class derivation in boost.python v2. Was Re: [C++-sig] Lifetime of Python object for a pointer argument

[Min Xu]

> Unfortunately, those features aren't specifically implemented in v2 yet.
> Operators are supported in the usual Python way (i.e. you can expose an
> __add__ function), but the automatic wrapping features of v1 are not yet
> available. I have not yet decided where this fits in the development plan.
> If you wanted to contribute some code it would be very much appreciated, of
> course.
I hope so.

> 
> Enums can be exposed as ints using the techniques with which scalars are
> exposed in libs/python/src/converter/builtin_converters.cpp, but that code
> was mostly written to be implementation detail. I guess I need to clean up
> and document most of those classes so that users can take advantage of them.
> 
> However, I think I've come to *yet another* realization about how the
> low-level from_python conversion mechanism should work, so I guess I will be
> re-engineering most of what's in builtin_converters.cpp at some point in the
> next month or so; you might not want to invest in understanding that.
> 
I redefine the enumeration as int as a temporal solution.

> Finally, <redfaced>I just realized that I haven't yet implemented the use of
> CallPolicies in __init__ functions</redfaced>, so this won't compile:
> 
>               .def_init(args<const grid*>()
>               // Keep the grid alive as long as the geometry is.
>                         , python::with_custodian_and_ward<1,2>())
> 
> Give me at least until Monday to take care of that.
> 
Thanks. However the following bug may be more severe. A very simple code
is as following. It compiles yet makes python2.2 core dump.

#include <boost/python/module.hpp>
#include <boost/python/class.hpp>

class A
{
public:
	A() : x(0) {}
	A(const A& a) : x(a.x) {}
private:
	double x;
};

class AA : public A
{
public:
	AA(const A& a) : A(a) {}
};

namespace python = boost::python;

BOOST_PYTHON_MODULE_INIT(AA)
{
  try
  {
      python::module("AA")
	  .add(
	      python::class_<A>("A")
	      .def_init(args<>())
	      )
	  .add(
	      python::class_<AA, bases<A> >("AA")
	      .def_init(args<const A&>())
	      );
  }
  catch(...)
  {
      //python::handle_exception(); // Deal with the exception for Python
  }
}

g++ -I/usr/local/include -I/usr/include/python2.2  -c -Wall
-ftemplate-depth-100  -DBOOST_PYTHON_DYNAMIC_LIB -DBOOST_PYTHON_V2  -g
-O0 -fno-inline -fPIC tst.C
g++ -g -fpic -shared -o AA.so -L/usr/lib/python2.2/config
-I/usr/include/python2.2 -I/usr/local/include tst.o -lutil  -lbpl

And in python2.2:
>>> import AA
Segmentation fault (core dumped)


Min Xu