Ruby: Nokogiri with XML namespace

gistfile1.txt

#!/usr/bin/env ruby

require 'pp'
require 'nokogiri'
require 'open-uri'

doc = Nokogiri::XML(open('http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml'))

cubes = doc.xpath("//ecb:Cube[@currency='CAD']",
                  'ecb' => 'http://www.ecb.int/vocabulary/2002-08-01/eurofxref')

cubes.each { |c|
  print c.attribute('currency'), "=", c.attribute('rate').value.to_f, "\n"
}