How Can I Parse XML with Namespaces Using Python's ElementTree?

Parsing XML with Namespaces in Python via 'ElementTree'

XML with namespaces can be encountered while working with various data sources. One such case is working with ontologies published using RDF, where the use of namespaces is common. This can cause issues when attempting to parse such XML using Python's ElementTree library.

Consider the following XML:

<rdf:RDF xml:base="http://dbpedia.org/ontology/"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns="http://dbpedia.org/ontology/">

    <owl:Class rdf:about="http://dbpedia.org/ontology/BasketballLeague">
        <rdfs:label xml:lang="en">basketball league</rdfs:label>
        <rdfs:comment xml:lang="en">
          a group of sports teams that compete against each other
          in Basketball
        </rdfs:comment>
    </owl:Class>

</rdf:RDF>

If you attempt to parse this XML using the following code:

tree = ET.parse("filename")
root = tree.getroot()
root.findall('owl:Class')

You will encounter the following error due to the presence of namespaces in the XML:

SyntaxError: prefix 'owl' not found in prefix map

To resolve this namespace issue, you need to provide an explicit namespace dictionary to the .find(), .findall(), and .iterfind() methods:

namespaces = {'owl': 'http://www.w3.org/2002/07/owl#'} # add more as needed

root.findall('owl:Class', namespaces)

This namespace dictionary will allow ElementTree to look up the correct namespace URL for the 'owl:' prefix and resolve the issue.

Alternatively, you can switch to using the lxml library, which offers superior namespace support and collects namespaces automatically in the .nsmap attribute on elements.

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