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

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

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