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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="/sitemap.html">Sitemap</a></li></ul></div></div><div class="banner"><div class="banner_image"><img src="python-xml-title.png" /></div><div class="banner_link"><a href="index.html#support-the-project">Like the tool? <br class="first" />Help making it better! <br class="second" />Your donation helps!</a></div></div><h1 class="title">The lxml.etree Tutorial</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>Stefan Behnel</td></tr>
</tbody>
</table>
<p>This is a tutorial on XML processing with <tt class="docutils literal">lxml.etree</tt>. It briefly
overviews the main concepts of the <a class="reference external" href="https://docs.python.org/3/library/xml.etree.elementtree.html">ElementTree API</a>, and some simple
enhancements that make your life as a programmer easier.</p>
<p>For a complete reference of the API, see the <a class="reference external" href="api/index.html">generated API
documentation</a>.</p>
<div class="contents topic" id="contents">
<p class="topic-title">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#the-element-class" id="toc-entry-1">The Element class</a><ul>
<li><a class="reference internal" href="#elements-are-lists" id="toc-entry-2">Elements are lists</a></li>
<li><a class="reference internal" href="#elements-carry-attributes-as-a-dict" id="toc-entry-3">Elements carry attributes as a dict</a></li>
<li><a class="reference internal" href="#elements-contain-text" id="toc-entry-4">Elements contain text</a></li>
<li><a class="reference internal" href="#using-xpath-to-find-text" id="toc-entry-5">Using XPath to find text</a></li>
<li><a class="reference internal" href="#tree-iteration" id="toc-entry-6">Tree iteration</a></li>
<li><a class="reference internal" href="#serialisation" id="toc-entry-7">Serialisation</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-elementtree-class" id="toc-entry-8">The ElementTree class</a></li>
<li><a class="reference internal" href="#parsing-from-strings-and-files" id="toc-entry-9">Parsing from strings and files</a><ul>
<li><a class="reference internal" href="#the-fromstring-function" id="toc-entry-10">The fromstring() function</a></li>
<li><a class="reference internal" href="#the-xml-function" id="toc-entry-11">The XML() function</a></li>
<li><a class="reference internal" href="#the-parse-function" id="toc-entry-12">The parse() function</a></li>
<li><a class="reference internal" href="#parser-objects" id="toc-entry-13">Parser objects</a></li>
<li><a class="reference internal" href="#incremental-parsing" id="toc-entry-14">Incremental parsing</a></li>
<li><a class="reference internal" href="#event-driven-parsing" id="toc-entry-15">Event-driven parsing</a></li>
</ul>
</li>
<li><a class="reference internal" href="#namespaces" id="toc-entry-16">Namespaces</a></li>
<li><a class="reference internal" href="#the-e-factory" id="toc-entry-17">The E-factory</a></li>
<li><a class="reference internal" href="#elementpath" id="toc-entry-18">ElementPath</a></li>
</ul>
</div>
<p>A common way to import <tt class="docutils literal">lxml.etree</tt> is as follows:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">lxml</span><span class="w"> </span><span class="kn">import</span> <span class="n">etree</span>
</pre></div>
<p>If your code only uses the ElementTree API and does not rely on any
functionality that is specific to <tt class="docutils literal">lxml.etree</tt>, you can also use the following
import chain as a fall-back to ElementTree in the Python standard library:</p>
<div class="syntax"><pre><span></span><span class="k">try</span><span class="p">:</span>
<span class="kn">from</span><span class="w"> </span><span class="nn">lxml</span><span class="w"> </span><span class="kn">import</span> <span class="n">etree</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"running with lxml.etree"</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">ImportError</span><span class="p">:</span>
<span class="kn">import</span><span class="w"> </span><span class="nn">xml.etree.ElementTree</span><span class="w"> </span><span class="k">as</span><span class="w"> </span><span class="nn">etree</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"running with Python's xml.etree.ElementTree"</span><span class="p">)</span>
</pre></div>
<p>To aid in writing portable code, this tutorial makes it clear in the examples
which part of the presented API is an extension of <tt class="docutils literal">lxml.etree</tt> over the
original <a class="reference external" href="https://docs.python.org/3/library/xml.etree.elementtree.html">ElementTree API</a>.</p>
<div class="section" id="the-element-class">
<h1>The Element class</h1>
<p>An <tt class="docutils literal">Element</tt> is the main container object for the ElementTree API. Most of
the XML tree functionality is accessed through this class. Elements are
easily created through the <tt class="docutils literal">Element</tt> factory:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</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="s2">"root"</span><span class="p">)</span>
</pre></div>
<p>The XML tag name of elements is accessed through the <tt class="docutils literal">tag</tt> property:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">root</span>
</pre></div>
<p>Elements are organised in an XML tree structure. To create child elements and
add them to a parent element, you can use the <tt class="docutils literal">append()</tt> method:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">etree</span><span class="o">.</span><span class="n">Element</span><span class="p">(</span><span class="s2">"child1"</span><span class="p">)</span> <span class="p">)</span>
</pre></div>
<p>However, this is so common that there is a shorter and much more efficient way
to do this: the <tt class="docutils literal">SubElement</tt> factory. It accepts the same arguments as the
<tt class="docutils literal">Element</tt> factory, but additionally requires the parent as first argument:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">child2</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">root</span><span class="p">,</span> <span class="s2">"child2"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">child3</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">root</span><span class="p">,</span> <span class="s2">"child3"</span><span class="p">)</span>
</pre></div>
<p>To see that this is really XML, you can serialise the tree you have created:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root><child1/><child2/><child3/></root>'</span>
</pre></div>
<p>We'll create a little helper function to pretty-print the XML for us:</p>
<blockquote>
<pre class="doctest-block">
>>> def prettyprint(element, **kwargs):
... xml = etree.tostring(element, pretty_print=True, **kwargs)
... print(xml.decode(), end='')
</pre>
<pre class="doctest-block">
>>> prettyprint(root)
<root>
<child1/>
<child2/>
<child3/>
</root>
</pre>
</blockquote>
<div class="section" id="elements-are-lists">
<h2>Elements are lists</h2>
<p>To make the access to these subelements easy and straight forward,
elements mimic the behaviour of normal Python lists as closely as
possible:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">child</span> <span class="o">=</span> <span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">child</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child1</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">root</span><span class="p">))</span>
<span class="go">3</span>
<span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">index</span><span class="p">(</span><span class="n">root</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span> <span class="c1"># lxml.etree only!</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="n">children</span> <span class="o">=</span> <span class="nb">list</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">child</span> <span class="ow">in</span> <span class="n">root</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">child</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child1</span>
<span class="go">child2</span>
<span class="go">child3</span>
<span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">insert</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="n">etree</span><span class="o">.</span><span class="n">Element</span><span class="p">(</span><span class="s2">"child0"</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">start</span> <span class="o">=</span> <span class="n">root</span><span class="p">[:</span><span class="mi">1</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">end</span> <span class="o">=</span> <span class="n">root</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">:]</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">start</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child0</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">end</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child3</span>
</pre></div>
<p>Prior to ElementTree 1.3 and lxml 2.0, you could also check the truth value of
an Element to see if it has children, i.e. if the list of children is empty:</p>
<div class="syntax"><pre><span></span><span class="k">if</span> <span class="n">root</span><span class="p">:</span> <span class="c1"># this no longer works!</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">"The root element has children"</span><span class="p">)</span>
</pre></div>
<p>This is no longer supported as people tend to expect that a "something"
evaluates to True and expect Elements to be "something", may they have
children or not. So, many users find it surprising that any Element
would evaluate to False in an if-statement like the above. Instead,
use <tt class="docutils literal">len(element)</tt>, which is both more explicit and less error prone.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">iselement</span><span class="p">(</span><span class="n">root</span><span class="p">))</span> <span class="c1"># test if it's some kind of Element</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">root</span><span class="p">):</span> <span class="c1"># test if it has children</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"The root element has children"</span><span class="p">)</span>
<span class="go">The root element has children</span>
</pre></div>
<p>There is another important case where the behaviour of Elements in lxml
(in 2.0 and later) deviates from that of lists and from that of the
original ElementTree (prior to version 1.3 or Python 2.7/3.2):</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="k">for</span> <span class="n">child</span> <span class="ow">in</span> <span class="n">root</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">child</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child0</span>
<span class="go">child1</span>
<span class="go">child2</span>
<span class="go">child3</span>
<span class="gp">>>> </span><span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="n">root</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="c1"># this moves the element in lxml.etree!</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">child</span> <span class="ow">in</span> <span class="n">root</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">child</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child3</span>
<span class="go">child1</span>
<span class="go">child2</span>
</pre></div>
<p>In this example, the last element is <em>moved</em> to a different position,
instead of being copied, i.e. it is automatically removed from its
previous position when it is put in a different place. In lists,
objects can appear in multiple positions at the same time, and the
above assignment would just copy the item reference into the first
position, so that both contain the exact same item:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">l</span> <span class="o">=</span> <span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">l</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="o">=</span> <span class="n">l</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
<span class="gp">>>> </span><span class="n">l</span>
<span class="go">[3, 1, 2, 3]</span>
</pre></div>
<p>Note that in the original ElementTree, a single Element object can sit
in any number of places in any number of trees, which allows for the same
copy operation as with lists. The obvious drawback is that modifications
to such an Element will apply to all places where it appears in a tree,
which may or may not be intended.</p>
<p>The upside of this difference is that an Element in <tt class="docutils literal">lxml.etree</tt> always
has exactly one parent, which can be queried through the <tt class="docutils literal">getparent()</tt>
method. This is not supported in the original ElementTree.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</span> <span class="ow">is</span> <span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">getparent</span><span class="p">()</span> <span class="c1"># lxml.etree only!</span>
<span class="go">True</span>
</pre></div>
<p>If you want to <em>copy</em> an element to a different position in <tt class="docutils literal">lxml.etree</tt>,
consider creating an independent <em>deep copy</em> using the <tt class="docutils literal">copy</tt> module
from Python's standard library:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">copy</span><span class="w"> </span><span class="kn">import</span> <span class="n">deepcopy</span>
<span class="gp">>>> </span><span class="n">element</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="s2">"neu"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">element</span><span class="o">.</span><span class="n">append</span><span class="p">(</span> <span class="n">deepcopy</span><span class="p">(</span><span class="n">root</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span> <span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">element</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">child1</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">([</span> <span class="n">c</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">c</span> <span class="ow">in</span> <span class="n">root</span> <span class="p">])</span>
<span class="go">['child3', 'child1', 'child2']</span>
</pre></div>
<p>The siblings (or neighbours) of an element are accessed as next and previous
elements:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="ow">is</span> <span class="n">root</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">getprevious</span><span class="p">()</span> <span class="c1"># lxml.etree only!</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">root</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="ow">is</span> <span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">getnext</span><span class="p">()</span> <span class="c1"># lxml.etree only!</span>
<span class="go">True</span>
</pre></div>
</div>
<div class="section" id="elements-carry-attributes-as-a-dict">
<h2>Elements carry attributes as a dict</h2>
<p>XML elements support attributes. You can create them directly in the Element
factory:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</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="s2">"root"</span><span class="p">,</span> <span class="n">interesting</span><span class="o">=</span><span class="s2">"totally"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root interesting="totally"/>'</span>
</pre></div>
<p>Attributes are just unordered name-value pairs, so a very convenient way
of dealing with them is through the dictionary-like interface of Elements:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"interesting"</span><span class="p">))</span>
<span class="go">totally</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"hello"</span><span class="p">))</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">set</span><span class="p">(</span><span class="s2">"hello"</span><span class="p">,</span> <span class="s2">"Huhu"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"hello"</span><span class="p">))</span>
<span class="go">Huhu</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root interesting="totally" hello="Huhu"/>'</span>
<span class="gp">>>> </span><span class="nb">sorted</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">keys</span><span class="p">())</span>
<span class="go">['hello', 'interesting']</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="nb">sorted</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">items</span><span class="p">()):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%s</span><span class="s1"> = </span><span class="si">%r</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">value</span><span class="p">))</span>
<span class="go">hello = 'Huhu'</span>
<span class="go">interesting = 'totally'</span>
</pre></div>
<p>For the cases where you want to do item lookup or have other reasons for
getting a 'real' dictionary-like object, e.g. for passing it around,
you can use the <tt class="docutils literal">attrib</tt> property:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">attributes</span> <span class="o">=</span> <span class="n">root</span><span class="o">.</span><span class="n">attrib</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">attributes</span><span class="p">[</span><span class="s2">"interesting"</span><span class="p">])</span>
<span class="go">totally</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">attributes</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"no-such-attribute"</span><span class="p">))</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="n">attributes</span><span class="p">[</span><span class="s2">"hello"</span><span class="p">]</span> <span class="o">=</span> <span class="s2">"Guten Tag"</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">attributes</span><span class="p">[</span><span class="s2">"hello"</span><span class="p">])</span>
<span class="go">Guten Tag</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"hello"</span><span class="p">))</span>
<span class="go">Guten Tag</span>
</pre></div>
<p>Note that <tt class="docutils literal">attrib</tt> is a dict-like object backed by the Element itself.
This means that any changes to the Element are reflected in <tt class="docutils literal">attrib</tt>
and vice versa. It also means that the XML tree stays alive in memory
as long as the <tt class="docutils literal">attrib</tt> of one of its Elements is in use. To get an
independent snapshot of the attributes that does not depend on the XML
tree, copy it into a dict:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">d</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">attrib</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">sorted</span><span class="p">(</span><span class="n">d</span><span class="o">.</span><span class="n">items</span><span class="p">())</span>
<span class="go">[('hello', 'Guten Tag'), ('interesting', 'totally')]</span>
</pre></div>
</div>
<div class="section" id="elements-contain-text">
<h2>Elements contain text</h2>
<p>Elements can contain text:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</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="s2">"root"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"TEXT"</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
<span class="go">TEXT</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root>TEXT</root>'</span>
</pre></div>
<p>In many XML documents (<em>data-centric</em> documents), this is the only place where
text can be found. It is encapsulated by a leaf tag at the very bottom of the
tree hierarchy.</p>
<p>However, if XML is used for tagged text documents such as (X)HTML, text can
also appear between different elements, right in the middle of the tree:</p>
<div class="syntax"><pre><span></span><span class="p"><</span><span class="nt">html</span><span class="p">><</span><span class="nt">body</span><span class="p">></span>Hello<span class="p"><</span><span class="nt">br</span><span class="p">/></span>World<span class="p"></</span><span class="nt">body</span><span class="p">></</span><span class="nt">html</span><span class="p">></span>
</pre></div>
<p>Here, the <tt class="docutils literal"><br/></tt> tag is surrounded by text. This is often referred to as
<em>document-style</em> or <em>mixed-content</em> XML. Elements support this through their
<tt class="docutils literal">tail</tt> property. It contains the text that directly follows the element, up
to the next element in the XML tree:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">html</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="s2">"html"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">body</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">html</span><span class="p">,</span> <span class="s2">"body"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">body</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"TEXT"</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">html</span><span class="p">)</span>
<span class="go">b'<html><body>TEXT</body></html>'</span>
<span class="gp">>>> </span><span class="n">br</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">body</span><span class="p">,</span> <span class="s2">"br"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">html</span><span class="p">)</span>
<span class="go">b'<html><body>TEXT<br/></body></html>'</span>
<span class="gp">>>> </span><span class="n">br</span><span class="o">.</span><span class="n">tail</span> <span class="o">=</span> <span class="s2">"TAIL"</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">html</span><span class="p">)</span>
<span class="go">b'<html><body>TEXT<br/>TAIL</body></html>'</span>
</pre></div>
<p>The two properties <tt class="docutils literal">.text</tt> and <tt class="docutils literal">.tail</tt> are enough to represent any
text content in an XML document. This way, the ElementTree API does
not require any <a class="reference external" href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#ID-1312295772">special text nodes</a> in addition to the Element
class, that tend to get in the way fairly often (as you might know
from classic <a class="reference external" href="http://www.w3.org/TR/DOM-Level-3-Core/core.html">DOM</a> APIs).</p>
<p>However, there are cases where the tail text also gets in the way.
For example, when you serialise an Element from within the tree, you
do not always want its tail text in the result (although you would
still want the tail text of its children). For this purpose, the
<tt class="docutils literal">tostring()</tt> function accepts the keyword argument <tt class="docutils literal">with_tail</tt>:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">br</span><span class="p">)</span>
<span class="go">b'<br/>TAIL'</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">br</span><span class="p">,</span> <span class="n">with_tail</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span> <span class="c1"># lxml.etree only!</span>
<span class="go">b'<br/>'</span>
</pre></div>
<p>If you want to read <em>only</em> the text, i.e. without any intermediate
tags, you have to recursively concatenate all <tt class="docutils literal">text</tt> and <tt class="docutils literal">tail</tt>
attributes in the correct order. Again, the <tt class="docutils literal">tostring()</tt> function
comes to the rescue, this time using the <tt class="docutils literal">method</tt> keyword:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">html</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s2">"text"</span><span class="p">)</span>
<span class="go">b'TEXTTAIL'</span>
</pre></div>
</div>
<div class="section" id="using-xpath-to-find-text">
<h2>Using XPath to find text</h2>
<p>Another way to extract the text content of a tree is <a class="reference external" href="xpathxslt.html#xpath">XPath</a>, which
also allows you to extract the separate text chunks into a list:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">html</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s2">"string()"</span><span class="p">))</span> <span class="c1"># lxml.etree only!</span>
<span class="go">TEXTTAIL</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">html</span><span class="o">.</span><span class="n">xpath</span><span class="p">(</span><span class="s2">"//text()"</span><span class="p">))</span> <span class="c1"># lxml.etree only!</span>
<span class="go">['TEXT', 'TAIL']</span>
</pre></div>
<p>If you want to use this more often, you can wrap it in a function:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">build_text_list</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPath</span><span class="p">(</span><span class="s2">"//text()"</span><span class="p">)</span> <span class="c1"># lxml.etree only!</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">build_text_list</span><span class="p">(</span><span class="n">html</span><span class="p">))</span>
<span class="go">['TEXT', 'TAIL']</span>
</pre></div>
<p>Note that a string result returned by XPath is a special 'smart'
object that knows about its origins. You can ask it where it came
from through its <tt class="docutils literal">getparent()</tt> method, just as you would with
Elements:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">texts</span> <span class="o">=</span> <span class="n">build_text_list</span><span class="p">(</span><span class="n">html</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">texts</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="go">TEXT</span>
<span class="gp">>>> </span><span class="n">parent</span> <span class="o">=</span> <span class="n">texts</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">getparent</span><span class="p">()</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">parent</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">body</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">texts</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span>
<span class="go">TAIL</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">texts</span><span class="p">[</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>
<span class="go">br</span>
</pre></div>
<p>You can also find out if it's normal text content or tail text:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">texts</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">is_text</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">texts</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">is_text</span><span class="p">)</span>
<span class="go">False</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">texts</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">is_tail</span><span class="p">)</span>
<span class="go">True</span>
</pre></div>
<p>While this works for the results of the <tt class="docutils literal">text()</tt> function, lxml will
not tell you the origin of a string value that was constructed by the
XPath functions <tt class="docutils literal">string()</tt> or <tt class="docutils literal">concat()</tt>:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">stringify</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XPath</span><span class="p">(</span><span class="s2">"string()"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">stringify</span><span class="p">(</span><span class="n">html</span><span class="p">))</span>
<span class="go">TEXTTAIL</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">stringify</span><span class="p">(</span><span class="n">html</span><span class="p">)</span><span class="o">.</span><span class="n">getparent</span><span class="p">())</span>
<span class="go">None</span>
</pre></div>
</div>
<div class="section" id="tree-iteration">
<h2>Tree iteration</h2>
<p>For problems like the above, where you want to recursively traverse the tree
and do something with its elements, tree iteration is a very convenient
solution. Elements provide a tree iterator for this purpose. It yields
elements in <em>document order</em>, i.e. in the order their tags would appear if you
serialised the tree to XML:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</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="s2">"root"</span><span class="p">)</span>
<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">root</span><span class="p">,</span> <span class="s2">"child"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Child 1"</span>
<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">root</span><span class="p">,</span> <span class="s2">"child"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Child 2"</span>
<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">root</span><span class="p">,</span> <span class="s2">"another"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Child 3"</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go"><root></span>
<span class="go"> <child>Child 1</child></span>
<span class="go"> <child>Child 2</child></span>
<span class="go"> <another>Child 3</another></span>
<span class="go"></root></span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">():</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">}</span><span class="s2"> - </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">root - None</span>
<span class="go">child - Child 1</span>
<span class="go">child - Child 2</span>
<span class="go">another - Child 3</span>
</pre></div>
<p>If you know you are only interested in a single tag, you can pass its name to
<tt class="docutils literal">iter()</tt> to have it filter for you. Starting with lxml 3.0, you can also
pass more than one tag to intercept on multiple tags during iteration.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s2">"child"</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">}</span><span class="s2"> - </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">child - Child 1</span>
<span class="go">child - Child 2</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s2">"another"</span><span class="p">,</span> <span class="s2">"child"</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">}</span><span class="s2"> - </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">child - Child 1</span>
<span class="go">child - Child 2</span>
<span class="go">another - Child 3</span>
</pre></div>
<p>By default, iteration yields all nodes in the tree, including
ProcessingInstructions, Comments and Entity instances. If you want to
make sure only Element objects are returned, you can pass the
<tt class="docutils literal">Element</tt> factory as tag parameter:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">Entity</span><span class="p">(</span><span class="s2">"#234"</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">Comment</span><span class="p">(</span><span class="s2">"some comment"</span><span class="p">))</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">if</span> <span class="nb">isinstance</span><span class="p">(</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="p">,</span> <span class="nb">str</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">}</span><span class="s2"> - </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">else</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"SPECIAL: </span><span class="si">{</span><span class="n">element</span><span class="si">}</span><span class="s2"> - </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">root - None</span>
<span class="go">child - Child 1</span>
<span class="go">child - Child 2</span>
<span class="go">another - Child 3</span>
<span class="go">SPECIAL: &#234; - &#234;</span>
<span class="go">SPECIAL: <!--some comment--> - some comment</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="n">tag</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="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">}</span><span class="s2"> - </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">root - None</span>
<span class="go">child - Child 1</span>
<span class="go">child - Child 2</span>
<span class="go">another - Child 3</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="n">tag</span><span class="o">=</span><span class="n">etree</span><span class="o">.</span><span class="n">Entity</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
<span class="go">&#234;</span>
</pre></div>
<p>Note that passing a wildcard <tt class="docutils literal">"*"</tt> tag name will also yield all
<tt class="docutils literal">Element</tt> nodes (and only elements).</p>
<p>In <tt class="docutils literal">lxml.etree</tt>, elements provide <a class="reference external" href="api.html#iteration">further iterators</a> for all directions in the
tree: children, parents (or rather ancestors) and siblings.</p>
</div>
<div class="section" id="serialisation">
<h2>Serialisation</h2>
<p>Serialisation commonly uses the <tt class="docutils literal">tostring()</tt> function that returns a
string, or the <tt class="docutils literal">ElementTree.write()</tt> method that writes to a file, a
file-like object, or a URL (via FTP PUT or HTTP POST). Both calls accept
the same keyword arguments like <tt class="docutils literal">pretty_print</tt> for formatted output
or <tt class="docutils literal">encoding</tt> to select a specific output encoding other than plain
ASCII:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="s1">'<root><a><b/></a></root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root><a><b/></a></root>'</span>
<span class="gp">>>> </span><span class="n">xml_string</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">xml_declaration</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">xml_string</span><span class="o">.</span><span class="n">decode</span><span class="p">(),</span> <span class="n">end</span><span class="o">=</span><span class="s1">''</span><span class="p">)</span>
<span class="go"><?xml version='1.0' encoding='ASCII'?></span>
<span class="go"><root><a><b/></a></root></span>
<span class="gp">>>> </span><span class="n">latin1_bytesstring</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s1">'iso8859-1'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">latin1_bytesstring</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">'iso8859-1'</span><span class="p">),</span> <span class="n">end</span><span class="o">=</span><span class="s1">''</span><span class="p">)</span>
<span class="go"><?xml version='1.0' encoding='iso8859-1'?></span>
<span class="go"><root><a><b/></a></root></span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">pretty_print</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span><span class="o">.</span><span class="n">decode</span><span class="p">(),</span> <span class="n">end</span><span class="o">=</span><span class="s1">''</span><span class="p">)</span>
<span class="go"><root></span>
<span class="go"> <a></span>
<span class="go"> <b/></span>
<span class="go"> </a></span>
<span class="go"></root></span>
</pre></div>
<p>Note that pretty printing appends a newline at the end.
We therefore use the <tt class="docutils literal"><span class="pre">end=''</span></tt> option here to prevent the <tt class="docutils literal">print()</tt>
function from adding another line break.</p>
<p>For more fine-grained control over the pretty-printing, you can add
whitespace indentation to the tree before serialising it, using the
<tt class="docutils literal">indent()</tt> function (added in lxml 4.5):</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="s1">'<root><a><b/></span><span class="se">\n</span><span class="s1"></a></root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>
<span class="go"><root><a><b/></span>
<span class="go"></a></root></span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">indent</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>
<span class="go"><root></span>
<span class="go"> <a></span>
<span class="go"> <b/></span>
<span class="go"> </a></span>
<span class="go"></root></span>
<span class="gp">>>> </span><span class="n">root</span><span class="o">.</span><span class="n">text</span>
<span class="go">'\n '</span>
<span class="gp">>>> </span><span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">text</span>
<span class="go">'\n '</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">indent</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">space</span><span class="o">=</span><span class="s2">" "</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>
<span class="go"><root></span>
<span class="go"> <a></span>
<span class="go"> <b/></span>
<span class="go"> </a></span>
<span class="go"></root></span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">indent</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">space</span><span class="o">=</span><span class="s2">"</span><span class="se">\t</span><span class="s2">"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root>\n\t<a>\n\t\t<b/>\n\t</a>\n</root>'</span>
</pre></div>
<p>In lxml 2.0 and later, as well as in <tt class="docutils literal">xml.etree</tt>, the serialisation
functions can do more than XML serialisation. You can serialise to
HTML or extract the text content by passing the <tt class="docutils literal">method</tt> keyword:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="gp">... </span> <span class="s1">'<html><head/><body><p>Hello<br/>World</p></body></html>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span> <span class="c1"># default: method = 'xml'</span>
<span class="go">b'<html><head/><body><p>Hello<br/>World</p></body></html>'</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'xml'</span><span class="p">)</span> <span class="c1"># same as above</span>
<span class="go">b'<html><head/><body><p>Hello<br/>World</p></body></html>'</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'html'</span><span class="p">)</span>
<span class="go">b'<html><head></head><body><p>Hello<br>World</p></body></html>'</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'html'</span><span class="p">)</span>
<span class="go"><html></span>
<span class="go"><head></head></span>
<span class="go"><body><p>Hello<br>World</p></body></span>
<span class="go"></html></span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'text'</span><span class="p">)</span>
<span class="go">b'HelloWorld'</span>
</pre></div>
<p>As for XML serialisation, the default encoding for plain text
serialisation is ASCII:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">br</span> <span class="o">=</span> <span class="nb">next</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'br'</span><span class="p">))</span> <span class="c1"># get first result of iteration</span>
<span class="gp">>>> </span><span class="n">br</span><span class="o">.</span><span class="n">tail</span> <span class="o">=</span> <span class="s1">'Wörld'</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'text'</span><span class="p">)</span> <span class="c1"># doctest: +ELLIPSIS</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="w"> </span><span class="c">...</span>
<span class="gr">UnicodeEncodeError</span>: <span class="n">'ascii' codec can't encode character '\xf6' ...</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'text'</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s2">"UTF-8"</span><span class="p">)</span>
<span class="go">b'HelloW\xc3\xb6rld'</span>
</pre></div>
<p>Here, serialising to a Python text string instead of a byte string
might become handy. Just pass the name <tt class="docutils literal">'unicode'</tt> as encoding:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s1">'unicode'</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s1">'text'</span><span class="p">)</span>
<span class="go">'HelloWörld'</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="n">encoding</span><span class="o">=</span><span class="s1">'unicode'</span><span class="p">)</span>
<span class="go">'<html><head/><body><p>Hello<br/>Wörld</p></body></html>'</span>
</pre></div>
<p>The W3C has a good article about the Unicode character set and character encodings
<<a class="reference external" href="http://www.w3.org/International/tutorials/tutorial-char-enc/">http://www.w3.org/International/tutorials/tutorial-char-enc/</a>>`_.</p>
</div>
</div>
<div class="section" id="the-elementtree-class">
<h1>The ElementTree class</h1>
<p>An <tt class="docutils literal">ElementTree</tt> is mainly a document wrapper around a tree with a
root node. It provides a couple of methods for serialisation and
general document handling.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><?xml version="1.0"?></span>
<span class="gp">... </span><span class="s1"><!DOCTYPE root SYSTEM "test" [ <!ENTITY tasty "parsnips"> ]></span>
<span class="gp">... </span><span class="s1"><root></span>
<span class="gp">... </span><span class="s1"> <a>&tasty;</a></span>
<span class="gp">... </span><span class="s1"></root></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">tree</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>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span><span class="o">.</span><span class="n">xml_version</span><span class="p">)</span>
<span class="go">1.0</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span><span class="o">.</span><span class="n">doctype</span><span class="p">)</span>
<span class="go"><!DOCTYPE root SYSTEM "test"></span>
<span class="gp">>>> </span><span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span><span class="o">.</span><span class="n">public_id</span> <span class="o">=</span> <span class="s1">'-//W3C//DTD XHTML 1.0 Transitional//EN'</span>
<span class="gp">>>> </span><span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span><span class="o">.</span><span class="n">system_url</span> <span class="o">=</span> <span class="s1">'file://local.dtd'</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span><span class="o">.</span><span class="n">doctype</span><span class="p">)</span>
<span class="go"><!DOCTYPE root PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "file://local.dtd"></span>
</pre></div>
<p>An <tt class="docutils literal">ElementTree</tt> is also what you get back when you call the
<tt class="docutils literal">parse()</tt> function to parse files or file-like objects (see the
parsing section below).</p>
<p>One of the important differences is that the <tt class="docutils literal">ElementTree</tt> class
serialises as a complete document, as opposed to a single <tt class="docutils literal">Element</tt>.
This includes top-level processing instructions and comments, as well
as a DOCTYPE and other DTD content in the document:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">tree</span><span class="p">)</span> <span class="c1"># lxml 1.3.4 and later</span>
<span class="go"><!DOCTYPE root PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "file://local.dtd" [</span>
<span class="go"><!ENTITY tasty "parsnips"></span>
<span class="go">]></span>
<span class="go"><root></span>
<span class="go"> <a>parsnips</a></span>
<span class="go"></root></span>
</pre></div>
<p>In the original xml.etree.ElementTree implementation and in lxml
up to 1.3.3, the output looks the same as when serialising only
the root Element:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">())</span>
<span class="go"><root></span>
<span class="go"> <a>parsnips</a></span>
<span class="go"></root></span>
</pre></div>
<p>This serialisation behaviour has changed in lxml 1.3.4. Before,
the tree was serialised without DTD content, which made lxml
lose DTD information in an input-output cycle.</p>
</div>
<div class="section" id="parsing-from-strings-and-files">
<h1>Parsing from strings and files</h1>
<p><tt class="docutils literal">lxml.etree</tt> supports parsing XML in a number of ways and from all
important sources, namely strings, files, URLs (http/ftp) and
file-like objects. The main parse functions are <tt class="docutils literal">fromstring()</tt> and
<tt class="docutils literal">parse()</tt>, both called with the source as first argument. By
default, they use the standard parser, but you can always pass a
different parser as second argument.</p>
<div class="section" id="the-fromstring-function">
<h2>The fromstring() function</h2>
<p>The <tt class="docutils literal">fromstring()</tt> function is the easiest way to parse a string:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">some_xml_data</span> <span class="o">=</span> <span class="s2">"<root>data</root>"</span>
<span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="n">some_xml_data</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">root</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root>data</root>'</span>
</pre></div>
</div>
<div class="section" id="the-xml-function">
<h2>The XML() function</h2>
<p>The <tt class="docutils literal">XML()</tt> function behaves like the <tt class="docutils literal">fromstring()</tt> function, but is
commonly used to write XML literals right into the source:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="s2">"<root>data</root>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">root</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root>data</root>'</span>
</pre></div>
<p>There is also a corresponding function <tt class="docutils literal">HTML()</tt> for HTML literals.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">HTML</span><span class="p">(</span><span class="s2">"<p>data</p>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<html><body><p>data</p></body></html>'</span>
</pre></div>
</div>
<div class="section" id="the-parse-function">
<h2>The parse() function</h2>
<p>The <tt class="docutils literal">parse()</tt> function is used to parse from files and file-like objects.</p>
<p>As an example of such a file-like object, the following code uses the
<tt class="docutils literal">BytesIO</tt> class for reading from a string instead of an external file.
However, in real life, you would obviously avoid doing this and use the
string parsing functions like <tt class="docutils literal">fromstring()</tt> above.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">io</span><span class="w"> </span><span class="kn">import</span> <span class="n">BytesIO</span>
<span class="gp">>>> </span><span class="n">some_file_or_file_like_object</span> <span class="o">=</span> <span class="n">BytesIO</span><span class="p">(</span><span class="sa">b</span><span class="s2">"<root>data</root>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">tree</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">some_file_or_file_like_object</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">tree</span><span class="p">)</span>
<span class="go">b'<root>data</root>'</span>
</pre></div>
<p>Note that <tt class="docutils literal">parse()</tt> returns an ElementTree object, not an Element object as
the string parser functions:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">()</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">root</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root>data</root>'</span>
</pre></div>
<p>The reasoning behind this difference is that <tt class="docutils literal">parse()</tt> returns a
complete document from a file, while the string parsing functions are
commonly used to parse XML fragments.</p>
<p>The <tt class="docutils literal">parse()</tt> function supports any of the following sources:</p>
<ul class="simple">
<li>an open file object (make sure to open it in binary mode)</li>
<li>a file-like object that has a <tt class="docutils literal">.read(byte_count)</tt> method returning
a byte string on each call</li>
<li>a filename string</li>
<li>an HTTP or FTP URL string</li>
</ul>
<p>Note that passing a filename or URL is usually faster than passing an
open file or file-like object. However, the HTTP/FTP client in libxml2
is rather simple, so things like HTTP authentication require a dedicated
URL request library, e.g. <tt class="docutils literal">urllib2</tt> or <tt class="docutils literal">requests</tt>. These libraries
usually provide a file-like object for the result that you can parse
from while the response is streaming in.</p>
</div>
<div class="section" id="parser-objects">
<h2>Parser objects</h2>
<p>By default, <tt class="docutils literal">lxml.etree</tt> uses a standard parser with a default setup. If
you want to configure the parser, you can create a new instance:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">remove_blank_text</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span> <span class="c1"># lxml.etree only!</span>
</pre></div>
<p>This creates a parser that removes empty text between tags while parsing,
which can reduce the size of the tree and avoid dangling tail text if you know
that whitespace-only content is not meaningful for your data. An example:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="s2">"<root> <a/> <b> </b> </root>"</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root><a/><b> </b></root>'</span>
</pre></div>
<p>Note that the whitespace content inside the <tt class="docutils literal"><b></tt> tag was not removed, as
content at leaf elements tends to be data content (even if blank). You can
easily remove it in an additional step by traversing the tree:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="k">for</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s2">"*"</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">element</span><span class="o">.</span><span class="n">text</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span> <span class="ow">and</span> <span class="ow">not</span> <span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="o">.</span><span class="n">strip</span><span class="p">():</span>
<span class="gp">... </span> <span class="n">element</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="kc">None</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root><a/><b/></root>'</span>
</pre></div>
<p>See <tt class="docutils literal">help(etree.XMLParser)</tt> to find out about the available parser options.</p>
</div>
<div class="section" id="incremental-parsing">
<h2>Incremental parsing</h2>
<p><tt class="docutils literal">lxml.etree</tt> provides two ways for incremental step-by-step parsing. One is
through file-like objects, where it calls the <tt class="docutils literal">read()</tt> method repeatedly.
This is best used where the data arrives from a source like <tt class="docutils literal">urllib</tt> or any
other file-like object that can provide data on request. Note that the parser
will block and wait until data becomes available in this case:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="k">class</span><span class="w"> </span><span class="nc">DataSource</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">data</span> <span class="o">=</span> <span class="p">[</span> <span class="sa">b</span><span class="s2">"<roo"</span><span class="p">,</span> <span class="sa">b</span><span class="s2">"t><"</span><span class="p">,</span> <span class="sa">b</span><span class="s2">"a/"</span><span class="p">,</span> <span class="sa">b</span><span class="s2">"><"</span><span class="p">,</span> <span class="sa">b</span><span class="s2">"/root>"</span> <span class="p">]</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">read</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">requested_size</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">try</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">data</span><span class="o">.</span><span class="n">pop</span><span class="p">(</span><span class="mi">0</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">except</span> <span class="ne">IndexError</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="sa">b</span><span class="s1">''</span>
<span class="gp">>>> </span><span class="n">tree</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">DataSource</span><span class="p">())</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">tree</span><span class="p">)</span>
<span class="go">b'<root><a/></root>'</span>
</pre></div>
<p>The second way is through a feed parser interface, given by the <tt class="docutils literal">feed(data)</tt>
and <tt class="docutils literal">close()</tt> methods:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s2">"<roo"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s2">"t><"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s2">"a/"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s2">"><"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s2">"/root>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root><a/></root>'</span>
</pre></div>
<p>Here, you can interrupt the parsing process at any time and continue it later
on with another call to the <tt class="docutils literal">feed()</tt> method. This comes in handy if you
want to avoid blocking calls to the parser, e.g. in frameworks like Twisted,
or whenever data comes in slowly or in chunks and you want to do other things
while waiting for the next chunk.</p>
<p>After calling the <tt class="docutils literal">close()</tt> method (or when an exception was raised
by the parser), you can reuse the parser by calling its <tt class="docutils literal">feed()</tt>
method again:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s2">"<root/>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">tostring</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="go">b'<root/>'</span>
</pre></div>
</div>
<div class="section" id="event-driven-parsing">
<h2>Event-driven parsing</h2>
<p>Sometimes, all you need from a document is a small fraction somewhere deep
inside the tree, so parsing the whole tree into memory, traversing it and
dropping it can be too much overhead. <tt class="docutils literal">lxml.etree</tt> supports this use case
with two event-driven parser interfaces, one that generates parser events
while building the tree (<tt class="docutils literal">iterparse</tt>), and one that does not build the tree
at all, and instead calls feedback methods on a target object in a SAX-like
fashion.</p>
<p>Here is a simple <tt class="docutils literal">iterparse()</tt> example:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">some_file_like</span> <span class="o">=</span> <span class="n">BytesIO</span><span class="p">(</span><span class="sa">b</span><span class="s2">"<root><a>data</a></root>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">some_file_like</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">event</span><span class="si">}</span><span class="s2">, </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">:</span><span class="s2">>4</span><span class="si">}</span><span class="s2">, </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">end, a, data</span>
<span class="go">end, root, None</span>
</pre></div>
<p>By default, <tt class="docutils literal">iterparse()</tt> only generates an event when it is done parsing an
element, but you can control this through the <tt class="docutils literal">events</tt> keyword argument:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">some_file_like</span> <span class="o">=</span> <span class="n">BytesIO</span><span class="p">(</span><span class="sa">b</span><span class="s2">"<root><a>data</a></root>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">some_file_like</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">events</span><span class="o">=</span><span class="p">(</span><span class="s2">"start"</span><span class="p">,</span> <span class="s2">"end"</span><span class="p">)):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">"</span><span class="si">{</span><span class="n">event</span><span class="si">:</span><span class="s2">>5</span><span class="si">}</span><span class="s2">, </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">tag</span><span class="si">:</span><span class="s2">>4</span><span class="si">}</span><span class="s2">, </span><span class="si">{</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="si">}</span><span class="s2">"</span><span class="p">)</span>
<span class="go">start, root, None</span>
<span class="go">start, a, data</span>
<span class="go"> end, a, data</span>
<span class="go"> end, root, None</span>
</pre></div>
<p>Note that the text, tail, and children of an Element are not necessarily present
yet when receiving the <tt class="docutils literal">start</tt> event. Only the <tt class="docutils literal">end</tt> event guarantees
that the Element has been parsed completely.</p>
<p>It also allows you to <tt class="docutils literal">.clear()</tt> or modify the content of an Element to
save memory. So if you parse a large tree and you want to keep memory
usage small, you should clean up parts of the tree that you no longer
need. The <tt class="docutils literal">keep_tail=True</tt> argument to <tt class="docutils literal">.clear()</tt> makes sure that
(tail) text content that follows the current element will not be touched.
It is highly discouraged to modify any content that the parser may not
have completely read through yet.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">some_file_like</span> <span class="o">=</span> <span class="n">BytesIO</span><span class="p">(</span>
<span class="gp">... </span> <span class="sa">b</span><span class="s2">"<root><a><b>data</b></a><a><b/></a></root>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">some_file_like</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">element</span><span class="o">.</span><span class="n">tag</span> <span class="o">==</span> <span class="s1">'b'</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">element</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">elif</span> <span class="n">element</span><span class="o">.</span><span class="n">tag</span> <span class="o">==</span> <span class="s1">'a'</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s2">"** cleaning up the subtree"</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">element</span><span class="o">.</span><span class="n">clear</span><span class="p">(</span><span class="n">keep_tail</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="go">data</span>
<span class="go">** cleaning up the subtree</span>
<span class="go">None</span>
<span class="go">** cleaning up the subtree</span>
</pre></div>
<p>A very important use case for <tt class="docutils literal">iterparse()</tt> is parsing large
generated XML files, e.g. database dumps. Most often, these XML
formats only have one main data item element that hangs directly below
the root node and that is repeated thousands of times. In this case,
it is best practice to let <tt class="docutils literal">lxml.etree</tt> do the tree building and only to
intercept on exactly this one Element, using the normal tree API
for data extraction.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">xml_file</span> <span class="o">=</span> <span class="n">BytesIO</span><span class="p">(</span><span class="sa">b</span><span class="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><root></span>
<span class="gp">... </span><span class="s1"> <a><b>ABC</b><c>abc</c></a></span>
<span class="gp">... </span><span class="s1"> <a><b>MORE DATA</b><c>more data</c></a></span>
<span class="gp">... </span><span class="s1"> <a><b>XYZ</b><c>xyz</c></a></span>
<span class="gp">... </span><span class="s1"></root>'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">_</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">xml_file</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="s1">'a'</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%s</span><span class="s1"> -- </span><span class="si">%s</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">element</span><span class="o">.</span><span class="n">findtext</span><span class="p">(</span><span class="s1">'b'</span><span class="p">),</span> <span class="n">element</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="o">.</span><span class="n">text</span><span class="p">))</span>
<span class="gp">... </span> <span class="n">element</span><span class="o">.</span><span class="n">clear</span><span class="p">(</span><span class="n">keep_tail</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>
<span class="go">ABC -- abc</span>
<span class="go">MORE DATA -- more data</span>
<span class="go">XYZ -- xyz</span>
</pre></div>
<p>If, for some reason, building the tree is not desired at all, the
target parser interface of <tt class="docutils literal">lxml.etree</tt> can be used. It creates
SAX-like events by calling the methods of a target object. By
implementing some or all of these methods, you can control which
events are generated:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="k">class</span><span class="w"> </span><span class="nc">ParserTarget</span><span class="p">:</span>
<span class="gp">... </span> <span class="n">events</span> <span class="o">=</span> <span class="p">[]</span>
<span class="gp">... </span> <span class="n">close_count</span> <span class="o">=</span> <span class="mi">0</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">start</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">tag</span><span class="p">,</span> <span class="n">attrib</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="o">.</span><span class="n">append</span><span class="p">((</span><span class="s2">"start"</span><span class="p">,</span> <span class="n">tag</span><span class="p">,</span> <span class="n">attrib</span><span class="p">))</span>
<span class="gp">... </span> <span class="k">def</span><span class="w"> </span><span class="nf">close</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">events</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">events</span><span class="p">,</span> <span class="p">[]</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">close_count</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">events</span>
<span class="gp">>>> </span><span class="n">parser_target</span> <span class="o">=</span> <span class="n">ParserTarget</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLParser</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">parser_target</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="s1">'<root test="true"/>'</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">parser_target</span><span class="o">.</span><span class="n">close_count</span><span class="p">)</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span> <span class="ow">in</span> <span class="n">events</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'event: </span><span class="si">{</span><span class="n">event</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="si">}</span><span class="s1"> - tag: </span><span class="si">{</span><span class="n">event</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">attr</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">event</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">' * </span><span class="si">{</span><span class="n">attr</span><span class="si">}</span><span class="s1"> = </span><span class="si">{</span><span class="n">value</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="go">event: start - tag: root</span>
<span class="go"> * test = true</span>
</pre></div>
<p>You can reuse the parser and its target as often as you like, so you
should take care that the <tt class="docutils literal">.close()</tt> method really resets the
target to a usable state (also in the case of an error!).</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="s1">'<root test="true"/>'</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">parser_target</span><span class="o">.</span><span class="n">close_count</span><span class="p">)</span>
<span class="go">2</span>
<span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="s1">'<root test="true"/>'</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">parser_target</span><span class="o">.</span><span class="n">close_count</span><span class="p">)</span>
<span class="go">3</span>
<span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="s1">'<root test="true"/>'</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">parser_target</span><span class="o">.</span><span class="n">close_count</span><span class="p">)</span>
<span class="go">4</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span> <span class="ow">in</span> <span class="n">events</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">'event: </span><span class="si">{</span><span class="n">event</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="si">}</span><span class="s1"> - tag: </span><span class="si">{</span><span class="n">event</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">attr</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">event</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">' * </span><span class="si">{</span><span class="n">attr</span><span class="si">}</span><span class="s1"> = </span><span class="si">{</span><span class="n">value</span><span class="si">}</span><span class="s1">'</span><span class="p">)</span>
<span class="go">event: start - tag: root</span>
<span class="go"> * test = true</span>
</pre></div>
</div>
</div>
<div class="section" id="namespaces">
<h1>Namespaces</h1>
<p>The ElementTree API avoids
<a class="reference external" href="http://www.w3.org/TR/xml-names/#ns-qualnames">namespace prefixes</a>
wherever possible and deploys the real namespace (the URI) instead:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">xhtml</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="s2">"{http://www.w3.org/1999/xhtml}html"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">body</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">xhtml</span><span class="p">,</span> <span class="s2">"{http://www.w3.org/1999/xhtml}body"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">body</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Hello World"</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">xhtml</span><span class="p">)</span>
<span class="go"><html:html xmlns:html="http://www.w3.org/1999/xhtml"></span>
<span class="go"> <html:body>Hello World</html:body></span>
<span class="go"></html:html></span>
</pre></div>
<p>The notation that ElementTree uses was originally brought up by
<a class="reference external" href="http://www.jclark.com/xml/xmlns.htm">James Clark</a>. It has the major
advantage of providing a universally qualified name for a tag, regardless
of any prefixes that may or may not have been used or defined in a document.
By moving the indirection of prefixes out of the way, it makes namespace
aware code much clearer and easier to get right.</p>
<p>As you can see from the example, prefixes only become important when
you serialise the result. However, the above code looks somewhat
verbose due to the lengthy namespace names. And retyping or copying a
string over and over again is error prone. It is therefore common
practice to store a namespace URI in a global variable. To adapt the
namespace prefixes for serialisation, you can also pass a mapping to
the Element factory function, e.g. to define the default namespace:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">XHTML_NAMESPACE</span> <span class="o">=</span> <span class="s2">"http://www.w3.org/1999/xhtml"</span>
<span class="gp">>>> </span><span class="n">XHTML</span> <span class="o">=</span> <span class="s2">"{</span><span class="si">%s</span><span class="s2">}"</span> <span class="o">%</span> <span class="n">XHTML_NAMESPACE</span>
<span class="gp">>>> </span><span class="n">NSMAP</span> <span class="o">=</span> <span class="p">{</span><span class="kc">None</span> <span class="p">:</span> <span class="n">XHTML_NAMESPACE</span><span class="p">}</span> <span class="c1"># the default namespace (no prefix)</span>
<span class="gp">>>> </span><span class="n">xhtml</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="n">XHTML</span> <span class="o">+</span> <span class="s2">"html"</span><span class="p">,</span> <span class="n">nsmap</span><span class="o">=</span><span class="n">NSMAP</span><span class="p">)</span> <span class="c1"># lxml only!</span>
<span class="gp">>>> </span><span class="n">body</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">xhtml</span><span class="p">,</span> <span class="n">XHTML</span> <span class="o">+</span> <span class="s2">"body"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">body</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"Hello World"</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">xhtml</span><span class="p">)</span>
<span class="go"><html xmlns="http://www.w3.org/1999/xhtml"></span>
<span class="go"> <body>Hello World</body></span>
<span class="go"></html></span>
</pre></div>
<p>You can also use the <tt class="docutils literal">QName</tt> helper class to build or split qualified
tag names:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">tag</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">QName</span><span class="p">(</span><span class="s1">'http://www.w3.org/1999/xhtml'</span><span class="p">,</span> <span class="s1">'html'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">localname</span><span class="p">)</span>
<span class="go">html</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">namespace</span><span class="p">)</span>
<span class="go">http://www.w3.org/1999/xhtml</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
<span class="go">{http://www.w3.org/1999/xhtml}html</span>
<span class="gp">>>> </span><span class="n">tag</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">QName</span><span class="p">(</span><span class="s1">'{http://www.w3.org/1999/xhtml}html'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">localname</span><span class="p">)</span>
<span class="go">html</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">namespace</span><span class="p">)</span>
<span class="go">http://www.w3.org/1999/xhtml</span>
<span class="gp">>>> </span><span class="n">root</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="s1">'{http://www.w3.org/1999/xhtml}html'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">tag</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">QName</span><span class="p">(</span><span class="n">root</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">localname</span><span class="p">)</span>
<span class="go">html</span>
<span class="gp">>>> </span><span class="n">tag</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">QName</span><span class="p">(</span><span class="n">root</span><span class="p">,</span> <span class="s1">'script'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
<span class="go">{http://www.w3.org/1999/xhtml}script</span>
<span class="gp">>>> </span><span class="n">tag</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">QName</span><span class="p">(</span><span class="s1">'{http://www.w3.org/1999/xhtml}html'</span><span class="p">,</span> <span class="s1">'script'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tag</span><span class="o">.</span><span class="n">text</span><span class="p">)</span>
<span class="go">{http://www.w3.org/1999/xhtml}script</span>
</pre></div>
<p>lxml.etree allows you to look up the current namespaces defined for a
node through the <tt class="docutils literal">.nsmap</tt> property:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">xhtml</span><span class="o">.</span><span class="n">nsmap</span>
<span class="go">{None: 'http://www.w3.org/1999/xhtml'}</span>
</pre></div>
<p>Note, however, that this includes all prefixes known in the context of
an Element, not only those that it defines itself.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">root</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="s1">'root'</span><span class="p">,</span> <span class="n">nsmap</span><span class="o">=</span><span class="p">{</span><span class="s1">'a'</span><span class="p">:</span> <span class="s1">'http://a.b/c'</span><span class="p">})</span>
<span class="gp">>>> </span><span class="n">child</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">root</span><span class="p">,</span> <span class="s1">'child'</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">nsmap</span><span class="o">=</span><span class="p">{</span><span class="s1">'b'</span><span class="p">:</span> <span class="s1">'http://b.c/d'</span><span class="p">})</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">nsmap</span><span class="p">)</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">child</span><span class="o">.</span><span class="n">nsmap</span><span class="p">)</span>
<span class="go">2</span>
<span class="gp">>>> </span><span class="n">child</span><span class="o">.</span><span class="n">nsmap</span><span class="p">[</span><span class="s1">'a'</span><span class="p">]</span>
<span class="go">'http://a.b/c'</span>
<span class="gp">>>> </span><span class="n">child</span><span class="o">.</span><span class="n">nsmap</span><span class="p">[</span><span class="s1">'b'</span><span class="p">]</span>
<span class="go">'http://b.c/d'</span>
</pre></div>
<p>Therefore, modifying the returned dict cannot have any meaningful
impact on the Element. Any changes to it are ignored.</p>
<p>Namespaces on attributes work alike, but as of version 2.3, <tt class="docutils literal">lxml.etree</tt>
will ensure that the attribute uses a prefixed namespace
declaration. This is because unprefixed attribute names are not
considered being in a namespace by the XML namespace specification
(<a class="reference external" href="http://www.w3.org/TR/2009/REC-xml-names-20091208/#defaulting">section 6.2</a>), so they may end up losing their namespace on a
serialise-parse roundtrip, even if they appear in a namespaced
element.</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">body</span><span class="o">.</span><span class="n">set</span><span class="p">(</span><span class="n">XHTML</span> <span class="o">+</span> <span class="s2">"bgcolor"</span><span class="p">,</span> <span class="s2">"#CCFFAA"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">xhtml</span><span class="p">)</span>
<span class="go"><html xmlns="http://www.w3.org/1999/xhtml"></span>
<span class="go"> <body xmlns:html="http://www.w3.org/1999/xhtml" html:bgcolor="#CCFFAA">Hello World</body></span>
<span class="go"></html></span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">body</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="s2">"bgcolor"</span><span class="p">))</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="n">body</span><span class="o">.</span><span class="n">get</span><span class="p">(</span><span class="n">XHTML</span> <span class="o">+</span> <span class="s2">"bgcolor"</span><span class="p">)</span>
<span class="go">'#CCFFAA'</span>
</pre></div>
<p>You can also use XPath with fully qualified names:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">find_xhtml_body</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">ETXPath</span><span class="p">(</span> <span class="c1"># lxml only !</span>
<span class="gp">... </span> <span class="s2">"//{</span><span class="si">%s</span><span class="s2">}body"</span> <span class="o">%</span> <span class="n">XHTML_NAMESPACE</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">results</span> <span class="o">=</span> <span class="n">find_xhtml_body</span><span class="p">(</span><span class="n">xhtml</span><span class="p">)</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">results</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">{http://www.w3.org/1999/xhtml}body</span>
</pre></div>
<p>For convenience, you can use <tt class="docutils literal">"*"</tt> wildcards in all iterators of <tt class="docutils literal">lxml.etree</tt>,
both for tag names and namespaces:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'*'</span><span class="p">):</span> <span class="nb">print</span><span class="p">(</span><span class="n">el</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span> <span class="c1"># any element</span>
<span class="go">{http://www.w3.org/1999/xhtml}html</span>
<span class="go">{http://www.w3.org/1999/xhtml}body</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'{http://www.w3.org/1999/xhtml}*'</span><span class="p">):</span> <span class="nb">print</span><span class="p">(</span><span class="n">el</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">{http://www.w3.org/1999/xhtml}html</span>
<span class="go">{http://www.w3.org/1999/xhtml}body</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'{*}body'</span><span class="p">):</span> <span class="nb">print</span><span class="p">(</span><span class="n">el</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">{http://www.w3.org/1999/xhtml}body</span>
</pre></div>
<p>To look for elements that do not have a namespace, either use the
plain tag name or provide the empty namespace explicitly:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="p">[</span> <span class="n">el</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'{http://www.w3.org/1999/xhtml}body'</span><span class="p">)</span> <span class="p">]</span>
<span class="go">['{http://www.w3.org/1999/xhtml}body']</span>
<span class="gp">>>> </span><span class="p">[</span> <span class="n">el</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'body'</span><span class="p">)</span> <span class="p">]</span>
<span class="go">[]</span>
<span class="gp">>>> </span><span class="p">[</span> <span class="n">el</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'</span><span class="si">{}</span><span class="s1">body'</span><span class="p">)</span> <span class="p">]</span>
<span class="go">[]</span>
<span class="gp">>>> </span><span class="p">[</span> <span class="n">el</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">xhtml</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s1">'</span><span class="si">{}</span><span class="s1">*'</span><span class="p">)</span> <span class="p">]</span>
<span class="go">[]</span>
</pre></div>
</div>
<div class="section" id="the-e-factory">
<h1>The E-factory</h1>
<p>The <tt class="docutils literal"><span class="pre">E-factory</span></tt> provides a simple and compact syntax for generating XML and
HTML:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">lxml.builder</span><span class="w"> </span><span class="kn">import</span> <span class="n">E</span>
<span class="gp">>>> </span><span class="k">def</span><span class="w"> </span><span class="nf">CLASS</span><span class="p">(</span><span class="o">*</span><span class="n">args</span><span class="p">):</span> <span class="c1"># class is a reserved word in Python</span>
<span class="gp">... </span> <span class="k">return</span> <span class="p">{</span><span class="s2">"class"</span><span class="p">:</span><span class="s1">' '</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">args</span><span class="p">)}</span>
<span class="gp">>>> </span><span class="n">html</span> <span class="o">=</span> <span class="n">page</span> <span class="o">=</span> <span class="p">(</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">html</span><span class="p">(</span> <span class="c1"># create an Element called "html"</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">head</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">title</span><span class="p">(</span><span class="s2">"This is a sample document"</span><span class="p">)</span>
<span class="gp">... </span> <span class="p">),</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">body</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">h1</span><span class="p">(</span><span class="s2">"Hello!"</span><span class="p">,</span> <span class="n">CLASS</span><span class="p">(</span><span class="s2">"title"</span><span class="p">)),</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">p</span><span class="p">(</span><span class="s2">"This is a paragraph with "</span><span class="p">,</span> <span class="n">E</span><span class="o">.</span><span class="n">b</span><span class="p">(</span><span class="s2">"bold"</span><span class="p">),</span> <span class="s2">" text in it!"</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">p</span><span class="p">(</span><span class="s2">"This is another paragraph, with a"</span><span class="p">,</span> <span class="s2">"</span><span class="se">\n</span><span class="s2"> "</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">a</span><span class="p">(</span><span class="s2">"link"</span><span class="p">,</span> <span class="n">href</span><span class="o">=</span><span class="s2">"http://www.python.org"</span><span class="p">),</span> <span class="s2">"."</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">E</span><span class="o">.</span><span class="n">p</span><span class="p">(</span><span class="s2">"Here are some reserved characters: <spam&egg>."</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s2">"<p>And finally an embedded XHTML fragment.</p>"</span><span class="p">),</span>
<span class="gp">... </span> <span class="p">)</span>
<span class="gp">... </span> <span class="p">)</span>
<span class="gp">... </span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">page</span><span class="p">)</span>
<span class="go"><html></span>
<span class="go"> <head></span>
<span class="go"> <title>This is a sample document</title></span>
<span class="go"> </head></span>
<span class="go"> <body></span>
<span class="go"> <h1 class="title">Hello!</h1></span>
<span class="go"> <p>This is a paragraph with <b>bold</b> text in it!</p></span>
<span class="go"> <p>This is another paragraph, with a</span>
<span class="go"> <a href="http://www.python.org">link</a>.</p></span>
<span class="go"> <p>Here are some reserved characters: &lt;spam&amp;egg&gt;.</p></span>
<span class="go"> <p>And finally an embedded XHTML fragment.</p></span>
<span class="go"> </body></span>
<span class="go"></html></span>
</pre></div>
<p>Element creation based on attribute access makes it easy to build up a
simple vocabulary for an XML language:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span><span class="w"> </span><span class="nn">lxml.builder</span><span class="w"> </span><span class="kn">import</span> <span class="n">ElementMaker</span> <span class="c1"># lxml only !</span>
<span class="gp">>>> </span><span class="n">E</span> <span class="o">=</span> <span class="n">ElementMaker</span><span class="p">(</span><span class="n">namespace</span><span class="o">=</span><span class="s2">"http://my.de/fault/namespace"</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">nsmap</span><span class="o">=</span><span class="p">{</span><span class="s1">'p'</span> <span class="p">:</span> <span class="s2">"http://my.de/fault/namespace"</span><span class="p">})</span>
<span class="gp">>>> </span><span class="n">DOC</span> <span class="o">=</span> <span class="n">E</span><span class="o">.</span><span class="n">doc</span>
<span class="gp">>>> </span><span class="n">TITLE</span> <span class="o">=</span> <span class="n">E</span><span class="o">.</span><span class="n">title</span>
<span class="gp">>>> </span><span class="n">SECTION</span> <span class="o">=</span> <span class="n">E</span><span class="o">.</span><span class="n">section</span>
<span class="gp">>>> </span><span class="n">PAR</span> <span class="o">=</span> <span class="n">E</span><span class="o">.</span><span class="n">par</span>
<span class="gp">>>> </span><span class="n">my_doc</span> <span class="o">=</span> <span class="n">DOC</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">TITLE</span><span class="p">(</span><span class="s2">"The dog and the hog"</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">SECTION</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">TITLE</span><span class="p">(</span><span class="s2">"The dog"</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">PAR</span><span class="p">(</span><span class="s2">"Once upon a time, ..."</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">PAR</span><span class="p">(</span><span class="s2">"And then ..."</span><span class="p">)</span>
<span class="gp">... </span> <span class="p">),</span>
<span class="gp">... </span> <span class="n">SECTION</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">TITLE</span><span class="p">(</span><span class="s2">"The hog"</span><span class="p">),</span>
<span class="gp">... </span> <span class="n">PAR</span><span class="p">(</span><span class="s2">"Sooner or later ..."</span><span class="p">)</span>
<span class="gp">... </span> <span class="p">)</span>
<span class="gp">... </span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">prettyprint</span><span class="p">(</span><span class="n">my_doc</span><span class="p">)</span>
<span class="go"><p:doc xmlns:p="http://my.de/fault/namespace"></span>
<span class="go"> <p:title>The dog and the hog</p:title></span>
<span class="go"> <p:section></span>
<span class="go"> <p:title>The dog</p:title></span>
<span class="go"> <p:par>Once upon a time, ...</p:par></span>
<span class="go"> <p:par>And then ...</p:par></span>
<span class="go"> </p:section></span>
<span class="go"> <p:section></span>
<span class="go"> <p:title>The hog</p:title></span>
<span class="go"> <p:par>Sooner or later ...</p:par></span>
<span class="go"> </p:section></span>
<span class="go"></p:doc></span>
</pre></div>
<p>One such example is the module <tt class="docutils literal">lxml.html.builder</tt>, which provides a
vocabulary for HTML.</p>
<p>When dealing with multiple namespaces, it is good practice to define
one ElementMaker for each namespace URI. Again, note how the above
example predefines the tag builders in named constants. That makes it
easy to put all tag declarations of a namespace into one Python module
and to import/use the tag name constants from there. This avoids
pitfalls like typos or accidentally missing namespaces.</p>
</div>
<div class="section" id="elementpath">
<h1>ElementPath</h1>
<p>The ElementTree library comes with a simple XPath-like path language
called <a class="reference external" href="http://effbot.org/zone/element-xpath.htm">ElementPath</a>. The main difference is that you can use the
<tt class="docutils literal">{namespace}tag</tt> notation in ElementPath expressions. However,
advanced features like value comparison and functions are not
available.</p>
<p>In addition to a <a class="reference external" href="xpathxslt.html#xpath">full XPath implementation</a>, <tt class="docutils literal">lxml.etree</tt> supports the
ElementPath language in the same way ElementTree does, even using
(almost) the same implementation. The API provides four methods here
that you can find on Elements and ElementTrees:</p>
<ul class="simple">
<li><tt class="docutils literal">iterfind()</tt> iterates over all Elements that match the path
expression</li>
<li><tt class="docutils literal">findall()</tt> returns a list of matching Elements</li>
<li><tt class="docutils literal">find()</tt> efficiently returns only the first match</li>
<li><tt class="docutils literal">findtext()</tt> returns the <tt class="docutils literal">.text</tt> content of the first match</li>
</ul>
<p>Here are some examples:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </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="s2">"<root><a x='123'>aText<b/><c/><b/></a></root>"</span><span class="p">)</span>
</pre></div>
<p>Find a child of an Element:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="s2">"b"</span><span class="p">))</span>
<span class="go">None</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="s2">"a"</span><span class="p">)</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">a</span>
</pre></div>
<p>Find an Element anywhere in the tree:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="s2">".//b"</span><span class="p">)</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">b</span>
<span class="gp">>>> </span><span class="p">[</span> <span class="n">b</span><span class="o">.</span><span class="n">tag</span> <span class="k">for</span> <span class="n">b</span> <span class="ow">in</span> <span class="n">root</span><span class="o">.</span><span class="n">iterfind</span><span class="p">(</span><span class="s2">".//b"</span><span class="p">)</span> <span class="p">]</span>
<span class="go">['b', 'b']</span>
</pre></div>
<p>Find Elements with a certain attribute:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="s2">".//a[@x]"</span><span class="p">)[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">a</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">findall</span><span class="p">(</span><span class="s2">".//a[@y]"</span><span class="p">))</span>
<span class="go">[]</span>
</pre></div>
<p>In lxml 3.4, there is a new helper to generate a structural ElementPath
expression for an Element:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="n">tree</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>
<span class="gp">>>> </span><span class="n">a</span> <span class="o">=</span> <span class="n">root</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getelementpath</span><span class="p">(</span><span class="n">a</span><span class="p">[</span><span class="mi">0</span><span class="p">]))</span>
<span class="go">a/b[1]</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getelementpath</span><span class="p">(</span><span class="n">a</span><span class="p">[</span><span class="mi">1</span><span class="p">]))</span>
<span class="go">a/c</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getelementpath</span><span class="p">(</span><span class="n">a</span><span class="p">[</span><span class="mi">2</span><span class="p">]))</span>
<span class="go">a/b[2]</span>
<span class="gp">>>> </span><span class="n">tree</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="n">tree</span><span class="o">.</span><span class="n">getelementpath</span><span class="p">(</span><span class="n">a</span><span class="p">[</span><span class="mi">2</span><span class="p">]))</span> <span class="o">==</span> <span class="n">a</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span>
<span class="go">True</span>
</pre></div>
<p>As long as the tree is not modified, this path expression represents an
identifier for a given element that can be used to <tt class="docutils literal">find()</tt> it in the same
tree later. Compared to XPath, ElementPath expressions have the advantage
of being self-contained even for documents that use namespaces.</p>
<p>The <tt class="docutils literal">.iter()</tt> method is a special case that only finds specific tags
in the tree by their name, not based on a path. That means that the
following commands are equivalent in the success case:</p>
<div class="syntax"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">find</span><span class="p">(</span><span class="s2">".//b"</span><span class="p">)</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">b</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">iterfind</span><span class="p">(</span><span class="s2">".//b"</span><span class="p">))</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">b</span>
<span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="nb">next</span><span class="p">(</span><span class="n">root</span><span class="o">.</span><span class="n">iter</span><span class="p">(</span><span class="s2">"b"</span><span class="p">))</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">b</span>
</pre></div>
<p>Note that the <tt class="docutils literal">.find()</tt> method simply returns None if no match is found,
whereas the other two examples would raise a <tt class="docutils literal">StopIteration</tt> exception.</p>
</div>
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