1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>boost/python/call_method.hpp</title> 5<link rel="stylesheet" href="../../boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Boost.Python Reference Manual"> 8<link rel="up" href="../function_invocation_and_creation.html" title="Chapter 4. Function Invocation and Creation"> 9<link rel="prev" href="boost_python_call_hpp.html" title="boost/python/call.hpp"> 10<link rel="next" href="boost_python_data_members_hpp.html" title="boost/python/data_members.hpp"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="" width="" height="" src="../../images/boost.png"></td></tr></table> 14<hr> 15<div class="spirit-nav"> 16<a accesskey="p" href="boost_python_call_hpp.html"><img src="../../images/prev.png" alt="Prev"></a><a accesskey="u" href="../function_invocation_and_creation.html"><img src="../../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../images/home.png" alt="Home"></a><a accesskey="n" href="boost_python_data_members_hpp.html"><img src="../../images/next.png" alt="Next"></a> 17</div> 18<div class="section"> 19<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 20<a name="function_invocation_and_creation.boost_python_call_method_hpp"></a><a class="link" href="boost_python_call_method_hpp.html" title="boost/python/call_method.hpp">boost/python/call_method.hpp</a> 21</h2></div></div></div> 22<div class="toc"><dl class="toc"> 23<dt><span class="section"><a href="boost_python_call_method_hpp.html#function_invocation_and_creation.boost_python_call_method_hpp.introduction">Introduction</a></span></dt> 24<dt><span class="section"><a href="boost_python_call_method_hpp.html#function_invocation_and_creation.boost_python_call_method_hpp.function_call_method">Function 25 <code class="computeroutput"><span class="identifier">call_method</span></code></a></span></dt> 26<dt><span class="section"><a href="boost_python_call_method_hpp.html#function_invocation_and_creation.boost_python_call_method_hpp.example">Example</a></span></dt> 27</dl></div> 28<div class="section"> 29<div class="titlepage"><div><div><h3 class="title"> 30<a name="function_invocation_and_creation.boost_python_call_method_hpp.introduction"></a><a class="link" href="boost_python_call_method_hpp.html#function_invocation_and_creation.boost_python_call_method_hpp.introduction" title="Introduction">Introduction</a> 31</h3></div></div></div> 32<p> 33 <boost/python/call_method.hpp> defines the call_method family of 34 overloaded function templates, used to invoke callable attributes of Python 35 objects from C++. 36 </p> 37</div> 38<div class="section"> 39<div class="titlepage"><div><div><h3 class="title"> 40<a name="function_invocation_and_creation.boost_python_call_method_hpp.function_call_method"></a><a class="link" href="boost_python_call_method_hpp.html#function_invocation_and_creation.boost_python_call_method_hpp.function_call_method" title="Function call_method">Function 41 <code class="computeroutput"><span class="identifier">call_method</span></code></a> 42</h3></div></div></div> 43<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">A1</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">A2</span><span class="special">,</span> <span class="special">...</span> <span class="keyword">class</span> <span class="identifier">An</span><span class="special">></span> 44<span class="identifier">R</span> <span class="identifier">call_method</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">self</span><span class="special">,</span> <span class="keyword">char</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">method</span><span class="special">,</span> <span class="identifier">A1</span> <span class="keyword">const</span><span class="special">&,</span> <span class="identifier">A2</span> <span class="keyword">const</span><span class="special">&,</span> <span class="special">...</span> <span class="identifier">An</span> <span class="keyword">const</span><span class="special">&)</span> 45</pre> 46<div class="variablelist"> 47<p class="title"><b></b></p> 48<dl class="variablelist"> 49<dt><span class="term">Requires</span></dt> 50<dd><p> 51 <code class="computeroutput"><span class="identifier">R</span></code> is a pointer type, 52 reference type, or a complete type with an accessible copy constructor 53 </p></dd> 54<dt><span class="term">Effects</span></dt> 55<dd><p> 56 Invokes <code class="computeroutput"><span class="identifier">self</span><span class="special">.</span><span class="identifier">method</span><span class="special">(</span><span class="identifier">a1</span><span class="special">,</span> <span class="identifier">a2</span><span class="special">,</span> <span class="special">...</span><span class="identifier">an</span><span class="special">)</span></code> in Python, where <code class="computeroutput"><span class="identifier">a1</span><span class="special">...</span><span class="identifier">an</span></code> 57 are the arguments to <code class="computeroutput"><span class="identifier">call_method</span><span class="special">()</span></code>, converted to Python objects. For 58 a complete semantic description, see this page. 59 </p></dd> 60<dt><span class="term">Returns</span></dt> 61<dd><p> 62 The result of the Python call, converted to the C++ type <code class="computeroutput"><span class="identifier">R</span></code>. 63 </p></dd> 64<dt><span class="term">Rationale</span></dt> 65<dd><p> 66 <code class="computeroutput"><span class="identifier">call_method</span></code> is critical 67 to implementing C++ virtual functions which are overridable in Python, 68 as shown by the example below. 69 </p></dd> 70</dl> 71</div> 72</div> 73<div class="section"> 74<div class="titlepage"><div><div><h3 class="title"> 75<a name="function_invocation_and_creation.boost_python_call_method_hpp.example"></a><a class="link" href="boost_python_call_method_hpp.html#function_invocation_and_creation.boost_python_call_method_hpp.example" title="Example">Example</a> 76</h3></div></div></div> 77<p> 78 The following C++ illustrates the use of <code class="computeroutput"><span class="identifier">call_method</span></code> 79 in wrapping a class with a virtual function that can be overridden in Python: 80 C++ Module Definition 81 </p> 82<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">python</span><span class="special">/</span><span class="identifier">module</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 83<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">python</span><span class="special">/</span><span class="keyword">class</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 84<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 85<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cstring</span><span class="special">></span> 86 87<span class="comment">// class to be wrapped</span> 88<span class="keyword">class</span> <span class="identifier">Base</span> 89<span class="special">{</span> 90 <span class="keyword">public</span><span class="special">:</span> 91 <span class="keyword">virtual</span> <span class="keyword">char</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">class_name</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="string">"Base"</span><span class="special">;</span> <span class="special">}</span> 92 <span class="keyword">virtual</span> <span class="special">~</span><span class="identifier">Base</span><span class="special">();</span> 93<span class="special">};</span> 94 95<span class="keyword">bool</span> <span class="identifier">is_base</span><span class="special">(</span><span class="identifier">Base</span><span class="special">*</span> <span class="identifier">b</span><span class="special">)</span> 96<span class="special">{</span> 97 <span class="keyword">return</span> <span class="special">!</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">strcmp</span><span class="special">(</span><span class="identifier">b</span><span class="special">-></span><span class="identifier">class_name</span><span class="special">(),</span> <span class="string">"Base"</span><span class="special">);</span> 98<span class="special">}</span> 99 100<span class="comment">// Wrapper code begins here</span> 101<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">python</span><span class="special">;</span> 102 103<span class="comment">// Callback class</span> 104<span class="keyword">class</span> <span class="identifier">Base_callback</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">Base</span> 105<span class="special">{</span> 106 <span class="keyword">public</span><span class="special">:</span> 107 <span class="identifier">Base_callback</span><span class="special">(</span><span class="identifier">PyObject</span><span class="special">*</span> <span class="identifier">self</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">m_self</span><span class="special">(</span><span class="identifier">self</span><span class="special">)</span> <span class="special">{}</span> 108 109 <span class="keyword">char</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">class_name</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">call_method</span><span class="special"><</span><span class="keyword">char</span> <span class="keyword">const</span><span class="special">*>(</span><span class="identifier">m_self</span><span class="special">,</span> <span class="string">"class_name"</span><span class="special">);</span> <span class="special">}</span> 110 <span class="keyword">char</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">Base_name</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">Base</span><span class="special">::</span><span class="identifier">class_name</span><span class="special">();</span> <span class="special">}</span> 111 <span class="keyword">private</span><span class="special">:</span> 112 <span class="identifier">PyObject</span><span class="special">*</span> <span class="keyword">const</span> <span class="identifier">m_self</span><span class="special">;</span> 113<span class="special">};</span> 114 115<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">python</span><span class="special">;</span> 116<span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">my_module</span><span class="special">)</span> 117<span class="special">{</span> 118 <span class="identifier">def</span><span class="special">(</span><span class="string">"is_base"</span><span class="special">,</span> <span class="identifier">is_base</span><span class="special">);</span> 119 120 <span class="identifier">class_</span><span class="special"><</span><span class="identifier">Base</span><span class="special">,</span><span class="identifier">Base_callback</span><span class="special">,</span> <span class="identifier">noncopyable</span><span class="special">>(</span><span class="string">"Base"</span><span class="special">)</span> 121 <span class="special">.</span><span class="identifier">def</span><span class="special">(</span><span class="string">"class_name"</span><span class="special">,</span> <span class="special">&</span><span class="identifier">Base_callback</span><span class="special">::</span><span class="identifier">Base_name</span><span class="special">)</span> 122 <span class="special">;</span> 123 124<span class="special">}</span> 125</pre> 126<p> 127 Python code: 128 </p> 129<pre class="programlisting"><span class="special">>>></span> <span class="identifier">from</span> <span class="identifier">my_module</span> <span class="identifier">import</span> <span class="special">*</span> 130<span class="special">>>></span> <span class="keyword">class</span> <span class="identifier">Derived</span><span class="special">(</span><span class="identifier">Base</span><span class="special">):</span> 131<span class="special">...</span> <span class="identifier">def</span> <span class="identifier">__init__</span><span class="special">(</span><span class="identifier">self</span><span class="special">):</span> 132<span class="special">...</span> <span class="identifier">Base</span><span class="special">.</span><span class="identifier">__init__</span><span class="special">(</span><span class="identifier">self</span><span class="special">)</span> 133<span class="special">...</span> <span class="identifier">def</span> <span class="identifier">class_name</span><span class="special">(</span><span class="identifier">self</span><span class="special">):</span> 134<span class="special">...</span> <span class="keyword">return</span> <span class="identifier">self</span><span class="special">.</span><span class="identifier">__class__</span><span class="special">.</span><span class="identifier">__name__</span> 135<span class="special">...</span> 136<span class="special">>>></span> <span class="identifier">is_base</span><span class="special">(</span><span class="identifier">Base</span><span class="special">())</span> <span class="special">#</span> <span class="identifier">calls</span> <span class="identifier">the</span> <span class="identifier">class_name</span><span class="special">()</span> <span class="identifier">method</span> <span class="identifier">from</span> <span class="identifier">C</span><span class="special">++</span> 137<span class="number">1</span> 138<span class="special">>>></span> <span class="identifier">is_base</span><span class="special">(</span><span class="identifier">Derived</span><span class="special">())</span> 139<span class="number">0</span> 140</pre> 141</div> 142</div> 143<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 144<td align="left"></td> 145<td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2015 David Abrahams, Stefan Seefeld<p> 146 Distributed under the Boost Software License, Version 1.0. (See accompanying 147 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a> 148 </p> 149</div></td> 150</tr></table> 151<hr> 152<div class="spirit-nav"> 153<a accesskey="p" href="boost_python_call_hpp.html"><img src="../../images/prev.png" alt="Prev"></a><a accesskey="u" href="../function_invocation_and_creation.html"><img src="../../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../images/home.png" alt="Home"></a><a accesskey="n" href="boost_python_data_members_hpp.html"><img src="../../images/next.png" alt="Next"></a> 154</div> 155</body> 156</html> 157
