DOM Parser vs SAX Parser

Estimated study time: 20 minutes.

The two classic approaches to XML parsing — DOM and SAX — take fundamentally different strategies, each with real trade-offs.

DOM (Document Object Model) Parser

Loads the entire XML document into memory as a tree structure, which you can then freely navigate, search, and modify in any order.

import xml.dom.minidom as minidom

doc = minidom.parse('course.xml')
titles = doc.getElementsByTagName('title')
print(titles[0].firstChild.data)

SAX (Simple API for XML) Parser

Reads the document sequentially from start to end, firing events (start tag, end tag, text) as it goes — without ever holding the whole document in memory.

import xml.sax

class CourseHandler(xml.sax.ContentHandler):
    def startElement(self, name, attrs):
        print("Start:", name)
    def endElement(self, name):
        print("End:", name)

xml.sax.parse('course.xml', CourseHandler())

Key Differences

• Memory usage — DOM loads everything at once (higher memory); SAX processes a stream (very low memory).
• Navigation — DOM allows random, repeated access to any part of the tree; SAX is forward-only, one pass.
• Modification — DOM lets you edit and rewrite the document; SAX is read-only by nature.
• Speed on large files — SAX is typically faster and more scalable for very large documents.

When to Use Which

• Use DOM for small-to-medium files where you need to navigate back and forth or edit the document.
• Use SAX for large files where memory efficiency matters more than convenience.