<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>General Techniques</title> <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../index.html" title="Chapter 1. python 2.0"> <link rel="up" href="../index.html" title="Chapter 1. python 2.0"> <link rel="prev" href="exception.html" title="Exception Translation"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="exception.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a> </div> <div class="section"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="python.techniques"></a> General Techniques</h2></div></div></div> <div class="toc"><dl> <dt><span class="section"><a href="techniques.html#python.creating_packages">Creating Packages</a></span></dt> <dt><span class="section"><a href="techniques.html#python.extending_wrapped_objects_in_python">Extending Wrapped Objects in Python</a></span></dt> <dt><span class="section"><a href="techniques.html#python.reducing_compiling_time">Reducing Compiling Time</a></span></dt> </dl></div> <p> Here are presented some useful techniques that you can use while wrapping code with Boost.Python. </p> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="python.creating_packages"></a>Creating Packages</h3></div></div></div> <p> A Python package is a collection of modules that provide to the user a certain functionality. If you're not familiar on how to create packages, a good introduction to them is provided in the <a href="http://www.python.org/doc/current/tut/node8.html" target="_top">Python Tutorial</a>. </p> <p> But we are wrapping C++ code, using Boost.Python. How can we provide a nice package interface to our users? To better explain some concepts, let's work with an example. </p> <p> We have a C++ library that works with sounds: reading and writing various formats, applying filters to the sound data, etc. It is named (conveniently) <code class="literal">sounds</code>. Our library already has a neat C++ namespace hierarchy, like so: </p> <pre class="programlisting"><span class="identifier">sounds</span><span class="special">::</span><span class="identifier">core</span> <span class="identifier">sounds</span><span class="special">::</span><span class="identifier">io</span> <span class="identifier">sounds</span><span class="special">::</span><span class="identifier">filters</span> </pre> <p> We would like to present this same hierarchy to the Python user, allowing him to write code like this: </p> <pre class="programlisting"><span class="keyword">import</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span><span class="special">.</span><span class="identifier">echo</span><span class="special">(...)</span> <span class="comment"># echo is a C++ function </span></pre> <p> The first step is to write the wrapping code. We have to export each module separately with Boost.Python, like this: </p> <pre class="programlisting"><span class="special">/*</span> <span class="identifier">file</span> <span class="identifier">core</span><span class="special">.</span><span class="identifier">cpp</span> <span class="special">*/</span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">core</span><span class="special">)</span> <span class="special">{</span> <span class="special">/*</span> <span class="identifier">export</span> <span class="identifier">everything</span> <span class="keyword">in</span> <span class="identifier">the</span> <span class="identifier">sounds</span><span class="special">::</span><span class="identifier">core</span> <span class="identifier">namespace</span> <span class="special">*/</span> <span class="special">...</span> <span class="special">}</span> <span class="special">/*</span> <span class="identifier">file</span> <span class="identifier">io</span><span class="special">.</span><span class="identifier">cpp</span> <span class="special">*/</span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">io</span><span class="special">)</span> <span class="special">{</span> <span class="special">/*</span> <span class="identifier">export</span> <span class="identifier">everything</span> <span class="keyword">in</span> <span class="identifier">the</span> <span class="identifier">sounds</span><span class="special">::</span><span class="identifier">io</span> <span class="identifier">namespace</span> <span class="special">*/</span> <span class="special">...</span> <span class="special">}</span> <span class="special">/*</span> <span class="identifier">file</span> <span class="identifier">filters</span><span class="special">.</span><span class="identifier">cpp</span> <span class="special">*/</span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">filters</span><span class="special">)</span> <span class="special">{</span> <span class="special">/*</span> <span class="identifier">export</span> <span class="identifier">everything</span> <span class="keyword">in</span> <span class="identifier">the</span> <span class="identifier">sounds</span><span class="special">::</span><span class="identifier">filters</span> <span class="identifier">namespace</span> <span class="special">*/</span> <span class="special">...</span> <span class="special">}</span> </pre> <p> Compiling these files will generate the following Python extensions: <code class="literal">core.pyd</code>, <code class="literal">io.pyd</code> and <code class="literal">filters.pyd</code>. </p> <div class="note"><table border="0" summary="Note"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td> <th align="left">Note</th> </tr> <tr><td align="left" valign="top"><p> The extension <code class="literal">.pyd</code> is used for python extension modules, which are just shared libraries. Using the default for your system, like <code class="literal">.so</code> for Unix and <code class="literal">.dll</code> for Windows, works just as well. </p></td></tr> </table></div> <p> Now, we create this directory structure for our Python package: </p> <pre class="programlisting">sounds/ __init__.py core.pyd filters.pyd io.pyd </pre> <p> The file <code class="literal">__init__.py</code> is what tells Python that the directory <code class="literal">sounds/</code> is actually a Python package. It can be a empty file, but can also perform some magic, that will be shown later. </p> <p> Now our package is ready. All the user has to do is put <code class="literal">sounds</code> into his <a href="http://www.python.org/doc/current/tut/node8.html#SECTION008110000000000000000" target="_top">PYTHONPATH</a> and fire up the interpreter: </p> <p> </p> <pre class="programlisting"><span class="special">>>></span> <span class="keyword">import</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">io</span> <span class="special">>>></span> <span class="keyword">import</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span> <span class="special">>>></span> <span class="identifier">sound</span> <span class="special">=</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">io</span><span class="special">.</span><span class="identifier">open</span><span class="special">(</span><span class="string">'file.mp3'</span><span class="special">)</span> <span class="special">>>></span> <span class="identifier">new_sound</span> <span class="special">=</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span><span class="special">.</span><span class="identifier">echo</span><span class="special">(</span><span class="identifier">sound</span><span class="special">,</span> <span class="number">1.0</span><span class="special">)</span> </pre> <p> Nice heh? </p> <p> This is the simplest way to create hierarchies of packages, but it is not very flexible. What if we want to add a <span class="emphasis"><em>pure</em></span> Python function to the filters package, for instance, one that applies 3 filters in a sound object at once? Sure, you can do this in C++ and export it, but why not do so in Python? You don't have to recompile the extension modules, plus it will be easier to write it. </p> <p> If we want this flexibility, we will have to complicate our package hierarchy a little. First, we will have to change the name of the extension modules: </p> <p> </p> <pre class="programlisting"><span class="comment">/* file core.cpp */</span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">_core</span><span class="special">)</span> <span class="special">{</span> <span class="special">...</span> <span class="comment">/* export everything in the sounds::core namespace */</span> <span class="special">}</span> </pre> <p> Note that we added an underscore to the module name. The filename will have to be changed to <code class="literal">_core.pyd</code> as well, and we do the same to the other extension modules. Now, we change our package hierarchy like so: </p> <pre class="programlisting">sounds/ __init__.py core/ __init__.py <span class="underline">core.pyd filters/ \</span>_init__.py <span class="underline">filters.pyd io/ \</span>_init__.py _io.pyd </pre> <p> Note that we created a directory for each extension module, and added a __init__.py to each one. But if we leave it that way, the user will have to access the functions in the core module with this syntax: </p> <p> </p> <pre class="programlisting"><span class="special">>>></span> <span class="keyword">import</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">_core</span> <span class="special">>>></span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">core</span><span class="special">.</span><span class="identifier">_core</span><span class="special">.</span><span class="identifier">foo</span><span class="special">(...)</span> </pre> <p> which is not what we want. But here enters the <code class="literal">__init__.py</code> magic: everything that is brought to the <code class="literal">__init__.py</code> namespace can be accessed directly by the user. So, all we have to do is bring the entire namespace from <code class="literal">_core.pyd</code> to <code class="literal">core/__init__.py</code>. So add this line of code to <code class="literal">sounds<span class="emphasis"><em>core</em></span>__init__.py</code>: </p> <pre class="programlisting"><span class="keyword">from</span> <span class="identifier">_core</span> <span class="keyword">import</span> <span class="special">*</span> </pre> <p> We do the same for the other packages. Now the user accesses the functions and classes in the extension modules like before: </p> <pre class="programlisting"><span class="special">>>></span> <span class="keyword">import</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span> <span class="special">>>></span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span><span class="special">.</span><span class="identifier">echo</span><span class="special">(...)</span> </pre> <p> with the additional benefit that we can easily add pure Python functions to any module, in a way that the user can't tell the difference between a C++ function and a Python function. Let's add a <span class="emphasis"><em>pure</em></span> Python function, <code class="literal">echo_noise</code>, to the <code class="literal">filters</code> package. This function applies both the <code class="literal">echo</code> and <code class="literal">noise</code> filters in sequence in the given <code class="literal">sound</code> object. We create a file named <code class="literal">sounds/filters/echo_noise.py</code> and code our function: </p> <pre class="programlisting"><span class="keyword">import</span> <span class="identifier">_filters</span> <span class="keyword">def</span> <span class="identifier">echo_noise</span><span class="special">(</span><span class="identifier">sound</span><span class="special">):</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">_filters</span><span class="special">.</span><span class="identifier">echo</span><span class="special">(</span><span class="identifier">sound</span><span class="special">)</span> <span class="identifier">s</span> <span class="special">=</span> <span class="identifier">_filters</span><span class="special">.</span><span class="identifier">noise</span><span class="special">(</span><span class="identifier">sound</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">s</span> </pre> <p> Next, we add this line to <code class="literal">sounds<span class="emphasis"><em>filters</em></span>__init__.py</code>: </p> <pre class="programlisting"><span class="keyword">from</span> <span class="identifier">echo_noise</span> <span class="keyword">import</span> <span class="identifier">echo_noise</span> </pre> <p> And that's it. The user now accesses this function like any other function from the <code class="literal">filters</code> package: </p> <pre class="programlisting"><span class="special">>>></span> <span class="keyword">import</span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span> <span class="special">>>></span> <span class="identifier">sounds</span><span class="special">.</span><span class="identifier">filters</span><span class="special">.</span><span class="identifier">echo_noise</span><span class="special">(...)</span> </pre> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="python.extending_wrapped_objects_in_python"></a>Extending Wrapped Objects in Python</h3></div></div></div> <p> Thanks to Python's flexibility, you can easily add new methods to a class, even after it was already created: </p> <pre class="programlisting"><span class="special">>>></span> <span class="keyword">class</span> <span class="identifier">C</span><span class="special">(</span><span class="identifier">object</span><span class="special">):</span> <span class="keyword">pass</span> <span class="special">>>></span> <span class="special">>>></span> <span class="comment"># a regular function </span><span class="special">>>></span> <span class="keyword">def</span> <span class="identifier">C_str</span><span class="special">(</span><span class="identifier">self</span><span class="special">):</span> <span class="keyword">return</span> <span class="string">'A C instance!'</span> <span class="special">>>></span> <span class="special">>>></span> <span class="comment"># now we turn it in a member function </span><span class="special">>>></span> <span class="identifier">C</span><span class="special">.</span><span class="identifier">__str__</span> <span class="special">=</span> <span class="identifier">C_str</span> <span class="special">>>></span> <span class="special">>>></span> <span class="identifier">c</span> <span class="special">=</span> <span class="identifier">C</span><span class="special">()</span> <span class="special">>>></span> <span class="keyword">print</span> <span class="identifier">c</span> <span class="identifier">A</span> <span class="identifier">C</span> <span class="identifier">instance</span><span class="special">!</span> <span class="special">>>></span> <span class="identifier">C_str</span><span class="special">(</span><span class="identifier">c</span><span class="special">)</span> <span class="identifier">A</span> <span class="identifier">C</span> <span class="identifier">instance</span><span class="special">!</span> </pre> <p> Yes, Python rox. <span class="inlinemediaobject"><img src="../images/smiley.png" alt="smiley"></span> </p> <p> We can do the same with classes that were wrapped with Boost.Python. Suppose we have a class <code class="literal">point</code> in C++: </p> <p> </p> <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">point</span> <span class="special">{...};</span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">_geom</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">class_</span><span class="special"><</span><span class="identifier">point</span><span class="special">>(</span><span class="string">"point"</span><span class="special">)...;</span> <span class="special">}</span> </pre> <p> If we are using the technique from the previous session, <a class="link" href="techniques.html#python.creating_packages" title="Creating Packages">Creating Packages</a>, we can code directly into <code class="literal">geom/__init__.py</code>: </p> <p> </p> <pre class="programlisting"><span class="keyword">from</span> <span class="identifier">_geom</span> <span class="keyword">import</span> <span class="special">*</span> <span class="comment"># a regular function </span><span class="keyword">def</span> <span class="identifier">point_str</span><span class="special">(</span><span class="identifier">self</span><span class="special">):</span> <span class="keyword">return</span> <span class="identifier">str</span><span class="special">((</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">self</span><span class="special">.</span><span class="identifier">y</span><span class="special">))</span> <span class="comment"># now we turn it into a member function </span><span class="identifier">point</span><span class="special">.</span><span class="identifier">__str__</span> <span class="special">=</span> <span class="identifier">point_str</span> </pre> <p> <span class="bold"><strong>All</strong></span> point instances created from C++ will also have this member function! This technique has several advantages: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> Cut down compile times to zero for these additional functions </li> <li class="listitem"> Reduce the memory footprint to virtually zero </li> <li class="listitem"> Minimize the need to recompile </li> <li class="listitem"> Rapid prototyping (you can move the code to C++ if required without changing the interface) </li> </ul></div> <p> You can even add a little syntactic sugar with the use of metaclasses. Let's create a special metaclass that "injects" methods in other classes. </p> <pre class="programlisting"><span class="comment"># The one Boost.Python uses for all wrapped classes. </span><span class="comment"># You can use here any class exported by Boost instead of "point" </span><span class="identifier">BoostPythonMetaclass</span> <span class="special">=</span> <span class="identifier">point</span><span class="special">.</span><span class="identifier">__class__</span> <span class="keyword">class</span> <span class="identifier">injector</span><span class="special">(</span><span class="identifier">object</span><span class="special">):</span> <span class="keyword">class</span> <span class="identifier">__metaclass__</span><span class="special">(</span><span class="identifier">BoostPythonMetaclass</span><span class="special">):</span> <span class="keyword">def</span> <span class="identifier">__init__</span><span class="special">(</span><span class="identifier">self</span><span class="special">,</span> <span class="identifier">name</span><span class="special">,</span> <span class="identifier">bases</span><span class="special">,</span> <span class="identifier">dict</span><span class="special">):</span> <span class="keyword">for</span> <span class="identifier">b</span> <span class="keyword">in</span> <span class="identifier">bases</span><span class="special">:</span> <span class="keyword">if</span> <span class="identifier">type</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span> <span class="keyword">not</span> <span class="keyword">in</span> <span class="special">(</span><span class="identifier">self</span><span class="special">,</span> <span class="identifier">type</span><span class="special">):</span> <span class="keyword">for</span> <span class="identifier">k</span><span class="special">,</span><span class="identifier">v</span> <span class="keyword">in</span> <span class="identifier">dict</span><span class="special">.</span><span class="identifier">items</span><span class="special">():</span> <span class="identifier">setattr</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span><span class="identifier">k</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">type</span><span class="special">.</span><span class="identifier">__init__</span><span class="special">(</span><span class="identifier">self</span><span class="special">,</span> <span class="identifier">name</span><span class="special">,</span> <span class="identifier">bases</span><span class="special">,</span> <span class="identifier">dict</span><span class="special">)</span> <span class="comment"># inject some methods in the point foo </span><span class="keyword">class</span> <span class="identifier">more_point</span><span class="special">(</span><span class="identifier">injector</span><span class="special">,</span> <span class="identifier">point</span><span class="special">):</span> <span class="keyword">def</span> <span class="identifier">__repr__</span><span class="special">(</span><span class="identifier">self</span><span class="special">):</span> <span class="keyword">return</span> <span class="string">'Point(x=%s, y=%s)'</span> <span class="special">%</span> <span class="special">(</span><span class="identifier">self</span><span class="special">.</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">self</span><span class="special">.</span><span class="identifier">y</span><span class="special">)</span> <span class="keyword">def</span> <span class="identifier">foo</span><span class="special">(</span><span class="identifier">self</span><span class="special">):</span> <span class="keyword">print</span> <span class="string">'foo!'</span> </pre> <p> Now let's see how it got: </p> <pre class="programlisting"><span class="special">>>></span> <span class="keyword">print</span> <span class="identifier">point</span><span class="special">()</span> <span class="identifier">Point</span><span class="special">(</span><span class="identifier">x</span><span class="special">=</span><span class="number">10</span><span class="special">,</span> <span class="identifier">y</span><span class="special">=</span><span class="number">10</span><span class="special">)</span> <span class="special">>>></span> <span class="identifier">point</span><span class="special">().</span><span class="identifier">foo</span><span class="special">()</span> <span class="identifier">foo</span><span class="special">!</span> </pre> <p> Another useful idea is to replace constructors with factory functions: </p> <pre class="programlisting"><span class="identifier">_point</span> <span class="special">=</span> <span class="identifier">point</span> <span class="keyword">def</span> <span class="identifier">point</span><span class="special">(</span><span class="identifier">x</span><span class="special">=</span><span class="number">0</span><span class="special">,</span> <span class="identifier">y</span><span class="special">=</span><span class="number">0</span><span class="special">):</span> <span class="keyword">return</span> <span class="identifier">_point</span><span class="special">(</span><span class="identifier">x</span><span class="special">,</span> <span class="identifier">y</span><span class="special">)</span> </pre> <p> In this simple case there is not much gained, but for constructurs with many overloads and/or arguments this is often a great simplification, again with virtually zero memory footprint and zero compile-time overhead for the keyword support. </p> </div> <div class="section"> <div class="titlepage"><div><div><h3 class="title"> <a name="python.reducing_compiling_time"></a>Reducing Compiling Time</h3></div></div></div> <p> If you have ever exported a lot of classes, you know that it takes quite a good time to compile the Boost.Python wrappers. Plus the memory consumption can easily become too high. If this is causing you problems, you can split the class_ definitions in multiple files: </p> <p> </p> <pre class="programlisting"><span class="comment">/* file point.cpp */</span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">point</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> <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">hpp</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">export_point</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">class_</span><span class="special"><</span><span class="identifier">point</span><span class="special">>(</span><span class="string">"point"</span><span class="special">)...;</span> <span class="special">}</span> <span class="comment">/* file triangle.cpp */</span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">triangle</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> <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">hpp</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">export_triangle</span><span class="special">()</span> <span class="special">{</span> <span class="identifier">class_</span><span class="special"><</span><span class="identifier">triangle</span><span class="special">>(</span><span class="string">"triangle"</span><span class="special">)...;</span> <span class="special">}</span> </pre> <p> Now you create a file <code class="literal">main.cpp</code>, which contains the <code class="literal">BOOST_PYTHON_MODULE</code> macro, and call the various export functions inside it. </p> <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">export_point</span><span class="special">();</span> <span class="keyword">void</span> <span class="identifier">export_triangle</span><span class="special">();</span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">_geom</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">export_point</span><span class="special">();</span> <span class="identifier">export_triangle</span><span class="special">();</span> <span class="special">}</span> </pre> <p> Compiling and linking together all this files produces the same result as the usual approach: </p> <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">hpp</span><span class="special">></span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">point</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">triangle</span><span class="special">.</span><span class="identifier">h</span><span class="special">></span> <span class="identifier">BOOST_PYTHON_MODULE</span><span class="special">(</span><span class="identifier">_geom</span><span class="special">)</span> <span class="special">{</span> <span class="identifier">class_</span><span class="special"><</span><span class="identifier">point</span><span class="special">>(</span><span class="string">"point"</span><span class="special">)...;</span> <span class="identifier">class_</span><span class="special"><</span><span class="identifier">triangle</span><span class="special">>(</span><span class="string">"triangle"</span><span class="special">)...;</span> <span class="special">}</span> </pre> <p> but the memory is kept under control. </p> <p> This method is recommended too if you are developing the C++ library and exporting it to Python at the same time: changes in a class will only demand the compilation of a single cpp, instead of the entire wrapper code. </p> <div class="note"><table border="0" summary="Note"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td> <th align="left">Note</th> </tr> <tr><td align="left" valign="top"><p> If you're exporting your classes with <a href="../../../../../pyste/index.html" target="_top">Pyste</a>, take a look at the <code class="literal">--multiple</code> option, that generates the wrappers in various files as demonstrated here. </p></td></tr> </table></div> <div class="note"><table border="0" summary="Note"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td> <th align="left">Note</th> </tr> <tr><td align="left" valign="top"><p> This method is useful too if you are getting the error message <span class="emphasis"><em>"fatal error C1204:Compiler limit:internal structure overflow"</em></span> when compiling a large source file, as explained in the <a href="../../../../v2/faq.html#c1204" target="_top">FAQ</a>. </p></td></tr> </table></div> </div> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2002-2005 Joel de Guzman, David Abrahams<p> Distributed under the Boost Software License, Version 1.0. (See accompanying 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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="exception.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a> </div> </body> </html>