xml.sax for Parsing XML Document

XML Tutorials - Herong's Tutorial Examples

∟xml.sax for Parsing XML Document

This section provides a tutorial example on how to parse an existing XML document with SAX event handlers with Python xml.sax package.

xml.sax sub-package offers the following functionalities to parse an XML document and access its elements/attributes through event handler functions.

class myHandler: - Define the myHandler class and implement functions to handle SAX events.
def startDocument(self): - Implement a function to handle "startDocument" SAX event.
def endDocument(self): - Implement a function to handle "endDocument" SAX event.
def startElement(self, name, attrs): - Implement a function to handle "startElement" SAX event. "name" is the tag name of the element. "attrs" is the list of attributes of an element.
def endElement(self, name): - Implement a function to handle "endElement" SAX event. "name" is the tag name of an element.
def characters(self, content): Implement a function to handle "characters" SAX event. "content" is the text string of a text node.
handler = myHandler() - Create an instance of the custom SAX events handler.
sax = xml.sax.make_parser() - Create a SAX parser instance.
sax.setContentHandler(handler) - Assign the SAC handler to the SAX parser.
sax.setFeature(feature_name, 1|0) - Turn on or off a given SAX parsing feature.
sax.parse(file) - Start the parsing process on the given XML document file.
sax.parseString(str) - Start the parsing process on the given XML document string.

Here is an example Python script that parses an XML document with my own SAX events handler class using the xml.sax sub-package:

#- xml_sax_Parser.py
#- Copyright (c) 2018 HerongYang.com. All Rights Reserved.
#
import xml.sax

#- My SAX event handler class
class myHandler(xml.sax.ContentHandler):
    def __init__(self):
        self.pad = "_"

    def startDocument(self):
        print("startDocument() called")
    def endDocument(self):
        print("endDocument() called")

    def startElement(self, name, attrs):
        att_str = ""
        for (key, value) in attrs.items(): 
            att_str += key+"="+value+", "
        print("e"+self.pad+name+": "+att_str)
        self.pad += "_"

    def endElement(self, name):
        self.pad = self.pad[:-1]

    def characters(self, content):
        txt_str = content.strip()
        if len(txt_str) > 0:
            print("c"+self.pad+content)

sax = xml.sax.make_parser()
sax.setContentHandler(myHandler())
sax.setFeature(xml.sax.handler.feature_namespaces, 0)

sax.parse("dictionary.xml")

Use the program from the last tutorial minidom_Build_XML.py to create an XML file. Then parse it with xml_sax_Parser.py:

herong> python minidom_Build_XML.py > dictionary.xml 

herong> python xml_sax_Parser.py

startDocument() called
e_dictionary: 
e__word: 
e___update: date=2100-01-01, 
e___name: is_acronym=true, 
c____DTD
e___definition: 
c____Document Type Definition
endDocument() called

Notes on the Python script and output:

"class myHandler(xml.sax.ContentHandler):" defines my SAX events handler class by extending the build-in xml.sax.ContentHandler class, which provides dummy functions for all SAX events.
"txt_str = content.strip()" is used to strip white spaces padded in the XML document for the pretty format.