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    64   <div class="section" id="custom-tales-extensions">
       
    65 <span id="tales"></span><h1>Custom TALES extensions<a class="headerlink" href="#custom-tales-extensions" title="Permalink to this headline">ΒΆ</a></h1>
       
    66 <p>PyAMS defines a custom expression for TALES called <em>extension</em>.</p>
       
    67 <p>When this expression is encountered, the renderer is looking for an
       
    68 <code class="xref py py-class docutils literal"><span class="pre">ITALESExtension</span></code>
       
    69 multi-adapter for the current <em>context</em>, <em>request</em> and <em>view</em>, for the current
       
    70 <em>context</em> and <em>request</em>, or only for the current <em>context</em>, in this order.
       
    71 If an adapter is found, the renderer call it&#8217;s <code class="xref py py-func docutils literal"><span class="pre">render()</span></code> method with
       
    72 the expression parameters as input parameters.</p>
       
    73 <p>For example, the <em>metas</em> extension is an <em>ITALESExtension</em> adapter defined into
       
    74 <code class="xref py py-mod docutils literal"><span class="pre">pyams_skin.metas</span></code> module which can be used to include all required headers in
       
    75 a page template. Extension is used like this in the page layout template:</p>
       
    76 <div class="highlight-html"><div class="highlight"><pre><span class="nt">&lt;tal:var</span> <span class="na">replace=</span><span class="s">&quot;structure extension:metas&quot;</span> <span class="nt">/&gt;</span>
       
    77 </pre></div>
       
    78 </div>
       
    79 <p>This extension is defined like this:</p>
       
    80 <div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">pyams_skin.interfaces.metas</span> <span class="kn">import</span> <span class="n">IHTMLContentMetas</span>
       
    81 <span class="kn">from</span> <span class="nn">pyams_utils.interfaces.tales</span> <span class="kn">import</span> <span class="n">ITALESExtension</span>
       
    82 <span class="kn">from</span> <span class="nn">pyramid.interfaces</span> <span class="kn">import</span> <span class="n">IRequest</span>
       
    83 
       
    84 <span class="kn">from</span> <span class="nn">pyams_utils.adapter</span> <span class="kn">import</span> <span class="n">adapter_config</span><span class="p">,</span> <span class="n">ContextRequestViewAdapter</span>
       
    85 
       
    86 <span class="nd">@adapter_config</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s">&#39;metas&#39;</span><span class="p">,</span> <span class="n">context</span><span class="o">=</span><span class="p">(</span><span class="n">Interface</span><span class="p">,</span> <span class="n">IRequest</span><span class="p">,</span> <span class="n">Interface</span><span class="p">),</span> <span class="n">provides</span><span class="o">=</span><span class="n">ITALESExtension</span><span class="p">)</span>
       
    87 <span class="k">class</span> <span class="nc">MetasTalesExtension</span><span class="p">(</span><span class="n">ContextRequestViewAdapter</span><span class="p">):</span>
       
    88     <span class="sd">&#39;&#39;&#39;extension:metas TALES extension&#39;&#39;&#39;</span>
       
    89 
       
    90     <span class="k">def</span> <span class="nf">render</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
       
    91         <span class="k">if</span> <span class="n">context</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
       
    92             <span class="n">context</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">context</span>
       
    93         <span class="n">result</span> <span class="o">=</span> <span class="p">[]</span>
       
    94         <span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">adapter</span> <span class="ow">in</span> <span class="nb">sorted</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="o">.</span><span class="n">registry</span><span class="o">.</span><span class="n">getAdapters</span><span class="p">((</span><span class="n">context</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">view</span><span class="p">),</span>
       
    95                                                                       <span class="n">IHTMLContentMetas</span><span class="p">),</span>
       
    96                                     <span class="n">key</span><span class="o">=</span><span class="k">lambda</span> <span class="n">x</span><span class="p">:</span> <span class="nb">getattr</span><span class="p">(</span><span class="n">x</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="s">&#39;order&#39;</span><span class="p">,</span> <span class="mi">9999</span><span class="p">)):</span>
       
    97             <span class="n">result</span><span class="o">.</span><span class="n">extend</span><span class="p">([</span><span class="n">meta</span><span class="o">.</span><span class="n">render</span><span class="p">()</span> <span class="k">for</span> <span class="n">meta</span> <span class="ow">in</span> <span class="n">adapter</span><span class="o">.</span><span class="n">get_metas</span><span class="p">()])</span>
       
    98         <span class="k">return</span> <span class="s">&#39;</span><span class="se">\n\t</span><span class="s">&#39;</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
       
    99 </pre></div>
       
   100 </div>
       
   101 <p>Some TALES extensions can require or accept arguments. For example, the <em>absolute_url</em> extension can accept
       
   102 a context and a view name:</p>
       
   103 <div class="highlight-html"><div class="highlight"><pre><span class="nt">&lt;tal:var</span> <span class="na">define=</span><span class="s">&quot;logo config.logo&quot;</span><span class="nt">&gt;</span>
       
   104     <span class="nt">&lt;img</span> <span class="na">tal:attributes=</span><span class="s">&quot;src extension:absolute_url(logo, &#39;++thumb++200x36.png&#39;);&quot;</span> <span class="nt">/&gt;</span>
       
   105 <span class="nt">&lt;/tal:var&gt;</span>
       
   106 </pre></div>
       
   107 </div>
       
   108 <p>The extension is defined like this:</p>
       
   109 <div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">persistent.interfaces</span> <span class="kn">import</span> <span class="n">IPersistent</span>
       
   110 <span class="kn">from</span> <span class="nn">pyams_utils.interfaces.tales</span> <span class="kn">import</span> <span class="n">ITALESExtension</span>
       
   111 
       
   112 <span class="kn">from</span> <span class="nn">pyams_utils.adapter</span> <span class="kn">import</span> <span class="n">adapter_config</span><span class="p">,</span> <span class="n">ContextRequestViewAdapter</span>
       
   113 <span class="kn">from</span> <span class="nn">pyramid.url</span> <span class="kn">import</span> <span class="n">resource_url</span>
       
   114 <span class="kn">from</span> <span class="nn">zope.interface</span> <span class="kn">import</span> <span class="n">Interface</span>
       
   115 
       
   116 <span class="nd">@adapter_config</span><span class="p">(</span><span class="n">name</span><span class="o">=</span><span class="s">&#39;absolute_url&#39;</span><span class="p">,</span> <span class="n">context</span><span class="o">=</span><span class="p">(</span><span class="n">IPersistent</span><span class="p">,</span> <span class="n">Interface</span><span class="p">,</span> <span class="n">Interface</span><span class="p">),</span> <span class="n">provides</span><span class="o">=</span><span class="n">ITALESExtension</span><span class="p">)</span>
       
   117 <span class="k">class</span> <span class="nc">AbsoluteUrlTalesExtension</span><span class="p">(</span><span class="n">ContextRequestViewAdapter</span><span class="p">):</span>
       
   118     <span class="sd">&#39;&#39;&#39;extension:absolute_url(context, view_name) TALES extension&#39;&#39;&#39;</span>
       
   119 
       
   120     <span class="k">def</span> <span class="nf">render</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="o">=</span><span class="bp">None</span><span class="p">,</span> <span class="n">view_name</span><span class="o">=</span><span class="bp">None</span><span class="p">):</span>
       
   121         <span class="k">if</span> <span class="n">context</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
       
   122             <span class="n">context</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">context</span>
       
   123         <span class="k">return</span> <span class="n">resource_url</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">request</span><span class="p">,</span> <span class="n">view_name</span><span class="p">)</span>
       
   124 </pre></div>
       
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