:
>
> -----------
> import gc
>
> class Cat(object):
>     pass
>
> class Dog(object):
>     pass
>
> def some_func():
>     the_dog = Dog()
>     the_cat = Cat()
>     the_dog.cat = the_cat
>     the_cat.dog = the_dog
>
> some_func()
>
> gc.set_debug(gc.DEBUG_LEAK)
> gc.collect()
> print gc.garbage
> -------------------
>
> I get this output:
>
> -----
> gc: collectable <Dog 0x56e10>
> gc: collectable <Cat 0x56e30>
> gc: collectable <dict 0x58270>
> gc: collectable <dict 0x43e40>
> [<__main__.Dog object at 0x56e10>, <__main__.Cat object at 0x56e30>,
> {'cat': <__main__.Cat object at 0x56e30>}, {'dog': <__main__.Dog
> object at 0x56e10>}]
> -----
>
> The docs say:
>
> ---------
> garbage
> A list of objects which the collector found to be unreachable but
> could not be freed (uncollectable objects).
> --------
>
> Since debugging doesn't show any uncollectable objects, why isn't
> gc.garbage empty?  The docs also say:
>
> ----
> garbage
> ...By default, this list contains only objects with __del__() methods.
> ----
>
> Does set_debug() change the default?
>

>From the last line of the documentation block you quoted above: "If
DEBUG_SAVEALL is set, then all unreachable objects will be added to
this list rather than freed."