turned by <code class="computeroutput"><span class="identifier">ptr</span><span class="special">()</span></code>, used to indicate reference semantics
          for pointers passed to Python callbacks.
        </p>
<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">python</span>
<span class="special">{</span>
    <span class="keyword">template</span><span class