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changes to no_init and deriving classes

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[SVN r15979]
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Joel de Guzman
2002-10-24 21:33:40 +00:00
parent da273519fd
commit 387e8aadc6
1 changed files with 12 additions and 4 deletions
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doc/tutorial/doc/class_virtual_functions.html
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@@ -113,14 +113,22 @@ In Python, let us try to instantiate our <tt>Base</tt> class:</p>
Why is it an error? <tt>Base</tt> is an abstract class. As such it is advisable
to define the Python wrapper with <tt>no_init</tt> as we have done above. Doing
so will disallow abstract base classes such as <tt>Base</tt> to be instantiated.</p>
<a name="deriving_a_python_class"></a><h2>Deriving a Python class</h2><p>
Now, at last, we can even derive from our base class <tt>Base</tt> in Python:</p>
<code><pre>
<a name="deriving_a_python_class"></a><h2>Deriving a Python class</h2>
<p> Now, at last, we can even derive from our base class <tt>Base</tt> in Python.
Before we can do that, we have to set up our <tt>class_</tt> wrapper as:</p>
<pre> <code><span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Base</span><span class=special>, </span><span class=identifier>BaseWrap</span><span class=special>, </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>noncopyable</span><span class=special>&gt;(</span><span class=string>&quot;Base&quot;</span><span class=special>)
</span><span class=special>;</span></code></pre>
<p>Otherwise, we have to suppress the Base class' <tt>no_init</tt> by adding an
<tt>__init__()</tt> method to all our derived classes. <tt>no_init </tt>actually
adds an <tt>__init__</tt> method that raises a Python RuntimeError exception.</p>
<code>
<pre>
<span class=special>&gt;&gt;&gt; </span><span class=keyword>class </span><span class=identifier>Derived</span><span class=special>(</span><span class=identifier>Base</span><span class=special>):
</span><span class=special>... </span><span class=identifier>def </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>self</span><span class=special>):
</span><span class=special>... </span><span class=keyword>return </span><span class=number>42
</span><span class=special>...
</span></pre></code>
</span></pre>
</code>
<p>
Cool eh? A Python class deriving from a C++ class!</p>
<p>