xpath error, XPath position >= 1 expected

Question

I am trying to parse a xml from a string.

Below is the xml in the string.

<xc:Application class="bril::lumistore::Application" id="111" instance="0" logpolicy="inherit" network="local" service="lumistore">
  <ns4:properties xsi_type="soapenc:Struct">
    <ns4:datasources soapenc_arrayType="xsd:ur-type[1]" xsi_type="soapenc:Array">
      <ns4:item soapenc_position="[0]" xsi_type="soapenc:Struct">
        <ns4:properties xsi_type="soapenc:Struct">
          <ns4:bus xsi_type="xsd:string">brildata</ns4:bus>
          <ns4:topics xsi_type="xsd:string">tcds,beam,bestlumi,bcm1fagghist,bcm1flumi,bcm1fbkg,pltaggzero,pltlumizero,hfoclumi,hfOcc1Agg,bunchmask,ScopeData,atlasbeam,hfetlumi,hfEtSumAgg,hfafterglowfrac,hfEtPedestal,dtlumi,bunchlength,radmonraw,radmonflux,radmonlumi,pltslinklumi,bcm1futca_bkg12,bcm1futca_background,bcm1futcalumi,remuslumi,remuslumi_5514,remuslumi_5515,remuslumi_5516,remuslumi_5517,bcm1futca_agg_hist</ns4:topics>
        </ns4:properties>
      </ns4:item>
    </ns4:datasources>
    <ns4:maxstalesec xsi_type="xsd:unsignedInt">30</ns4:maxstalesec>
    <ns4:checkagesec xsi_type="xsd:unsignedInt">10</ns4:checkagesec>
    <ns4:maxsizeMB xsi_type="xsd:unsignedInt">120</ns4:maxsizeMB>
    <ns4:fileformat xsi_type="xsd:string">hd5</ns4:fileformat>
    <ns4:filepath xsi_type="xsd:string">/scratch/central_current</ns4:filepath>
    <ns4:nrowperwbuf xsi_type="xsd:unsignedInt">102</ns4:nrowperwbuf>
    <ns4:workinterval xsi_type="xsd:unsignedInt">50000</ns4:workinterval>
  </ns4:properties>
</xc:Application>

This is the code i use to parse the string

import xml.etree.ElementTree as ET

root = ET.fromstring(xml)
node = root.find(field['xpath'], ns)

where

field['xpath'] = ".//xc:Application[@class='bril::lumistore::Application']/lst:properties/lst:datasources/lst:item[0]/lst:properties/lst:topics"

and

ns = {'xc': 'http://path/XMLConfiguration-30', 'lst': 'urn:application-urn:bril::lumistore::Application'}

I get the following error

XPath position >= 1 expected
Traceback (most recent call last):
File "/usr/lib64/python3.6/xml/etree/ElementPath.py", line 263, in iterfind
    selector = _cache[cache_key]
KeyError: (".//xc:Application[@class='bril::lumistore::Application']/lst:properties/lst:datasources/lst:item[0]/lst:properties/lst:topics", (('lst', 'urn:application-urn:bril::lumistore::Application'), ('xc', 'http://path/XMLConfiguration-30')))
During handling of the above exception, another exception occurred:
SyntaxError: XPath position >= 1 expected

Any help is much appreciated

Note: Usin Python 2.7 seems to work fine, not with Python 3.6 though.

Asked By: Dia

||

Source

Answer 1

Positions in XPath start at 1; not 0.

So the positional predicate [0] in:

lst:item[0]

isn’t going to select anything.

If you want to select the first lst:item child of lst:datasources, use:

lst:item[1]

Answered By: Daniel Haley

xpath error, XPath position >= 1 expected

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