Estoy tratando de analizar un documento XML con múltiples espacios de nombres con lxml, y estoy atascado en obtener el método findall () para devolver algo.

Mi XML:

<MeasurementRecords xmlns="http://www.company.com/common/rsp/2012/07"
                    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         
                    xsi:schemaLocation="http://www.company.com/common/rsp/2012/07 RSP_EWS_V1.6.xsd">
    <HistoryRecords>
        <ValueItemId>100_0000100004_3788_Resource-0.customId_WSx Data Precip Type</ValueItemId>
            <List>
                <HistoryRecord>
                    <Value>60</Value>
                    <State>Valid</State>
                    <TimeStamp>2016-04-20T12:40:00Z</TimeStamp>
                </HistoryRecord>
            </List>
        </HistoryRecords>
    <HistoryRecords>
</MeasurementRecords>

Mi código:

from lxml import etree
from pprint import pprint

RSPxmlFile = '/home/user/Desktop/100_0000100004_3788_20160420144011263_records.xml'

with open (RSPxmlFile, 'rt') as f:
    tree = etree.parse(f)

root = tree.getroot()

for node in tree.findall('MeasurementRecords', root.nsmap):
    print node
    print "parameter = ", node.text

Da:

ValueError: empty namespace prefix is not supported in ElementPath

Algunos experimentos que he probado después de leeresta:

>>> root.nsmap
{'xsi': 'http://www.w3.org/2001/XMLSchema-instance', None: http://www.company.com/common/rsp/2012/07'}

>>> nsmap['foo']=nsmap[None]
>>> nsmap.pop(None)
'http://www.company.com/common/rsp/2012/07'
>>> nsmap
{'xsi': 'http://www.w3.org/2001/XMLSchema-instance', 'foo': 'http://www.company.com/common/rsp/2012/07'}
>>> tree.xpath("//MeasurementRecords", namespaces=nsmap)
[]
>>> tree.xpath('/foo:MeasurementRecords', namespaces=nsmap)
[<Element {http://www.company.com/common/rsp/2012/07}MeasurementRecords at 0x6ffffda5290>]
>>> tree.xpath('/foo:MeasurementRecords/HistoryRecords', namespaces=nsmap)
[]

Pero eso no pareció ayudar.

Entonces, más experimentos:

>>> tree.findall('//{http://www.company.com/common/rsp/2012/07}MeasurementRecords')
[]
>>> print root
<Element {http://www.company.com/common/rsp/2012/07}MeasurementRecords at 0x6ffffda5290>
>>> print tree
<lxml.etree._ElementTree object at 0x6ffffda5368>
>>> for node in tree.iter():
...     print node
...
<Element {http://www.company.com/common/rsp/2012/07}MeasurementRecords at 0x6ffffda5290>
<Element {http://www.company.com/common/rsp/2012/07}HistoryRecords at 0x6ffffda5cf8>
<Element {http://www.company.com/common/rsp/2012/07}ValueItemId at 0x6ffffda5f38>
...etc...
>>> tree.findall("//HistoryRecords", namespaces=nsmap)
[]
>>> tree.findall("//foo:MeasurementRecords/HistoryRecords", namespaces=nsmap)
[]

Estoy perplejo. No tengo idea de lo que está mal.