Python XML Parsing with xml.etree

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Overview of xml.etree in Python

xml.etree is a built-in Python module (specifically xml.etree.ElementTree) for parsing and manipulating XML data. It provides a tree-like structure where you can read, write, modify, and navigate XML elements efficiently. It’s lightweight and doesn’t require external libraries, making it ideal for basic XML tasks. Import it with import xml.etree.ElementTree as ET.

Parsing XML

To load XML into memory, use parsing methods:

From a string: ET.fromstring(xml_string) returns an Element object representing the root.
From a file: ET.parse(filename) returns an ElementTree object, which you can access via .getroot().

import xml.etree.ElementTree as ET

# Parse from string
xml_data = "<root><child>text</child></root>"
root = ET.fromstring(xml_data)

# Parse from file
tree = ET.parse('example.xml')
root = tree.getroot()

Navigating Elements

Once parsed, you can traverse the XML tree:

Access children: Use root[0] for indexed access or iterate with for child in root:.
Find elements:
- root.find('tag') gets the first matching child.
- root.findall('tag') gets all matching children.
Access text and attributes:
- Text content: element.text
- Attributes: element.attrib (a dict)

# Example XML: <bookstore><book id="1"><title>Python</title></book></bookstore>
for book in root.findall('book'):
    title = book.find('title').text
    book_id = book.attrib['id']
    print(f"Book {book_id}: {title}")

Modifying XML

Edit elements dynamically:

Add elements: ET.SubElement(parent, 'new_tag') creates and attaches a new child.
Set text/attributes: element.text = 'new text'; element.set('attr', 'value').
Remove elements: root.remove(child).

new_child = ET.SubElement(root, 'new_element')
new_child.text = 'Added content'
new_child.set('attr', 'value')

Writing XML

To save modifications back to XML:

To a string: ET.tostring(root, encoding='unicode').
To a file: tree.write('output.xml').

xml_output = ET.tostring(root, encoding='unicode')
with open('output.xml', 'w') as f:
    f.write(xml_output)

# Or directly
tree.write('output.xml')

Complete Example

Here’s a full script to parse, modify, and write XML:

import xml.etree.ElementTree as ET

# Input XML string
xml_str = """<library>
  <book id="1"><title>1984</title><author>Orwell</author></book>
</library>"""

root = ET.fromstring(xml_str)

# Add a new book
new_book = ET.SubElement(root, 'book', id="2")
ET.SubElement(new_book, 'title').text = 'Brave New World'
ET.SubElement(new_book, 'author').text = 'Huxley'

# Print all books
for book in root:
    title = book.find('title').text
    author = book.find('author').text
    print(f"{title} by {author}")

# Write to file
ET.tostring(root, encoding='unicode')
# Or root.write('library.xml')

Notes

Handle namespaces with xmlns='{namespace}' in find queries, e.g., root.find('{http://example.com}tag').
For large files, consider iterative parsing with ET.iterparse().
Be cautious with user-input XML to avoid XML vulnerabilities like injection.
For complex needs, libraries like lxml offer extended features.

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