Using lxml xpath to get elements with a default namespace

xml_string="""

<a xmlns="http://www.w3.org/1999/xhtml">

  <b>
    <r>
      <Value>string</Value>

    </r>

    <r>

      <Value>string</Value>

    </r>

  </b>

  <e>

    <string>string1</string>

    <string>string2</string>

  </e>

</a>

"""

from lxml import etree

xml = etree.fromstring(xml_string)

xml.xpath('/w3:a/w3:b/w3:r/w3:Value/text()', namespaces={'w3':'http://www.w3.org/1999/xhtml'})