Fetching Data from Web APIs

From Response Text to Usable Data

When XML data arrives from a web service, a file, or another system, it arrives as a flat string of characters. The string contains tags, nesting, attributes, and values, but Python cannot conveniently search that raw text as a tree. ElementTree provides the parsing step that turns the string into a structured object.

Building the XML Tree

ET.fromstring converts an XML string into a tree structure. ElementTree parses the XML tags, nesting, and attributes, then builds an in-memory object representing the document. The result is no longer merely a sequence of characters: it is a nested hierarchy that Python code can navigate and query.

The outermost XML tag becomes the root element. Elements inside it become child elements. Each element can have child elements, text content, and attributes. This structure is what makes later operations such as locating name or email meaningful.

Finding and Reading Elements

After parsing, find searches the tree for the first element matching a supplied tag name. It returns an element object when a match is found, or None when no matching element is found. The returned object is not the text itself, so you read its text separately with .text.

import xml.etree.ElementTree as ET

xml_text = "<person><name>Alice</name><email hide=\"true\">alice@example.com</email></person>"
root = ET.fromstring(xml_text)

name_element = root.find("name")
email_element = root.find("email")

print(name_element.text)
print(email_element.get("hide"))

Alice
true

The first lookup returns the name element object. Accessing name_element.text reads the content between the name tags. The second lookup returns the email element object. Accessing email_element.get("hide") reads the value of the hide attribute. Text content and attributes are separate parts of an XML element and are accessed separately.

Tracing the Complete Operation

Mistakes in XML Queries

• Treating the result of find as though it were already a string

  find returns an element object or None, not the element's text value.

  Fix: Use name_element.text to read the text content.

• Reading an attribute with .text

  The email text and the hide attribute are separate parts of the element.

  Fix: Use email_element.get("hide") to retrieve the hide attribute.

• Changing the capitalization of a tag or attribute name

  XML tag names and attribute names are case-sensitive.

  Fix: Match the exact spelling used in the XML, such as "name" and "hide".

• Assuming every search succeeds

  find returns None when no matching element is found.

  Fix: Handle the None case before attempting to access element data.

Practice the Parse-Search-Extract Pattern

1. Start with the XML string received from the web service or another source.
2. Pass the string to ET.fromstring to create the tree and obtain its root element.
3. Call find with the exact tag name to locate the desired element.
4. Read element text with .text or read an attribute with .get("attribute_name").
5. Check for None when a requested element might not exist.

Key Takeaways

1. An XML response begins as a flat string of characters.
2. ET.fromstring parses that string into a hierarchical ElementTree object.
3. The root element represents the outermost tag, and nested elements form the parent-child structure.
4. find locates the first matching element and returns an element object or None.
5. Use .text for element content and .get("attribute_name") for attributes, while preserving exact case.