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 to:</a></li></ul></li></ul></li><li><a href="http://lxml.de/sitemap.html">Sitemap</a></li></ul></div><h1 class="title">Validation with lxml</h1>
  12
  13 <p>Apart from the built-in DTD support in parsers, lxml currently supports three
  14 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
  15 identical APIs in lxml, represented by validator classes with the obvious
  16 names.</p>
  17 <p>lxml also provides support for ISO-<a class="reference external" href="http://www.schematron.com">Schematron</a>, based on the pure-XSLT
  18 <a class="reference external" href="http://www.schematron.com/implementation.html">skeleton implementation</a> of Schematron:</p>
  19 <p>There is also basic support for <cite>pre-ISO-Schematron</cite> through the libxml2
  20 Schematron features. However, this does not currently support error reporting
  21 in the validation phase due to insufficiencies in the implementation as of
  22 libxml2 2.6.30.</p>
  23 <div class="contents topic" id="contents">
  24 <p class="topic-title first">Contents</p>
  25 <ul class="simple">
  26 <li><a class="reference internal" href="#validation-at-parse-time" id="id4">Validation at parse time</a></li>
  27 <li><a class="reference internal" href="#id1" id="id5">DTD</a></li>
  28 <li><a class="reference internal" href="#relaxng" id="id6">RelaxNG</a></li>
  29 <li><a class="reference internal" href="#xmlschema" id="id7">XMLSchema</a></li>
  30 <li><a class="reference internal" href="#id2" id="id8">Schematron</a></li>
  31 <li><a class="reference internal" href="#id3" id="id9">(Pre-ISO-Schematron)</a></li>
  32 </ul>
  33 </div>
  34 <p>The usual setup procedure:</p>
  35 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">lxml</span> <span class="kn">import</span> <span class="n">etree</span>
  36 </pre></div>
  37 <div class="section" id="validation-at-parse-time">
  38 <h1>Validation at parse time</h1>
  39 <p>The parser in lxml can do on-the-fly validation of a document against
  40 a DTD or an XML schema.  The DTD is retrieved automatically based on
  41 the DOCTYPE of the parsed document.  All you have to do is use a
  42 parser that has DTD validation enabled:</p>
  43 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
  44 </pre></div>
  45 <p>Obviously, a request for validation enables the DTD loading feature.
  46 There are two other options that enable loading the DTD, but that do
  47 not perform any validation.  The first is the <tt class="docutils literal">load_dtd</tt> keyword
  48 option, which simply loads the DTD into the parser and makes it
  49 available to the document as external subset.  You can retrieve the
  50 DTD from the parsed document using the <tt class="docutils literal">docinfo</tt> property of the
  51 result ElementTree object.  The internal subset is available as
  52 <tt class="docutils literal">internalDTD</tt>, the external subset is provided as <tt class="docutils literal">externalDTD</tt>.</p>
  53 <p>The third way way to activate DTD loading is with the
  54 <tt class="docutils literal">attribute_defaults</tt> option, which loads the DTD and weaves
  55 attribute default values into the document.  Again, no validation is
  56 performed unless explicitly requested.</p>
  57 <p>XML schema is supported in a similar way, but requires an explicit
  58 schema to be provided:</p>
  59 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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="s">'''</span><span class="se">\</span>
  60 <span class="gp">... </span><span class="s">  &lt;xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"&gt;</span>
  61 <span class="gp">... </span><span class="s">    &lt;xsd:element name="a" type="xsd:integer"/&gt;</span>
  62 <span class="gp">... </span><span class="s">  &lt;/xsd:schema&gt;</span>
  63 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
  64 <span class="gp">&gt;&gt;&gt; </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>
  65
  66 <span class="gp">&gt;&gt;&gt; </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>
  67 <span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="s">"&lt;a&gt;5&lt;/a&gt;"</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
  68 </pre></div>
  69 <p>If the validation fails (be it for a DTD or an XML schema), the parser
  70 will raise an exception:</p>
  71 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">fromstring</span><span class="p">(</span><span class="s">"&lt;a&gt;no int&lt;/a&gt;"</span><span class="p">,</span> <span class="n">parser</span><span class="p">)</span>
  72 <span class="gt">Traceback (most recent call last):</span>
  73 <span class="gr">lxml.etree.XMLSyntaxError: Element 'a'</span>: <span class="n">'no int' is not a valid value of the atomic type 'xs:integer'.</span>
  74 </pre></div>
  75 <p>If you want the parser to succeed regardless of the outcome of the
  76 validation, you should use a non validating parser and run the
  77 validation separately after parsing the document.</p>
  78 </div>
  79 <div class="section" id="id1">
  80 <h1>DTD</h1>
  81 <p>As described above, the parser support for DTDs depends on internal or
  82 external subsets of the XML file.  This means that the XML file itself
  83 must either contain a DTD or must reference a DTD to make this work.
  84 If you want to validate an XML document against a DTD that is not
  85 referenced by the document itself, you can use the <tt class="docutils literal">DTD</tt> class.</p>
  86 <p>To use the <tt class="docutils literal">DTD</tt> class, you must first pass a filename or file-like object
  87 into the constructor to parse a DTD:</p>
  88 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">"&lt;!ELEMENT b EMPTY&gt;"</span><span class="p">)</span>
  89 <span class="gp">&gt;&gt;&gt; </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>
  90 </pre></div>
  91 <p>Now you can use it to validate documents:</p>
  92 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"&lt;b/&gt;"</span><span class="p">)</span>
  93 <span class="gp">&gt;&gt;&gt; </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>
  94 <span class="go">True</span>
  95
  96 <span class="gp">&gt;&gt;&gt; </span><span class="n">root</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">XML</span><span class="p">(</span><span class="s">"&lt;b&gt;&lt;a/&gt;&lt;/b&gt;"</span><span class="p">)</span>
  97 <span class="gp">&gt;&gt;&gt; </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>
  98 <span class="go">False</span>
  99 </pre></div>
 100 <p>The reason for the validation failure can be found in the error log:</p>
 101 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 102 <span class="go">&lt;string&gt;:1:0:ERROR:VALID:DTD_NOT_EMPTY: Element b was declared EMPTY this one has content</span>
 103 </pre></div>
 104 <p>As an alternative to parsing from a file, you can use the
 105 <tt class="docutils literal">external_id</tt> keyword argument to parse from a catalog.  The
 106 following example reads the DocBook DTD in version 4.2, if available
 107 in the system catalog:</p>
 108 <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="s">"-//OASIS//DTD DocBook XML V4.2//EN"</span><span class="p">)</span>
 109 </pre></div>
 110 </div>
 111 <div class="section" id="relaxng">
 112 <h1>RelaxNG</h1>
 113 <p>The <tt class="docutils literal">RelaxNG</tt> class takes an ElementTree object to construct a Relax NG
 114 validator:</p>
 115 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 116 <span class="gp">... </span><span class="s">&lt;element name="a" xmlns="http://relaxng.org/ns/structure/1.0"&gt;</span>
 117 <span class="gp">... </span><span class="s"> &lt;zeroOrMore&gt;</span>
 118 <span class="gp">... </span><span class="s">    &lt;element name="b"&gt;</span>
 119 <span class="gp">... </span><span class="s">      &lt;text /&gt;</span>
 120 <span class="gp">... </span><span class="s">    &lt;/element&gt;</span>
 121 <span class="gp">... </span><span class="s"> &lt;/zeroOrMore&gt;</span>
 122 <span class="gp">... </span><span class="s">&lt;/element&gt;</span>
 123 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 124 <span class="gp">&gt;&gt;&gt; </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>
 125 <span class="gp">&gt;&gt;&gt; </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>
 126 </pre></div>
 127 <p>Alternatively, pass a filename to the <tt class="docutils literal">file</tt> keyword argument to parse from
 128 a file.  This also enables correct handling of include files from within the
 129 RelaxNG parser.</p>
 130 <p>You can then validate some ElementTree document against the schema. You'll get
 131 back True if the document is valid against the Relax NG schema, and False if
 132 not:</p>
 133 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;b&gt;&lt;/b&gt;&lt;/a&gt;'</span><span class="p">)</span>
 134 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
 135 <span class="gp">&gt;&gt;&gt; </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>
 136 <span class="go">True</span>
 137
 138 <span class="gp">&gt;&gt;&gt; </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;c&gt;&lt;/c&gt;&lt;/a&gt;'</span><span class="p">)</span>
 139 <span class="gp">&gt;&gt;&gt; </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>
 140 <span class="gp">&gt;&gt;&gt; </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>
 141 <span class="go">False</span>
 142 </pre></div>
 143 <p>Calling the schema object has the same effect as calling its validate
 144 method. This is sometimes used in conditional statements:</p>
 145 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;c&gt;&lt;/c&gt;&lt;/a&gt;'</span><span class="p">)</span>
 146 <span class="gp">&gt;&gt;&gt; </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>
 147 <span class="gp">&gt;&gt;&gt; </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>
 148 <span class="gp">... </span>    <span class="k">print</span><span class="p">(</span><span class="s">"invalid!"</span><span class="p">)</span>
 149 <span class="go">invalid!</span>
 150 </pre></div>
 151 <p>If you prefer getting an exception when validating, you can use the
 152 <tt class="docutils literal">assert_</tt> or <tt class="docutils literal">assertValid</tt> methods:</p>
 153 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 154 <span class="gt">Traceback (most recent call last):</span>
 155   <span class="c">...</span>
 156 <span class="gr">lxml.etree.DocumentInvalid</span>: <span class="n">Did not expect element c there, line 1</span>
 157
 158 <span class="gp">&gt;&gt;&gt; </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>
 159 <span class="gt">Traceback (most recent call last):</span>
 160   <span class="c">...</span>
 161 <span class="gr">AssertionError</span>: <span class="n">Did not expect element c there, line 1</span>
 162 </pre></div>
 163 <p>If you want to find out why the validation failed in the second case, you can
 164 look up the error log of the validation process and check it for relevant
 165 messages:</p>
 166 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 167 <span class="gp">&gt;&gt;&gt; </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>
 168 <span class="go">&lt;string&gt;:1:0:ERROR:RELAXNGV:RELAXNG_ERR_ELEMWRONG: Did not expect element c there</span>
 169 </pre></div>
 170 <p>You can see that the error (ERROR) happened during RelaxNG validation
 171 (RELAXNGV).  The message then tells you what went wrong.  You can also
 172 look at the error domain and its type directly:</p>
 173 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 174 <span class="gp">&gt;&gt;&gt; </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>
 175 <span class="go">RELAXNGV</span>
 176 <span class="gp">&gt;&gt;&gt; </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>
 177 <span class="go">RELAXNG_ERR_ELEMWRONG</span>
 178 </pre></div>
 179 <p>Note that this error log is local to the RelaxNG object.  It will only
 180 contain log entries that appeared during the validation.</p>
 181 <p>Similar to XSLT, there's also a less efficient but easier shortcut method to
 182 do one-shot RelaxNG validation:</p>
 183 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 184 <span class="go">True</span>
 185 <span class="gp">&gt;&gt;&gt; </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>
 186 <span class="go">False</span>
 187 </pre></div>
 188 <p>libxml2 does not currently support the <a class="reference external" href="http://www.thaiopensource.com/relaxng/trang.html">RelaxNG Compact Syntax</a>.
 189 However, the <a class="reference external" href="http://www.thaiopensource.com/relaxng/trang.html">trang</a> translator can convert the compact syntax to the
 190 XML syntax, which can then be used with lxml.</p>
 191 </div>
 192 <div class="section" id="xmlschema">
 193 <h1>XMLSchema</h1>
 194 <p>lxml.etree also has XML Schema (XSD) support, using the class
 195 lxml.etree.XMLSchema.  The API is very similar to the Relax NG and DTD
 196 classes.  Pass an ElementTree object to construct a XMLSchema validator:</p>
 197 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 198 <span class="gp">... </span><span class="s">&lt;xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"&gt;</span>
 199 <span class="gp">... </span><span class="s">&lt;xsd:element name="a" type="AType"/&gt;</span>
 200 <span class="gp">... </span><span class="s">&lt;xsd:complexType name="AType"&gt;</span>
 201 <span class="gp">... </span><span class="s">  &lt;xsd:sequence&gt;</span>
 202 <span class="gp">... </span><span class="s">    &lt;xsd:element name="b" type="xsd:string" /&gt;</span>
 203 <span class="gp">... </span><span class="s">  &lt;/xsd:sequence&gt;</span>
 204 <span class="gp">... </span><span class="s">&lt;/xsd:complexType&gt;</span>
 205 <span class="gp">... </span><span class="s">&lt;/xsd:schema&gt;</span>
 206 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 207 <span class="gp">&gt;&gt;&gt; </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>
 208 <span class="gp">&gt;&gt;&gt; </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>
 209 </pre></div>
 210 <p>You can then validate some ElementTree document with this.  Like with RelaxNG,
 211 you'll get back true if the document is valid against the XML schema, and
 212 false if not:</p>
 213 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;b&gt;&lt;/b&gt;&lt;/a&gt;'</span><span class="p">)</span>
 214 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
 215 <span class="gp">&gt;&gt;&gt; </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>
 216 <span class="go">True</span>
 217
 218 <span class="gp">&gt;&gt;&gt; </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;c&gt;&lt;/c&gt;&lt;/a&gt;'</span><span class="p">)</span>
 219 <span class="gp">&gt;&gt;&gt; </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>
 220 <span class="gp">&gt;&gt;&gt; </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>
 221 <span class="go">False</span>
 222 </pre></div>
 223 <p>Calling the schema object has the same effect as calling its validate method.
 224 This is sometimes used in conditional statements:</p>
 225 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">invalid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'&lt;a&gt;&lt;c&gt;&lt;/c&gt;&lt;/a&gt;'</span><span class="p">)</span>
 226 <span class="gp">&gt;&gt;&gt; </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>
 227 <span class="gp">&gt;&gt;&gt; </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>
 228 <span class="gp">... </span>    <span class="k">print</span><span class="p">(</span><span class="s">"invalid!"</span><span class="p">)</span>
 229 <span class="go">invalid!</span>
 230 </pre></div>
 231 <p>If you prefer getting an exception when validating, you can use the
 232 <tt class="docutils literal">assert_</tt> or <tt class="docutils literal">assertValid</tt> methods:</p>
 233 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 234 <span class="gt">Traceback (most recent call last):</span>
 235   <span class="c">...</span>
 236 <span class="gr">lxml.etree.DocumentInvalid: Element 'c'</span>: <span class="n">This element is not expected. Expected is ( b )., line 1</span>
 237
 238 <span class="gp">&gt;&gt;&gt; </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>
 239 <span class="gt">Traceback (most recent call last):</span>
 240   <span class="c">...</span>
 241 <span class="gr">AssertionError: Element 'c'</span>: <span class="n">This element is not expected. Expected is ( b )., line 1</span>
 242 </pre></div>
 243 <p>Error reporting works as for the RelaxNG class:</p>
 244 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 245 <span class="gp">&gt;&gt;&gt; </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>
 246 <span class="gp">&gt;&gt;&gt; </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>
 247 <span class="go">SCHEMASV</span>
 248 <span class="gp">&gt;&gt;&gt; </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>
 249 <span class="go">SCHEMAV_ELEMENT_CONTENT</span>
 250 </pre></div>
 251 <p>If you were to print this log entry, you would get something like the
 252 following.  Note that the error message depends on the libxml2 version in
 253 use:</p>
 254 <pre class="literal-block">
 255 &lt;string&gt;:1:ERROR::SCHEMAV_ELEMENT_CONTENT: Element 'c': This element is not expected. Expected is ( b ).
 256 </pre>
 257 <p>Similar to XSLT and RelaxNG, there's also a less efficient but easier shortcut
 258 method to do XML Schema validation:</p>
 259 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 260 <span class="go">True</span>
 261 <span class="gp">&gt;&gt;&gt; </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>
 262 <span class="go">False</span>
 263 </pre></div>
 264 </div>
 265 <div class="section" id="id2">
 266 <h1>Schematron</h1>
 267 <p>From version 2.3 on lxml features ISO-<a class="reference external" href="http://www.schematron.com">Schematron</a> support built on the
 268 de-facto reference implementation of Schematron, the pure-XSLT-1.0
 269 <a class="reference external" href="http://www.schematron.com/implementation.html">skeleton implementation</a>. This is provided by the lxml.isoschematron package
 270 that implements the Schematron class, with an API compatible to the other
 271 validators'.  Pass an Element or ElementTree object to construct a Schematron
 272 validator:</p>
 273 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">lxml</span> <span class="kn">import</span> <span class="n">isoschematron</span>
 274 <span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 275 <span class="gp">... </span><span class="s">&lt;schema xmlns="http://purl.oclc.org/dsdl/schematron" &gt;</span>
 276 <span class="gp">... </span><span class="s">  &lt;pattern id="sum_equals_100_percent"&gt;</span>
 277 <span class="gp">... </span><span class="s">    &lt;title&gt;Sum equals 100%.&lt;/title&gt;</span>
 278 <span class="gp">... </span><span class="s">    &lt;rule context="Total"&gt;</span>
 279 <span class="gp">... </span><span class="s">      &lt;assert test="sum(//Percent)=100"&gt;Sum is not 100%.&lt;/assert&gt;</span>
 280 <span class="gp">... </span><span class="s">    &lt;/rule&gt;</span>
 281 <span class="gp">... </span><span class="s">  &lt;/pattern&gt;</span>
 282 <span class="gp">... </span><span class="s">&lt;/schema&gt;</span>
 283 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 284
 285 <span class="gp">&gt;&gt;&gt; </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>
 286 <span class="gp">&gt;&gt;&gt; </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>
 287 </pre></div>
 288 <p>You can then validate some ElementTree document with this. Just like with
 289 XMLSchema or RelaxNG, you'll get back true if the document is valid against the
 290 schema, and false if not:</p>
 291 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 292 <span class="gp">... </span><span class="s">&lt;Total&gt;</span>
 293 <span class="gp">... </span><span class="s">  &lt;Percent&gt;20&lt;/Percent&gt;</span>
 294 <span class="gp">... </span><span class="s">  &lt;Percent&gt;30&lt;/Percent&gt;</span>
 295 <span class="gp">... </span><span class="s">  &lt;Percent&gt;50&lt;/Percent&gt;</span>
 296 <span class="gp">... </span><span class="s">&lt;/Total&gt;</span>
 297 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 298
 299 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
 300 <span class="gp">&gt;&gt;&gt; </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>
 301 <span class="go">True</span>
 302
 303 <span class="gp">&gt;&gt;&gt; </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="s">"Percent"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"10"</span>
 304
 305 <span class="gp">&gt;&gt;&gt; </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>
 306 <span class="go">False</span>
 307 </pre></div>
 308 <p>Calling the schema object has the same effect as calling its validate method.
 309 This can be useful for conditional statements:</p>
 310 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 311
 312 <span class="gp">&gt;&gt;&gt; </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>
 313 <span class="gp">... </span>    <span class="k">print</span><span class="p">(</span><span class="s">"invalid!"</span><span class="p">)</span>
 314 <span class="go">invalid!</span>
 315 </pre></div>
 316 <p>Built on a pure-xslt implementation, the actual validator is created as an
 317 XSLT 1.0 stylesheet using these steps:</p>
 318 <ol class="arabic simple" start="0">
 319 <li>(Extract embedded Schematron from XML Schema or RelaxNG schema)</li>
 320 <li>Process inclusions</li>
 321 <li>Process abstract patterns</li>
 322 <li>Compile the schematron schema to XSLT</li>
 323 </ol>
 324 <p>To allow more control over the individual steps, isoschematron.Schematron
 325 supports an extended API:</p>
 326 <p>The <tt class="docutils literal">include</tt> and <tt class="docutils literal">expand</tt> keyword arguments can be used to switch off
 327 steps 1) and 2).</p>
 328 <p>To set parameters for steps 1), 2) and 3) dictionaries containing parameters
 329 for XSLT can be provided using the keyword arguments <tt class="docutils literal">include_params</tt>,
 330 <tt class="docutils literal">expand_params</tt> or <tt class="docutils literal">compile_params</tt>. Schematron automatically converts these
 331 parameters to stylesheet parameters so you need not worry to set string
 332 parameters using quotes or to use XSLT.strparam(). If you ever need to pass an
 333 XPath as argument to the XSLT stylesheet you can pass in an etree.XPath object
 334 (see XPath and XSLT with lxml: <a class="reference external" href="xpathxslt.html#stylesheet-parameters">Stylesheet-parameters</a> for background on this).</p>
 335 <p>The <tt class="docutils literal">phase</tt> parameter of the compile step is additionally exposed as a keyword
 336 argument. If set, it overrides occurrence in <tt class="docutils literal">compile_params</tt>. Note that
 337 isoschematron.Schematron might expose more common parameters as additional keyword
 338 args in the future.</p>
 339 <p>By setting <tt class="docutils literal">store_schematron</tt> to True, the (included-and-expanded) schematron
 340 document tree is stored and made available through the <tt class="docutils literal">schematron</tt> property.</p>
 341 <p>Similarly, setting <tt class="docutils literal">store_xslt</tt> to True will result in the validation XSLT
 342 document tree being kept; it can be retrieved through the <tt class="docutils literal">validator_xslt</tt>
 343 property.</p>
 344 <p>Finally, with <tt class="docutils literal">store_report</tt> set to True (default: False), the resulting
 345 validation report document gets stored and can be accessed as the
 346 <tt class="docutils literal">validation_report</tt> property.</p>
 347 <p>Using the <tt class="docutils literal">phase</tt> parameter of isoschematron.Schematron allows for selective
 348 validation of predefined pattern groups:</p>
 349 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 350 <span class="gp">... </span><span class="s">&lt;schema xmlns="http://purl.oclc.org/dsdl/schematron" &gt;</span>
 351 <span class="gp">... </span><span class="s">  &lt;phase id="phase.sum_check"&gt;</span>
 352 <span class="gp">... </span><span class="s">    &lt;active pattern="sum_equals_100_percent"/&gt;</span>
 353 <span class="gp">... </span><span class="s">  &lt;/phase&gt;</span>
 354 <span class="gp">... </span><span class="s">  &lt;phase id="phase.entries_check"&gt;</span>
 355 <span class="gp">... </span><span class="s">    &lt;active pattern="all_positive"/&gt;</span>
 356 <span class="gp">... </span><span class="s">  &lt;/phase&gt;</span>
 357 <span class="gp">... </span><span class="s">  &lt;pattern id="sum_equals_100_percent"&gt;</span>
 358 <span class="gp">... </span><span class="s">    &lt;title&gt;Sum equals 100%.&lt;/title&gt;</span>
 359 <span class="gp">... </span><span class="s">    &lt;rule context="Total"&gt;</span>
 360 <span class="gp">... </span><span class="s">      &lt;assert test="sum(//Percent)=100"&gt;Sum is not 100%.&lt;/assert&gt;</span>
 361 <span class="gp">... </span><span class="s">    &lt;/rule&gt;</span>
 362 <span class="gp">... </span><span class="s">  &lt;/pattern&gt;</span>
 363 <span class="gp">... </span><span class="s">  &lt;pattern id="all_positive"&gt;</span>
 364 <span class="gp">... </span><span class="s">    &lt;title&gt;All entries must be positive.&lt;/title&gt;</span>
 365 <span class="gp">... </span><span class="s">    &lt;rule context="Percent"&gt;</span>
 366 <span class="gp">... </span><span class="s">      &lt;assert test="number(.)&gt;0"&gt;Number (&lt;value-of select="."/&gt;) not positive&lt;/assert&gt;</span>
 367 <span class="gp">... </span><span class="s">    &lt;/rule&gt;</span>
 368 <span class="gp">... </span><span class="s">  &lt;/pattern&gt;</span>
 369 <span class="gp">... </span><span class="s">&lt;/schema&gt;</span>
 370 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 371
 372 <span class="gp">&gt;&gt;&gt; </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>
 373 <span class="gp">&gt;&gt;&gt; </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>
 374
 375 <span class="gp">&gt;&gt;&gt; </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 376 <span class="gp">... </span><span class="s">&lt;Total&gt;</span>
 377 <span class="gp">... </span><span class="s">  &lt;Percent&gt;20&lt;/Percent&gt;</span>
 378 <span class="gp">... </span><span class="s">  &lt;Percent&gt;30&lt;/Percent&gt;</span>
 379 <span class="gp">... </span><span class="s">  &lt;Percent&gt;50&lt;/Percent&gt;</span>
 380 <span class="gp">... </span><span class="s">&lt;/Total&gt;</span>
 381 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 382
 383 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
 384 <span class="gp">&gt;&gt;&gt; </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>
 385 <span class="go">True</span>
 386
 387 <span class="gp">&gt;&gt;&gt; </span><span class="n">invalid_positive</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 388 <span class="gp">... </span><span class="s">&lt;Total&gt;</span>
 389 <span class="gp">... </span><span class="s">  &lt;Percent&gt;0&lt;/Percent&gt;</span>
 390 <span class="gp">... </span><span class="s">  &lt;Percent&gt;50&lt;/Percent&gt;</span>
 391 <span class="gp">... </span><span class="s">  &lt;Percent&gt;50&lt;/Percent&gt;</span>
 392 <span class="gp">... </span><span class="s">&lt;/Total&gt;</span>
 393 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 394
 395 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">invalid_positive</span><span class="p">)</span>
 396
 397 <span class="gp">&gt;&gt;&gt; </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>
 398 <span class="go">False</span>
 399 </pre></div>
 400 <p>If the constraint of Percent entries being positive is not of interest in a
 401 certain validation scenario, it can now be disabled:</p>
 402 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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="s">"phase.sum_check"</span><span class="p">)</span>
 403 <span class="gp">&gt;&gt;&gt; </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>
 404 <span class="go">True</span>
 405 </pre></div>
 406 <p>The usage of validation phases is a unique feature of ISO-Schematron and can be
 407 a very powerful tool e.g. for establishing validation stages or to provide
 408 different validators for different "validation audiences".</p>
 409 </div>
 410 <div class="section" id="id3">
 411 <h1>(Pre-ISO-Schematron)</h1>
 412 <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
 413 class lxml.etree.Schematron.  It requires at least libxml2 2.6.21 to
 414 work.  The API is the same as for the other validators.  Pass an
 415 ElementTree object to construct a Schematron validator:</p>
 416 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">f</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 417 <span class="gp">... </span><span class="s">&lt;schema xmlns="http://www.ascc.net/xml/schematron" &gt;</span>
 418 <span class="gp">... </span><span class="s">  &lt;pattern name="Sum equals 100%."&gt;</span>
 419 <span class="gp">... </span><span class="s">    &lt;rule context="Total"&gt;</span>
 420 <span class="gp">... </span><span class="s">      &lt;assert test="sum(//Percent)=100"&gt;Sum is not 100%.&lt;/assert&gt;</span>
 421 <span class="gp">... </span><span class="s">    &lt;/rule&gt;</span>
 422 <span class="gp">... </span><span class="s">  &lt;/pattern&gt;</span>
 423 <span class="gp">... </span><span class="s">&lt;/schema&gt;</span>
 424 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 425
 426 <span class="gp">&gt;&gt;&gt; </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>
 427 <span class="gp">&gt;&gt;&gt; </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>
 428 </pre></div>
 429 <p>You can then validate some ElementTree document with this.  Like with RelaxNG,
 430 you'll get back true if the document is valid against the schema, and false if
 431 not:</p>
 432 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">valid</span> <span class="o">=</span> <span class="n">StringIO</span><span class="p">(</span><span class="s">'''</span><span class="se">\</span>
 433 <span class="gp">... </span><span class="s">&lt;Total&gt;</span>
 434 <span class="gp">... </span><span class="s">  &lt;Percent&gt;20&lt;/Percent&gt;</span>
 435 <span class="gp">... </span><span class="s">  &lt;Percent&gt;30&lt;/Percent&gt;</span>
 436 <span class="gp">... </span><span class="s">  &lt;Percent&gt;50&lt;/Percent&gt;</span>
 437 <span class="gp">... </span><span class="s">&lt;/Total&gt;</span>
 438 <span class="gp">... </span><span class="s">'''</span><span class="p">)</span>
 439
 440 <span class="gp">&gt;&gt;&gt; </span><span class="n">doc</span> <span class="o">=</span> <span class="n">etree</span><span class="o">.</span><span class="n">parse</span><span class="p">(</span><span class="n">valid</span><span class="p">)</span>
 441 <span class="gp">&gt;&gt;&gt; </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>
 442 <span class="go">True</span>
 443
 444 <span class="gp">&gt;&gt;&gt; </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="s">"Percent"</span><span class="p">)</span><span class="o">.</span><span class="n">text</span> <span class="o">=</span> <span class="s">"10"</span>
 445
 446 <span class="gp">&gt;&gt;&gt; </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>
 447 <span class="go">False</span>
 448 </pre></div>
 449 <p>Calling the schema object has the same effect as calling its validate method.
 450 This is sometimes used in conditional statements:</p>
 451 <div class="syntax"><pre><span class="gp">&gt;&gt;&gt; </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>
 452
 453 <span class="gp">&gt;&gt;&gt; </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>
 454 <span class="gp">... </span>    <span class="k">print</span><span class="p">(</span><span class="s">"invalid!"</span><span class="p">)</span>
 455 <span class="go">invalid!</span>
 456 </pre></div>
 457 <p>Note that libxml2 restricts error reporting to the parsing step (when creating
 458 the Schematron instance).  There is not currently any support for error
 459 reporting during validation.</p>
 460 </div>
 461 </div>
 462 <div class="footer">
 463 <hr class="footer" />
 464 Generated on: 2012-07-31.
 465
 466 </div>
 467 </body>
 468 </html>