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class="title">Parsing XML and HTML with lxml</h1>
<p>lxml provides a very simple and powerful API for parsing XML and HTML. It
supports one-step parsing as well as step-by-step parsing using an
event-driven API (currently only for XML).</p>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#parsers" id="id1">Parsers</a><ul>
<li><a class="reference internal" href="#parser-options" id="id2">Parser options</a></li>
<li><a class="reference internal" href="#error-log" id="id3">Error log</a></li>
<li><a class="reference internal" href="#parsing-html" id="id4">Parsing HTML</a></li>
<li><a class="reference internal" href="#doctype-information" id="id5">Doctype information</a></li>
</ul>
</li>
<li><a class="reference internal" href="#the-target-parser-interface" id="id6">The target parser interface</a></li>
<li><a class="reference internal" href="#the-feed-parser-interface" id="id7">The feed parser interface</a></li>
<li><a class="reference internal" href="#incremental-event-parsing" id="id8">Incremental event parsing</a><ul>
<li><a class="reference internal" href="#event-types" id="id9">Event types</a></li>
<li><a class="reference internal" href="#modifying-the-tree" id="id10">Modifying the tree</a></li>
<li><a class="reference internal" href="#selective-tag-events" id="id11">Selective tag events</a></li>
<li><a class="reference internal" href="#comments-and-pis" id="id12">Comments and PIs</a></li>
<li><a class="reference internal" href="#events-with-custom-targets" id="id13">Events with custom targets</a></li>
</ul>
</li>
<li><a class="reference internal" href="#iterparse-and-iterwalk" id="id14">iterparse and iterwalk</a><ul>
<li><a class="reference internal" href="#iterwalk" id="id15">iterwalk</a></li>
</ul>
</li>
<li><a class="reference internal" href="#python-unicode-strings" id="id16">Python unicode strings</a><ul>
<li><a class="reference internal" href="#serialising-to-unicode-strings" id="id17">Serialising to Unicode strings</a></li>
</ul>
</li>
</ul>
</div>
<p>The usual setup procedure:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">lxml</span> <span class="kn">import</span> <span class="n">etree</span>
</pre></div>
<p>The following examples also use StringIO or BytesIO to show how to parse
from files and file-like objects. Both are available in the <tt class="docutils literal">io</tt> module:</p>
<div class="syntax"><pre><span class="kn">from</span> <span class="nn">io</span> <span class="kn">import</span> <span class="n">StringIO</span><span class="p">,</span> <span class="n">BytesIO</span>
</pre></div>
<div class="section" id="parsers">
<h1>Parsers</h1>
<p>Parsers are represented by parser objects. There is support for parsing both
XML and (broken) HTML. Note that XHTML is best parsed as XML, parsing it with
the HTML parser can lead to unexpected results. Here is a simple example for
parsing XML from an in-memory string:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">xml</span> <span class="o">=</span> <span class="s1">'<a xmlns="test"><b xmlns="test"/></a>'</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">xml</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'<a xmlns="test"><b xmlns="test"/></a>'</span>
</pre></div>
<p>To read from a file or file-like object, you can use the <tt class="docutils literal">parse()</tt> function,
which returns an <tt class="docutils literal">ElementTree</tt> object:</p>
<div class="syntax"><pre><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">StringIO</span><span class="p">(</span><span class="n">xml</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="o">.</span><span class="n">getroot</span><span class="p">())</span>
<span class="go">b'<a xmlns="test"><b xmlns="test"/></a>'</span>
</pre></div>
<p>Note how the <tt class="docutils literal">parse()</tt> function reads from a file-like object here. If
parsing is done from a real file, it is more common (and also somewhat more
efficient) to pass a filename:</p>
<div class="syntax"><pre><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="s2">"doc/test.xml"</span><span class="p">)</span>
</pre></div>
<p>lxml can parse from a local file, an HTTP URL or an FTP URL. It also
auto-detects and reads gzip-compressed XML files (.gz).</p>
<p>If you want to parse from memory and still provide a base URL for the document
(e.g. to support relative paths in an XInclude), you can pass the <tt class="docutils literal">base_url</tt>
keyword argument:</p>
<div class="syntax"><pre><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">xml</span><span class="p">,</span> <span class="n">base_url</span><span class="o">=</span><span class="s2">"http://where.it/is/from.xml"</span><span class="p">)</span>
</pre></div>
<div class="section" id="parser-options">
<h2>Parser options</h2>
<p>The parsers accept a number of setup options as keyword arguments. The above
example is easily extended to clean up namespaces during parsing:</p>
<div class="syntax"><pre><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">ns_clean</span><span class="o">=</span><span class="bp">True</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">StringIO</span><span class="p">(</span><span class="n">xml</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">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">())</span>
<span class="go">b'<a xmlns="test"><b/></a>'</span>
</pre></div>
<p>The keyword arguments in the constructor are mainly based on the libxml2
parser configuration. A DTD will also be loaded if validation or attribute
default values are requested.</p>
<p>Available boolean keyword arguments:</p>
<ul class="simple">
<li>attribute_defaults - read the DTD (if referenced by the document) and add
the default attributes from it</li>
<li>dtd_validation - validate while parsing (if a DTD was referenced)</li>
<li>load_dtd - load and parse the DTD while parsing (no validation is performed)</li>
<li>no_network - prevent network access when looking up external
documents (on by default)</li>
<li>ns_clean - try to clean up redundant namespace declarations</li>
<li>recover - try hard to parse through broken XML</li>
<li>remove_blank_text - discard blank text nodes between tags, also known as
ignorable whitespace. This is best used together with a DTD or schema
(which tells data and noise apart), otherwise a heuristic will be applied.</li>
<li>remove_comments - discard comments</li>
<li>remove_pis - discard processing instructions</li>
<li>strip_cdata - replace CDATA sections by normal text content (on by
default)</li>
<li>resolve_entities - replace entities by their text value (on by
default)</li>
<li>huge_tree - disable security restrictions and support very deep trees
and very long text content (only affects libxml2 2.7+)</li>
<li>compact - use compact storage for short text content (on by default)</li>
<li>collect_ids - collect XML IDs in a hash table while parsing (on by default).
Disabling this can substantially speed up parsing of documents with many
different IDs if the hash lookup is not used afterwards.</li>
</ul>
<p>Other keyword arguments:</p>
<ul class="simple">
<li>encoding - override the document encoding</li>
<li>target - a parser target object that will receive the parse events
(see <a class="reference internal" href="#the-target-parser-interface">The target parser interface</a>)</li>
<li>schema - an XMLSchema to validate against (see <a class="reference external" href="validation.html#xmlschema">validation</a>)</li>
</ul>
</div>
<div class="section" id="error-log">
<h2>Error log</h2>
<p>Parsers have an <tt class="docutils literal">error_log</tt> property that lists the errors and
warnings of the last parser run:</p>
<div class="syntax"><pre><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="k">print</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">parser</span><span class="o">.</span><span class="n">error_log</span><span class="p">))</span>
<span class="go">0</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">XML</span><span class="p">(</span><span class="s2">"<root></span><span class="se">\n</span><span class="s2"></b>"</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span> <span class="c1"># doctest: +ELLIPSIS</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">lxml.etree.XMLSyntaxError</span>: <span class="n">Opening and ending tag mismatch: root line 1 and b, line 2, column 5...</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">parser</span><span class="o">.</span><span class="n">error_log</span><span class="p">))</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="n">error</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">error_log</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">error</span><span class="o">.</span><span class="n">message</span><span class="p">)</span>
<span class="go">Opening and ending tag mismatch: root line 1 and b</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">error</span><span class="o">.</span><span class="n">line</span><span class="p">)</span>
<span class="go">2</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">error</span><span class="o">.</span><span class="n">column</span><span class="p">)</span>
<span class="go">5</span>
</pre></div>
<p>Each entry in the log has the following properties:</p>
<ul class="simple">
<li><tt class="docutils literal">message</tt>: the message text</li>
<li><tt class="docutils literal">domain</tt>: the domain ID (see the lxml.etree.ErrorDomains class)</li>
<li><tt class="docutils literal">type</tt>: the message type ID (see the lxml.etree.ErrorTypes class)</li>
<li><tt class="docutils literal">level</tt>: the log level ID (see the lxml.etree.ErrorLevels class)</li>
<li><tt class="docutils literal">line</tt>: the line at which the message originated (if applicable)</li>
<li><tt class="docutils literal">column</tt>: the character column at which the message originated (if applicable)</li>
<li><tt class="docutils literal">filename</tt>: the name of the file in which the message originated (if applicable)</li>
</ul>
<p>For convenience, there are also three properties that provide readable
names for the ID values:</p>
<ul class="simple">
<li><tt class="docutils literal">domain_name</tt></li>
<li><tt class="docutils literal">type_name</tt></li>
<li><tt class="docutils literal">level_name</tt></li>
</ul>
<p>To filter for a specific kind of message, use the different
<tt class="docutils literal"><span class="pre">filter_*()</span></tt> methods on the error log (see the
lxml.etree._ListErrorLog class).</p>
</div>
<div class="section" id="parsing-html">
<h2>Parsing HTML</h2>
<p>HTML parsing is similarly simple. The parsers have a <tt class="docutils literal">recover</tt>
keyword argument that the HTMLParser sets by default. It lets libxml2
try its best to return a valid HTML tree with all content it can
manage to parse. It will not raise an exception on parser errors.
You should use libxml2 version 2.6.21 or newer to take advantage of
this feature.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">broken_html</span> <span class="o">=</span> <span class="s2">"<html><head><title>test<body><h1>page title</h3>"</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">HTMLParser</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">StringIO</span><span class="p">(</span><span class="n">broken_html</span><span class="p">),</span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">result</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">tree</span><span class="o">.</span><span class="n">getroot</span><span class="p">(),</span>
<span class="gp">... </span> <span class="n">pretty_print</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s2">"html"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go"><html></span>
<span class="go"> <head></span>
<span class="go"> <title>test</title></span>
<span class="go"> </head></span>
<span class="go"> <body></span>
<span class="go"> <h1>page title</h1></span>
<span class="go"> </body></span>
<span class="go"></html></span>
</pre></div>
<p>Lxml has an HTML function, similar to the XML shortcut known from
ElementTree:</p>
<div class="syntax"><pre><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">HTML</span><span class="p">(</span><span class="n">broken_html</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">result</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">html</span><span class="p">,</span> <span class="n">pretty_print</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span> <span class="n">method</span><span class="o">=</span><span class="s2">"html"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go"><html></span>
<span class="go"> <head></span>
<span class="go"> <title>test</title></span>
<span class="go"> </head></span>
<span class="go"> <body></span>
<span class="go"> <h1>page title</h1></span>
<span class="go"> </body></span>
<span class="go"></html></span>
</pre></div>
<p>The support for parsing broken HTML depends entirely on libxml2's recovery
algorithm. It is <em>not</em> the fault of lxml if you find documents that are so
heavily broken that the parser cannot handle them. There is also no guarantee
that the resulting tree will contain all data from the original document. The
parser may have to drop seriously broken parts when struggling to keep
parsing. Especially misplaced meta tags can suffer from this, which may lead
to encoding problems.</p>
<p>Note that the result is a valid HTML tree, but it may not be a
well-formed XML tree. For example, XML forbids double hyphens in
comments, which the HTML parser will happily accept in recovery mode.
Therefore, if your goal is to serialise an HTML document as an
XML/XHTML document after parsing, you may have to apply some manual
preprocessing first.</p>
<p>Also note that the HTML parser is meant to parse HTML documents. For
XHTML documents, use the XML parser, which is namespace aware.</p>
</div>
<div class="section" id="doctype-information">
<h2>Doctype information</h2>
<p>The use of the libxml2 parsers makes some additional information available at
the API level. Currently, ElementTree objects can access the DOCTYPE
information provided by a parsed document, as well as the XML version and the
original encoding. Since lxml 3.5, the doctype references are mutable.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">pub_id</span> <span class="o">=</span> <span class="s2">"-//W3C//DTD XHTML 1.0 Transitional//EN"</span>
<span class="gp">>>> </span><span class="n">sys_url</span> <span class="o">=</span> <span class="s2">"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"</span>
<span class="gp">>>> </span><span class="n">doctype_string</span> <span class="o">=</span> <span class="s1">'<!DOCTYPE html PUBLIC "</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">pub_id</span><span class="p">,</span> <span class="n">sys_url</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">xml_header</span> <span class="o">=</span> <span class="s1">'<?xml version="1.0" encoding="ascii"?>'</span>
<span class="gp">>>> </span><span class="n">xhtml</span> <span class="o">=</span> <span class="n">xml_header</span> <span class="o">+</span> <span class="n">doctype_string</span> <span class="o">+</span> <span class="s1">'<html><body></body></html>'</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">StringIO</span><span class="p">(</span><span class="n">xhtml</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">docinfo</span> <span class="o">=</span> <span class="n">tree</span><span class="o">.</span><span class="n">docinfo</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">public_id</span><span class="p">)</span>
<span class="go">-//W3C//DTD XHTML 1.0 Transitional//EN</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">system_url</span><span class="p">)</span>
<span class="go">http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd</span>
<span class="gp">>>> </span><span class="n">docinfo</span><span class="o">.</span><span class="n">doctype</span> <span class="o">==</span> <span class="n">doctype_string</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</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="k">print</span><span class="p">(</span><span class="n">docinfo</span><span class="o">.</span><span class="n">encoding</span><span class="p">)</span>
<span class="go">ascii</span>
<span class="gp">>>> </span><span class="n">docinfo</span><span class="o">.</span><span class="n">system_url</span> <span class="o">=</span> <span class="bp">None</span>
<span class="gp">>>> </span><span class="n">docinfo</span><span class="o">.</span><span class="n">public_id</span> <span class="o">=</span> <span class="bp">None</span>
<span class="gp">>>> </span><span class="k">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">tree</span><span class="p">))</span>
<span class="go"><!DOCTYPE html></span>
<span class="go"><html><body/></html></span>
</pre></div>
</div>
</div>
<div class="section" id="the-target-parser-interface">
<h1>The target parser interface</h1>
<p><a class="reference external" href="http://effbot.org/elementtree/elementtree-xmlparser.htm">As in ElementTree</a>, and similar to a SAX event handler, you can pass
a target object to the parser:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">EchoTarget</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</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="k">print</span><span class="p">(</span><span class="s2">"start </span><span class="si">%s</span><span class="s2"> </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">tag</span><span class="p">,</span> <span class="nb">dict</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="nf">end</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="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"end </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="n">tag</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">data</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"data </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="n">data</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">comment</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">text</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"comment </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="n">text</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</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="k">print</span><span class="p">(</span><span class="s2">"close"</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s2">"closed!"</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">EchoTarget</span><span class="p">())</span>
<span class="gp">>>> </span><span class="n">result</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">"<element>some<!--comment-->text</element>"</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">parser</span><span class="p">)</span>
<span class="go">start element {}</span>
<span class="go">data u'some'</span>
<span class="go">comment comment</span>
<span class="go">data u'text'</span>
<span class="go">end element</span>
<span class="go">close</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go">closed!</span>
</pre></div>
<p>It is important for the <tt class="docutils literal">.close()</tt> method to reset the parser target
to a usable state, so that you can reuse the parser as often as you
like:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">result</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">"<element>some<!--comment-->text</element>"</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">parser</span><span class="p">)</span>
<span class="go">start element {}</span>
<span class="go">data u'some'</span>
<span class="go">comment comment</span>
<span class="go">data u'text'</span>
<span class="go">end element</span>
<span class="go">close</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go">closed!</span>
</pre></div>
<p>Starting with lxml 2.3, the <tt class="docutils literal">.close()</tt> method will also be called in
the error case. This diverges from the behaviour of ElementTree, but
allows target objects to clean up their state in all situations, so
that the parser can reuse them afterwards.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">CollectorTarget</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</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="p">[]</span>
<span class="gp">... </span> <span class="k">def</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="si">%s</span><span class="s2"> </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">tag</span><span class="p">,</span> <span class="nb">dict</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="nf">end</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="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">"end </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="n">tag</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">data</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</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">"data </span><span class="si">%r</span><span class="s2">"</span> <span class="o">%</span> <span class="n">data</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">comment</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">text</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">"comment </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="n">text</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</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="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">"close"</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s2">"closed!"</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">CollectorTarget</span><span class="p">())</span>
<span class="gp">>>> </span><span class="n">result</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">"<element>some</error>"</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">parser</span><span class="p">)</span> <span class="c1"># doctest: +ELLIPSIS</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">lxml.etree.XMLSyntaxError</span>: <span class="n">Opening and ending tag mismatch...</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">event</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">target</span><span class="o">.</span><span class="n">events</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="n">event</span><span class="p">)</span>
<span class="go">start element {}</span>
<span class="go">data u'some'</span>
<span class="go">close</span>
</pre></div>
<p>Note that the parser does <em>not</em> build a tree when using a parser
target. The result of the parser run is whatever the target object
returns from its <tt class="docutils literal">.close()</tt> method. If you want to return an XML
tree here, you have to create it programmatically in the target
object. An example for a parser target that builds a tree is the
<tt class="docutils literal">TreeBuilder</tt>:</p>
<div class="syntax"><pre><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">etree</span><span class="o">.</span><span class="n">TreeBuilder</span><span class="p">())</span>
<span class="gp">>>> </span><span class="n">result</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">"<element>some<!--comment-->text</element>"</span><span class="p">,</span>
<span class="gp">... </span> <span class="n">parser</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="o">.</span><span class="n">tag</span><span class="p">)</span>
<span class="go">element</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</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="p">)</span>
<span class="go">comment</span>
</pre></div>
</div>
<div class="section" id="the-feed-parser-interface">
<h1>The feed parser interface</h1>
<p>Since lxml 2.0, the parsers have a feed parser interface that is
compatible to the <a class="reference external" href="http://effbot.org/elementtree/elementtree-xmlparser.htm">ElementTree parsers</a>. You can use it to feed data
into the parser in a controlled step-by-step way.</p>
<p>In lxml.etree, you can use both interfaces to a parser at the same
time: the <tt class="docutils literal">parse()</tt> or <tt class="docutils literal">XML()</tt> functions, and the feed parser
interface. Both are independent and will not conflict (except if used
in conjunction with a parser target object as described above).</p>
<p>To start parsing with a feed parser, just call its <tt class="docutils literal">feed()</tt> method
to feed it some data.</p>
<div class="syntax"><pre><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="k">for</span> <span class="n">data</span> <span class="ow">in</span> <span class="p">(</span><span class="s1">'<?xml versio'</span><span class="p">,</span> <span class="s1">'n="1.0"?'</span><span class="p">,</span> <span class="s1">'><roo'</span><span class="p">,</span> <span class="s1">'t><a'</span><span class="p">,</span> <span class="s1">'/></root>'</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="n">data</span><span class="p">)</span>
</pre></div>
<p>When you are done parsing, you <strong>must</strong> call the <tt class="docutils literal">close()</tt> method to
retrieve the root Element of the parse result document, and to unlock the
parser:</p>
<div class="syntax"><pre><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="k">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="k">print</span><span class="p">(</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">tag</span><span class="p">)</span>
<span class="go">a</span>
</pre></div>
<p>If you do not call <tt class="docutils literal">close()</tt>, the parser will stay locked and
subsequent feeds will keep appending data, usually resulting in a non
well-formed document and an unexpected parser error. So make sure you
always close the parser after use, also in the exception case.</p>
<p>Another way of achieving the same step-by-step parsing is by writing your own
file-like object that returns a chunk of data on each <tt class="docutils literal">read()</tt> call. Where
the feed parser interface allows you to actively pass data chunks into the
parser, a file-like object passively responds to <tt class="docutils literal">read()</tt> requests of the
parser itself. Depending on the data source, either way may be more natural.</p>
<p>Note that the feed parser has its own error log called
<tt class="docutils literal">feed_error_log</tt>. Errors in the feed parser do not show up in the
normal <tt class="docutils literal">error_log</tt> and vice versa.</p>
<p>You can also combine the feed parser interface with the target parser:</p>
<div class="syntax"><pre><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">EchoTarget</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">"<eleme"</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">"nt>some text</elem"</span><span class="p">)</span>
<span class="go">start element {}</span>
<span class="go">data u'some text'</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">"ent>"</span><span class="p">)</span>
<span class="go">end element</span>
<span class="gp">>>> </span><span class="n">result</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="go">close</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">result</span><span class="p">)</span>
<span class="go">closed!</span>
</pre></div>
<p>Again, this prevents the automatic creation of an XML tree and leaves
all the event handling to the target object. The <tt class="docutils literal">close()</tt> method
of the parser forwards the return value of the target's <tt class="docutils literal">close()</tt>
method.</p>
</div>
<div class="section" id="incremental-event-parsing">
<h1>Incremental event parsing</h1>
<p>In Python 3.4, the <tt class="docutils literal">xml.etree.ElementTree</tt> package gained an extension
to the feed parser interface that is implemented by the <tt class="docutils literal">XMLPullParser</tt>
class. It additionally allows processing parse events after each
incremental parsing step, by calling the <tt class="docutils literal">.read_events()</tt> method and
iterating over the result. This is most useful for non-blocking execution
environments where data chunks arrive one after the other and should be
processed as far as possible in each step.</p>
<p>The same feature is available in lxml 3.3. The basic usage is as follows:</p>
<div class="syntax"><pre><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">XMLPullParser</span><span class="p">(</span><span class="n">events</span><span class="o">=</span><span class="p">(</span><span class="s1">'start'</span><span class="p">,</span> <span class="s1">'end'</span><span class="p">))</span>
<span class="gp">>>> </span><span class="k">def</span> <span class="nf">print_events</span><span class="p">(</span><span class="n">parser</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">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">action</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="gp">>>> </span><span class="n">parser</span><span class="o">.</span><span class="n">feed</span><span class="p">(</span><span class="s1">'<root>some text'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">parser</span><span class="p">)</span>
<span class="go">start: root</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">parser</span><span class="p">)</span> <span class="c1"># well, no more events, as before ...</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="s1">'<child><a />'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">parser</span><span class="p">)</span>
<span class="go">start: child</span>
<span class="go">start: a</span>
<span class="go">end: a</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="s1">'</child></roo'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">parser</span><span class="p">)</span>
<span class="go">end: child</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="s1">'t>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">parser</span><span class="p">)</span>
<span class="go">end: root</span>
</pre></div>
<p>Just like the normal feed parser, the <tt class="docutils literal">XMLPullParser</tt> builds a tree in
memory (and you should always call the <tt class="docutils literal">.close()</tt> method when done with
parsing):</p>
<div class="syntax"><pre><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>some text<child><a/></child></root>'</span>
</pre></div>
<p>However, since the parser provides incremental access to that tree,
you can explicitly delete content that you no longer need once you
have processed it. Read the section on <a class="reference internal" href="#modifying-the-tree">Modifying the tree</a> below
to see what you can do here and what kind of modifications you should
avoid.</p>
<p>In lxml, it is enough to call the <tt class="docutils literal">.read_events()</tt> method once as
the iterator it returns can be reused when new events are available.</p>
<p>Also, as known from other iterators in lxml, you can pass a <tt class="docutils literal">tag</tt>
argument that selects which parse events are returned by the
<tt class="docutils literal">.read_events()</tt> iterator.</p>
<div class="section" id="event-types">
<h2>Event types</h2>
<p>The parse events are tuples <tt class="docutils literal"><span class="pre">(event-type,</span> object)</tt>. The event types
supported by ElementTree and lxml.etree are the strings 'start', 'end',
'start-ns' and 'end-ns'. The 'start' and 'end' events represent opening
and closing elements. They are accompanied by the respective Element
instance. By default, only 'end' events are generated, whereas the
example above requested the generation of both 'start' and 'end' events.</p>
<p>The 'start-ns' and 'end-ns' events notify about namespace declarations.
They do not come with Elements. Instead, the value of the 'start-ns'
event is a tuple <tt class="docutils literal">(prefix, namespaceURI)</tt> that designates the beginning
of a prefix-namespace mapping. The corresponding <tt class="docutils literal"><span class="pre">end-ns</span></tt> event does
not have a value (None). It is common practice to use a list as namespace
stack and pop the last entry on the 'end-ns' event.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="k">def</span> <span class="nf">print_events</span><span class="p">(</span><span class="n">events</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">obj</span> <span class="ow">in</span> <span class="n">events</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">action</span> <span class="ow">in</span> <span class="p">(</span><span class="s1">'start'</span><span class="p">,</span> <span class="s1">'end'</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">obj</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="gp">... </span> <span class="k">elif</span> <span class="n">action</span> <span class="o">==</span> <span class="s1">'start-ns'</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">obj</span><span class="p">))</span>
<span class="gp">... </span> <span class="k">else</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="n">action</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">event_types</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="s2">"start-ns"</span><span class="p">,</span> <span class="s2">"end-ns"</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">XMLPullParser</span><span class="p">(</span><span class="n">event_types</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</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="s1">'<root><element>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">events</span><span class="p">)</span>
<span class="go">start: root</span>
<span class="go">start: element</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="s1">'text</element><element>text</element>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">events</span><span class="p">)</span>
<span class="go">end: element</span>
<span class="go">start: element</span>
<span class="go">end: element</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="s1">'<empty-element xmlns="http://testns/" />'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">events</span><span class="p">)</span>
<span class="go">start-ns: ('', 'http://testns/')</span>
<span class="go">start: {http://testns/}empty-element</span>
<span class="go">end: {http://testns/}empty-element</span>
<span class="go">end-ns</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="s1">'</root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">print_events</span><span class="p">(</span><span class="n">events</span><span class="p">)</span>
<span class="go">end: root</span>
</pre></div>
</div>
<div class="section" id="modifying-the-tree">
<h2>Modifying the tree</h2>
<p>You can modify the element and its descendants when handling the
'end' event. To save memory, for example, you can remove subtrees
that are no longer needed:</p>
<div class="syntax"><pre><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">XMLPullParser</span><span class="p">()</span>
<span class="gp">>>> </span><span class="n">events</span> <span class="o">=</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</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="s1">'<root><element key="value">text</element>'</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="s1">'<element><child /></element>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">events</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%s</span><span class="s1">: </span><span class="si">%d</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">elem</span><span class="p">)))</span> <span class="c1"># processing</span>
<span class="gp">... </span> <span class="n">elem</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span> <span class="c1"># delete children</span>
<span class="go">element: 0</span>
<span class="go">child: 0</span>
<span class="go">element: 1</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="s1">'<empty-element xmlns="http://testns/" /></root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">events</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s1">'</span><span class="si">%s</span><span class="s1">: </span><span class="si">%d</span><span class="s1">'</span> <span class="o">%</span> <span class="p">(</span><span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="n">elem</span><span class="p">)))</span> <span class="c1"># processing</span>
<span class="gp">... </span> <span class="n">elem</span><span class="o">.</span><span class="n">clear</span><span class="p">()</span> <span class="c1"># delete children</span>
<span class="go">{http://testns/}empty-element: 0</span>
<span class="go">root: 3</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>
<p><strong>WARNING</strong>: During the 'start' event, any content of the element,
such as the descendants, following siblings or text, is not yet
available and should not be accessed. Only attributes are guaranteed
to be set. During the 'end' event, the element and its descendants
can be freely modified, but its following siblings should not be
accessed. During either of the two events, you <strong>must not</strong> modify or
move the ancestors (parents) of the current element. You should also
avoid moving or discarding the element itself. The golden rule is: do
not touch anything that will have to be touched again by the parser
later on.</p>
<p>If you have elements with a long list of children in your XML file and want
to save more memory during parsing, you can clean up the preceding siblings
of the current element:</p>
<div class="syntax"><pre><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">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="c1"># ... do something with the element</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="c1"># clean up children</span>
<span class="gp">... </span> <span class="k">while</span> <span class="n">element</span><span class="o">.</span><span class="n">getprevious</span><span class="p">()</span> <span class="ow">is</span> <span class="ow">not</span> <span class="bp">None</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">del</span> <span class="n">element</span><span class="o">.</span><span class="n">getparent</span><span class="p">()[</span><span class="mi">0</span><span class="p">]</span> <span class="c1"># clean up preceding siblings</span>
</pre></div>
<p>The <tt class="docutils literal">while</tt> loop deletes multiple siblings in a row. This is only necessary
if you skipped over some of them using the <tt class="docutils literal">tag</tt> keyword argument.
Otherwise, a simple <tt class="docutils literal">if</tt> should do. The more selective your tag is,
however, the more thought you will have to put into finding the right way to
clean up the elements that were skipped. Therefore, it is sometimes easier to
traverse all elements and do the tag selection by hand in the event handler
code.</p>
</div>
<div class="section" id="selective-tag-events">
<h2>Selective tag events</h2>
<p>As an extension over ElementTree, lxml.etree accepts a <tt class="docutils literal">tag</tt> keyword
argument just like <tt class="docutils literal">element.iter(tag)</tt>. This restricts events to a
specific tag or namespace:</p>
<div class="syntax"><pre><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">XMLPullParser</span><span class="p">(</span><span class="n">tag</span><span class="o">=</span><span class="s2">"element"</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="s1">'<root><element key="value">text</element>'</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="s1">'<element><child /></element>'</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="s1">'<empty-element xmlns="http://testns/" /></root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="go">end: element</span>
<span class="go">end: element</span>
<span class="gp">>>> </span><span class="n">event_types</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="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLPullParser</span><span class="p">(</span><span class="n">event_types</span><span class="p">,</span> <span class="n">tag</span><span class="o">=</span><span class="s2">"{http://testns/}*"</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="s1">'<root><element key="value">text</element>'</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="s1">'<element><child /></element>'</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="s1">'<empty-element xmlns="http://testns/" /></root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="go">start: {http://testns/}empty-element</span>
<span class="go">end: {http://testns/}empty-element</span>
</pre></div>
</div>
<div class="section" id="comments-and-pis">
<h2>Comments and PIs</h2>
<p>As an extension over ElementTree, the <tt class="docutils literal">XMLPullParser</tt> in lxml.etree
also supports the event types 'comment' and 'pi' for the respective
XML structures.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">event_types</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="s2">"comment"</span><span class="p">,</span> <span class="s2">"pi"</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">XMLPullParser</span><span class="p">(</span><span class="n">event_types</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="s1">'<?some pi ?><!-- a comment --><root>'</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="s1">'<element key="value">text</element>'</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="s1">'<!-- another comment -->'</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="s1">'<element>text</element>tail'</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="s1">'<empty-element xmlns="http://testns/" />'</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="s1">'</root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">action</span> <span class="ow">in</span> <span class="p">(</span><span class="s1">'start'</span><span class="p">,</span> <span class="s1">'end'</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="gp">... </span> <span class="k">elif</span> <span class="n">action</span> <span class="o">==</span> <span class="s1">'pi'</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: -</span><span class="si">%s</span><span class="s2">=</span><span class="si">%s</span><span class="s2">-"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">target</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">text</span><span class="p">))</span>
<span class="gp">... </span> <span class="k">else</span><span class="p">:</span> <span class="c1"># 'comment'</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: -</span><span class="si">%s</span><span class="s2">-"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">text</span><span class="p">))</span>
<span class="go">pi: -some=pi -</span>
<span class="go">comment: - a comment -</span>
<span class="go">start: root</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="go">comment: - another comment -</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="go">start: {http://testns/}empty-element</span>
<span class="go">end: {http://testns/}empty-element</span>
<span class="go">end: root</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="k">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>
</div>
<div class="section" id="events-with-custom-targets">
<h2>Events with custom targets</h2>
<p>You can combine the pull parser with a parser target. In that case,
it is the target's responsibility to generate event values. Whatever
it returns from its <tt class="docutils literal">.start()</tt> and <tt class="docutils literal">.end()</tt> methods will be returned
by the pull parser as the second item of the parse events tuple.</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Target</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</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="k">print</span><span class="p">(</span><span class="s1">'-> start(</span><span class="si">%s</span><span class="s1">)'</span> <span class="o">%</span> <span class="n">tag</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s1">'>>START: </span><span class="si">%s</span><span class="s1"><<'</span> <span class="o">%</span> <span class="n">tag</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">end</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="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s1">'-> end(</span><span class="si">%s</span><span class="s1">)'</span> <span class="o">%</span> <span class="n">tag</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s1">'>>END: </span><span class="si">%s</span><span class="s1"><<'</span> <span class="o">%</span> <span class="n">tag</span>
<span class="gp">... </span> <span class="k">def</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="k">print</span><span class="p">(</span><span class="s1">'-> close()'</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s2">"CLOSED!"</span>
<span class="gp">>>> </span><span class="n">event_types</span> <span class="o">=</span> <span class="p">(</span><span class="s1">'start'</span><span class="p">,</span> <span class="s1">'end'</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">XMLPullParser</span><span class="p">(</span><span class="n">event_types</span><span class="p">,</span> <span class="n">target</span><span class="o">=</span><span class="n">Target</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="s1">'<root><child1 /><child2 /></root>'</span><span class="p">)</span>
<span class="go">-> start(root)</span>
<span class="go">-> start(child1)</span>
<span class="go">-> end(child1)</span>
<span class="go">-> start(child2)</span>
<span class="go">-> end(child2)</span>
<span class="go">-> end(root)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">value</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">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">action</span><span class="p">,</span> <span class="n">value</span><span class="p">))</span>
<span class="go">start: >>START: root<<</span>
<span class="go">start: >>START: child1<<</span>
<span class="go">end: >>END: child1<<</span>
<span class="go">start: >>START: child2<<</span>
<span class="go">end: >>END: child2<<</span>
<span class="go">end: >>END: root<<</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">parser</span><span class="o">.</span><span class="n">close</span><span class="p">())</span>
<span class="go">-> close()</span>
<span class="go">CLOSED!</span>
</pre></div>
<p>As you can see, the event values do not even have to be Element objects.
The target is generally free to decide how it wants to create an XML tree
or whatever else it wants to make of the parser callbacks. In many cases,
however, you will want to make your custom target inherit from the
<tt class="docutils literal">TreeBuilder</tt> class in order to have it build a tree that you can process
normally. The <tt class="docutils literal">start()</tt> and <tt class="docutils literal">.end()</tt> methods of <tt class="docutils literal">TreeBuilder</tt> return
the Element object that was created, so you can override them and modify
the input or output according to your needs. Here is an example that
filters attributes before they are being added to the tree:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="k">class</span> <span class="nc">AttributeFilter</span><span class="p">(</span><span class="n">etree</span><span class="o">.</span><span class="n">TreeBuilder</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</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="n">attrib</span> <span class="o">=</span> <span class="nb">dict</span><span class="p">(</span><span class="n">attrib</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">if</span> <span class="s1">'evil'</span> <span class="ow">in</span> <span class="n">attrib</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">del</span> <span class="n">attrib</span><span class="p">[</span><span class="s1">'evil'</span><span class="p">]</span>
<span class="gp">... </span> <span class="k">return</span> <span class="nb">super</span><span class="p">(</span><span class="n">AttributeFilter</span><span class="p">,</span> <span class="bp">self</span><span class="p">)</span><span class="o">.</span><span class="n">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="n">parser</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLPullParser</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">AttributeFilter</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="s1">'<root><child1 test="123" /><child2 evil="YES" /></root>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">element</span> <span class="ow">in</span> <span class="n">parser</span><span class="o">.</span><span class="n">read_events</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">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="si">%r</span><span class="s1">)'</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</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="n">element</span><span class="o">.</span><span class="n">attrib</span><span class="p">))</span>
<span class="go">end: child1({'test': '123'})</span>
<span class="go">end: child2({})</span>
<span class="go">end: root({})</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>
</pre></div>
</div>
</div>
<div class="section" id="iterparse-and-iterwalk">
<h1>iterparse and iterwalk</h1>
<p>As known from ElementTree, the <tt class="docutils literal">iterparse()</tt> utility function
returns an iterator that generates parser events for an XML file (or
file-like object), while building the tree. You can think of it as
a blocking wrapper around the <tt class="docutils literal">XMLPullParser</tt> that automatically and
incrementally reads data from the input file for you and provides a
single iterator for them:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">xml</span> <span class="o">=</span> <span class="s1">'''</span>
<span class="gp">... </span><span class="s1"><root></span>
<span class="gp">... </span><span class="s1"> <element key='value'>text</element></span>
<span class="gp">... </span><span class="s1"> <element>text</element>tail</span>
<span class="gp">... </span><span class="s1"> <empty-element xmlns="http://testns/" /></span>
<span class="gp">... </span><span class="s1"></root></span>
<span class="gp">... </span><span class="s1">'''</span>
<span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">))</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="go">end: element</span>
<span class="go">end: element</span>
<span class="go">end: {http://testns/}empty-element</span>
<span class="go">end: root</span>
</pre></div>
<p>After parsing, the resulting tree is available through the <tt class="docutils literal">root</tt> property
of the iterator:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">context</span><span class="o">.</span><span class="n">root</span><span class="o">.</span><span class="n">tag</span>
<span class="go">'root'</span>
</pre></div>
<p>The other event types can be activated with the <tt class="docutils literal">events</tt> keyword argument:</p>
<div class="syntax"><pre><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="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">),</span> <span class="n">events</span><span class="o">=</span><span class="n">events</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="go">start: root</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="go">start: {http://testns/}empty-element</span>
<span class="go">end: {http://testns/}empty-element</span>
<span class="go">end: root</span>
</pre></div>
<p><tt class="docutils literal">iterparse()</tt> also supports the <tt class="docutils literal">tag</tt> argument for selective event
iteration and several other parameters that control the parser setup.
The <tt class="docutils literal">tag</tt> argument can be a single tag or a sequence of tags.
You can also use it to parse HTML input by passing <tt class="docutils literal">html=True</tt>.</p>
<div class="section" id="iterwalk">
<h2>iterwalk</h2>
<p>For convenience, lxml also provides an <tt class="docutils literal">iterwalk()</tt> function.
It behaves exactly like <tt class="docutils literal">iterparse()</tt>, but works on Elements and
ElementTrees. Here is an example for a tree parsed by <tt class="docutils literal">iterparse()</tt>:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="n">xml</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterparse</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">f</span><span class="p">,</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="n">tag</span><span class="o">=</span><span class="s2">"element"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="gp">>>> </span><span class="n">root</span> <span class="o">=</span> <span class="n">context</span><span class="o">.</span><span class="n">root</span>
</pre></div>
<p>And now we can take the resulting in-memory tree and iterate over it
using <tt class="docutils literal">iterwalk()</tt> to get the exact same events without parsing the
input again:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterwalk</span><span class="p">(</span>
<span class="gp">... </span> <span class="n">root</span><span class="p">,</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="n">tag</span><span class="o">=</span><span class="s2">"element"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
<span class="go">start: element</span>
<span class="go">end: element</span>
</pre></div>
<p>In order to avoid wasting time on uninteresting parts of the tree, the <tt class="docutils literal">iterwalk</tt>
iterator can be instructed to skip over an entire subtree with its
<tt class="docutils literal">.skip_subtree()</tt> method.</p>
<div class="syntax"><pre><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="gp">... </span><span class="s1"><root></span>
<span class="gp">... </span><span class="s1"> <a> <b /> </a></span>
<span class="gp">... </span><span class="s1"> <c /></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">context</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">iterwalk</span><span class="p">(</span><span class="n">root</span><span class="p">,</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="k">for</span> <span class="n">action</span><span class="p">,</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">context</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"</span><span class="si">%s</span><span class="s2">: </span><span class="si">%s</span><span class="s2">"</span> <span class="o">%</span> <span class="p">(</span><span class="n">action</span><span class="p">,</span> <span class="n">elem</span><span class="o">.</span><span class="n">tag</span><span class="p">))</span>
<span class="gp">... </span> <span class="k">if</span> <span class="n">action</span> <span class="o">==</span> <span class="s1">'start'</span> <span class="ow">and</span> <span class="n">elem</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="n">context</span><span class="o">.</span><span class="n">skip_subtree</span><span class="p">()</span> <span class="c1"># ignore <b></span>
<span class="go">start: root</span>
<span class="go">start: a</span>
<span class="go">end: a</span>
<span class="go">start: c</span>
<span class="go">end: c</span>
<span class="go">end: root</span>
</pre></div>
<p>Note that <tt class="docutils literal">.skip_subtree()</tt> only has an effect when handling <tt class="docutils literal">start</tt> or
<tt class="docutils literal"><span class="pre">start-ns</span></tt> events.</p>
</div>
</div>
<div class="section" id="python-unicode-strings">
<h1>Python unicode strings</h1>
<p>lxml.etree has broader support for Python unicode strings than the ElementTree
library. First of all, where ElementTree would raise an exception, the
parsers in lxml.etree can handle unicode strings straight away. This is most
helpful for XML snippets embedded in source code using the <tt class="docutils literal">XML()</tt>
function:</p>
<div class="syntax"><pre><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">u'<test> </span><span class="se">\uf8d1</span><span class="s1"> + </span><span class="se">\uf8d2</span><span class="s1"> </test>'</span> <span class="p">)</span>
</pre></div>
<p>This requires, however, that unicode strings do not specify a conflicting
encoding themselves and thus lie about their real encoding:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span> <span class="s1">u'<?xml version="1.0" encoding="ASCII"?></span><span class="se">\n</span><span class="s1">'</span> <span class="o">+</span>
<span class="gp">... </span> <span class="s1">u'<test> </span><span class="se">\uf8d1</span><span class="s1"> + </span><span class="se">\uf8d2</span><span class="s1"> </test>'</span> <span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">Unicode strings with encoding declaration are not supported. Please use bytes input or XML fragments without declaration.</span>
</pre></div>
<p>Similarly, you will get errors when you try the same with HTML data in a
unicode string that specifies a charset in a meta tag of the header. You
should generally avoid converting XML/HTML data to unicode before passing it
into the parsers. It is both slower and error prone.</p>
<div class="section" id="serialising-to-unicode-strings">
<h2>Serialising to Unicode strings</h2>
<p>To serialize the result, you would normally use the <tt class="docutils literal">tostring()</tt>
module function, which serializes to plain ASCII by default or a
number of other byte encodings if asked for:</p>
<div class="syntax"><pre><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'<test> &#63697; + &#63698; </test>'</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">'UTF-8'</span><span class="p">,</span> <span class="n">xml_declaration</span><span class="o">=</span><span class="bp">False</span><span class="p">)</span>
<span class="go">b'<test> \xef\xa3\x91 + \xef\xa3\x92 </test>'</span>
</pre></div>
<p>As an extension, lxml.etree recognises the name 'unicode' as an argument
to the encoding parameter to build a Python unicode representation of a tree:</p>
<div class="syntax"><pre><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">u'<test> \uf8d1 + \uf8d2 </test>'</span>
<span class="gp">>>> </span><span class="n">el</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">"test"</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">el</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">u'<test/>'</span>
<span class="gp">>>> </span><span class="n">subel</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">el</span><span class="p">,</span> <span class="s2">"subtest"</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">el</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">u'<test><subtest/></test>'</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">el</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="n">encoding</span><span class="o">=</span><span class="s1">'unicode'</span><span class="p">)</span>
<span class="go">u'<test><subtest/></test>'</span>
</pre></div>
<p>The result of <tt class="docutils literal"><span class="pre">tostring(encoding='unicode')</span></tt> can be treated like any
other Python unicode string and then passed back into the parsers.
However, if you want to save the result to a file or pass it over the
network, you should use <tt class="docutils literal">write()</tt> or <tt class="docutils literal">tostring()</tt> with a byte
encoding (typically UTF-8) to serialize the XML. The main reason is
that unicode strings returned by <tt class="docutils literal"><span class="pre">tostring(encoding='unicode')</span></tt> are
not byte streams and they never have an XML declaration to specify
their encoding. These strings are most likely not parsable by other
XML libraries.</p>
<p>For normal byte encodings, the <tt class="docutils literal">tostring()</tt> function automatically
adds a declaration as needed that reflects the encoding of the
returned string. This makes it possible for other parsers to
correctly parse the XML byte stream. Note that using <tt class="docutils literal">tostring()</tt>
with UTF-8 is also considerably faster in most cases.</p>
</div>
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