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<title>Exposing Classes</title>
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Exposing Classes</b></font>
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<p>
Now let's expose a C++ class to Python.</p>
<p>
Consider a C++ class/struct that we want to expose to Python:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>World
</span><span class=special>{
</span><span class=keyword>void </span><span class=identifier>set</span><span class=special>(</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>) </span><span class=special>{ </span><span class=keyword>this</span><span class=special>-></span><span class=identifier>msg </span><span class=special>= </span><span class=identifier>msg</span><span class=special>; </span><span class=special>}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>greet</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>msg</span><span class=special>; </span><span class=special>}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<p>
We can expose this to Python by writing a corresponding Boost.Python
C++ Wrapper:</p>
<code><pre>
<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>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><span class=identifier>BOOST_PYTHON_MODULE</span><span class=special>(</span><span class=identifier>hello</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>class_</span><span class=special><</span><span class=identifier>World</span><span class=special>>(</span><span class=string>"World"</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>"greet"</span><span class=special>, </span><span class=special>&</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>greet</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>"set"</span><span class=special>, </span><span class=special>&</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>set</span><span class=special>)
</span><span class=special>;
</span><span class=special>}
</span></pre></code>
<p>
Here, we wrote a C++ class wrapper that exposes the member functions
<tt>greet</tt> and <tt>set</tt>. Now, after building our module as a shared library, we
may use our class <tt>World</tt> in Python. Here's a sample Python session:</p>
<code><pre>
<span class=special>>>> </span><span class=identifier>import </span><span class=identifier>hello
</span><span class=special>>>> </span><span class=identifier>planet </span><span class=special>= </span><span class=identifier>hello</span><span class=special>.</span><span class=identifier>World</span><span class=special>()
</span><span class=special>>>> </span><span class=identifier>planet</span><span class=special>.</span><span class=identifier>set</span><span class=special>(</span><span class=literal>'howdy'</span><span class=special>)
</span><span class=special>>>> </span><span class=identifier>planet</span><span class=special>.</span><span class=identifier>greet</span><span class=special>()
</span><span class=literal>'howdy'
</span></pre></code>
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<hr size="1"><p class="copyright">Copyright © 2002 David Abrahams<br>Copyright © 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
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