How to Iterate XML Elements Using a namespace Prefix in Python lxml

Learn how to handle XML files with default namespaces in Python using lxml by defining namespace prefixes for querying elements effectively.
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This video is based on the question https://stackoverflow.com/q/79483931/ asked by the user 'Michel de Ruiter' ( https://stackoverflow.com/u/357313/ ) and on the answer https://stackoverflow.com/a/79484495/ provided by the user 'Lewis' ( https://stackoverflow.com/u/28442916/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Handling XML Namespaces with lxml in Python

When working with XML files that declare a default namespace (i.e., an XML element with xmlns="somelongnamespace" but no prefix), querying these elements directly with lxml's findall or XPath methods can be tricky.

The Problem

Consider this XML structure:

[[See Video to Reveal this Text or Code Snippet]]

If you try to find child elements using root.findall('child') in Python, it won't return any nodes because lxml strictly requires you to specify the namespace.

The Concept

Even though the XML doesn't use an explicit prefix, internally, the elements belong to a namespace URI (here: somelongnamespace).

To query these elements, you must:

Define a prefix-to-namespace mapping in Python

Use this prefix in your search paths

How to Do It

Create a namespace mapping dictionary: Map your chosen prefix (e.g., 'ns') to the actual namespace URI.

Use the namespaces parameter in findall or similar methods: Pass this dictionary when querying.

Here's a concrete example:

[[See Video to Reveal this Text or Code Snippet]]

Why This Works

lxml expects element names with namespace prefixes in the XPath query and a dictionary that defines those prefixes. This way, it can resolve the prefix to the full namespace URI and find the elements correctly.

Optional: Encapsulating Namespace Logic

If you are making many queries and want to keep code cleaner, encapsulate this behavior in a helper class:

[[See Video to Reveal this Text or Code Snippet]]

This approach improves readability and reuse when working with namespaced XMLs.



Summary: Always create a namespace mapping dict and specify the namespaces argument with your queries in lxml to handle XML with default namespaces effectively.