Re: Py::Object( NULL ) and PySequence_DelItem() support

[Barry S. <ba...@ba...>]

This is proving harder to change then I expected.

This is because Py::Object( NULL ) most work and be assignable etc.

I came across a case where I needed the ability to return a NULL as 
Py:Object() which is why the Python 3 has that API.

Until there are more use cases to consider I want to leave the code as
it is.

Barry


On Friday 18 September 2015 09:47:05 Barry Scott wrote:
> Thanks for the feedback. I hope to have something to test next week.
> 
> Barry
> 
> > On 12 Sep 2015, at 20:59, Vivian De Smedt <vd...@gm...> wrote:
> > 
> > Hi Barry,
> > 
> > I understand and share your concerns, backward compatibility is important.
> > 
> > Personally I prefer you second solution based on Py::ObjectAllowNull.
> > I think construct object that could accept NULL should be rare and easily
> > identifiable in a code.
> > 
> > Best regards,
> > Vivian.
> > 
> > 
> > 
> > 
> > Le mar. 1 sept. 2015 à 18:13, Vivian De Smedt <vd...@gm...
> > <mailto:vd...@gm...>> a écrit : Hi Barry,
> > 
> > Thanks for your detailed analysis. I'm currently in Holidays in Scotland.
> > I'll read your mail carefully next week.
> > 
> > Best regards,
> > Vivian
> > 
> > 
> > On Tuesday, September 1, 2015, Barry Scott <ba...@ba...
> > <mailto:ba...@ba...>> wrote: Vivian,
> > 
> > I think I have 2 patches to work on from you.
> > 
> > * Add the ability to react to PySequence_DelItem()
> > * Make py2 and py3 handling of Py::Object( NULL ) consistent
> > 
> > I was worried that someone might be relying on being able to use
> > detect the NULL value in sequence_ass_item(). Given that Py2 cannot
> > call the sequence_ass_item() because of the NULL check. I will take
> > your patch to all sequence_ass_del(). It is a nice API.
> > 
> > My feeling that it should be possible to create Py::Object from NULL.
> > But there are clearly cases when its not a reasonable thing to do.
> > 
> > I wondering what the API should look like.
> > 
> > Adding another bool to the c’tor is possible.
> > 
> > Py::Object( PyObject *, bool owner, bool accept_null );
> > Then have validate() change behaviour on accept_null.
> > 
> > Or use two classes:
> > 
> > * a Py::Object which Allows Null
> > * a Py::Object which Disallows Null
> > 
> > Take the current Py::Object and rename to Py::ObjectAllowNull.
> > 
> > class Py::ObjectAllowNull;
> > with validate() { return true; }
> > add new predicate hasObject() { return p != NULL; }
> > 
> > Then derive Py::Object from Py::ObjectAllowNull.
> > 
> > class Py::Object(Py::ObjectALllowNull);
> > with validate() { return p!=NULL; }
> > 
> > All the existing classes like Py::Int, Py::List derive from Py::Object
> > that rejects Null.
> > 
> > With the accept_null c’tor it would be possible to have a Py::Int that
> > accepts NULL.
> > 
> > Any thoughts?
> > 
> > Barry