[Python-ideas] Put default setstate and getstate on object for use in coöperative inheritance.

[Neil Girdhar]

Hi Steven,

Have you tried implementing getstate and setstate with cooperatively
inherited classes?  You'll need to call super().__getstate__(), which won't
exist, but it really should.  What I'm proposing is to move the default
behaviour out of the pickle and copy internals to an object-level
implementation of getstate and setstate where I think it belongs.

Regarding Guido's point that object doesn't have a dict, as weird as that
is, then I think a default getstate could just check for that with hasattr
and if it's missing return the empty dict.

Best,

Neil

On Sat, Jun 7, 2014 at 5:10 AM, Steven D'Aprano <steve at pearwood.info> wrote:

> On Sat, Jun 07, 2014 at 02:10:15AM -0400, Neil Girdhar wrote:
> > Hi Steven,
> >
> > If you don't know about getstate and setstate, I suggest you take a look
> at
> > the documentation:
> > https://docs.python.org/3.3/library/pickle.html#object.__getstate__.
>
> I know about getstate as it regards to pickle, that's why I asked if you
> were talking about serialization. Unfortunately you never mentioned
> pickle, or copy, you talked about cooperative inheritence which is a
> generic concept that applies much more broadly than just copying or
> serializing instances.
>
>
> > Besides allowing objects to be pickled, providing these methods allows
> > them to be copied with the copy module.
>
> objects can already be copied and pickled:
>
> py> import copy, pickle
> py> x = object()
> py> copy.copy(x)
> <object object at 0xb7ce9588>
> py> pickle.dumps(x)
> b'\x80\x03cbuiltins\nobject\nq\x00)\x81q\x01.'
>
> Copying and pickling are defined by protocols, not inheritence, so
> there's no need for a single root method.  As the documentation states,
> you only need to define a __getstate__ and __setstate__ method when the
> default protocol behaviour is not sufficient for your class, so adding
> these methods to object is unnecessary.
>



>
> There's a historical reason for doing it this way: in Python 2, not
> everything inherits from object.
>
>
> --
> Steven
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