What does gc.get_objects() return?

Chris Angelico rosuav at gmail.com
Wed Mar 12 22:44:56 CET 2014

On Thu, Mar 13, 2014 at 8:28 AM, Jurko Gospodnetić
<jurko.gospodnetic at pke.hr> wrote:
>   So gc.collect() returns a list of all the objects GC is in charge of, and
> which instances are and are not tracked by the GC is, I guess, an
> interpreter implementation detail.

I assume you don't mean collect() there, as that returns the amount of
garbage that it just collected :)

It's not strictly an implementation detail, beyond that there are
certain optimizations. For instance...

>   For CPython 3.4 I guess strings and other atomic types such as ints are
> not, as well as raw object() instances. Custom class instances on the other
> hand seem to be under GC control.

... strings and ints should never be listed, and custom objects should
always be listed, but I'd say the non-tracking of object() would be an
implementation-specific optimization. Definitely the non-tracking of a
dict of nothing but atomic keys and values would be that.

The concept is that the GC tracks (in that sense; everything in
CPython is refcounted, but that's not what these functions look at)
anything that could be a part of a reference cycle. That's all it
concerns itself with, so something that can't have references to
arbitrary objects can't possibly be worth tracking. Interestingly, a
tuple of integers is tracked:

>>> a=1,2,3
>>> gc.is_tracked(a)

So not all optimizations are done that could be done.


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