XPath and Namespaces¶

Namespaces are the most common source of confusion with XPath. An element in a namespace will not be found by a bare name — you must register a prefix and use it in the query.

The Problem¶

Given this document:

<feed xmlns="http://www.w3.org/2005/Atom">
  <title>My Feed</title>
  <entry>
    <title>First Post</title>
  </entry>
</feed>

This XPath will find nothing:

doc.find('//title')  # => empty, because "title" is in the Atom namespace

The Solution: Register a Prefix¶

# Pass a namespace string — "prefix:uri"
doc.find('//atom:title', 'atom:http://www.w3.org/2005/Atom')

The prefix you choose (atom here) does not have to match the document — it's just a local binding for the XPath query. The URI must match exactly.

Multiple Namespaces¶

Array Form¶

doc.find('//atom:entry/dc:creator', [
  'atom:http://www.w3.org/2005/Atom',
  'dc:http://purl.org/dc/elements/1.1/'
])

Hash Form¶

doc.find('//atom:entry/dc:creator', {
  'atom' => 'http://www.w3.org/2005/Atom',
  'dc'   => 'http://purl.org/dc/elements/1.1/'
})

Default Namespace Shortcut¶

If you query the same namespace-heavy document repeatedly, set a default prefix:

doc.root.namespaces.default_prefix = 'atom'

# Now queries automatically use the 'atom' prefix
doc.find('//atom:title')
doc.find('//atom:entry')

Complex Namespace Example¶

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <getResponse xmlns="http://services.example.com">
      <IDList xmlns="http://services.example.com">
        <ns1:Item xmlns:ns1="http://domain.example.com"/>
      </IDList>
    </getResponse>
  </soap:Body>
</soap:Envelope>

# soap: is defined on the root, so it's automatically available
doc.find('/soap:Envelope')

# ns1: is defined deeper, register it explicitly
doc.find('//ns1:Item', 'ns1:http://domain.example.com')

# The default namespace on getResponse needs a prefix
doc.find('//svc:getResponse', 'svc:http://services.example.com')

# Combine multiple registrations
doc.find('/soap:Envelope/soap:Body/svc:getResponse/svc:IDList/ns1:Item', [
  'svc:http://services.example.com',
  'ns1:http://domain.example.com'
])