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The public C-API of lxml.etree
As of version 1.1, lxml.etree provides a public C-API. This allows external
C extensions to efficiently access public functions and classes of lxml,
without going through the Python API.
The API is described in the file `etreepublic.pxd`_, which is directly
c-importable by extension modules implemented in Pyrex_ or Cython_.
.. _`etreepublic.pxd`:
.. _Cython:
.. _Pyrex:
.. contents::
1 Writing external modules in Cython
2 Writing external modules in C
Writing external modules in Cython
This is the easiest way of extending lxml at the C level. A Cython_
(or Pyrex_) module should start like this::
# My Cython extension
# import the public functions and classes of lxml.etree
cimport etreepublic as cetree
# import the lxml.etree module in Python
cdef object etree
from lxml import etree
# initialize the access to the C-API of lxml.etree
From this line on, you can access all public functions of lxml.etree
from the ``cetree`` namespace like this::
# build a tag name from namespace and element name
py_tag = cetree.namespacedNameFromNsName("http://some/url", "myelement")
Public lxml classes are easily subclassed. For example, to implement
and set a new default element class, you can write Cython code like
the following::
from etreepublic cimport ElementBase
cdef class NewElementClass(ElementBase):
def set_value(self, myval):
self.set("my_attribute", myval)
Writing external modules in C
If you really feel like it, you can also interface with lxml.etree straight
from C code. All you have to do is include the header file for the public
API, import the ``lxml.etree`` module and then call the import function:
.. sourcecode:: c
/* My C extension */
/* common includes */
#include "Python.h"
#include "stdio.h"
#include "string.h"
#include "stdarg.h"
#include "libxml/xmlversion.h"
#include "libxml/encoding.h"
#include "libxml/hash.h"
#include "libxml/tree.h"
#include "libxml/xmlIO.h"
#include "libxml/xmlsave.h"
#include "libxml/globals.h"
#include "libxml/xmlstring.h"
/* lxml.etree specific includes */
#include "lxml-version.h"
#include "etree_defs.h"
#include "etree.h"
/* setup code */
Note that including ``etree.h`` does not automatically include the
header files it requires. Note also that the above list of common
includes may not be sufficient.
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