XML - Processing
What is XML?
XML is a portable, open source language that allows programmers to develop applications that can be read by other applications, regardless of operating system and/or developmental language.
The Extensible Markup Language (XML) is a markup language much like HTML or SGML. This is recommended by the World Wide Web Consortium and available as an open standard.
XML is extremely useful for keeping track of small to medium amounts of data without requiring a SQL-based backbone.
XML Parser Architectures and APIs The Python standard library provides a minimal but useful set of interfaces to work with XML.
Parser example: https://www.w3schools.com/xml/xml_parser.asp
The two most basic and broadly used APIs to XML data are the SAX and DOM interfaces.
Simple API for XML (SAX) − Here, you register callbacks for events of interest and then let the parser proceed through the document. This is useful when your documents are large or you have memory limitations, it parses the file as it reads it from disk and the entire file is never stored in memory.
Document Object Model (DOM) API − This is a World Wide Web Consortium recommendation wherein the entire file is read into memory and stored in a hierarchical (tree-based) form to represent all the features of an XML document.
SAX obviously cannot process information as fast as DOM can when working with large files. On the other hand, using DOM exclusively can really kill your resources, especially if used on a lot of small files.
SAX is read-only, while DOM allows changes to the XML file. Since these two different APIs literally complement each other, there is no reason why you cannot use them both for large projects.
For all our XML code examples, let's use a simple XML file movies.xml as an input −
Example
xmlstring − This is the name of the XML string to read from.
contenthandler − This must be a ContentHandler object.
errorhandler − If specified, errorhandler must be a SAX ErrorHandler object.
Parsing XML with SAX APIs
SAX is a standard interface for event-driven XML parsing. Parsing XML with SAX generally requires you to create your own ContentHandler by subclassing xml.sax.ContentHandler.
Your ContentHandler handles the particular tags and attributes of your flavor(s) of XML. A ContentHandler object provides methods to handle various parsing events. Its owning parser calls ContentHandler methods as it parses the XML file.
The methods startDocument and endDocument are called at the start and the end of the XML file. The method characters(text) is passed character data of the XML file via the parameter text.
The ContentHandler is called at the start and end of each element. If the parser is not in namespace mode, the methods startElement(tag, attributes) and endElement(tag) are called; otherwise, the corresponding methods startElementNS and endElementNS are called. Here, tag is the element tag, and attributes is an Attributes object.
Here are other important methods to understand before proceeding −
The make_parser Method Following method creates a new parser object and returns it. The parser object created will be of the first parser type the system finds.
