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<!DOCTYPE html>

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<title>Genshi: Using XPath in Genshi</title>
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<div class="document" id="using-xpath-in-genshi">
    <div id="navigation">
      <span class="projinfo">Genshi 0.6</span>
      <a href="index.html">Documentation Index</a>
    </div>
<h1 class="title">Using XPath in Genshi</h1>
<p>Genshi provides basic <a class="reference external" href="http://www.w3.org/TR/xpath">XPath</a> support for matching and querying event streams.</p>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="auto-toc simple">
<li><a class="reference internal" href="#limitations" id="id1">1   Limitations</a></li>
<li><a class="reference internal" href="#querying-streams" id="id2">2   Querying Streams</a></li>
<li><a class="reference internal" href="#matching-in-templates" id="id3">3   Matching in Templates</a></li>
</ul>
</div>
<div class="section" id="limitations">
<h1>1   Limitations</h1>
<p>Due to the streaming nature of the processing model, Genshi uses only a subset
of the <a class="reference external" href="http://www.w3.org/TR/xpath">XPath 1.0</a> language.</p>
<p>In particular, only the following axes are supported:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">attribute</span></tt></li>
<li><tt class="docutils literal"><span class="pre">child</span></tt></li>
<li><tt class="docutils literal"><span class="pre">descendant</span></tt></li>
<li><tt class="docutils literal"><span class="pre">descendant-or-self</span></tt></li>
<li><tt class="docutils literal"><span class="pre">self</span></tt></li>
</ul>
<p>This means you can't use the <tt class="docutils literal"><span class="pre">parent</span></tt>, ancestor, or sibling axes in Genshi
(the <tt class="docutils literal"><span class="pre">namespace</span></tt> axis isn't supported either, but what you'd ever need that
for I don't know). Basically, any path expression that would require buffering
of the stream is not supported.</p>
<p>Predicates are of course supported, but path expressions <em>inside</em> predicates
are restricted to attribute lookups (again due to the lack of buffering).</p>
<p>Most of the XPath functions and operators are supported, however they
(currently) only work inside predicates. The following functions are <strong>not</strong>
supported:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">count()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">id()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">lang()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">last()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">position()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">string()</span></tt></li>
<li><tt class="docutils literal"><span class="pre">sum()</span></tt></li>
</ul>
<p>The mathematical operators (<tt class="docutils literal"><span class="pre">+</span></tt>, <tt class="docutils literal"><span class="pre">-</span></tt>, <tt class="docutils literal"><span class="pre">*</span></tt>, <tt class="docutils literal"><span class="pre">div</span></tt>, and <tt class="docutils literal"><span class="pre">mod</span></tt>) are not
yet supported, whereas sub-expressions and the various comparison and logical
operators should work as expected.</p>
<p>You can also use XPath variable references (<tt class="docutils literal"><span class="pre">$var</span></tt>) inside predicates.</p>
</div>
<div class="section" id="querying-streams">
<h1>2   Querying Streams</h1>
<p>The <tt class="docutils literal"><span class="pre">Stream</span></tt> class provides a <tt class="docutils literal"><span class="pre">select(path)</span></tt> function that can be used to
retrieve subsets of the stream:</p>
<div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">genshi.input</span> <span class="kn">import</span> <span class="n">XML</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">XML</span><span class="p">(</span><span class="s">'''&lt;doc&gt;</span>
<span class="gp">... </span><span class="s"> &lt;items count="4"&gt;</span>
<span class="gp">... </span><span class="s">      &lt;item status="new"&gt;</span>
<span class="gp">... </span><span class="s">        &lt;summary&gt;Foo&lt;/summary&gt;</span>
<span class="gp">... </span><span class="s">      &lt;/item&gt;</span>
<span class="gp">... </span><span class="s">      &lt;item status="closed"&gt;</span>
<span class="gp">... </span><span class="s">        &lt;summary&gt;Bar&lt;/summary&gt;</span>
<span class="gp">... </span><span class="s">      &lt;/item&gt;</span>
<span class="gp">... </span><span class="s">      &lt;item status="closed" resolution="invalid"&gt;</span>
<span class="gp">... </span><span class="s">        &lt;summary&gt;Baz&lt;/summary&gt;</span>
<span class="gp">... </span><span class="s">      &lt;/item&gt;</span>
<span class="gp">... </span><span class="s">      &lt;item status="closed" resolution="fixed"&gt;</span>
<span class="gp">... </span><span class="s">        &lt;summary&gt;Waz&lt;/summary&gt;</span>
<span class="gp">... </span><span class="s">      &lt;/item&gt;</span>
<span class="gp">... </span><span class="s">  &lt;/items&gt;</span>
<span class="gp">... </span><span class="s">&lt;/doc&gt;'''</span><span class="p">)</span>

<span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">doc</span><span class="o">.</span><span class="n">select</span><span class="p">(</span><span class="s">'items/item[@status="closed" and '</span>
<span class="gp">... </span>    <span class="s">'(@resolution="invalid" or not(@resolution))]/summary/text()'</span><span class="p">))</span>
<span class="go">BarBaz</span>
</pre></div>
</div>
<div class="section" id="matching-in-templates">
<h1>3   Matching in Templates</h1>
<p>See the directive <tt class="docutils literal"><span class="pre">py:match</span></tt> in the <a class="reference external" href="xml-templates.html">XML Template Language Specification</a>.</p>
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