doc/html/extensions.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>Python extensions for XPath and XSLT</title>
   7 <link rel="stylesheet" href="style.css" type="text/css" />
   8 </head>
   9 <body>
  10 <div class="document" id="python-extensions-for-xpath-and-xslt">
  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 foreign" 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 current" 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">Python extensions for XPath and XSLT</h1>
  12
  13 <p>This document describes how to use Python extension functions in XPath
  14 and XSLT like this:</p>
  15 <div class="syntax"><pre><span class="nt">&lt;xsl:value-of</span> <span class="na">select=</span><span class="s">"f:myPythonFunction(.//sometag)"</span> <span class="nt">/&gt;</span>
  16 </pre></div>
  17 <p>and extension elements in XSLT as in the following example:</p>
  18 <div class="syntax"><pre><span class="nt">&lt;xsl:template</span> <span class="na">match=</span><span class="s">"*"</span><span class="nt">&gt;</span>
  19     <span class="nt">&lt;my:python-extension&gt;</span>
  20         <span class="nt">&lt;some-content</span> <span class="nt">/&gt;</span>
  21     <span class="nt">&lt;/my:python-extension&gt;</span>
  22 <span class="nt">&lt;/xsl:template&gt;</span>
  23 </pre></div>
  24 <div class="contents topic" id="contents">
  25 <p class="topic-title first">Contents</p>
  26 <ul class="simple">
  27 <li><a class="reference internal" href="#xpath-extension-functions" id="id1">XPath Extension functions</a><ul>
  28 <li><a class="reference internal" href="#the-functionnamespace" id="id2">The FunctionNamespace</a></li>
  29 <li><a class="reference internal" href="#global-prefix-assignment" id="id3">Global prefix assignment</a></li>
  30 <li><a class="reference internal" href="#the-xpath-context" id="id4">The XPath context</a></li>
  31 <li><a class="reference internal" href="#evaluators-and-xslt" id="id5">Evaluators and XSLT</a></li>
  32 <li><a class="reference internal" href="#evaluator-local-extensions" id="id6">Evaluator-local extensions</a></li>
  33 <li><a class="reference internal" href="#what-to-return-from-a-function" id="id7">What to return from a function</a></li>
  34 </ul>
  35 </li>
  36 <li><a class="reference internal" href="#xslt-extension-elements" id="id8">XSLT extension elements</a><ul>
  37 <li><a class="reference internal" href="#declaring-extension-elements" id="id9">Declaring extension elements</a></li>
  38 <li><a class="reference internal" href="#applying-xsl-templates" id="id10">Applying XSL templates</a></li>
  39 <li><a class="reference internal" href="#working-with-read-only-elements" id="id11">Working with read-only elements</a></li>
  40 </ul>
  41 </li>
  42 </ul>
  43 </div>
  44 <div class="section" id="xpath-extension-functions">
  45 <h1>XPath Extension functions</h1>
  46 <p>Here is how an extension function looks like.  As the first argument,
  47 it always receives a context object (see below).  The other arguments
  48 are provided by the respective call in the XPath expression, one in
  49 the following examples.  Any number of arguments is allowed:</p>
  50 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">hello</span><span class="p">(</span><span class="n">dummy</span><span class="p">,</span> <span class="n">a</span><span class="p">):</span>
  51 <span class="gp">... </span>   <span class="k">return</span> <span class="s">"Hello </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="n">a</span>
  52 <span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">ola</span><span class="p">(</span><span class="n">dummy</span><span class="p">,</span> <span class="n">a</span><span class="p">):</span>
  53 <span class="gp">... </span>   <span class="k">return</span> <span class="s">"Ola </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="n">a</span>
  54 <span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">loadsofargs</span><span class="p">(</span><span class="n">dummy</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">):</span>
  55 <span class="gp">... </span>   <span class="k">return</span> <span class="s">"Got </span><span class="si">%d</span><span class="s"> arguments."</span> <span class="o">%</span> <span class="nb">len</span><span class="p">(</span><span class="n">args</span><span class="p">)</span>
  56 </pre></div>
  57 <div class="section" id="the-functionnamespace">
  58 <h2>The FunctionNamespace</h2>
  59 <p>In order to use a function in XPath or XSLT, it needs to have a
  60 (namespaced) name by which it can be called during evaluation.  This
  61 is done using the FunctionNamespace class.  For simplicity, we choose
  62 the empty namespace (None):</p>
  63 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">lxml</span> <span class="kn">import</span> <span class="n">etree</span>
  64 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">FunctionNamespace</span><span class="p">(</span><span class="bp">None</span><span class="p">)</span>
  65 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'hello'</span><span class="p">]</span> <span class="o">=</span> <span class="n">hello</span>
  66 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'countargs'</span><span class="p">]</span> <span class="o">=</span> <span class="n">loadsofargs</span>
  67 </pre></div>
  68 <p>This registers the function <cite>hello</cite> with the name <cite>hello</cite> in the default
  69 namespace (None), and the function <cite>loadsofargs</cite> with the name <cite>countargs</cite>.
  70 Now we're going to create a document that we can run XPath expressions
  71 against:</p>
  72 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;b&gt;Haegar&lt;/b&gt;&lt;/a&gt;'</span><span class="p">)</span>
  73 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">ElementTree</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
  74 </pre></div>
  75 <p>Done. Now we can have XPath expressions call our new function:</p>
  76 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">"hello('Dr. Falken')"</span><span class="p">))</span>
  77 <span class="go">Hello Dr. Falken</span>
  78 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">'hello(local-name(*))'</span><span class="p">))</span>
  79 <span class="go">Hello b</span>
  80 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">'hello(string(b))'</span><span class="p">))</span>
  81 <span class="go">Hello Haegar</span>
  82 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">'countargs(., b, ./*)'</span><span class="p">))</span>
  83 <span class="go">Got 3 arguments.</span>
  84 </pre></div>
  85 <p>Note how we call both a Python function (<cite>hello</cite>) and an XPath built-in
  86 function (<cite>string</cite>) in exactly the same way.  Normally, however, you would
  87 want to separate the two in different namespaces.  The FunctionNamespace class
  88 allows you to do this:</p>
  89 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">FunctionNamespace</span><span class="p">(</span><span class="s">'http://mydomain.org/myfunctions'</span><span class="p">)</span>
  90 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'hello'</span><span class="p">]</span> <span class="o">=</span> <span class="n">hello</span>
  91 <span class="gp">&gt;&gt;&gt; </span><span class="n">prefixmap</span> <span class="o">=</span> <span class="p">{</span><span class="s">'f'</span> <span class="p">:</span> <span class="s">'http://mydomain.org/myfunctions'</span><span class="p">}</span>
  92 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">'f:hello(local-name(*))'</span><span class="p">,</span> <span class="n">namespaces</span><span class="o">=</span><span class="n">prefixmap</span><span class="p">))</span>
  93 <span class="go">Hello b</span>
  94 </pre></div>
  95 </div>
  96 <div class="section" id="global-prefix-assignment">
  97 <h2>Global prefix assignment</h2>
  98 <p>In the last example, you had to specify a prefix for the function namespace.
  99 If you always use the same prefix for a function namespace, you can also
 100 register it with the namespace:</p>
 101 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">FunctionNamespace</span><span class="p">(</span><span class="s">'http://mydomain.org/myother/functions'</span><span class="p">)</span>
 102 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="o">.</span><span class="n">prefix</span> <span class="o">=</span> <span class="s">'es'</span>
 103 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'hello'</span><span class="p">]</span> <span class="o">=</span> <span class="n">ola</span>
 104 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">'es:hello(local-name(*))'</span><span class="p">))</span>
 105 <span class="go">Ola b</span>
 106 </pre></div>
 107 <p>This is a global assignment, so take care not to assign the same prefix to
 108 more than one namespace.  The resulting behaviour in that case is completely
 109 undefined.  It is always a good idea to consistently use the same meaningful
 110 prefix for each namespace throughout your application.</p>
 111 <p>The prefix assignment only works with functions and FunctionNamespace objects,
 112 not with the general Namespace object that registers element classes.  The
 113 reasoning is that elements in lxml do not care about prefixes anyway, so it
 114 would rather complicate things than be of any help.</p>
 115 </div>
 116 <div class="section" id="the-xpath-context">
 117 <h2>The XPath context</h2>
 118 <p>Functions get a context object as first parameter.  In lxml 1.x, this value
 119 was None, but since lxml 2.0 it provides two properties: <tt class="docutils literal">eval_context</tt> and
 120 <tt class="docutils literal">context_node</tt>.  The context node is the Element where the current function
 121 is called:</p>
 122 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">print_tag</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="n">nodes</span><span class="p">):</span>
 123 <span class="gp">... </span>    <span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s">: </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">context</span><span class="o">.</span><span class="n">context_node</span><span class="o">.</span><span class="n">tag</span><span class="p">,</span> <span class="p">[</span> <span class="n">n</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="n">nodes</span> <span class="p">]))</span>
 124
 125 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">FunctionNamespace</span><span class="p">(</span><span class="s">'http://mydomain.org/printtag'</span><span class="p">)</span>
 126 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="o">.</span><span class="n">prefix</span> <span class="o">=</span> <span class="s">"pt"</span>
 127 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">"print_tag"</span><span class="p">]</span> <span class="o">=</span> <span class="n">print_tag</span>
 128
 129 <span class="gp">&gt;&gt;&gt; </span><span class="n">ignore</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">"//*[pt:print_tag(.//*)]"</span><span class="p">)</span>
 130 <span class="go">a: ['b']</span>
 131 <span class="go">b: []</span>
 132 </pre></div>
 133 <p>The <tt class="docutils literal">eval_context</tt> is a dictionary that is local to the evaluation.  It
 134 allows functions to keep state:</p>
 135 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">print_context</span><span class="p">(</span><span class="n">context</span><span class="p">):</span>
 136 <span class="gp">... </span>    <span class="n">context</span><span class="o">.</span><span class="n">eval_context</span><span class="p">[</span><span class="n">context</span><span class="o">.</span><span class="n">context_node</span><span class="o">.</span><span class="n">tag</span><span class="p">]</span> <span class="o">=</span> <span class="s">"done"</span>
 137 <span class="gp">... </span>    <span class="n">entries</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">context</span><span class="o">.</span><span class="n">eval_context</span><span class="o">.</span><span class="n">items</span><span class="p">())</span>
 138 <span class="gp">... </span>    <span class="n">entries</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span>
 139 <span class="gp">... </span>    <span class="k">print</span><span class="p">(</span><span class="n">entries</span><span class="p">)</span>
 140 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">"print_context"</span><span class="p">]</span> <span class="o">=</span> <span class="n">print_context</span>
 141
 142 <span class="gp">&gt;&gt;&gt; </span><span class="n">ignore</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s">"//*[pt:print_context()]"</span><span class="p">)</span>
 143 <span class="go">[('a', 'done')]</span>
 144 <span class="go">[('a', 'done'), ('b', 'done')]</span>
 145 </pre></div>
 146 </div>
 147 <div class="section" id="evaluators-and-xslt">
 148 <h2>Evaluators and XSLT</h2>
 149 <p>Extension functions work for all ways of evaluating XPath expressions and for
 150 XSL transformations:</p>
 151 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
 152 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'es:hello(local-name(/a))'</span><span class="p">))</span>
 153 <span class="go">Ola a</span>
 154
 155 <span class="gp">&gt;&gt;&gt; </span><span class="n">namespaces</span> <span class="o">=</span> <span class="p">{</span><span class="s">'f'</span> <span class="p">:</span> <span class="s">'http://mydomain.org/myfunctions'</span><span class="p">}</span>
 156 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">namespaces</span><span class="o">=</span><span class="n">namespaces</span><span class="p">)</span>
 157 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'f:hello(local-name(/a))'</span><span class="p">))</span>
 158 <span class="go">Hello a</span>
 159
 160 <span class="gp">&gt;&gt;&gt; </span><span class="n">xslt</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XSLT</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">'''</span>
 161 <span class="gp">... </span><span class="s">  &lt;stylesheet version="1.0"</span>
 162 <span class="gp">... </span><span class="s">         xmlns="http://www.w3.org/1999/XSL/Transform"</span>
 163 <span class="gp">... </span><span class="s">         xmlns:es="http://mydomain.org/myother/functions"&gt;</span>
 164 <span class="gp">... </span><span class="s">    &lt;output method="text" encoding="ASCII"/&gt;</span>
 165 <span class="gp">... </span><span class="s">    &lt;template match="/"&gt;</span>
 166 <span class="gp">... </span><span class="s">      &lt;value-of select="es:hello(string(//b))"/&gt;</span>
 167 <span class="gp">... </span><span class="s">    &lt;/template&gt;</span>
 168 <span class="gp">... </span><span class="s">  &lt;/stylesheet&gt;</span>
 169 <span class="gp">... </span><span class="s">'''</span><span class="p">))</span>
 170 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">xslt</span><span class="p">(</span><span class="n">doc</span><span class="p">))</span>
 171 <span class="go">Ola Haegar</span>
 172 </pre></div>
 173 <p>It is also possible to register namespaces with a single evaluator after its
 174 creation.  While the following example involves no functions, the idea should
 175 still be clear:</p>
 176 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a xmlns="http://mydomain.org/myfunctions" /&gt;'</span><span class="p">)</span>
 177 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns_doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
 178 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">ns_doc</span><span class="p">)</span>
 179 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="p">(</span><span class="s">'/a'</span><span class="p">)</span>
 180 <span class="go">[]</span>
 181 </pre></div>
 182 <p>This returns nothing, as we did not ask for the right namespace.  When we
 183 register the namespace with the evaluator, however, we can access it via a
 184 prefix:</p>
 185 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="o">.</span><span class="n">register_namespace</span><span class="p">(</span><span class="s">'foo'</span><span class="p">,</span> <span class="s">'http://mydomain.org/myfunctions'</span><span class="p">)</span>
 186 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="p">(</span><span class="s">'/foo:a'</span><span class="p">)[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span>
 187 <span class="go">'{http://mydomain.org/myfunctions}a'</span>
 188 </pre></div>
 189 <p>Note that this prefix mapping is only known to this evaluator, as opposed to
 190 the global mapping of the FunctionNamespace objects:</p>
 191 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">e2</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">ns_doc</span><span class="p">)</span>
 192 <span class="gp">&gt;&gt;&gt; </span><span class="n">e2</span><span class="p">(</span><span class="s">'/foo:a'</span><span class="p">)</span>
 193 <span class="gt">Traceback (most recent call last):</span>
 194 <span class="c">...</span>
 195 <span class="gr">lxml.etree.XPathEvalError</span>: <span class="n">Undefined namespace prefix</span>
 196 </pre></div>
 197 </div>
 198 <div class="section" id="evaluator-local-extensions">
 199 <h2>Evaluator-local extensions</h2>
 200 <p>Apart from the global registration of extension functions, there is also a way
 201 of making extensions known to a single Evaluator or XSLT.  All evaluators and
 202 the XSLT object accept a keyword argument <tt class="docutils literal">extensions</tt> in their constructor.
 203 The value is a dictionary mapping (namespace, name) tuples to functions:</p>
 204 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="p">{(</span><span class="s">'local-ns'</span><span class="p">,</span> <span class="s">'local-hello'</span><span class="p">)</span> <span class="p">:</span> <span class="n">hello</span><span class="p">}</span>
 205 <span class="gp">&gt;&gt;&gt; </span><span class="n">namespaces</span> <span class="o">=</span> <span class="p">{</span><span class="s">'l'</span> <span class="p">:</span> <span class="s">'local-ns'</span><span class="p">}</span>
 206
 207 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">namespaces</span><span class="o">=</span><span class="n">namespaces</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="n">extensions</span><span class="p">)</span>
 208 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'l:local-hello(string(b))'</span><span class="p">))</span>
 209 <span class="go">Hello Haegar</span>
 210 </pre></div>
 211 <p>For larger numbers of extension functions, you can define classes or modules
 212 and use the <tt class="docutils literal">Extension</tt> helper:</p>
 213 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span> <span class="nc">MyExt</span><span class="p">:</span>
 214 <span class="gp">... </span>    <span class="k">def</span> <span class="nf">function1</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">_</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>
 215 <span class="gp">... </span>        <span class="k">return</span> <span class="s">'1'</span><span class="o">+</span><span class="n">arg</span>
 216 <span class="gp">... </span>    <span class="k">def</span> <span class="nf">function2</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">_</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>
 217 <span class="gp">... </span>        <span class="k">return</span> <span class="s">'2'</span><span class="o">+</span><span class="n">arg</span>
 218 <span class="gp">... </span>    <span class="k">def</span> <span class="nf">function3</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">_</span><span class="p">,</span> <span class="n">arg</span><span class="p">):</span>
 219 <span class="gp">... </span>        <span class="k">return</span> <span class="s">'3'</span><span class="o">+</span><span class="n">arg</span>
 220
 221 <span class="gp">&gt;&gt;&gt; </span><span class="n">ext_module</span> <span class="o">=</span> <span class="n">MyExt</span><span class="p">()</span>
 222 <span class="gp">&gt;&gt;&gt; </span><span class="n">functions</span> <span class="o">=</span> <span class="p">(</span><span class="s">'function1'</span><span class="p">,</span> <span class="s">'function2'</span><span class="p">)</span>
 223 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span> <span class="n">ext_module</span><span class="p">,</span> <span class="n">functions</span><span class="p">,</span> <span class="n">ns</span><span class="o">=</span><span class="s">'local-ns'</span> <span class="p">)</span>
 224
 225 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">namespaces</span><span class="o">=</span><span class="n">namespaces</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="n">extensions</span><span class="p">)</span>
 226 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'l:function1(string(b))'</span><span class="p">))</span>
 227 <span class="go">1Haegar</span>
 228 </pre></div>
 229 <p>The optional second argument to <tt class="docutils literal">Extension</tt> can either be be a
 230 sequence of names to select from the module, a dictionary that
 231 explicitly maps function names to their XPath alter-ego or <tt class="docutils literal">None</tt>
 232 (explicitly passed) to take all available functions under their
 233 original name (if their name does not start with '_').</p>
 234 <p>The additional <tt class="docutils literal">ns</tt> keyword argument takes a namespace URI or
 235 <tt class="docutils literal">None</tt> (also if left out) for the default namespace.  The following
 236 examples will therefore all do the same thing:</p>
 237 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">functions</span> <span class="o">=</span> <span class="p">(</span><span class="s">'function1'</span><span class="p">,</span> <span class="s">'function2'</span><span class="p">,</span> <span class="s">'function3'</span><span class="p">)</span>
 238 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span> <span class="n">ext_module</span><span class="p">,</span> <span class="n">functions</span> <span class="p">)</span>
 239 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="n">extensions</span><span class="p">)</span>
 240 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'function1(function2(function3(string(b))))'</span><span class="p">))</span>
 241 <span class="go">123Haegar</span>
 242
 243 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span> <span class="n">ext_module</span><span class="p">,</span> <span class="n">functions</span><span class="p">,</span> <span class="n">ns</span><span class="o">=</span><span class="bp">None</span> <span class="p">)</span>
 244 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="n">extensions</span><span class="p">)</span>
 245 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'function1(function2(function3(string(b))))'</span><span class="p">))</span>
 246 <span class="go">123Haegar</span>
 247
 248 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span><span class="n">ext_module</span><span class="p">)</span>
 249 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="n">extensions</span><span class="p">)</span>
 250 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'function1(function2(function3(string(b))))'</span><span class="p">))</span>
 251 <span class="go">123Haegar</span>
 252
 253 <span class="gp">&gt;&gt;&gt; </span><span class="n">functions</span> <span class="o">=</span> <span class="p">{</span>
 254 <span class="gp">... </span>    <span class="s">'function1'</span> <span class="p">:</span> <span class="s">'function1'</span><span class="p">,</span>
 255 <span class="gp">... </span>    <span class="s">'function2'</span> <span class="p">:</span> <span class="s">'function2'</span><span class="p">,</span>
 256 <span class="gp">... </span>    <span class="s">'function3'</span> <span class="p">:</span> <span class="s">'function3'</span>
 257 <span class="gp">... </span>    <span class="p">}</span>
 258 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span><span class="n">ext_module</span><span class="p">,</span> <span class="n">functions</span><span class="p">)</span>
 259 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="n">extensions</span><span class="p">)</span>
 260 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'function1(function2(function3(string(b))))'</span><span class="p">))</span>
 261 <span class="go">123Haegar</span>
 262 </pre></div>
 263 <p>For convenience, you can also pass a sequence of extensions:</p>
 264 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">extensions1</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span><span class="n">ext_module</span><span class="p">)</span>
 265 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions2</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Extension</span><span class="p">(</span><span class="n">ext_module</span><span class="p">,</span> <span class="n">ns</span><span class="o">=</span><span class="s">'local-ns'</span><span class="p">)</span>
 266 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">,</span> <span class="n">extensions</span><span class="o">=</span><span class="p">[</span><span class="n">extensions1</span><span class="p">,</span> <span class="n">extensions2</span><span class="p">],</span>
 267 <span class="gp">... </span>                         <span class="n">namespaces</span><span class="o">=</span><span class="n">namespaces</span><span class="p">)</span>
 268 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">e</span><span class="p">(</span><span class="s">'function1(l:function2(function3(string(b))))'</span><span class="p">))</span>
 269 <span class="go">123Haegar</span>
 270 </pre></div>
 271 </div>
 272 <div class="section" id="what-to-return-from-a-function">
 273 <h2>What to return from a function</h2>
 274 <p>Extension functions can return any data type for which there is an XPath
 275 equivalent (see the documentation on <cite>XPath return values</cite>).  This includes
 276 numbers, boolean values, elements and lists of elements.  Note that integers
 277 will also be returned as floats:</p>
 278 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">returnsFloat</span><span class="p">(</span><span class="n">_</span><span class="p">):</span>
 279 <span class="gp">... </span>   <span class="k">return</span> <span class="mf">1.7</span>
 280 <span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">returnsInteger</span><span class="p">(</span><span class="n">_</span><span class="p">):</span>
 281 <span class="gp">... </span>   <span class="k">return</span> <span class="mi">1</span>
 282 <span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">returnsBool</span><span class="p">(</span><span class="n">_</span><span class="p">):</span>
 283 <span class="gp">... </span>   <span class="k">return</span> <span class="bp">True</span>
 284 <span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">returnFirstNode</span><span class="p">(</span><span class="n">_</span><span class="p">,</span> <span class="n">nodes</span><span class="p">):</span>
 285 <span class="gp">... </span>   <span class="k">return</span> <span class="n">nodes</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
 286
 287 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">FunctionNamespace</span><span class="p">(</span><span class="bp">None</span><span class="p">)</span>
 288 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'float'</span><span class="p">]</span> <span class="o">=</span> <span class="n">returnsFloat</span>
 289 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'int'</span><span class="p">]</span>   <span class="o">=</span> <span class="n">returnsInteger</span>
 290 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'bool'</span><span class="p">]</span>  <span class="o">=</span> <span class="n">returnsBool</span>
 291 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'first'</span><span class="p">]</span> <span class="o">=</span> <span class="n">returnFirstNode</span>
 292
 293 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
 294 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="p">(</span><span class="s">"float()"</span><span class="p">)</span>
 295 <span class="go">1.7</span>
 296 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="p">(</span><span class="s">"int()"</span><span class="p">)</span>
 297 <span class="go">1.0</span>
 298 <span class="gp">&gt;&gt;&gt; </span><span class="nb">int</span><span class="p">(</span> <span class="n">e</span><span class="p">(</span><span class="s">"int()"</span><span class="p">)</span> <span class="p">)</span>
 299 <span class="go">1</span>
 300 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="p">(</span><span class="s">"bool()"</span><span class="p">)</span>
 301 <span class="go">True</span>
 302 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span><span class="p">(</span><span class="s">"count(first(//b))"</span><span class="p">)</span>
 303 <span class="go">1.0</span>
 304 </pre></div>
 305 <p>As the last example shows, you can pass the results of functions back into
 306 the XPath expression.  Elements and sequences of elements are treated as
 307 XPath node-sets:</p>
 308 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">returnsNodeSet</span><span class="p">(</span><span class="n">_</span><span class="p">):</span>
 309 <span class="gp">... </span>    <span class="n">results1</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Element</span><span class="p">(</span><span class="s">'results1'</span><span class="p">)</span>
 310 <span class="gp">... </span>    <span class="n">etree</span><span class="o">.</span><span class="n">SubElement</span><span class="p">(</span><span class="n">results1</span><span class="p">,</span> <span class="s">'result'</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"Alpha"</span>
 311 <span class="gp">... </span>    <span class="n">etree</span><span class="o">.</span><span class="n">SubElement</span><span class="p">(</span><span class="n">results1</span><span class="p">,</span> <span class="s">'result'</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"Beta"</span>
 312 <span class="gp">...</span>
 313 <span class="gp">... </span>    <span class="n">results2</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Element</span><span class="p">(</span><span class="s">'results2'</span><span class="p">)</span>
 314 <span class="gp">... </span>    <span class="n">etree</span><span class="o">.</span><span class="n">SubElement</span><span class="p">(</span><span class="n">results2</span><span class="p">,</span> <span class="s">'result'</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"Gamma"</span>
 315 <span class="gp">... </span>    <span class="n">etree</span><span class="o">.</span><span class="n">SubElement</span><span class="p">(</span><span class="n">results2</span><span class="p">,</span> <span class="s">'result'</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"Delta"</span>
 316 <span class="gp">...</span>
 317 <span class="gp">... </span>    <span class="n">results3</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">SubElement</span><span class="p">(</span><span class="n">results2</span><span class="p">,</span> <span class="s">'subresult'</span><span class="p">)</span>
 318 <span class="gp">... </span>    <span class="k">return</span> <span class="p">[</span><span class="n">results1</span><span class="p">,</span> <span class="n">results2</span><span class="p">,</span> <span class="n">results3</span><span class="p">]</span>
 319
 320 <span class="gp">&gt;&gt;&gt; </span><span class="n">ns</span><span class="p">[</span><span class="s">'new-node-set'</span><span class="p">]</span> <span class="o">=</span> <span class="n">returnsNodeSet</span>
 321
 322 <span class="gp">&gt;&gt;&gt; </span><span class="n">e</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPathEvaluator</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
 323
 324 <span class="gp">&gt;&gt;&gt; </span><span class="n">r</span> <span class="o">=</span> <span class="n">e</span><span class="p">(</span><span class="s">"new-node-set()/result"</span><span class="p">)</span>
 325 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">([</span> <span class="n">t</span><span class="o">.</span><span class="n">text</span> <span class="k">for</span> <span class="n">t</span> <span class="ow">in</span> <span class="n">r</span> <span class="p">])</span>
 326 <span class="go">['Alpha', 'Beta', 'Gamma', 'Delta']</span>
 327
 328 <span class="gp">&gt;&gt;&gt; </span><span class="n">r</span> <span class="o">=</span> <span class="n">e</span><span class="p">(</span><span class="s">"new-node-set()"</span><span class="p">)</span>
 329 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">([</span> <span class="n">t</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">t</span> <span class="ow">in</span> <span class="n">r</span> <span class="p">])</span>
 330 <span class="go">['results1', 'results2', 'subresult']</span>
 331 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">([</span> <span class="nb">len</span><span class="p">(</span><span class="n">t</span><span class="p">)</span> <span class="k">for</span> <span class="n">t</span> <span class="ow">in</span> <span class="n">r</span> <span class="p">])</span>
 332 <span class="go">[2, 3, 0]</span>
 333 <span class="gp">&gt;&gt;&gt; </span><span class="n">r</span><span class="p">[</span><span class="mi">0</span><span class="p">][</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">text</span>
 334 <span class="go">'Alpha'</span>
 335
 336 <span class="gp">&gt;&gt;&gt; </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
 337 <span class="go">b'&lt;results1&gt;&lt;result&gt;Alpha&lt;/result&gt;&lt;result&gt;Beta&lt;/result&gt;&lt;/results1&gt;'</span>
 338
 339 <span class="gp">&gt;&gt;&gt; </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span>
 340 <span class="go">b'&lt;results2&gt;&lt;result&gt;Gamma&lt;/result&gt;&lt;result&gt;Delta&lt;/result&gt;&lt;subresult/&gt;&lt;/results2&gt;'</span>
 341
 342 <span class="gp">&gt;&gt;&gt; </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">2</span><span class="p">])</span>
 343 <span class="go">b'&lt;subresult/&gt;'</span>
 344 </pre></div>
 345 <p>The current implementation deep-copies newly created elements in node-sets.
 346 Only the elements and their children are passed on, no outlying parents or
 347 tail texts will be available in the result.  This also means that in the above
 348 example, the <cite>subresult</cite> elements in <cite>results2</cite> and <cite>results3</cite> are no longer
 349 identical within the node-set, they belong to independent trees:</p>
 350 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="s">"</span><span class="si">%s</span><span class="s"> - </span><span class="si">%s</span><span class="s">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">1</span><span class="p">][</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">,</span> <span class="n">r</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
 351 <span class="go">subresult - subresult</span>
 352 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">1</span><span class="p">][</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">==</span> <span class="n">r</span><span class="p">[</span><span class="mi">2</span><span class="p">])</span>
 353 <span class="go">False</span>
 354 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">1</span><span class="p">][</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">getparent</span><span class="p">()</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
 355 <span class="go">results2</span>
 356 <span class="gp">&gt;&gt;&gt; </span><span class="k">print</span><span class="p">(</span><span class="n">r</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="o">.</span><span class="n">getparent</span><span class="p">())</span>
 357 <span class="go">None</span>
 358 </pre></div>
 359 <p>This is an implementation detail that you should be aware of, but you should
 360 avoid relying on it in your code.  Note that elements taken from the source
 361 document (the most common case) do not suffer from this restriction.  They
 362 will always be passed unchanged.</p>
 363 </div>
 364 </div>
 365 <div class="section" id="xslt-extension-elements">
 366 <h1>XSLT extension elements</h1>
 367 <p>Just like the XPath extension functions described above, lxml supports
 368 custom extension <em>elements</em> in XSLT.  This means, you can write XSLT
 369 code like this:</p>
 370 <div class="syntax"><pre><span class="nt">&lt;xsl:template</span> <span class="na">match=</span><span class="s">"*"</span><span class="nt">&gt;</span>
 371     <span class="nt">&lt;my:python-extension&gt;</span>
 372         <span class="nt">&lt;some-content</span> <span class="nt">/&gt;</span>
 373     <span class="nt">&lt;/my:python-extension&gt;</span>
 374 <span class="nt">&lt;/xsl:template&gt;</span>
 375 </pre></div>
 376 <p>And then you can implement the element in Python like this:</p>
 377 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span> <span class="nc">MyExtElement</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">XSLTExtension</span><span class="p">):</span>
 378 <span class="gp">... </span>    <span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">,</span> <span class="n">self_node</span><span class="p">,</span> <span class="n">input_node</span><span class="p">,</span> <span class="n">output_parent</span><span class="p">):</span>
 379 <span class="gp">... </span>        <span class="k">print</span><span class="p">(</span><span class="s">"Hello from XSLT!"</span><span class="p">)</span>
 380 <span class="gp">... </span>        <span class="n">output_parent</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"I did it!"</span>
 381 <span class="gp">... </span>        <span class="c"># just copy own content input to output</span>
 382 <span class="gp">... </span>        <span class="n">output_parent</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span> <span class="nb">list</span><span class="p">(</span><span class="n">self_node</span><span class="p">)</span> <span class="p">)</span>
 383 </pre></div>
 384 <p>The arguments passed to the <tt class="docutils literal">.execute()</tt> method  are</p>
 385 <dl class="docutils">
 386 <dt>context</dt>
 387 <dd>The opaque evaluation context.  You need this when calling back
 388 into the XSLT processor.</dd>
 389 <dt>self_node</dt>
 390 <dd>A read-only Element object that represents the extension element
 391 in the stylesheet.</dd>
 392 <dt>input_node</dt>
 393 <dd>The current context Element in the input document (also read-only).</dd>
 394 <dt>output_parent</dt>
 395 <dd>The current insertion point in the output document.  You can
 396 append elements or set the text value (not the tail).  Apart from
 397 that, the Element is read-only.</dd>
 398 </dl>
 399 <div class="section" id="declaring-extension-elements">
 400 <h2>Declaring extension elements</h2>
 401 <p>In XSLT, extension elements can be used like any other XSLT element,
 402 except that they must be declared as extensions using the standard
 403 XSLT <tt class="docutils literal"><span class="pre">extension-element-prefixes</span></tt> option:</p>
 404 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">xslt_ext_tree</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">'''</span>
 405 <span class="gp">... </span><span class="s">&lt;xsl:stylesheet version="1.0"</span>
 406 <span class="gp">... </span><span class="s">    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"</span>
 407 <span class="gp">... </span><span class="s">    xmlns:my="testns"</span>
 408 <span class="gp">... </span><span class="s">    extension-element-prefixes="my"&gt;</span>
 409 <span class="gp">... </span><span class="s">    &lt;xsl:template match="/"&gt;</span>
 410 <span class="gp">... </span><span class="s">        &lt;foo&gt;&lt;my:ext&gt;&lt;child&gt;XYZ&lt;/child&gt;&lt;/my:ext&gt;&lt;/foo&gt;</span>
 411 <span class="gp">... </span><span class="s">    &lt;/xsl:template&gt;</span>
 412 <span class="gp">... </span><span class="s">    &lt;xsl:template match="child"&gt;</span>
 413 <span class="gp">... </span><span class="s">        &lt;CHILD&gt;--xyz--&lt;/CHILD&gt;</span>
 414 <span class="gp">... </span><span class="s">    &lt;/xsl:template&gt;</span>
 415 <span class="gp">... </span><span class="s">&lt;/xsl:stylesheet&gt;'''</span><span class="p">)</span>
 416 </pre></div>
 417 <p>To register the extension, add its namespace and name to the extension
 418 mapping of the XSLT object:</p>
 419 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">my_extension</span> <span class="o">=</span> <span class="n">MyExtElement</span><span class="p">()</span>
 420 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="p">{</span> <span class="p">(</span><span class="s">'testns'</span><span class="p">,</span> <span class="s">'ext'</span><span class="p">)</span> <span class="p">:</span> <span class="n">my_extension</span> <span class="p">}</span>
 421 <span class="gp">&gt;&gt;&gt; </span><span class="n">transform</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XSLT</span><span class="p">(</span><span class="n">xslt_ext_tree</span><span class="p">,</span> <span class="n">extensions</span> <span class="o">=</span> <span class="n">extensions</span><span class="p">)</span>
 422 </pre></div>
 423 <p>Note how we pass an instance here, not the class of the extension.
 424 Now we can run the transformation and see how our extension is
 425 called:</p>
 426 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">'&lt;dummy/&gt;'</span><span class="p">)</span>
 427 <span class="gp">&gt;&gt;&gt; </span><span class="n">result</span> <span class="o">=</span> <span class="n">transform</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
 428 <span class="go">Hello from XSLT!</span>
 429 <span class="gp">&gt;&gt;&gt; </span><span class="nb">str</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
 430 <span class="go">'&lt;?xml version="1.0"?&gt;\n&lt;foo&gt;I did it!&lt;child&gt;XYZ&lt;/child&gt;&lt;/foo&gt;\n'</span>
 431 </pre></div>
 432 </div>
 433 <div class="section" id="applying-xsl-templates">
 434 <h2>Applying XSL templates</h2>
 435 <p>XSLT extensions are a very powerful feature that allows you to
 436 interact directly with the XSLT processor.  You have full read-only
 437 access to the input document and the stylesheet, and you can even call
 438 back into the XSLT processor to process templates.  Here is an example
 439 that passes an Element into the <tt class="docutils literal">.apply_templates()</tt> method of the
 440 <tt class="docutils literal">XSLTExtension</tt> instance:</p>
 441 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="k">class</span> <span class="nc">MyExtElement</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">XSLTExtension</span><span class="p">):</span>
 442 <span class="gp">... </span>    <span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">,</span> <span class="n">self_node</span><span class="p">,</span> <span class="n">input_node</span><span class="p">,</span> <span class="n">output_parent</span><span class="p">):</span>
 443 <span class="gp">... </span>        <span class="n">child</span> <span class="o">=</span> <span class="n">self_node</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
 444 <span class="gp">... </span>        <span class="n">results</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">apply_templates</span><span class="p">(</span><span class="n">context</span><span class="p">,</span> <span class="n">child</span><span class="p">)</span>
 445 <span class="gp">... </span>        <span class="n">output_parent</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">results</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
 446
 447 <span class="gp">&gt;&gt;&gt; </span><span class="n">my_extension</span> <span class="o">=</span> <span class="n">MyExtElement</span><span class="p">()</span>
 448 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="p">{</span> <span class="p">(</span><span class="s">'testns'</span><span class="p">,</span> <span class="s">'ext'</span><span class="p">)</span> <span class="p">:</span> <span class="n">my_extension</span> <span class="p">}</span>
 449 <span class="gp">&gt;&gt;&gt; </span><span class="n">transform</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XSLT</span><span class="p">(</span><span class="n">xslt_ext_tree</span><span class="p">,</span> <span class="n">extensions</span> <span class="o">=</span> <span class="n">extensions</span><span class="p">)</span>
 450
 451 <span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">'&lt;dummy/&gt;'</span><span class="p">)</span>
 452 <span class="gp">&gt;&gt;&gt; </span><span class="n">result</span> <span class="o">=</span> <span class="n">transform</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
 453 <span class="gp">&gt;&gt;&gt; </span><span class="nb">str</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
 454 <span class="go">'&lt;?xml version="1.0"?&gt;\n&lt;foo&gt;&lt;CHILD&gt;--xyz--&lt;/CHILD&gt;&lt;/foo&gt;\n'</span>
 455 </pre></div>
 456 <p>Note how we applied the templates to a child of the extension element
 457 itself, i.e. to an element inside the stylesheet instead of an element
 458 of the input document.</p>
 459 </div>
 460 <div class="section" id="working-with-read-only-elements">
 461 <h2>Working with read-only elements</h2>
 462 <p>There is one important thing to keep in mind: all Elements that the
 463 <tt class="docutils literal">execute()</tt> method gets to deal with are read-only Elements, so you
 464 cannot modify them.  They also will not easily work in the API.  For
 465 example, you cannot pass them to the <tt class="docutils literal">tostring()</tt> function or wrap
 466 them in an <tt class="docutils literal">ElementTree</tt>.</p>
 467 <p>What you can do, however, is to deepcopy them to make them normal
 468 Elements, and then modify them using the normal etree API.  So this
 469 will work:</p>
 470 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">copy</span> <span class="kn">import</span> <span class="n">deepcopy</span>
 471 <span class="gp">&gt;&gt;&gt; </span><span class="k">class</span> <span class="nc">MyExtElement</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">XSLTExtension</span><span class="p">):</span>
 472 <span class="gp">... </span>    <span class="k">def</span> <span class="nf">execute</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">context</span><span class="p">,</span> <span class="n">self_node</span><span class="p">,</span> <span class="n">input_node</span><span class="p">,</span> <span class="n">output_parent</span><span class="p">):</span>
 473 <span class="gp">... </span>        <span class="n">child</span> <span class="o">=</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">self_node</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
 474 <span class="gp">... </span>        <span class="n">child</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"NEW TEXT"</span>
 475 <span class="gp">... </span>        <span class="n">output_parent</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">child</span><span class="p">)</span>
 476
 477 <span class="gp">&gt;&gt;&gt; </span><span class="n">my_extension</span> <span class="o">=</span> <span class="n">MyExtElement</span><span class="p">()</span>
 478 <span class="gp">&gt;&gt;&gt; </span><span class="n">extensions</span> <span class="o">=</span> <span class="p">{</span> <span class="p">(</span><span class="s">'testns'</span><span class="p">,</span> <span class="s">'ext'</span><span class="p">)</span> <span class="p">:</span> <span class="n">my_extension</span> <span class="p">}</span>
 479 <span class="gp">&gt;&gt;&gt; </span><span class="n">transform</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XSLT</span><span class="p">(</span><span class="n">xslt_ext_tree</span><span class="p">,</span> <span class="n">extensions</span> <span class="o">=</span> <span class="n">extensions</span><span class="p">)</span>
 480
 481 <span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">'&lt;dummy/&gt;'</span><span class="p">)</span>
 482 <span class="gp">&gt;&gt;&gt; </span><span class="n">result</span> <span class="o">=</span> <span class="n">transform</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
 483 <span class="gp">&gt;&gt;&gt; </span><span class="nb">str</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
 484 <span class="go">'&lt;?xml version="1.0"?&gt;\n&lt;foo&gt;&lt;child&gt;NEW TEXT&lt;/child&gt;&lt;/foo&gt;\n'</span>
 485 </pre></div>
 486 </div>
 487 </div>
 488 </div>
 489 <div class="footer">
 490 <hr class="footer" />
 491 Generated on: 2012-07-31.
 492
 493 </div>
 494 </body>
 495 </html>