XML: ElementTree (etree)

SAX and DOM

SAX Event-driven (elements start and end) Commonly used to parse long streams of structured data “De-facto” standard Available in multiple languages Python: xml.sax

DOM: “Document Object Model” Document available as a tree Programmatically navigable as a tree Relatively comfortable Python: xml.dom Problems Only relatively comfortable Not Pythonic enough

ElementTree

xml.etree: Python specific ⟶ absolutely

comfortable

• Seamless integration in Python (⟶ iteration)

• A document is a tree, and trees are lists of lists

• XML attributes represented as dictionaries

⟶ simple!

A Very Simple Document

Python code

from xml.etree.ElementTree import Element
element = Element("root")
child = Element("child")
element.append(child)

Or alternatively …

element = Element("root")
SubElement(element, "child")

XML

<root>
  <child />
</root>

Attributes

• XML elements have attributes

• Python’s XML elements have the attrib dictionary

element = Element("root")
child = SubElement(element, "child")
child.attrib['age'] = '15'
child = SubElement(element, "child")
child.attrib['age'] = '17'

<root>
  <child age="15" />
  <child age="17" />
</root>

Text (1)

In XML documents, free text is permitted …

• Inside one element

• After one element, but before the start of another element

Accordingly, Python elements have members …

• element.text

• element.tail

• No text ⟶ None

Text (2)

element = Element("root")
child = SubElement(element, "child")
child.text = 'Text'
child.tail = 'Tail'

<root><child>Text</child>Tail</root>

Careful with indentation

• Whitespace, linefeed etc. is text, no matter what

• str.strip() may be helpful

Writing XML Documents

• We have created Element objects

• Added child elements

• Now how do we create XML?

• Wrap into ElementTree - a helper

from xml.etree.ElementTree import ElementTree
tree = ElementTree(element)
tree.write(sys.stdout) # oder file(..., 'w')

• Output is very tight

• Text is preserved as-is

• Pretty output would be incorrect

  • Linefeed and indentation is text

Reading XML Documents

This is simple …

from xml.etree.ElementTree import parse

tree = parse(sys.stdin)
for child in tree.getroot():
    age = child.attrib.get('age')
    if age is not None:
        print age
    if child.text is not None:
        print child.text