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<h1>Class-based event handlers<a class="headerlink" href="#class-based-event-handlers" title="Permalink to this headline">ΒΆ</a></h1>
<p>A light-weight event-handler framework based on event classes is
provided by the <code class="docutils literal notranslate"><span class="pre">zope.event.classhandler</span></code> module.</p>
<p>Handlers are registered for event classes:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">zope.event.classhandler</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">MyEvent</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span><span class="o">.</span><span class="vm">__name__</span>
</pre></div>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">def</span> <span class="nf">handler1</span><span class="p">(</span><span class="n">event</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"handler1 </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="n">event</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">event</span><span class="o">.</span><span class="n">classhandler</span><span class="o">.</span><span class="n">handler</span><span class="p">(</span><span class="n">MyEvent</span><span class="p">,</span> <span class="n">handler1</span><span class="p">)</span>
</pre></div>
</div>
<p>Descriptor syntax:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@zope</span><span class="o">.</span><span class="n">event</span><span class="o">.</span><span class="n">classhandler</span><span class="o">.</span><span class="n">handler</span><span class="p">(</span><span class="n">MyEvent</span><span class="p">)</span>
<span class="gp">... </span><span class="k">def</span> <span class="nf">handler2</span><span class="p">(</span><span class="n">event</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"handler2 </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="n">event</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">MySubEvent</span><span class="p">(</span><span class="n">MyEvent</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nd">@zope</span><span class="o">.</span><span class="n">event</span><span class="o">.</span><span class="n">classhandler</span><span class="o">.</span><span class="n">handler</span><span class="p">(</span><span class="n">MySubEvent</span><span class="p">)</span>
<span class="gp">... </span><span class="k">def</span> <span class="nf">handler3</span><span class="p">(</span><span class="n">event</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"handler3 </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="n">event</span><span class="p">)</span>
</pre></div>
</div>
<p>Subscribers are called in class method-resolution order, so only
new-style event classes are supported, and then by order of registry.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">zope.event</span>
<span class="gp">>>> </span><span class="n">zope</span><span class="o">.</span><span class="n">event</span><span class="o">.</span><span class="n">notify</span><span class="p">(</span><span class="n">MySubEvent</span><span class="p">())</span>
<span class="go">handler3 MySubEvent</span>
<span class="go">handler1 MySubEvent</span>
<span class="go">handler2 MySubEvent</span>
</pre></div>
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