Re: [boost] Implementing callbacks from C++ to Python Script.

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2002-01-05 09:02:46

----- Original Message -----
From: "jefflholle" <jeff.holle_at_[hidden]>

> I'm failing to understand examples of this in boost_1_24_0
> Boost.Python.
>
> Basically, my problem is in obtaining the PyObject * value needed to
> make a callback.
>
> The simplest example of this is abstract.cpp/test_abstract.py.
> It is more complicated that what I'm after since it involves an
> abstract C++ class that is interfaced to python.
>
> I've modified this module to reflect what I'm really after

What /are/ you really after? Please spell it out carefully and precisely...

> and gotten
> it to behave in the manner that my code is.  It follows:
> // Example by Ullrich Koethe
<snip>
> BOOST_PYTHON_MODULE_INIT(abstract)
> {
>     boost::python::module_builder a("abstract");
>
>     boost::python::class_builder<Abstract_callback> a_class
> (a, "Abstract");
>     a_class.def(boost::python::constructor<>()); // wrap a constructor
>     a_class.def(&Abstract_callback::test, "test");
> }
>
> This module doesn't compile for want of a default constructor in
> Abstract_callback.

Because you changed the class_builder declaration (why?) from:

    boost::python::class_builder<Abstract, Abstract_callback>

to:

    boost::python::class_builder<Abstract_callback>

> It doesn't exist because I want to make the
> constructor of this class provide the needed PyObject,

How would the constructor "provide" it? Are you planning to do a PyList_New
or something?

> so a callback
> can be done.
>
> If I modify the "boost::python::constructor<>());"
> to "boost::python::constructor<Python *>());"  I run into conversion
> problems.

What sort of conversion problems?

> Actually, I've found that I run into such trouble passing
> any pointer and a lot of complex things.

I don't understand the above sentence.

> How do I do this?

Do what?

> One more thing.  I've tried just adding another method to deliver the
> self pointer of the class and get a runtime error saying that a
> string or unicode object expected but an instance was found when
> calling it from python.

That's description is open to lots of interpretations; code helps.