Python: how to parse this with lxml?

Question

Python

How to parse this piece using the lxml (python)
code library

<gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01" xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
<gesmes:subject>Reference rates</gesmes:subject>
<gesmes:Sender>
<gesmes:name>European Central Bank</gesmes:name>
</gesmes:Sender>
<Cube>
<Cube time="2015-01-02">
<Cube currency="USD" rate="1.2043"/>
<Cube currency="JPY" rate="145.21"/>
<Cube currency="BGN" rate="1.9558"/>
<Cube currency="CZK" rate="27.693"/>
<Cube

when I write tree.xpath('/gesmes:Envelope/Cube/Cube')
error: lxml.etree.XPathEvalError: Undefined namespace prefix

Answer 1

Namespaces in lxml lxml.de/tutorial.html#namespaces

Answer 2

You can try lxml.etree.iterparse

Answer 3

still returns empty sheet...
so i get tree

# читаем страницу с сети
        xml_obj = urllib2.urlopen(self.source_url)
        xml_str = xml_obj.read()

        # import io
        # xml_str = io.BytesIO(xml_str)
        # строим дерево
        tree = etree.XML(xml_str)