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| <boost/python/to_python_converter.hpp></title> |
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| <h3><a href="../../../../index.htm"><img height="86" width="277" |
| alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3> |
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| |
| <td valign="top"> |
| <h1 align="center"><a href="../index.html">Boost.Python</a></h1> |
| |
| <h2 align="center">Header |
| <boost/python/to_python_converter.hpp></h2> |
| </td> |
| </tr> |
| </table> |
| <hr> |
| |
| <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="#to_python_converter-spec">Class Template |
| <code>to_python_converter</code></a></dt> |
| |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#to_python_converter-spec-synopsis">Class Template |
| <code>to_python_converter</code> synopsis</a></dt> |
| |
| <dt><a href="#to_python_converter-spec-ctors">Class Template |
| <code>to_python_converter</code> constructor</a></dt> |
| </dl> |
| </dd> |
| </dl> |
| </dd> |
| |
| <dt><a href="#examples">Example</a></dt> |
| </dl> |
| <hr> |
| |
| <h2><a name="introduction"></a>Introduction</h2> |
| <code>to_python_converter</code> registers a conversion from objects of a |
| given C++ type into a Python object. |
| |
| <h2><a name="classes"></a>Classes</h2> |
| |
| <h3><a name="to_python_converter-spec"></a>Class template |
| <code>to_python_converter</code></h3> |
| <code>to_python_converter</code> adds a wrapper around a static member |
| function of its second template parameter, handling low-level details |
| such as insertion into the converter registry. |
| |
| <table border="1" summary="to_python_converter template parameters"> |
| <caption> |
| <b><code>to_python_converter</code> template parameters</b><br> |
| In the table below, <b><code>x</code></b> denotes an object of type |
| <code>T</code> |
| </caption> |
| |
| <tr> |
| <th>Parameter</th> |
| |
| <th>Requirements</th> |
| |
| <th>Description</th> |
| </tr> |
| |
| <tr> |
| <td><code>T</code></td> |
| |
| <td> |
| </td> |
| |
| <td>The C++ type of the source object in the conversion</td> |
| </tr> |
| |
| <tr> |
| <td><code>Conversion</code></td> |
| |
| <td> |
| <code>PyObject* p = Conversion::convert(x)</code>,<br> |
| if <code>p == 0</code>, <code><a href= |
| "http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>() != 0</code>.</td> |
| |
| <td>A class type whose static member function <code>convert</code> |
| does the real work of the conversion.</td> |
| </tr> |
| <tr> |
| <td><code>bool has_get_pytype = false</code></td> |
| |
| <td> |
| <code>PyTypeObject const * p = Conversion::get_pytype() </code>.</td> |
| |
| <td><b>Optional member</b> - if <code>Conversion</code> has <code>get_pytype</code> member supply |
| <code>true</code> for this parameters. |
| If present <code>get_pytype</code> is used to document the return type |
| of functions using this conversion. The <code>get_pytype</code> may be implemented |
| using the classes and functions |
| from <a href="pytype_function.html"><code>pytype_function.hpp</code></a> |
| <b>NOTE :</b> For backward compatibility this parameter may be passed after |
| checking if <code>BOOST_PYTHON_SUPPORTS_PY_SIGNATURES</code> is defined (see |
| <a href="pytype_function.html#examples">here</a>). |
| </td> |
| </tr> |
| </table> |
| |
| <h4><a name="to_python_converter-spec-synopsis"></a>Class template |
| <code>to_python_converter</code> synopsis</h4> |
| <pre> |
| namespace boost { namespace python |
| { |
| template <class T, class Conversion, bool convertion_has_get_pytype_member=false> |
| struct to_python_converter |
| { |
| to_python_converter(); |
| }; |
| }} |
| </pre> |
| |
| <h4><a name="to_python_converter-spec-ctors"></a>Class template |
| <code>to_python_converter</code> constructor</h4> |
| <pre> |
| to_python_converter(); |
| </pre> |
| |
| <dl class="function-semantics"> |
| <dt><b>Effects:</b> Registers a to_python converter which uses |
| <code>Conversion::convert()</code> to do its work.</dt> |
| </dl> |
| |
| <h2><a name="examples"></a>Example</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 <boost/python/reference.hpp> |
| #include <boost/python/module.hpp> |
| #include "noddy.h" |
| |
| struct tag {}; |
| tag make_tag() { return tag(); } |
| |
| using namespace boost::python; |
| |
| struct tag_to_noddy |
| { |
| static PyObject* convert(tag const& x) |
| { |
| return PyObject_New(noddy_NoddyObject, &noddy_NoddyType); |
| } |
| static PyTypeObject const* get_pytype() |
| { |
| return &noddy_NoddyType; |
| } |
| }; |
| |
| BOOST_PYTHON_MODULE(to_python_converter) |
| { |
| def("make_tag", make_tag); |
| to_python_converter<tag, tag_to_noddy, true>(); //"true" because tag_to_noddy has member get_pytype |
| } |
| </pre> |
| |
| <h3>Python code</h3> |
| <pre> |
| >>> import to_python_converter |
| >>> def always_none(): |
| ... return None |
| ... |
| >>> def choose_function(x): |
| ... if (x % 2 != 0): |
| ... return to_python_converter.make_tag |
| ... else: |
| ... return always_none |
| ... |
| >>> a = [ choose_function(x) for x in range(5) ] |
| >>> b = [ f() for f in a ] |
| >>> type(b[0]) |
| <type 'NoneType'> |
| >>> type(b[1]) |
| <type 'Noddy'> |
| >>> type(b[2]) |
| <type 'NoneType'> |
| >>> type(b[3]) |
| <type 'Noddy'> |
| </pre> |
| |
| <p>Revised |
| <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
| 11 June, 2007 |
| <!--webbot bot="Timestamp" endspan i-checksum="39359" --> |
| </p> |
| |
| <p><i>© Copyright <a href= |
| "http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p> |
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