doc/html/cssselect.html

   1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
   2 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
   3 <head>
   4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
   5 <meta name="generator" content="Docutils 0.8.1: http://docutils.sourceforge.net/" />
   6 <title>lxml.cssselect</title>
   7 <link rel="stylesheet" href="style.css" type="text/css" />
   8 </head>
   9 <body>
  10 <div class="document" id="lxml-cssselect">
  11 <div class="sidemenu"><ul id="lxml-section"><li><span class="section title">lxml</span><ul class="menu foreign" id="index-menu"><li class="menu title"><a href="index.html">lxml</a><ul class="submenu"><li class="menu item"><a href="index.html#introduction">Introduction</a></li><li class="menu item"><a href="index.html#support-the-project">Support the project</a></li><li class="menu item"><a href="index.html#documentation">Documentation</a></li><li class="menu item"><a href="index.html#download">Download</a></li><li class="menu item"><a href="index.html#mailing-list">Mailing list</a></li><li class="menu item"><a href="index.html#bug-tracker">Bug tracker</a></li><li class="menu item"><a href="index.html#license">License</a></li><li class="menu item"><a href="index.html#old-versions">Old Versions</a></li><li class="menu item"><a href="index.html#legal-notice-for-donations">Legal Notice for Donations</a></li></ul></li></ul><ul class="menu foreign" id="intro-menu"><li class="menu title"><a href="intro.html">Why lxml?</a><ul class="submenu"><li class="menu item"><a href="intro.html#motto">Motto</a></li><li class="menu item"><a href="intro.html#aims">Aims</a></li></ul></li></ul><ul class="menu foreign" id="installation-menu"><li class="menu title"><a href="installation.html">Installing lxml</a><ul class="submenu"><li class="menu item"><a href="installation.html#requirements">Requirements</a></li><li class="menu item"><a href="installation.html#installation">Installation</a></li><li class="menu item"><a href="installation.html#building-lxml-from-sources">Building lxml from sources</a></li><li class="menu item"><a href="installation.html#using-lxml-with-python-libxml2">Using lxml with python-libxml2</a></li><li class="menu item"><a href="installation.html#ms-windows">MS Windows</a></li><li class="menu item"><a href="installation.html#macos-x">MacOS-X</a></li></ul></li></ul><ul class="menu foreign" id="performance-menu"><li class="menu title"><a href="performance.html">Benchmarks and Speed</a><ul class="submenu"><li class="menu item"><a href="performance.html#general-notes">General notes</a></li><li class="menu item"><a href="performance.html#how-to-read-the-timings">How to read the timings</a></li><li class="menu item"><a href="performance.html#parsing-and-serialising">Parsing and Serialising</a></li><li class="menu item"><a href="performance.html#the-elementtree-api">The ElementTree API</a></li><li class="menu item"><a href="performance.html#xpath">XPath</a></li><li class="menu item"><a href="performance.html#a-longer-example">A longer example</a></li><li class="menu item"><a href="performance.html#lxml-objectify">lxml.objectify</a></li></ul></li></ul><ul class="menu foreign" id="compatibility-menu"><li class="menu title"><a href="compatibility.html">ElementTree compatibility of lxml.etree</a></li></ul><ul class="menu foreign" id="FAQ-menu"><li class="menu title"><a href="FAQ.html">lxml FAQ - Frequently Asked Questions</a><ul class="submenu"><li class="menu item"><a href="FAQ.html#general-questions">General Questions</a></li><li class="menu item"><a href="FAQ.html#installation">Installation</a></li><li class="menu item"><a href="FAQ.html#contributing">Contributing</a></li><li class="menu item"><a href="FAQ.html#bugs">Bugs</a></li><li class="menu item"><a href="FAQ.html#id1">Threading</a></li><li class="menu item"><a href="FAQ.html#parsing-and-serialisation">Parsing and Serialisation</a></li><li class="menu item"><a href="FAQ.html#xpath-and-document-traversal">XPath and Document Traversal</a></li></ul></li></ul></li></ul><ul id="Developing with lxml-section"><li><span class="section title">Developing with lxml</span><ul class="menu foreign" id="tutorial-menu"><li class="menu title"><a href="tutorial.html">The lxml.etree Tutorial</a><ul class="submenu"><li class="menu item"><a href="tutorial.html#the-element-class">The Element class</a></li><li class="menu item"><a href="tutorial.html#the-elementtree-class">The ElementTree class</a></li><li class="menu item"><a href="tutorial.html#parsing-from-strings-and-files">Parsing from strings and files</a></li><li class="menu item"><a href="tutorial.html#namespaces">Namespaces</a></li><li class="menu item"><a href="tutorial.html#the-e-factory">The E-factory</a></li><li class="menu item"><a href="tutorial.html#elementpath">ElementPath</a></li></ul></li></ul><ul class="menu foreign" id="api index-menu"><li class="menu title"><a href="api/index.html">API reference</a></li></ul><ul class="menu foreign" id="api-menu"><li class="menu title"><a href="api.html">APIs specific to lxml.etree</a><ul class="submenu"><li class="menu item"><a href="api.html#lxml-etree">lxml.etree</a></li><li class="menu item"><a href="api.html#other-element-apis">Other Element APIs</a></li><li class="menu item"><a href="api.html#trees-and-documents">Trees and Documents</a></li><li class="menu item"><a href="api.html#iteration">Iteration</a></li><li class="menu item"><a href="api.html#error-handling-on-exceptions">Error handling on exceptions</a></li><li class="menu item"><a href="api.html#error-logging">Error logging</a></li><li class="menu item"><a href="api.html#serialisation">Serialisation</a></li><li class="menu item"><a href="api.html#cdata">CDATA</a></li><li class="menu item"><a href="api.html#xinclude-and-elementinclude">XInclude and ElementInclude</a></li><li class="menu item"><a href="api.html#write-c14n-on-elementtree">write_c14n on ElementTree</a></li></ul></li></ul><ul class="menu foreign" id="parsing-menu"><li class="menu title"><a href="parsing.html">Parsing XML and HTML with lxml</a><ul class="submenu"><li class="menu item"><a href="parsing.html#parsers">Parsers</a></li><li class="menu item"><a href="parsing.html#the-target-parser-interface">The target parser interface</a></li><li class="menu item"><a href="parsing.html#the-feed-parser-interface">The feed parser interface</a></li><li class="menu item"><a href="parsing.html#iterparse-and-iterwalk">iterparse and iterwalk</a></li><li class="menu item"><a href="parsing.html#python-unicode-strings">Python unicode strings</a></li></ul></li></ul><ul class="menu foreign" id="validation-menu"><li class="menu title"><a href="validation.html">Validation with lxml</a><ul class="submenu"><li class="menu item"><a href="validation.html#validation-at-parse-time">Validation at parse time</a></li><li class="menu item"><a href="validation.html#id1">DTD</a></li><li class="menu item"><a href="validation.html#relaxng">RelaxNG</a></li><li class="menu item"><a href="validation.html#xmlschema">XMLSchema</a></li><li class="menu item"><a href="validation.html#id2">Schematron</a></li><li class="menu item"><a href="validation.html#id3">(Pre-ISO-Schematron)</a></li></ul></li></ul><ul class="menu foreign" id="xpathxslt-menu"><li class="menu title"><a href="xpathxslt.html">XPath and XSLT with lxml</a><ul class="submenu"><li class="menu item"><a href="xpathxslt.html#xpath">XPath</a></li><li class="menu item"><a href="xpathxslt.html#xslt">XSLT</a></li></ul></li></ul><ul class="menu foreign" id="objectify-menu"><li class="menu title"><a href="objectify.html">lxml.objectify</a><ul class="submenu"><li class="menu item"><a href="objectify.html#the-lxml-objectify-api">The lxml.objectify API</a></li><li class="menu item"><a href="objectify.html#asserting-a-schema">Asserting a Schema</a></li><li class="menu item"><a href="objectify.html#objectpath">ObjectPath</a></li><li class="menu item"><a href="objectify.html#python-data-types">Python data types</a></li><li class="menu item"><a href="objectify.html#how-data-types-are-matched">How data types are matched</a></li><li class="menu item"><a href="objectify.html#what-is-different-from-lxml-etree">What is different from lxml.etree?</a></li></ul></li></ul><ul class="menu foreign" id="lxmlhtml-menu"><li class="menu title"><a href="lxmlhtml.html">lxml.html</a><ul class="submenu"><li class="menu item"><a href="lxmlhtml.html#parsing-html">Parsing HTML</a></li><li class="menu item"><a href="lxmlhtml.html#html-element-methods">HTML Element Methods</a></li><li class="menu item"><a href="lxmlhtml.html#running-html-doctests">Running HTML doctests</a></li><li class="menu item"><a href="lxmlhtml.html#creating-html-with-the-e-factory">Creating HTML with the E-factory</a></li><li class="menu item"><a href="lxmlhtml.html#working-with-links">Working with links</a></li><li class="menu item"><a href="lxmlhtml.html#forms">Forms</a></li><li class="menu item"><a href="lxmlhtml.html#cleaning-up-html">Cleaning up HTML</a></li><li class="menu item"><a href="lxmlhtml.html#html-diff">HTML Diff</a></li><li class="menu item"><a href="lxmlhtml.html#examples">Examples</a></li></ul></li></ul><ul class="menu current" id="cssselect-menu"><li class="menu title"><a href="cssselect.html">lxml.cssselect</a><ul class="submenu"><li class="menu item"><a href="cssselect.html#the-cssselector-class">The CSSSelector class</a></li><li class="menu item"><a href="cssselect.html#css-selectors">CSS Selectors</a></li><li class="menu item"><a href="cssselect.html#namespaces">Namespaces</a></li><li class="menu item"><a href="cssselect.html#limitations">Limitations</a></li></ul></li></ul><ul class="menu foreign" id="elementsoup-menu"><li class="menu title"><a href="elementsoup.html">BeautifulSoup Parser</a><ul class="submenu"><li class="menu item"><a href="elementsoup.html#parsing-with-the-soupparser">Parsing with the soupparser</a></li><li class="menu item"><a href="elementsoup.html#entity-handling">Entity handling</a></li><li class="menu item"><a href="elementsoup.html#using-soupparser-as-a-fallback">Using soupparser as a fallback</a></li><li class="menu item"><a href="elementsoup.html#using-only-the-encoding-detection">Using only the encoding detection</a></li></ul></li></ul><ul class="menu foreign" id="html5parser-menu"><li class="menu title"><a href="html5parser.html">html5lib Parser</a><ul class="submenu"><li class="menu item"><a href="html5parser.html#differences-to-regular-html-parsing">Differences to regular HTML parsing</a></li><li class="menu item"><a href="html5parser.html#function-reference">Function Reference</a></li></ul></li></ul></li></ul><ul id="Extending lxml-section"><li><span class="section title">Extending lxml</span><ul class="menu foreign" id="resolvers-menu"><li class="menu title"><a href="resolvers.html">Document loading and URL resolving</a><ul class="submenu"><li class="menu item"><a href="resolvers.html#xml-catalogs">XML Catalogs</a></li><li class="menu item"><a href="resolvers.html#uri-resolvers">URI Resolvers</a></li><li class="menu item"><a href="resolvers.html#document-loading-in-context">Document loading in context</a></li><li class="menu item"><a href="resolvers.html#i-o-access-control-in-xslt">I/O access control in XSLT</a></li></ul></li></ul><ul class="menu foreign" id="extensions-menu"><li class="menu title"><a href="extensions.html">Python extensions for XPath and XSLT</a><ul class="submenu"><li class="menu item"><a href="extensions.html#xpath-extension-functions">XPath Extension functions</a></li><li class="menu item"><a href="extensions.html#xslt-extension-elements">XSLT extension elements</a></li></ul></li></ul><ul class="menu foreign" id="element classes-menu"><li class="menu title"><a href="element_classes.html">Using custom Element classes in lxml</a><ul class="submenu"><li class="menu item"><a href="element_classes.html#background-on-element-proxies">Background on Element proxies</a></li><li class="menu item"><a href="element_classes.html#element-initialization">Element initialization</a></li><li class="menu item"><a href="element_classes.html#setting-up-a-class-lookup-scheme">Setting up a class lookup scheme</a></li><li class="menu item"><a href="element_classes.html#generating-xml-with-custom-classes">Generating XML with custom classes</a></li><li class="menu item"><a href="element_classes.html#id1">Implementing namespaces</a></li></ul></li></ul><ul class="menu foreign" id="sax-menu"><li class="menu title"><a href="sax.html">Sax support</a><ul class="submenu"><li class="menu item"><a href="sax.html#building-a-tree-from-sax-events">Building a tree from SAX events</a></li><li class="menu item"><a href="sax.html#producing-sax-events-from-an-elementtree-or-element">Producing SAX events from an ElementTree or Element</a></li><li class="menu item"><a href="sax.html#interfacing-with-pulldom-minidom">Interfacing with pulldom/minidom</a></li></ul></li></ul><ul class="menu foreign" id="capi-menu"><li class="menu title"><a href="capi.html">The public C-API of lxml.etree</a><ul class="submenu"><li class="menu item"><a href="capi.html#writing-external-modules-in-cython">Writing external modules in Cython</a></li><li class="menu item"><a href="capi.html#writing-external-modules-in-c">Writing external modules in C</a></li></ul></li></ul></li></ul><ul id="Developing lxml-section"><li><span class="section title">Developing lxml</span><ul class="menu foreign" id="build-menu"><li class="menu title"><a href="build.html">How to build lxml from source</a><ul class="submenu"><li class="menu item"><a href="build.html#cython">Cython</a></li><li class="menu item"><a href="build.html#github-git-and-hg">Github, git and hg</a></li><li class="menu item"><a href="build.html#id2">Setuptools</a></li><li class="menu item"><a href="build.html#running-the-tests-and-reporting-errors">Running the tests and reporting errors</a></li><li class="menu item"><a href="build.html#building-an-egg">Building an egg</a></li><li class="menu item"><a href="build.html#building-lxml-on-macos-x">Building lxml on MacOS-X</a></li><li class="menu item"><a href="build.html#static-linking-on-windows">Static linking on Windows</a></li><li class="menu item"><a href="build.html#building-debian-packages-from-svn-sources">Building Debian packages from SVN sources</a></li></ul></li></ul><ul class="menu foreign" id="lxml source howto-menu"><li class="menu title"><a href="lxml-source-howto.html">How to read the source of lxml</a><ul class="submenu"><li class="menu item"><a href="lxml-source-howto.html#what-is-cython">What is Cython?</a></li><li class="menu item"><a href="lxml-source-howto.html#where-to-start">Where to start?</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-etree">lxml.etree</a></li><li class="menu item"><a href="lxml-source-howto.html#python-modules">Python modules</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-objectify">lxml.objectify</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-html">lxml.html</a></li></ul></li></ul><ul class="menu foreign" id="changes 2 3 5-menu"><li class="menu title"><a href="changes-2.3.5.html">Release Changelog</a></li></ul><ul class="menu foreign" id="credits-menu"><li class="menu title"><a href="credits.html">Credits</a><ul class="submenu"><li class="menu item"><a href="credits.html#main-contributors">Main contributors</a></li><li class="menu item"><a href="credits.html#special-thanks-goes-to">Special thanks goes to:</a></li></ul></li></ul></li><li><a href="http://lxml.de/sitemap.html">Sitemap</a></li></ul></div><h1 class="title">lxml.cssselect</h1>
  12
  13 <p>lxml supports a number of interesting languages for tree traversal and element
  14 selection.  The most important is obviously <a class="reference external" href="xpathxslt.html#xpath">XPath</a>, but there is also
  15 <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
  16 is <a class="reference external" href="http://www.w3.org/TR/CSS21/selector.html">CSS selection</a>, which is implemented in the new <tt class="docutils literal">lxml.cssselect</tt> module.</p>
  17 <div class="contents topic" id="contents">
  18 <p class="topic-title first">Contents</p>
  19 <ul class="simple">
  20 <li><a class="reference internal" href="#the-cssselector-class" id="id1">The CSSSelector class</a></li>
  21 <li><a class="reference internal" href="#css-selectors" id="id2">CSS Selectors</a></li>
  22 <li><a class="reference internal" href="#namespaces" id="id3">Namespaces</a></li>
  23 <li><a class="reference internal" href="#limitations" id="id4">Limitations</a></li>
  24 </ul>
  25 </div>
  26 <div class="section" id="the-cssselector-class">
  27 <h1>The CSSSelector class</h1>
  28 <p>The most important class in the <tt class="docutils literal">cssselect</tt> module is <tt class="docutils literal">CSSSelector</tt>.  It
  29 provides the same interface as the <a class="reference external" href="xpathxslt.html#xpath">XPath</a> class, but accepts a CSS selector
  30 expression as input:</p>
  31 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">lxml.cssselect</span> <span class="kn">import</span> <span class="n">CSSSelector</span>
  32 <span class="gp">&gt;&gt;&gt; </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>
  33 <span class="gp">&gt;&gt;&gt; </span><span class="n">sel</span>  <span class="c">#doctest: +ELLIPSIS</span>
  34 <span class="go">&lt;CSSSelector ... for 'div.content'&gt;</span>
  35 <span class="gp">&gt;&gt;&gt; </span><span class="n">sel</span><span class="o">.</span><span class="n">css</span>
  36 <span class="go">'div.content'</span>
  37 </pre></div>
  38 <p>The selector actually compiles to XPath, and you can see the
  39 expression by inspecting the object:</p>
  40 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">sel</span><span class="o">.</span><span class="n">path</span>
  41 <span class="go">"descendant-or-self::div[contains(concat(' ', normalize-space(@class), ' '), ' content ')]"</span>
  42 </pre></div>
  43 <p>To use the selector, simply call it with a document or element
  44 object:</p>
  45 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">lxml.etree</span> <span class="kn">import</span> <span class="n">fromstring</span>
  46 <span class="gp">&gt;&gt;&gt; </span><span class="n">h</span> <span class="o">=</span> <span class="n">fromstring</span><span class="p">(</span><span class="s">'''&lt;div id="outer"&gt;</span>
  47 <span class="gp">... </span><span class="s">  &lt;div id="inner" class="content body"&gt;</span>
  48 <span class="gp">... </span><span class="s">      text</span>
  49 <span class="gp">... </span><span class="s">  &lt;/div&gt;&lt;/div&gt;'''</span><span class="p">)</span>
  50 <span class="gp">&gt;&gt;&gt; </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>
  51 <span class="go">['inner']</span>
  52 </pre></div>
  53 </div>
  54 <div class="section" id="css-selectors">
  55 <h1>CSS Selectors</h1>
  56 <p>This libraries attempts to implement CSS selectors <a class="reference external" href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113/">as described in
  57 the w3c specification</a>.  Many of
  58 the pseudo-classes do not apply in this context, including all
  59 <a class="reference external" href="http://www.w3.org/TR/2001/CR-css3-selectors-20011113/#dynamic-pseudos">dynamic pseudo-classes</a>.
  60 In particular these will not be available:</p>
  61 <ul class="simple">
  62 <li>link state: <tt class="docutils literal">:link</tt>, <tt class="docutils literal">:visited</tt>, <tt class="docutils literal">:target</tt></li>
  63 <li>actions: <tt class="docutils literal">:hover</tt>, <tt class="docutils literal">:active</tt>, <tt class="docutils literal">:focus</tt></li>
  64 <li>UI states: <tt class="docutils literal">:enabled</tt>, <tt class="docutils literal">:disabled</tt>, <tt class="docutils literal">:indeterminate</tt>
  65 (<tt class="docutils literal">:checked</tt> and <tt class="docutils literal">:unchecked</tt> <em>are</em> available)</li>
  66 </ul>
  67 <p>Also, none of the pseudo-elements apply, because the selector only
  68 returns elements and pseudo-elements select portions of text, like
  69 <tt class="docutils literal"><span class="pre">::first-line</span></tt>.</p>
  70 </div>
  71 <div class="section" id="namespaces">
  72 <h1>Namespaces</h1>
  73 <p>In CSS you can use <tt class="docutils literal"><span class="pre">namespace-prefix|element</span></tt>, similar to
  74 <tt class="docutils literal"><span class="pre">namespace-prefix:element</span></tt> in an XPath expression.  In fact, it maps
  75 one-to-one, and the same rules are used to map namespace prefixes to
  76 namespace URIs.</p>
  77 </div>
  78 <div class="section" id="limitations">
  79 <h1>Limitations</h1>
  80 <p>These applicable pseudoclasses are not yet implemented:</p>
  81 <ul class="simple">
  82 <li><tt class="docutils literal">:lang(language)</tt></li>
  83 <li><tt class="docutils literal">:root</tt></li>
  84 <li><tt class="docutils literal"><span class="pre">*:first-of-type</span></tt>, <tt class="docutils literal"><span class="pre">*:last-of-type</span></tt>, <tt class="docutils literal"><span class="pre">*:nth-of-type</span></tt>,
  85 <tt class="docutils literal"><span class="pre">*:nth-last-of-type</span></tt>, <tt class="docutils literal"><span class="pre">*:only-of-type</span></tt>.  All of these work when
  86 you specify an element type, but not with <tt class="docutils literal">*</tt></li>
  87 </ul>
  88 <p>Unlike XPath you cannot provide parameters in your expressions -- all
  89 expressions are completely static.</p>
  90 <p>XPath has underspecified string quoting rules (there seems to be no
  91 string quoting at all), so if you use expressions that contain
  92 characters that requiring quoting you might have problems with the
  93 translation from CSS to XPath.</p>
  94 </div>
  95 </div>
  96 <div class="footer">
  97 <hr class="footer" />
  98 Generated on: 2012-07-31.
  99
 100 </div>
 101 </body>
 102 </html>