Python Cookbook

Transforming an XML Document Using Python

Credit: David Ascher

Problem

You have an XML document that you want to tweak.

Solution

Suppose that you want to convert element attributes into child elements. A simple subclass of the XMLGenerator object gives you complete freedom in such XML-to-XML transformation tasks:

from xml.sax import saxutils, make_parser
import sys

class Tweak(saxutils.XMLGenerator):
    def startElement(self, name, attrs):
        saxutils.XMLGenerator.startElement(self, name, {})
        attributes = attrs.keys(  )
        attributes.sort(  )
        for attribute in attributes:
            self._out.write("<%s>%s</%s>" % (attribute,
                            attrs[attribute], attribute))

parser = make_parser(  )
dh = Tweak(sys.stdout)
parser.setContentHandler(dh)
parser.parse(sys.argv[1])

Discussion

This particular recipe defines a Tweak subclass of the XMLGenerator class provided by the xml.sax.saxutils module. The only purpose of the subclass is to perform special handling of element starts while relying on its base class to do everything else. SAX is a nice and simple (after all, that’s what the S stands for) API for processing XML documents. It defines various kinds of events that occur when an XML document is being processed, such as startElement and endElement.

The key to understanding this recipe is to understand that Python’s XML library provides a base class, XMLGenerator, which performs an identity transform. If you feed it an XML document, it will output an equivalent XML document. Using standard Python object-oriented techniques ...