XML handling in Python - SAX, DOM and XSLT examples

For 2023 - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

XML is the "eXtensible Markup Language" ... a set of rules to which a language must adhere, rather than a complete language definition - you need to add other elements such as a DTD or Schema to complete the definition of a language that conforms to an XML standard.

How do you process XML, then?

There are three common ways.

a) You can use a SAX parser. SAX is the Simple API for XML. With a SAX parser, you pass the data through a handler which extracts pertinent information as it's passed through - so this is ideally suited to extracting a few very specific bits of information from what is potentially a huge data flow.

b) You can use DOM (the Domain Object Model). Here, you read data into a structure in memory and can process it within that structure. Because XML tags can be nested, you'll end up with nested structures in memory, with the result that you'll probably find yourself writing recursive code

c) XSLT - X Stylesheet Language Transforms - are a way of defining how a file of XSLT is transformed into some other format. XSLT is a programming language itself.

Can we use SAX, DOM, or XSLT in Python?

Yes - you can use any of them. There are many classes supplied with Python, and others which are easy to download. I've uploaded some recent demonstrations - firstly, there's some XML that I've used [here] ... with sample processing of that in Python via SAX [here] and in Python via DOM [here].

There's an example (using different data) with XSLT [here] - and you'll note that the XSLT example is much shorter. That's because a lot of the work has been transferred to the XSLT code (see [here]). The XML for that last example is also available - [here].
(written 2010-12-09, updated 2010-12-10)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

Y151 - Python & XML
  [2378] Handling XML in Perl - introduction and early examples - (2009-08-27)
  [2506] Good example of recursion in Python - analyse an RSS feed - (2009-11-18)
  [2555] Bookkeeping - (2009-12-29)
  [4594] XML handling in Python - a new teaching example using etree - (2015-12-09)
  [4710] Searching a Json or XML structure for a specific key / value pair in Python - (2016-10-30)

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