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class="menu item"><a href="lxml-source-howto.html#where-to-start">Where to start?</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-etree">lxml.etree</a></li><li class="menu item"><a href="lxml-source-howto.html#python-modules">Python modules</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-objectify">lxml.objectify</a></li><li class="menu item"><a href="lxml-source-howto.html#lxml-html">lxml.html</a></li></ul></li></ul><ul class="menu foreign" id="changes 4 2 3-menu"><li class="menu title"><a href="changes-4.2.3.html">Release Changelog</a></li></ul><ul class="menu foreign" id="credits-menu"><li class="menu title"><a href="credits.html">Credits</a><ul class="submenu"><li class="menu item"><a href="credits.html#main-contributors">Main contributors</a></li><li class="menu item"><a href="credits.html#special-thanks-goes-to">Special thanks goes to:</a></li></ul></li></ul></li><li><a href="/sitemap.html">Sitemap</a></li></ul></div></div><h1 class="title">Validation with lxml</h1>
<p>Apart from the built-in DTD support in parsers, lxml currently supports three
schema languages: <a class="reference external" href="http://en.wikipedia.org/wiki/Document_Type_Definition">DTD</a>, <a class="reference external" href="http://www.relaxng.org/">Relax NG</a> and <a class="reference external" href="http://www.w3.org/XML/Schema">XML Schema</a>. All three provide
identical APIs in lxml, represented by validator classes with the obvious
names.</p>
<p>lxml also provides support for ISO-<a class="reference external" href="http://www.schematron.com">Schematron</a>, based on the pure-XSLT
<a class="reference external" href="http://www.schematron.com/implementation.html">skeleton implementation</a> of Schematron:</p>
<p>There is also basic support for <cite>pre-ISO-Schematron</cite> through the libxml2
Schematron features. However, this does not currently support error reporting
in the validation phase due to insufficiencies in the implementation as of
libxml2 2.6.30.</p>
<div class="contents topic" id="contents">
<p class="topic-title first">Contents</p>
<ul class="simple">
<li><a class="reference internal" href="#validation-at-parse-time" id="id4">Validation at parse time</a></li>
<li><a class="reference internal" href="#id1" id="id5">DTD</a></li>
<li><a class="reference internal" href="#relaxng" id="id6">RelaxNG</a></li>
<li><a class="reference internal" href="#xmlschema" id="id7">XMLSchema</a></li>
<li><a class="reference internal" href="#id2" id="id8">Schematron</a></li>
<li><a class="reference internal" href="#id3" id="id9">(Pre-ISO-Schematron)</a></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>
<div class="section" id="validation-at-parse-time">
<h1>Validation at parse time</h1>
<p>The parser in lxml can do on-the-fly validation of a document against
a DTD or an XML schema. The DTD is retrieved automatically based on
the DOCTYPE of the parsed document. All you have to do is use a
parser that has DTD validation enabled:</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">dtd_validation</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
<p>Obviously, a request for validation enables the DTD loading feature.
There are two other options that enable loading the DTD, but that do
not perform any validation. The first is the <tt class="docutils literal">load_dtd</tt> keyword
option, which simply loads the DTD into the parser and makes it
available to the document as external subset. You can retrieve the
DTD from the parsed document using the <tt class="docutils literal">docinfo</tt> property of the
result ElementTree object. The internal subset is available as
<tt class="docutils literal">internalDTD</tt>, the external subset is provided as <tt class="docutils literal">externalDTD</tt>.</p>
<p>The third way to activate DTD loading is with the
<tt class="docutils literal">attribute_defaults</tt> option, which loads the DTD and weaves
attribute default values into the document. Again, no validation is
performed unless explicitly requested.</p>
<p>XML schema is supported in a similar way, but requires an explicit
schema to be provided:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">schema_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"> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"></span>
<span class="gp">... </span><span class="s1"> <xsd:element name="a" type="xsd:integer"/></span>
<span class="gp">... </span><span class="s1"> </xsd:schema></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schema</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLSchema</span><span class="p">(</span><span class="n">schema_root</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">schema</span> <span class="o">=</span> <span class="n">schema</span><span class="p">)</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="s2">"<a>5</a>"</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
</pre></div>
<p>If the validation fails (be it for a DTD or an XML schema), the parser
will raise an exception:</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="s2">"<a>no int</a>"</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="gr">lxml.etree.XMLSyntaxError</span>: <span class="n">Element 'a': 'no int' is not a valid value of the atomic type 'xs:integer'...</span>
</pre></div>
<p>If you want the parser to succeed regardless of the outcome of the
validation, you should use a non validating parser and run the
validation separately after parsing the document.</p>
</div>
<div class="section" id="id1">
<h1>DTD</h1>
<p>As described above, the parser support for DTDs depends on internal or
external subsets of the XML file. This means that the XML file itself
must either contain a DTD or must reference a DTD to make this work.
If you want to validate an XML document against a DTD that is not
referenced by the document itself, you can use the <tt class="docutils literal">DTD</tt> class.</p>
<p>To use the <tt class="docutils literal">DTD</tt> class, you must first pass a filename or file-like object
into the constructor to parse a DTD:</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="s2">"<!ELEMENT b EMPTY>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">dtd</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">DTD</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
</pre></div>
<p>Now you can use it to validate documents:</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="s2">"<b/>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">dtd</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">root</span><span class="p">))</span>
<span class="go">True</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">"<b><a/></b>"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">dtd</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">root</span><span class="p">))</span>
<span class="go">False</span>
</pre></div>
<p>The reason for the validation failure can be found in the error log:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">dtd</span><span class="o">.</span><span class="n">error_log</span><span class="o">.</span><span class="n">filter_from_errors</span><span class="p">()[</span><span class="mi">0</span><span class="p">])</span>
<span class="go"><string>:1:0:ERROR:VALID:DTD_NOT_EMPTY: Element b was declared EMPTY this one has content</span>
</pre></div>
<p>As an alternative to parsing from a file, you can use the
<tt class="docutils literal">external_id</tt> keyword argument to parse from a catalog. The
following example reads the DocBook DTD in version 4.2, if available
in the system catalog:</p>
<div class="syntax"><pre><span class="n">dtd</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">DTD</span><span class="p">(</span><span class="n">external_id</span> <span class="o">=</span> <span class="s2">"-//OASIS//DTD DocBook XML V4.2//EN"</span><span class="p">)</span>
</pre></div>
<p>The DTD information is available as attributes on the DTD object. The method
<tt class="docutils literal">iterelements</tt> provides an iterator over the element declarations:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">dtd</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">DTD</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="s1">'<!ELEMENT a EMPTY><!ELEMENT b EMPTY>'</span><span class="p">))</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">el</span> <span class="ow">in</span> <span class="n">dtd</span><span class="o">.</span><span class="n">iterelements</span><span class="p">():</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="n">el</span><span class="o">.</span><span class="n">name</span><span class="p">)</span>
<span class="go">a</span>
<span class="go">b</span>
</pre></div>
<p>The method <tt class="docutils literal">elements</tt> returns the element declarations as a list:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">dtd</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">DTD</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="s1">'<!ELEMENT a EMPTY><!ELEMENT b EMPTY>'</span><span class="p">))</span>
<span class="gp">>>> </span><span class="nb">len</span><span class="p">(</span><span class="n">dtd</span><span class="o">.</span><span class="n">elements</span><span class="p">())</span>
<span class="go">2</span>
</pre></div>
<p>An element declaration object provides the following attributes/methods:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal">name</tt>: The name of the element;</li>
<li><tt class="docutils literal">type</tt>: The element type, one of "undefined", "empty", "any", "mixed", or "element";</li>
<li><tt class="docutils literal">content</tt>: Element content declaration (see below);</li>
<li><tt class="docutils literal">iterattributes()</tt>: Return an iterator over attribute declarations (see below);</li>
<li><tt class="docutils literal">attributes()</tt>: Return a list of attribute declarations.</li>
</ul>
</blockquote>
<p>The <tt class="docutils literal">content</tt> attribute contains information about the content model of the element.
These element content declaration objects form a binary tree (via the <tt class="docutils literal">left</tt> and <tt class="docutils literal">right</tt>
attributes), that makes it possible to reconstruct the content model expression. Here's a
list of all attributes:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal">name</tt>: If this object represents an element in the content model expression,
<tt class="docutils literal">name</tt> is the name of the element, otherwise it is <tt class="docutils literal">None</tt>;</li>
<li><tt class="docutils literal">type</tt>: The type of the node: one of "pcdata", "element", "seq", or "or";</li>
<li><tt class="docutils literal">occur</tt>: How often this element (or this combination of elements) may occur:
one of "once", "opt", "mult", or "plus"</li>
<li><tt class="docutils literal">left</tt>: The left hand subexpression</li>
<li><tt class="docutils literal">right</tt>: The right hand subexpression</li>
</ul>
</blockquote>
<p>For example, the element declaration <tt class="docutils literal"><!ELEMENT a <span class="pre">(a|b)+></span></tt> results
in the following element content declaration objects:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">dtd</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">DTD</span><span class="p">(</span><span class="n">StringIO</span><span class="p">(</span><span class="s1">'<!ELEMENT a (a|b)+>'</span><span class="p">))</span>
<span class="gp">>>> </span><span class="n">content</span> <span class="o">=</span> <span class="n">dtd</span><span class="o">.</span><span class="n">elements</span><span class="p">()[</span><span class="mi">0</span><span class="p">]</span><span class="o">.</span><span class="n">content</span>
<span class="gp">>>> </span><span class="n">content</span><span class="o">.</span><span class="n">type</span><span class="p">,</span> <span class="n">content</span><span class="o">.</span><span class="n">occur</span><span class="p">,</span> <span class="n">content</span><span class="o">.</span><span class="n">name</span>
<span class="go">('or', 'plus', None)</span>
<span class="gp">>>> </span><span class="n">left</span><span class="p">,</span> <span class="n">right</span> <span class="o">=</span> <span class="n">content</span><span class="o">.</span><span class="n">left</span><span class="p">,</span> <span class="n">content</span><span class="o">.</span><span class="n">right</span>
<span class="gp">>>> </span><span class="n">left</span><span class="o">.</span><span class="n">type</span><span class="p">,</span> <span class="n">left</span><span class="o">.</span><span class="n">occur</span><span class="p">,</span> <span class="n">left</span><span class="o">.</span><span class="n">name</span>
<span class="go">('element', 'once', 'a')</span>
<span class="gp">>>> </span><span class="n">right</span><span class="o">.</span><span class="n">type</span><span class="p">,</span> <span class="n">right</span><span class="o">.</span><span class="n">occur</span><span class="p">,</span> <span class="n">right</span><span class="o">.</span><span class="n">name</span>
<span class="go">('element', 'once', 'b')</span>
</pre></div>
<p>Attributes declarations have the following attributes/methods:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal">name</tt>: The name of the attribute;</li>
<li><tt class="docutils literal">elemname</tt>: The name of the element the attribute belongs to;</li>
<li><tt class="docutils literal">type</tt>: The attribute type, one of "cdata", "id", "idref", "idrefs", "entity",
"entities", "nmtoken", "nmtokens", "enumeration", or "notation";</li>
<li><tt class="docutils literal">default</tt>: The type of the default value, one of "none", "required", "implied",
or "fixed";</li>
<li><tt class="docutils literal">defaultValue</tt>: The default value;</li>
<li><tt class="docutils literal">itervalues()</tt>: Return an iterator over the allowed attribute values (if the attribute
is of type "enumeration");</li>
<li><tt class="docutils literal">values()</tt>: Return a list of allowed attribute values.</li>
</ul>
</blockquote>
<p>Entity declarations are available via the <tt class="docutils literal">iterentities</tt> and <tt class="docutils literal">entities</tt> methods:</p>
<blockquote>
<pre class="doctest-block">
>>> dtd = etree.DTD(StringIO('<!ENTITY hurz "&#x40;">'))
>>> entity = dtd.entities()[0]
>>> entity.name, entity.orig, entity.content
('hurz', '&#x40;', '@')
</pre>
</blockquote>
</div>
<div class="section" id="relaxng">
<h1>RelaxNG</h1>
<p>The <tt class="docutils literal">RelaxNG</tt> class takes an ElementTree object to construct a Relax NG
validator:</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="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><element name="a" xmlns="http://relaxng.org/ns/structure/1.0"></span>
<span class="gp">... </span><span class="s1"> <zeroOrMore></span>
<span class="gp">... </span><span class="s1"> <element name="b"></span>
<span class="gp">... </span><span class="s1"> <text /></span>
<span class="gp">... </span><span class="s1"> </element></span>
<span class="gp">... </span><span class="s1"> </zeroOrMore></span>
<span class="gp">... </span><span class="s1"></element></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">relaxng_doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">relaxng</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">RelaxNG</span><span class="p">(</span><span class="n">relaxng_doc</span><span class="p">)</span>
</pre></div>
<p>Alternatively, pass a filename to the <tt class="docutils literal">file</tt> keyword argument to parse from
a file. This also enables correct handling of include files from within the
RelaxNG parser.</p>
<p>You can then validate some ElementTree document against the schema. You'll get
back True if the document is valid against the Relax NG schema, and False if
not:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'<a><b></b></a>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">relaxng</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'<a><c></c></a>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc2</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">invalid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">relaxng</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc2</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
<p>Calling the schema object has the same effect as calling its validate
method. This is sometimes used in conditional statements:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'<a><c></c></a>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc2</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">invalid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">if</span> <span class="ow">not</span> <span class="n">relaxng</span><span class="p">(</span><span class="n">doc2</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"invalid!"</span><span class="p">)</span>
<span class="go">invalid!</span>
</pre></div>
<p>If you prefer getting an exception when validating, you can use the
<tt class="docutils literal">assert_</tt> or <tt class="docutils literal">assertValid</tt> methods:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">relaxng</span><span class="o">.</span><span class="n">assertValid</span><span class="p">(</span><span class="n">doc2</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">lxml.etree.DocumentInvalid</span>: <span class="n">Did not expect element c there, line 1</span>
<span class="gp">>>> </span><span class="n">relaxng</span><span class="o">.</span><span class="n">assert_</span><span class="p">(</span><span class="n">doc2</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">AssertionError</span>: <span class="n">Did not expect element c there, line 1</span>
</pre></div>
<p>If you want to find out why the validation failed in the second case, you can
look up the error log of the validation process and check it for relevant
messages:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">log</span> <span class="o">=</span> <span class="n">relaxng</span><span class="o">.</span><span class="n">error_log</span>
<span class="gp">>>> </span><span class="k">print</span><span class="p">(</span><span class="n">log</span><span class="o">.</span><span class="n">last_error</span><span class="p">)</span>
<span class="go"><string>:1:0:ERROR:RELAXNGV:RELAXNG_ERR_ELEMWRONG: Did not expect element c there</span>
</pre></div>
<p>You can see that the error (ERROR) happened during RelaxNG validation
(RELAXNGV). The message then tells you what went wrong. You can also
look at the error domain and its type directly:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">error</span> <span class="o">=</span> <span class="n">log</span><span class="o">.</span><span class="n">last_error</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">domain_name</span><span class="p">)</span>
<span class="go">RELAXNGV</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">type_name</span><span class="p">)</span>
<span class="go">RELAXNG_ERR_ELEMWRONG</span>
</pre></div>
<p>Note that this error log is local to the RelaxNG object. It will only
contain log entries that appeared during the validation.</p>
<p>Similar to XSLT, there's also a less efficient but easier shortcut method to
do one-shot RelaxNG validation:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">doc</span><span class="o">.</span><span class="n">relaxng</span><span class="p">(</span><span class="n">relaxng_doc</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">doc2</span><span class="o">.</span><span class="n">relaxng</span><span class="p">(</span><span class="n">relaxng_doc</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
<p>libxml2 does not currently support the <a class="reference external" href="http://relaxng.org/compact-tutorial.html">RelaxNG Compact Syntax</a>.
However, if <a class="reference external" href="https://pypi.python.org/pypi/rnc2rng">rnc2rng</a> is installed, lxml 3.6 and later can use it
internally to parse the input schema. It recognises the <cite>.rnc</cite> file
extension and also allows parsing an RNC schema from a string using
<cite>RelaxNG.from_rnc_string()</cite>.</p>
<p>Alternatively, the <a class="reference external" href="http://www.thaiopensource.com/relaxng/trang.html">trang</a> translator can convert the compact syntax
to the XML syntax, which can then be used with lxml.</p>
</div>
<div class="section" id="xmlschema">
<h1>XMLSchema</h1>
<p>lxml.etree also has XML Schema (XSD) support, using the class
lxml.etree.XMLSchema. The API is very similar to the Relax NG and DTD
classes. Pass an ElementTree object to construct a XMLSchema validator:</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="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"></span>
<span class="gp">... </span><span class="s1"><xsd:element name="a" type="AType"/></span>
<span class="gp">... </span><span class="s1"><xsd:complexType name="AType"></span>
<span class="gp">... </span><span class="s1"> <xsd:sequence></span>
<span class="gp">... </span><span class="s1"> <xsd:element name="b" type="xsd:string" /></span>
<span class="gp">... </span><span class="s1"> </xsd:sequence></span>
<span class="gp">... </span><span class="s1"></xsd:complexType></span>
<span class="gp">... </span><span class="s1"></xsd:schema></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">xmlschema_doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">xmlschema</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XMLSchema</span><span class="p">(</span><span class="n">xmlschema_doc</span><span class="p">)</span>
</pre></div>
<p>You can then validate some ElementTree document with this. Like with RelaxNG,
you'll get back true if the document is valid against the XML schema, and
false if not:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'<a><b></b></a>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">xmlschema</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'<a><c></c></a>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc2</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">invalid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">xmlschema</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc2</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
<p>Calling the schema object has the same effect as calling its validate method.
This is sometimes used in conditional statements:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'<a><c></c></a>'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc2</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">invalid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">if</span> <span class="ow">not</span> <span class="n">xmlschema</span><span class="p">(</span><span class="n">doc2</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"invalid!"</span><span class="p">)</span>
<span class="go">invalid!</span>
</pre></div>
<p>If you prefer getting an exception when validating, you can use the
<tt class="docutils literal">assert_</tt> or <tt class="docutils literal">assertValid</tt> methods:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">xmlschema</span><span class="o">.</span><span class="n">assertValid</span><span class="p">(</span><span class="n">doc2</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">lxml.etree.DocumentInvalid</span>: <span class="n">Element 'c': This element is not expected. Expected is ( b )., line 1</span>
<span class="gp">>>> </span><span class="n">xmlschema</span><span class="o">.</span><span class="n">assert_</span><span class="p">(</span><span class="n">doc2</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">AssertionError</span>: <span class="n">Element 'c': This element is not expected. Expected is ( b )., line 1</span>
</pre></div>
<p>Error reporting works as for the RelaxNG class:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">log</span> <span class="o">=</span> <span class="n">xmlschema</span><span class="o">.</span><span class="n">error_log</span>
<span class="gp">>>> </span><span class="n">error</span> <span class="o">=</span> <span class="n">log</span><span class="o">.</span><span class="n">last_error</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">domain_name</span><span class="p">)</span>
<span class="go">SCHEMASV</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">type_name</span><span class="p">)</span>
<span class="go">SCHEMAV_ELEMENT_CONTENT</span>
</pre></div>
<p>If you were to print this log entry, you would get something like the
following. Note that the error message depends on the libxml2 version in
use:</p>
<pre class="literal-block">
<string>:1:ERROR::SCHEMAV_ELEMENT_CONTENT: Element 'c': This element is not expected. Expected is ( b ).
</pre>
<p>Similar to XSLT and RelaxNG, there's also a less efficient but easier shortcut
method to do XML Schema validation:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">doc</span><span class="o">.</span><span class="n">xmlschema</span><span class="p">(</span><span class="n">xmlschema_doc</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">doc2</span><span class="o">.</span><span class="n">xmlschema</span><span class="p">(</span><span class="n">xmlschema_doc</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
<div class="section" id="id2">
<h1>Schematron</h1>
<p>From version 2.3 on lxml features ISO-<a class="reference external" href="http://www.schematron.com">Schematron</a> support built on the
de-facto reference implementation of Schematron, the pure-XSLT-1.0
<a class="reference external" href="http://www.schematron.com/implementation.html">skeleton implementation</a>. This is provided by the lxml.isoschematron package
that implements the Schematron class, with an API compatible to the other
validators'. Pass an Element or ElementTree object to construct a Schematron
validator:</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">isoschematron</span>
<span class="gp">>>> </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><schema xmlns="http://purl.oclc.org/dsdl/schematron" ></span>
<span class="gp">... </span><span class="s1"> <pattern id="sum_equals_100_percent"></span>
<span class="gp">... </span><span class="s1"> <title>Sum equals 100%.</title></span>
<span class="gp">... </span><span class="s1"> <rule context="Total"></span>
<span class="gp">... </span><span class="s1"> <assert test="sum(//Percent)=100">Sum is not 100%.</assert></span>
<span class="gp">... </span><span class="s1"> </rule></span>
<span class="gp">... </span><span class="s1"> </pattern></span>
<span class="gp">... </span><span class="s1"></schema></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">sct_doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span> <span class="o">=</span> <span class="n">isoschematron</span><span class="o">.</span><span class="n">Schematron</span><span class="p">(</span><span class="n">sct_doc</span><span class="p">)</span>
</pre></div>
<p>You can then validate some ElementTree document with this. Just like with
XMLSchema or RelaxNG, you'll get back true if the document is valid against the
schema, and false if not:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><Total></span>
<span class="gp">... </span><span class="s1"> <Percent>20</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>30</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>50</Percent></span>
<span class="gp">... </span><span class="s1"></Total></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">True</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">doc</span><span class="o">.</span><span class="n">getroot</span><span class="p">(),</span> <span class="s2">"Percent"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"10"</span>
<span class="gp">>>> </span><span class="n">schematron</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
<p>Calling the schema object has the same effect as calling its validate method.
This can be useful for conditional statements:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">is_valid</span> <span class="o">=</span> <span class="n">isoschematron</span><span class="o">.</span><span class="n">Schematron</span><span class="p">(</span><span class="n">sct_doc</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">if</span> <span class="ow">not</span> <span class="n">is_valid</span><span class="p">(</span><span class="n">doc</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"invalid!"</span><span class="p">)</span>
<span class="go">invalid!</span>
</pre></div>
<p>Built on a pure-xslt implementation, the actual validator is created as an
XSLT 1.0 stylesheet using these steps:</p>
<ol class="arabic simple" start="0">
<li>(Extract embedded Schematron from XML Schema or RelaxNG schema)</li>
<li>Process inclusions</li>
<li>Process abstract patterns</li>
<li>Compile the schematron schema to XSLT</li>
</ol>
<p>To allow more control over the individual steps, isoschematron.Schematron
supports an extended API:</p>
<p>The <tt class="docutils literal">include</tt> and <tt class="docutils literal">expand</tt> keyword arguments can be used to switch off
steps 1) and 2).</p>
<p>To set parameters for steps 1), 2) and 3) dictionaries containing parameters
for XSLT can be provided using the keyword arguments <tt class="docutils literal">include_params</tt>,
<tt class="docutils literal">expand_params</tt> or <tt class="docutils literal">compile_params</tt>. Schematron automatically converts these
parameters to stylesheet parameters so you need not worry to set string
parameters using quotes or to use XSLT.strparam(). If you ever need to pass an
XPath as argument to the XSLT stylesheet you can pass in an etree.XPath object
(see XPath and XSLT with lxml: <a class="reference external" href="xpathxslt.html#stylesheet-parameters">Stylesheet-parameters</a> for background on this).</p>
<p>The <tt class="docutils literal">phase</tt> parameter of the compile step is additionally exposed as a keyword
argument. If set, it overrides occurrence in <tt class="docutils literal">compile_params</tt>. Note that
isoschematron.Schematron might expose more common parameters as additional keyword
args in the future.</p>
<p>By setting <tt class="docutils literal">store_schematron</tt> to True, the (included-and-expanded) schematron
document tree is stored and made available through the <tt class="docutils literal">schematron</tt> property.</p>
<p>Similarly, setting <tt class="docutils literal">store_xslt</tt> to True will result in the validation XSLT
document tree being kept; it can be retrieved through the <tt class="docutils literal">validator_xslt</tt>
property.</p>
<p>Finally, with <tt class="docutils literal">store_report</tt> set to True (default: False), the resulting
validation report document gets stored and can be accessed as the
<tt class="docutils literal">validation_report</tt> property.</p>
<p>Using the <tt class="docutils literal">phase</tt> parameter of isoschematron.Schematron allows for selective
validation of predefined pattern groups:</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="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><schema xmlns="http://purl.oclc.org/dsdl/schematron" ></span>
<span class="gp">... </span><span class="s1"> <phase id="phase.sum_check"></span>
<span class="gp">... </span><span class="s1"> <active pattern="sum_equals_100_percent"/></span>
<span class="gp">... </span><span class="s1"> </phase></span>
<span class="gp">... </span><span class="s1"> <phase id="phase.entries_check"></span>
<span class="gp">... </span><span class="s1"> <active pattern="all_positive"/></span>
<span class="gp">... </span><span class="s1"> </phase></span>
<span class="gp">... </span><span class="s1"> <pattern id="sum_equals_100_percent"></span>
<span class="gp">... </span><span class="s1"> <title>Sum equals 100%.</title></span>
<span class="gp">... </span><span class="s1"> <rule context="Total"></span>
<span class="gp">... </span><span class="s1"> <assert test="sum(//Percent)=100">Sum is not 100%.</assert></span>
<span class="gp">... </span><span class="s1"> </rule></span>
<span class="gp">... </span><span class="s1"> </pattern></span>
<span class="gp">... </span><span class="s1"> <pattern id="all_positive"></span>
<span class="gp">... </span><span class="s1"> <title>All entries must be positive.</title></span>
<span class="gp">... </span><span class="s1"> <rule context="Percent"></span>
<span class="gp">... </span><span class="s1"> <assert test="number(.)>0">Number (<value-of select="."/>) not positive</assert></span>
<span class="gp">... </span><span class="s1"> </rule></span>
<span class="gp">... </span><span class="s1"> </pattern></span>
<span class="gp">... </span><span class="s1"></schema></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">sct_doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span> <span class="o">=</span> <span class="n">isoschematron</span><span class="o">.</span><span class="n">Schematron</span><span class="p">(</span><span class="n">sct_doc</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><Total></span>
<span class="gp">... </span><span class="s1"> <Percent>20</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>30</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>50</Percent></span>
<span class="gp">... </span><span class="s1"></Total></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">invalid_positive</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><Total></span>
<span class="gp">... </span><span class="s1"> <Percent>0</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>50</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>50</Percent></span>
<span class="gp">... </span><span class="s1"></Total></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">invalid_positive</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
<p>If the constraint of Percent entries being positive is not of interest in a
certain validation scenario, it can now be disabled:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">selective</span> <span class="o">=</span> <span class="n">isoschematron</span><span class="o">.</span><span class="n">Schematron</span><span class="p">(</span><span class="n">sct_doc</span><span class="p">,</span> <span class="n">phase</span><span class="o">=</span><span class="s2">"phase.sum_check"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">selective</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">True</span>
</pre></div>
<p>The usage of validation phases is a unique feature of ISO-Schematron and can be
a very powerful tool e.g. for establishing validation stages or to provide
different validators for different "validation audiences".</p>
</div>
<div class="section" id="id3">
<h1>(Pre-ISO-Schematron)</h1>
<p>Since version 2.0, lxml.etree features <a class="reference external" href="http://www.ascc.net/xml/schematron">pre-ISO-Schematron</a> support, using the
class lxml.etree.Schematron. It requires at least libxml2 2.6.21 to
work. The API is the same as for the other validators. Pass an
ElementTree object to construct a Schematron validator:</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="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><schema xmlns="http://www.ascc.net/xml/schematron" ></span>
<span class="gp">... </span><span class="s1"> <pattern name="Sum equals 100%."></span>
<span class="gp">... </span><span class="s1"> <rule context="Total"></span>
<span class="gp">... </span><span class="s1"> <assert test="sum(//Percent)=100">Sum is not 100%.</assert></span>
<span class="gp">... </span><span class="s1"> </rule></span>
<span class="gp">... </span><span class="s1"> </pattern></span>
<span class="gp">... </span><span class="s1"></schema></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">sct_doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Schematron</span><span class="p">(</span><span class="n">sct_doc</span><span class="p">)</span>
</pre></div>
<p>You can then validate some ElementTree document with this. Like with RelaxNG,
you'll get back true if the document is valid against the schema, and false if
not:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
<span class="gp">... </span><span class="s1"><Total></span>
<span class="gp">... </span><span class="s1"> <Percent>20</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>30</Percent></span>
<span class="gp">... </span><span class="s1"> <Percent>50</Percent></span>
<span class="gp">... </span><span class="s1"></Total></span>
<span class="gp">... </span><span class="s1">'''</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">schematron</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">True</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">doc</span><span class="o">.</span><span class="n">getroot</span><span class="p">(),</span> <span class="s2">"Percent"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s2">"10"</span>
<span class="gp">>>> </span><span class="n">schematron</span><span class="o">.</span><span class="n">validate</span><span class="p">(</span><span class="n">doc</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
<p>Calling the schema object has the same effect as calling its validate method.
This is sometimes used in conditional statements:</p>
<div class="syntax"><pre><span class="gp">>>> </span><span class="n">is_valid</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">Schematron</span><span class="p">(</span><span class="n">sct_doc</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">if</span> <span class="ow">not</span> <span class="n">is_valid</span><span class="p">(</span><span class="n">doc</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">print</span><span class="p">(</span><span class="s2">"invalid!"</span><span class="p">)</span>
<span class="go">invalid!</span>
</pre></div>
<p>Note that libxml2 restricts error reporting to the parsing step (when creating
the Schematron instance). There is not currently any support for error
reporting during validation.</p>
</div>
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