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<p>lxml supports a number of interesting languages for tree traversal and element
selection. The most important is obviously <a class="reference external" href="xpathxslt.html#xpath">XPath</a>, but there is also
<a class="reference external" href="objectify.html#objectpath">ObjectPath</a> in the <a class="reference external" href="objectify.html">lxml.objectify</a> module. The newest child of this family
is <a class="reference external" href="http://www.w3.org/TR/CSS21/selector.html">CSS selection</a>, which is made available in form of the <tt class="docutils literal">lxml.cssselect</tt>
module.</p>
<p>Although it started its life in lxml, <a class="reference external" href="http://packages.python.org/cssselect/">cssselect</a> is now an independent project.
It translates CSS selectors to XPath 1.0 expressions that can be used with
lxml's XPath engine. <tt class="docutils literal">lxml.cssselect</tt> adds a few convenience shortcuts into
that package.</p>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#the-cssselector-class" id="id1">The CSSSelector class</a></li>
<li><a class="reference internal" href="#the-cssselect-method" id="id2">The cssselect method</a></li>
<li><a class="reference internal" href="#supported-selectors" id="id3">Supported Selectors</a></li>
<li><a class="reference internal" href="#namespaces" id="id4">Namespaces</a></li>
</ul>
</div>
<div class="section" id="the-cssselector-class">
<h1>The CSSSelector class</h1>
<p>The most important class in the <tt class="docutils literal">lxml.cssselect</tt> module is <tt class="docutils literal">CSSSelector</tt>. It
provides the same interface as the <a class="reference external" href="xpathxslt.html#xpath">XPath</a> class, but accepts a CSS selector
expression as input:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">lxml.cssselect</span> <span class="kn">import</span> <span class="n">CSSSelector</span>
<span class="gp">>>> </span><span class="n">sel</span> <span class="o">=</span> <span class="n">CSSSelector</span><span class="p">(</span><span class="s">'div.content'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">sel</span> <span class="c">#doctest: +ELLIPSIS</span>
<span class="go"><CSSSelector ... for 'div.content'></span>
<span class="gp">>>> </span><span class="n">sel</span><span class="o">.</span><span class="n">css</span>
<span class="go">'div.content'</span>
</pre></div>
<p>The selector actually compiles to XPath, and you can see the
expression by inspecting the object:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">sel</span><span class="o">.</span><span class="n">path</span>
<span class="go">"descendant-or-self::div[@class and contains(concat(' ', normalize-space(@class), ' '), ' content ')]"</span>
</pre></div>
<p>To use the selector, simply call it with a document or element
object:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">lxml.etree</span> <span class="kn">import</span> <span class="n">fromstring</span>
<span class="gp">>>> </span><span class="n">h</span> <span class="o">=</span> <span class="n">fromstring</span><span class="p">(</span><span class="s">'''<div id="outer"></span>
<span class="gp">... </span><span class="s"> <div id="inner" class="content body"></span>
<span class="gp">... </span><span class="s"> text</span>
<span class="gp">... </span><span class="s"> </div></div>'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="p">[</span><span class="n">e</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s">'id'</span><span class="p">)</span> <span class="k">for</span> <span class="n">e</span> <span class="ow">in</span> <span class="n">sel</span><span class="p">(</span><span class="n">h</span><span class="p">)]</span>
<span class="go">['inner']</span>
</pre></div>
<p>Using <tt class="docutils literal">CSSSelector</tt> is equivalent to translating with <tt class="docutils literal">cssselect</tt>
and using the <tt class="docutils literal">XPath</tt> class:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">cssselect</span> <span class="kn">import</span> <span class="n">GenericTranslator</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">lxml.etree</span> <span class="kn">import</span> <span class="n">XPath</span>
<span class="gp">>>> </span><span class="n">sel</span> <span class="o">=</span> <span class="n">XPath</span><span class="p">(</span><span class="n">GenericTranslator</span><span class="p">()</span><span class="o">.</span><span class="n">css_to_xpath</span><span class="p">(</span><span class="s">'div.content'</span><span class="p">))</span>
</pre></div>
<p><tt class="docutils literal">CSSSelector</tt> takes a <tt class="docutils literal">translator</tt> parameter to let you choose which
translator to use. It can be <tt class="docutils literal">'xml'</tt> (the default), <tt class="docutils literal">'xhtml'</tt>, <tt class="docutils literal">'html'</tt>
or a <a class="reference external" href="http://packages.python.org/cssselect/#cssselect.GenericTranslator">Translator object</a>.</p>
</div>
<div class="section" id="the-cssselect-method">
<h1>The cssselect method</h1>
<p>lxml <tt class="docutils literal">Element</tt> objects have a <tt class="docutils literal">cssselect</tt> convenience method.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">h</span><span class="o">.</span><span class="n">cssselect</span><span class="p">(</span><span class="s">'div.content'</span><span class="p">)</span> <span class="o">==</span> <span class="n">sel</span><span class="p">(</span><span class="n">h</span><span class="p">)</span>
<span class="go">True</span>
</pre></div>
<p>Note however that pre-compiling the expression with the <tt class="docutils literal">CSSSelector</tt> or
<tt class="docutils literal">XPath</tt> class can provide a substantial speedup.</p>
<p>The method also accepts a <tt class="docutils literal">translator</tt> parameter. On <tt class="docutils literal">HtmlElement</tt>
objects, the default is changed to <tt class="docutils literal">'html'</tt>.</p>
</div>
<div class="section" id="supported-selectors">
<h1>Supported Selectors</h1>
<p>Most <a class="reference external" href="http://www.w3.org/TR/2011/REC-css3-selectors-20110929/">Level 3</a> selectors are supported. The details are in the
<a class="reference external" href="http://packages.python.org/cssselect/#supported-selectors">cssselect documentation</a>.</p>
</div>
<div class="section" id="namespaces">
<h1>Namespaces</h1>
<p>In CSS you can use <tt class="docutils literal"><span class="pre">namespace-prefix|element</span></tt>, similar to
<tt class="docutils literal"><span class="pre">namespace-prefix:element</span></tt> in an XPath expression. In fact, it maps
one-to-one, and the same rules are used to map namespace prefixes to
namespace URIs: the <tt class="docutils literal">CSSSelector</tt> class accepts a dictionary as its
<tt class="docutils literal">namespaces</tt> argument.</p>
</div>
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