Boost python library

[Rosbach, Hans A.]

Thanks for your reply.

> Hi Hans,
> 
> ----- Original Message -----
> From: "Rosbach, Hans A." <Hans.A.Rosbach at dnv.com>
> 
> 
> > I'm making a test using the boost python library in order to get
> > an understanding of how to use it ahead of actual use in real
> > code. The test is done to enable us to compare different methods to
> > make our applications scriptable.
> >
> > We have some big applications, and a COM based scripting using
> > Jscript/Javascript/Ecmascript as language.  This code we want to replace
> > with something better, and boost python is one of the alternatives.
> >
> > We will both use embedding of python and extending with our own
> > user visible classes.
> >
> > Our C++ classes will be thin, just a wrapper for the real data within
> > the application. In the test I found that using a static inline member
> > function,
> > I could place the boost python code in the same header file as the rest
of
> > the
> > class definition.  I.e. one place for both the C++ and python definition
> of
> > the class.
> > Ideal for making the code easy to maintain.
> 
> It sounds like a great application for Boost.Python, and the plans we have
> for the near future will make it even better.
> 
> > However, when I wanted to have my classes in different modules, I was
> unable
> > to do so with the inline init functions.  I got an error message from
the
> > MSVC6 compiler - ambiguous call to overloaded function.
> 
> I think you'll need to show me a lot more detail before I have even a clue
> of what's going wrong.
> 

Ok, let me show you my test example.  The relevant part consists of
two Python modules, with one wrapped class in each.

The classes: point and line - 

    #ifndef POINT_H
    #define POINT_H

    #include <../application/application_config.h>

    #include <iostream>
    #include <string>

    #include <boost/python/class_builder.hpp>
    #include <boost/python/cross_module.hpp>



    namespace python = boost::python;

    class APPLICATION_IMPORT_EXPORT point
    {
    public:
       point(double x,double y,double z);
       point(const point& p);
       ~point();
       virtual double x() const;
       virtual double y() const;
       virtual double z() const;

       virtual void X(double x);
    
    /*   static void init(python::class_builder<point>& point_class,
           python::module_builder& module);
     */    
    private:
       double m_x;
       double m_y;
       double m_z;
     
    };
    /*
    inline void point::init(python::class_builder<point>& point_class,
                            python::module_builder& module)
    {
         point_class.def(python::constructor<double,double,double>());
         point_class.def(python::constructor<const point>());
         point_class.def(&point::x,"x");
         point_class.def(&point::y,"y");
         point_class.def(&point::z,"z");
         point_class.def(&point::x,"__getattr__X__");
         point_class.def(&point::X,"__setattr__X__");
    }
    
    */
    #endif  // POINT_H
    
    
    #ifndef LINE_H
    #define LINE_H

    #include <../application/application_config.h>
    #include <../application/point.h>
    
    #include <boost/python/class_builder.hpp>
    #include <boost/python/cross_module.hpp>
    
    namespace python = boost::python;
    
    class APPLICATION_IMPORT_EXPORT line
    {
    public:
       line(const point& p1,const point& p2);
       virtual ~line();
       virtual point p1() const;
       virtual point p2() const;
    
      static void init(python::class_builder<line>& line_class,
           python::module_builder& module);
       
    protected:
       
    private:
       point m_p1;
       point m_p2;
       
    };
    
    inline void line::init(python::class_builder<line>& line_class,
                           python::module_builder& module)
    {
         line_class.def(python::constructor<point,point>());
         line_class.def(&line::p1,"p1");
         line_class.def(&line::p2,"p2");
    }
    
    
    #endif  // LINE_H


You can see the inline functions.  When these are called making a
single module, everything works fine.  Using

    #include <iostream>
    #include <string>
    
    #include <boost/python/class_builder.hpp>
    
    namespace python = boost::python;
    
    #include <../application/point.h>
    #include <../application/line.h>
    #include <../application/pypseudofile.h>
    
    
    
    BOOST_PYTHON_MODULE_INIT(geotest)
    {
      try
      {
         // Create an object representing this extension module.
         python::module_builder this_module("geotest");
         
         python::class_builder<point> point_class(this_module,"point");
         python::export_converters(point_class);
    /*
         point_class.def(python::constructor<double,double,double>());
         point_class.def(python::constructor<const point>());
         point_class.def(&point::x,"x");
         point_class.def(&point::y,"y");
         point_class.def(&point::z,"z");
         point_class.def(&point::x,"__getattr__X__");
         point_class.def(&point::X,"__setattr__X__");
    */
         point::init(point_class,this_module);
     }
      catch(...)
      {
        python::handle_exception(); // Deal with the exception for Python
      }
    }

and

    #include <iostream>
    #include <string>
    
    #include <boost/python/class_builder.hpp>
    
    namespace python = boost::python;
    
    #include <../application/point.h>
    #include <../application/line.h>
    #include <../application/pypseudofile.h>
    
    
    
    BOOST_PYTHON_MODULE_INIT(geotest2)
    {
      try
      {
         python::module_builder this_module("geotest2");
         python::import_converters<point>
point_class_converters("geotest","point");
         python::class_builder<line> line_class(this_module,"line");
        
         line_class.def(python::constructor<point,point>());
         line_class.def(&line::p1,"p1");
         line_class.def(&line::p2,"p2");
    
    //	 line::init(line_class,this_module);
         
      }
      catch(...)
      {
        python::handle_exception(); // Deal with the exception for Python
      }
    }
    
gives me these messages from MSVC6

 
    geotest2.cpp
    e:\boost_1_25_1\boost/python/detail/init_function.hpp(265) : error
C2668: 'from_python' : ambiguous call to overloaded function
            e:\boost_1_25_1\boost/python/detail/init_function.hpp(260) :
while compiling class-template member function 'class
boost::python::detail::instance_holder_base *__thiscall
boost::python::detail::init1<class boost::python::detail::instance_val
    ue_holder<class point,class boost::python::detail::held_instance<class
point> >,class point const &>::create_holder(class
boost::python::detail::extension_instance *,struct _object *,struct _object
*) const'
    e:\boost_1_25_1\boost/python/detail/init_function.hpp(266) : error
C2661: 'instance_value_holder<class point,class
boost::python::detail::held_instance<class point>
>::instance_value_holder<class point,class
boost::python::detail::held_instance<clas
    s point> >' : no overloaded function takes 2 parameters
            e:\boost_1_25_1\boost/python/detail/init_function.hpp(260) :
while compiling class-template member function 'class
boost::python::detail::instance_holder_base *__thiscall
boost::python::detail::init1<class boost::python::detail::instance_val
    ue_holder<class point,class boost::python::detail::held_instance<class
point> >,class point const &>::create_holder(class
boost::python::detail::extension_instance *,struct _object *,struct _object
*) const'
    



I hope this is both shows my problem and my wish.  I can make it
compile fine by using the explicite code instead of the calls to the
inline init functions.  It is thus possible to create a working
example, but not as clean as I would like it.  I would prefer the
definitions for python and for C++ to reside in the same file.

[cuts]
> 
> > I have used boost 1.25.1.
> 
> The latest CVS state moves all of Boost.Python into a shared library,
which
> should produces /significantly/ smaller executable sizes for any
application
> which uses multiple extension modules. I suggest you try that out. Of
> course, I realize that has nothing to do with your questions.
> 
> Regards,
> Dave

We don't use CVS, thus I have no experience with it, although I would
imagine that my favorite editor probably would make it easy if I got
around to it.  Any pointers to an easy introduction to setting up CVS
for cygwin and/or emacs on ms nt4?

Regards,
Hans



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