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  <title>Boost.Python -
  &lt;boost/python/doobject/pytype_function.hpp&gt;</title>
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        <h3><a href="../../../../index.htm"><img height="86" width=
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        <h1 align="center"><a href=
        "../index.html">Boost.Python</a></h1>

        <h2 align="center">Header
        &lt;boost/python/converter/pytype_function.hpp&gt;</h2>
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  <h2>Contents</h2>

  <dl class="page-index">
    <dt><a href="#introduction">Introduction</a></dt>

    <dt><a href="#classes">Classes</a></dt>

    <dd>
      <dl class="page-index">
        <dt><a href="#wrap_pytype-spec">Class
        <code>wrap_pytype</code></a></dt>

        <dd>
          <dl class="page-index">
            <dt><a href="#wrap_pytype-spec-synopsis">Class
            <code>wrap_pytype</code> synopsis</a></dt>

          </dl>
        </dd>
      </dl>
    </dd>

    <dd>
      <dl class="page-index">
        <dt><a href="#registered_pytype-spec">Class
        <code>registered_pytype</code></a></dt>

        <dd>
          <dl class="page-index">
            <dt><a href="#registered_pytype-spec-synopsis">Class
            <code>registered_pytype</code> synopsis</a></dt>

          </dl>
        </dd>
      </dl>
    </dd>

    <dd>
      <dl class="page-index">
        <dt><a href="#expected_from_python_type-spec">Class
        <code>expected_from_python_type</code></a></dt>

        <dd>
          <dl class="page-index">
            <dt><a href="#expected_from_python_type-spec-synopsis">Class
            <code>expected_from_python_type</code> synopsis</a></dt>

          </dl>
        </dd>
      </dl>
    </dd>

    <dd>
      <dl class="page-index">
        <dt><a href="#to_python_target_type-spec">Class
        <code>to_python_target_type</code></a></dt>

        <dd>
          <dl class="page-index">
            <dt><a href="#to_python_target_type-spec-synopsis">Class
            <code>to_python_target_type</code> synopsis</a></dt>

          </dl>
        </dd>
      </dl>
    </dd>

    <dt><a href="#examples">Examples</a></dt>
  </dl>
  <hr>

  <h2><a name="introduction" id=
  "introduction"></a>Introduction</h2>

  <p>To support Pythonic signatures the converters should supply a <code>get_pytype</code> function
  returning a pointer to the associated <code>PyTypeObject</code>. See for example
  <a href="ResultConverter.html#ResultConverter-concept">ResultConverter</a> or 
  <a href="to_python_converter.html#to_python_converter-spec">to_python_converter</a>.
  The classes in this header file are meant to be used when implmenting <code>get_pytype</code>.
  There are also <code>_direct</code> versions of the templates of <code>class T</code> which
  should be used with undecorated type parameter, expected to be in the conversion registry when the module loads.
  </p>

  <h2><a name="classes" id="classes"></a>Classes</h2>

  <h3><a name="wrap_pytype-spec" id=
  "wrap_pytype-spec"></a>Class
  <code>wrap_pytype</code></h3>

  <p>
   This template generates a static <code>get_pytype</code> member returning the template parameter.
  </p>

  <h4><a name="wrap_pytype-spec-synopsis" id=
  "wrap_pytype-spec-synopsis"></a>Class
  <code>wrap_pytype</code> synopsis</h4>
  <pre>
namespace boost { namespace python { namespace converter{

    template &lt; PyTypeObject const *pytype &gt;
    class wrap_pytype 
    {
      public:
          static PyTypeObject const *get_pytype(){return pytype; }
    };

}}}
</pre>


  <h3><a name="registered_pytype-spec" id=
  "registered_pytype-spec"></a>Class
  <code>registered_pytype</code></h3>

  <p>
   This template should be used with template parameters which are (possibly decorated)
   types exported to python using <a href="class.html"><code>class_</code></a>.
   The generated a static <code>get_pytype</code> member 
   returns the corresponding python type.
  </p>

  <h4><a name="registered_pytype-spec-synopsis" id=
  "registered_pytype-spec-synopsis"></a>Class
  <code>registered_pytype</code> synopsis</h4>
  <pre>
namespace boost { namespace python { namespace converter{

    template &lt; class T &gt;
    class registered_pytype 
    {
      public:
          static PyTypeObject const *get_pytype();
    };

}}}
</pre>


  <h3><a name="expected_from_python_type-spec" id=
  "expected_from_python_type-spec"></a>Class
  <code>expected_from_python_type</code></h3>

  <p>
   This template generates a static <code>get_pytype</code> member which inspects the registered
   <code>from_python</code> converters for the type <code>T</code> and returns a matching python type.
  </p>

  <h4><a name="expected_from_python_type-spec-synopsis" id=
  "expected_from_python_type-spec-synopsis"></a>Class
  <code>expected_from_python_type</code> synopsis</h4>
  <pre>
namespace boost { namespace python { namespace converter{

    template &lt; class T &gt;
    class expected_from_python_type 
    {
      public:
          static PyTypeObject const *get_pytype();
    };

}}}
</pre>


  <h3><a name="to_python_target_type-spec" id=
  "to_python_target_type-spec"></a>Class
  <code>to_python_target_type</code></h3>

  <p>
   This template generates a static <code>get_pytype</code> member returning the 
   python type to which T can be converted.
  </p>

  <h4><a name="to_python_target_type-spec-synopsis" id=
  "to_python_target_type-spec-synopsis"></a>Class
  <code>to_python_target_type</code> synopsis</h4>
  <pre>
namespace boost { namespace python { namespace converter{

    template &lt; class T &gt;
    class to_python_target_type 
    {
      public:
          static PyTypeObject const *get_pytype();
    };

}}}
</pre>


  <h2><a name="examples" id="examples"></a>Examples</h2>

    This example presumes that someone has implemented the standard <a href=
    "http://www.python.org/doc/2.2/ext/dnt-basics.html">noddy example
    module</a> from the Python documentation, and placed the corresponding
    declarations in <code>"noddy.h"</code>. Because
    <code>noddy_NoddyObject</code> is the ultimate trivial extension type,
    the example is a bit contrived: it wraps a function for which all
    information is contained in the <i>type</i> of its return value.

    <h3>C++ module definition</h3>
<pre>
#include &lt;boost/python/reference.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
#include "noddy.h"

struct tag {};
tag make_tag() { return tag(); }

using namespace boost::python;

struct tag_to_noddy 
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //unnecessary overhead if py signatures are not supported
: wrap_pytype<&amp;noddy_NoddyType> //inherits get_pytype from wrap_pytype
#endif
{
    static PyObject* convert(tag const&amp; x)
    {
        return PyObject_New(noddy_NoddyObject, &amp;noddy_NoddyType);
    }
};

BOOST_PYTHON_MODULE(to_python_converter)
{
    def("make_tag", make_tag);
    to_python_converter&lt;tag, tag_to_noddy
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //invalid if py signatures are not supported
          , true
#endif
          &gt;(); //"true" because tag_to_noddy has member get_pytype
}
</pre>


<p>The following example registers to and from python converters using the templates
<code>expected_from_python_type</code> and <code>to_pyhton_target_type</code>.
</p>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/def.hpp&gt;
#include &lt;boost/python/extract.hpp&gt;
#include &lt;boost/python/to_python_converter.hpp&gt;
#include &lt;boost/python/class.hpp&gt;

using namespace boost::python;

struct A
{
};

struct B
{
  A a;
  B(const A& a_):a(a_){}
};

// Converter from A to python int
struct BToPython 
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //unnecessary overhead if py signatures are not supported
   : converter::to_python_target_type&lt;A&gt;  //inherits get_pytype
#endif
{
  static PyObject* convert(const B& b)
  {
    return incref(object(b.a).ptr());
  }
};

// Conversion from python int to A
struct BFromPython
{
  BFromPython()
  {
    boost::python::converter::registry::push_back
        ( &amp;convertible
        , &amp;construct
        , type_id&lt; B &gt;()
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //invalid if py signatures are not supported
        , &amp;converter::expected_from_python_type&lt;A&gt;::get_pytype//convertible to A can be converted to B
#endif
        );
  }

  static void* convertible(PyObject* obj_ptr)
  {
      extract&lt;const A&&gt; ex(obj_ptr);
      if (!ex.check()) return 0;
      return obj_ptr;
  }

  static void construct(
      PyObject* obj_ptr,
      converter::rvalue_from_python_stage1_data* data)
  {
    void* storage = (
        (converter::rvalue_from_python_storage&lt; B &gt;*)data)-&gt; storage.bytes;

    extract&lt;const A&&gt; ex(obj_ptr);
    new (storage) B(ex());
    data->convertible = storage;
  }
};


B func(const B& b) { return b ; }

BOOST_PYTHON_MODULE(pytype_function_ext)
{
  to_python_converter&lt; B , BToPython
#if defined BOOST_PYTHON_SUPPORTS_PY_SIGNATURES //invalid if py signatures are not supported
             ,true 
#endif
             &gt;(); //has get_pytype
  BFromPython();

  class_&lt;A&gt;("A") ;

  def("func", &amp;func);

}



&gt;&gt;&gt; from pytype_function_ext import *
&gt;&gt;&gt; print func.__doc__
func( (A)arg1) -> A :
    C++ signature:
         struct B func(struct B)
</pre>


  <p><i>&copy; Copyright <a href="mailto:nickm at sitius dot com">Nikolay Mladenov</a> 2007.</i></p>
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