[lxml-dev] XSLT extension elements landed on trunk

[Stefan Behnel]

Hi,

the current trunk now has support for Python implemented XSLT extension
elements. It's sort of a sandbox environment with read-only Elements, where
you can do basically anything based on the stylesheet and the input document,
and then append some result subtree to the XSLT output tree.

Here's a short XSLT snippet that uses an extension, and a Python class that
provides such an extension:

  <xsl:stylesheet version="1.0"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        xmlns:myns="testns"
        extension-element-prefixes="myns">
    <xsl:template match="a">
      <A>
        <myns:myext><x>X</x><y>Y</y><z/></myns:myext>
      </A>
    </xsl:template>
  </xsl:stylesheet>


  class MyExt(etree.XSLTExtension):
      def execute(self, context, self_node, input_node, output_parent):
          # apply templates to my own children and process the result
          for child in self_node:
              for result in self.apply_templates(context, child):
                  if isinstance(result, basestring):
                      el = etree.Element("T")
                      el.text = result
                  else:
                      el = result
                  output_parent.append(el)


I don't remember when I first started thinking about this, but it was actually
pretty hard to get right until now. I uploaded some docs to the dev site:

http://codespeak.net/lxml/dev/xpathxslt.html#extension-elements

Note that this is currently an experimental feature that will go into lxml
2.1. Any comments and bug reports will be very much appreciated.

Have fun,
Stefan