Python Cookbook

Parsing an XML File with xml.parsers.expat

Credit: Mark Nenadov

Problem

The expat parser is normally used through the SAX interface, but sometimes you may want to use expat directly to extract the best possible performance.

Solution

Python is very explicit about the lower-level mechanisms that its higher-level modules’ packages use. You’re normally better off accessing the higher levels, but sometimes, in the last few stages of an optimization quest, or just to gain better understanding of what, exactly, is going on, you may want to access the lower levels directly from your code. For example, here is how you can use Expat directly, rather than through SAX:

import xml.parsers.expat, sys

class MyXML:
    Parser = ""

    # Prepare for parsing
    def _ _init_ _(self, xml_filename):
        assert xml_filename != ""
        self.xml_filename = xml_filename
        self.Parser = xml.parsers.expat.ParserCreate(  )

        self.Parser.CharacterDataHandler = self.handleCharData
        self.Parser.StartElementHandler = self.handleStartElement
        self.Parser.EndElementHandler = self.handleEndElement

    # Parse the XML file
    def parse(self):
        try:
            xml_file = open(self.xml_filename, "r")
        except:
            print "ERROR: Can't open XML file %s"%self.xml_filename
            raise
        else:
            try: self.Parser.ParseFile(xml_file)
            finally: xml_file.close(  )

    # to be overridden by implementation-specific methods
    def handleCharData(self, data): pass
    def handleStartElement(self, name, attrs): pass
    def handleEndElement(self, name): pass

Discussion

This recipe presents a reusable way to use ...