Python in a Nutshell, 2nd Edition

An Overview of XML Parsing

When your application must parse XML documents, your first, fundamental choice is what kind of parsing to use. You can use event-driven parsing, in which the parser reads the document sequentially and calls back to your application each time it parses a significant aspect of the document (such as an element), or you can use object-based parsing, in which the parser reads the whole document and builds in-memory data structures, representing the document, that you can then navigate. SAX is the main way to perform event-driven parsing, and DOM is the main way to perform object-based parsing. In each case, there are alternatives, such as direct use of expat for event-driven parsing, or ElementTree for object-based parsing, but I do not cover these alternatives in this book. Another interesting possibility is pull-based parsing, supported by pulldom, covered later in this chapter (and also, to some extent, by ElementTree, via the iterparse function of C-coded module cElementTree).

Event-driven parsing requires fewer resources, which makes it particularly suitable to parse very large documents. However, event-driven parsing requires you to structure your application accordingly, performing your processing (and typically building auxiliary data structures) in your methods called by the parser. Object-based parsing gives you more flexibility to structure your application, which may make it more suitable when you need to perform very complicated processing, as long ...