Python in a Nutshell, 2nd Edition

Parsing XML with DOM

SAX parsing does not build any structure in memory to represent the XML document. This makes SAX fast and highly scalable, as your application builds exactly as little or as much in-memory structure as needed for its specific tasks. However, for particularly complicated processing tasks involving reasonably small XML documents, you may prefer to let the library build in-memory structures that represent the whole XML document, and then traverse those structures. The XML standards describe the DOM (Document Object Model) for XML. A DOM object represents an XML document as a tree whose root is the document object, while other nodes correspond to elements, text contents, element attributes, and so on. The ElementTree module mentioned in the introduction of this chapter provides a different, more Pythonic (and faster) approach to build an in-memory representation of an XML document, while DOM mimics existing W3C standards (mostly developed with other languages, such as Java, in mind).

The Python standard library supplies a minimal implementation of the XML DOM standard: xml.dom.minidom. minidom builds everything up in memory, with the typical pros and cons of the DOM approach to parsing. The Python standard library also supplies a different DOM-like approach in module xml.dom.pulldom. pulldom occupies an interesting middle ground between SAX and DOM, presenting the stream of parsing events as a Python iterator object so that you do not code callbacks, but rather loop ...