doc/html/capi.html

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  12
  13 <p>As of version 1.1, lxml.etree provides a public C-API.  This allows external
  14 C extensions to efficiently access public functions and classes of lxml,
  15 without going through the Python API.</p>
  16 <p>The API is described in the file <a class="reference external" href="http://codespeak.net/svn/lxml/trunk/src/lxml/etreepublic.pxd">etreepublic.pxd</a>, which is directly
  17 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://www.cython.org">Cython</a>.</p>
  18 <div class="contents topic" id="contents">
  19 <p class="topic-title first">Contents</p>
  20 <ul class="simple">
  21 <li><a class="reference internal" href="#writing-external-modules-in-cython" id="id1">Writing external modules in Cython</a></li>
  22 <li><a class="reference internal" href="#writing-external-modules-in-c" id="id2">Writing external modules in C</a></li>
  23 </ul>
  24 </div>
  25 <div class="section" id="writing-external-modules-in-cython">
  26 <h1>Writing external modules in Cython</h1>
  27 <p>This is the easiest way of extending lxml at the C level.  A <a class="reference external" href="http://www.cython.org">Cython</a>
  28 (or <a class="reference external" href="http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/">Pyrex</a>) module should start like this:</p>
  29 <pre class="literal-block">
  30 # My Cython extension
  31
  32 # import the public functions and classes of lxml.etree
  33 cimport etreepublic as cetree
  34
  35 # import the lxml.etree module in Python
  36 cdef object etree
  37 from lxml import etree
  38
  39 # initialize the access to the C-API of lxml.etree
  40 cetree.import_lxml__etree()
  41 </pre>
  42 <p>From this line on, you can access all public functions of lxml.etree
  43 from the <tt class="docutils literal"><span class="pre">cetree</span></tt> namespace like this:</p>
  44 <pre class="literal-block">
  45 # build a tag name from namespace and element name
  46 py_tag = cetree.namespacedNameFromNsName("http://some/url", "myelement")
  47 </pre>
  48 <p>Public lxml classes are easily subclassed.  For example, to implement
  49 and set a new default element class, you can write Cython code like
  50 the following:</p>
  51 <pre class="literal-block">
  52 from etreepublic cimport ElementBase
  53 cdef class NewElementClass(ElementBase):
  54      def set_value(self, myval):
  55          self.set("my_attribute", myval)
  56
  57 etree.set_element_class_lookup(
  58      etree.DefaultElementClassLookup(element=NewElementClass))
  59 </pre>
  60 </div>
  61 <div class="section" id="writing-external-modules-in-c">
  62 <h1>Writing external modules in C</h1>
  63 <p>If you really feel like it, you can also interface with lxml.etree straight
  64 from C code.  All you have to do is include the header file for the public
  65 API, import the <tt class="docutils literal"><span class="pre">lxml.etree</span></tt> module and then call the import function:</p>
  66 <div class="syntax"><pre><span class="cm">/* My C extension */</span>
  67
  68 <span class="cm">/* common includes */</span>
  69 <span class="cp">#include "Python.h"</span>
  70 <span class="cp">#include "stdio.h"</span>
  71 <span class="cp">#include "string.h"</span>
  72 <span class="cp">#include "stdarg.h"</span>
  73 <span class="cp">#include "libxml/xmlversion.h"</span>
  74 <span class="cp">#include "libxml/encoding.h"</span>
  75 <span class="cp">#include "libxml/hash.h"</span>
  76 <span class="cp">#include "libxml/tree.h"</span>
  77 <span class="cp">#include "libxml/xmlIO.h"</span>
  78 <span class="cp">#include "libxml/xmlsave.h"</span>
  79 <span class="cp">#include "libxml/globals.h"</span>
  80 <span class="cp">#include "libxml/xmlstring.h"</span>
  81
  82 <span class="cm">/* lxml.etree specific includes */</span>
  83 <span class="cp">#include "lxml-version.h"</span>
  84 <span class="cp">#include "etree_defs.h"</span>
  85 <span class="cp">#include "etree.h"</span>
  86
  87 <span class="cm">/* setup code */</span>
  88 <span class="n">import_lxml__etree</span><span class="p">()</span>
  89 </pre></div>
  90 <p>Note that including <tt class="docutils literal"><span class="pre">etree.h</span></tt> does not automatically include the
  91 header files it requires.  Note also that the above list of common
  92 includes may not be sufficient.</p>
  93 </div>
  94 </div>
  95 <div class="footer">
  96 <hr class="footer" />
  97 Generated on: 2009-10-30.
  98
  99 </div>
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