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  28
  29 <p>As of version 1.1, lxml.etree provides a public C-API.  This allows external
  30 C extensions to efficiently access public functions and classes of lxml,
  31 without going through the Python API.</p>
  32 <p>The API is described in the file <a class="reference external" href="https://github.com/lxml/lxml/blob/master/src/lxml/includes/etreepublic.pxd">etreepublic.pxd</a>, which is directly
  33 c-importable by extension modules implemented in <a class="reference external" href="http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/">Pyrex</a> or <a class="reference external" href="http://cython.org">Cython</a>.</p>
  34 <div class="contents topic" id="contents">
  35 <p class="topic-title">Contents</p>
  36 <ul class="simple">
  37 <li><a class="reference internal" href="#passing-generated-trees-through-python" id="id1">Passing generated trees through Python</a></li>
  38 <li><a class="reference internal" href="#writing-external-modules-in-cython" id="id2">Writing external modules in Cython</a></li>
  39 <li><a class="reference internal" href="#writing-external-modules-in-c" id="id3">Writing external modules in C</a></li>
  40 </ul>
  41 </div>
  42 <div class="section" id="passing-generated-trees-through-python">
  43 <h1>Passing generated trees through Python</h1>
  44 <p>This is the most simple way to integrate with lxml.  It does not require
  45 any C-level integration but uses a Python function to wrap an externally
  46 generated libxml2 document in lxml.</p>
  47 <p>The external module that creates the libxml2 tree must pack the document
  48 pointer into a <a class="reference external" href="https://docs.python.org/3/c-api/capsule.html">PyCapsule</a>
  49 object.  This can then be passed into lxml with the function
  50 <tt class="docutils literal">lxml.etree.adopt_external_document()</tt>.  It also takes an optional lxml
  51 parser instance to associate with the document, in order to configure the
  52 Element class lookup, relative URL lookups, etc.</p>
  53 <p>See the <a class="reference external" href="api/lxml.etree-module.html#adopt_external_document">API reference</a>
  54 for further details.</p>
  55 <p>The same functionality is available as part of the public C-API in form
  56 of the C function <tt class="docutils literal">adoptExternalDocument()</tt>.</p>
  57 </div>
  58 <div class="section" id="writing-external-modules-in-cython">
  59 <h1>Writing external modules in Cython</h1>
  60 <p>This is the easiest way of extending lxml at the C level.  A <a class="reference external" href="http://cython.org">Cython</a>
  61 (or <a class="reference external" href="http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/">Pyrex</a>) module should start like this:</p>
  62 <pre class="literal-block">
  63 # My Cython extension
  64
  65 # directive pointing compiler to lxml header files;
  66 # use ``aliases={"LXML_PACKAGE_DIR": lxml.__path__}``
  67 # argument to cythonize in setup.py to dynamically
  68 # determine dir at compile time
  69 # distutils: include_dirs = LXML_PACKAGE_DIR
  70
  71 # import the public functions and classes of lxml.etree
  72 cimport lxml.includes.etreepublic as cetree
  73
  74 # import the lxml.etree module in Python
  75 cdef object etree
  76 from lxml import etree
  77
  78 # initialize the access to the C-API of lxml.etree
  79 cetree.import_lxml__etree()
  80 </pre>
  81 <p>From this line on, you can access all public functions of lxml.etree
  82 from the <tt class="docutils literal">cetree</tt> namespace like this:</p>
  83 <pre class="literal-block">
  84 # build a tag name from namespace and element name
  85 py_tag = cetree.namespacedNameFromNsName("http://some/url", "myelement")
  86 </pre>
  87 <p>Public lxml classes are easily subclassed.  For example, to implement
  88 and set a new default element class, you can write Cython code like
  89 the following:</p>
  90 <pre class="literal-block">
  91 from lxml.includes.etreepublic cimport ElementBase
  92 cdef class NewElementClass(ElementBase):
  93      def set_value(self, myval):
  94          self.set("my_attribute", myval)
  95
  96 etree.set_element_class_lookup(
  97      etree.ElementDefaultClassLookup(element=NewElementClass))
  98 </pre>
  99 </div>
 100 <div class="section" id="writing-external-modules-in-c">
 101 <h1>Writing external modules in C</h1>
 102 <p>If you really feel like it, you can also interface with lxml.etree straight
 103 from C code.  All you have to do is include the header file for the public
 104 API, import the <tt class="docutils literal">lxml.etree</tt> module and then call the import function:</p>
 105 <div class="syntax"><pre><span></span><span class="cm">/* My C extension */</span>
 106
 107 <span class="cm">/* common includes */</span>
 108 <span class="cp">#include</span> <span class="cpf">"Python.h"</span><span class="cp"></span>
 109 <span class="cp">#include</span> <span class="cpf">"stdio.h"</span><span class="cp"></span>
 110 <span class="cp">#include</span> <span class="cpf">"string.h"</span><span class="cp"></span>
 111 <span class="cp">#include</span> <span class="cpf">"stdarg.h"</span><span class="cp"></span>
 112 <span class="cp">#include</span> <span class="cpf">"libxml/xmlversion.h"</span><span class="cp"></span>
 113 <span class="cp">#include</span> <span class="cpf">"libxml/encoding.h"</span><span class="cp"></span>
 114 <span class="cp">#include</span> <span class="cpf">"libxml/hash.h"</span><span class="cp"></span>
 115 <span class="cp">#include</span> <span class="cpf">"libxml/tree.h"</span><span class="cp"></span>
 116 <span class="cp">#include</span> <span class="cpf">"libxml/xmlIO.h"</span><span class="cp"></span>
 117 <span class="cp">#include</span> <span class="cpf">"libxml/xmlsave.h"</span><span class="cp"></span>
 118 <span class="cp">#include</span> <span class="cpf">"libxml/globals.h"</span><span class="cp"></span>
 119 <span class="cp">#include</span> <span class="cpf">"libxml/xmlstring.h"</span><span class="cp"></span>
 120
 121 <span class="cm">/* lxml.etree specific includes */</span>
 122 <span class="cp">#include</span> <span class="cpf">"lxml-version.h"</span><span class="cp"></span>
 123 <span class="cp">#include</span> <span class="cpf">"etree_defs.h"</span><span class="cp"></span>
 124 <span class="cp">#include</span> <span class="cpf">"etree.h"</span><span class="cp"></span>
 125
 126 <span class="cm">/* setup code */</span>
 127 <span class="n">import_lxml__etree</span><span class="p">()</span>
 128 </pre></div>
 129 <p>Note that including <tt class="docutils literal">etree.h</tt> does not automatically include the
 130 header files it requires.  Note also that the above list of common
 131 includes may not be sufficient.</p>
 132 </div>
 133 </div>
 134 <div class="footer">
 135 <hr class="footer" />
 136 Generated on: 2020-10-17.
 137
 138 </div>
 139 </body>
 140 </html>