13.1: eXtensible Markup Language - XML

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XML looks very similar to HTML, but XML is more structured than HTML. Here is a sample of an XML document:

<person>
  <name>Chuck</name>
  <phone type="intl">
     +1 734 303 4456
   </phone>
   <email hide="yes"/>
</person>

Often it is helpful to think of an XML document as a tree structure where there is a top tag person and other tags such as phone are drawn as children of their parent nodes.

A Tree Representation of XML

Parsing XML

Here is a simple application that parses some XML and extracts some data elements from the XML:

Code 13.1.1 (Python)

%%python3

import xml.etree.ElementTree as ET

data = '''
<person>
  <name>Chuck</name>
  <phone type=\"intl\">
     +1 734 303 4456
   </phone>
   <email hide=\"yes\"/>
</person>'''

tree = ET.fromstring(data)
print('Name:', tree.find('name').text)
print('Attr:', tree.find('email').get('hide'))

# Code: http://www.py4e.com/code3/xml1.py

Calling fromstring converts the string representation of the XML into a "tree" of XML nodes. When the XML is in a tree, we have a series of methods we can call to extract portions of data from the XML.

The find function searches through the XML tree and retrieves a node that matches the specified tag. Each node can have some text, some attributes (like hide), and some "child" nodes. Each node can be the top of a tree of nodes.

Name: Chuck
Attr: yes

Using an XML parser such as ElementTree has the advantage that while the XML in this example is quite simple, it turns out there are many rules regarding valid XML and using ElementTree allows us to extract data from XML without worrying about the rules of XML syntax.