Re: [lxml-dev] Bug in XPath evaluation - not a bug :)

April 24, 2007


      Hi,
...
The only solution I see right now is to scan the XML data prior to the
XPath query in order to map each prefix to its namespace-uri. 
I do understand now that this is such an exotic use case that it
wouldn't make much sense to have lxml do these mappings automatically if
the second argument of .xpath() is omitted.
The reason I gave this rather lengthy example was to find out if anyone
reading this has an idea of an alternative solution for my problem
(applying metadata to specific parts of an XML document without making
the XPath expressions to address these parts too complex).
Might be you can take advantage of nsmap (don't get confused by the result output, I'm using the lxml.objectify notion)?
...
...
...
root = etree.fromstring("""
... <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
...       xmlns:py="http://codespeak.net/lxml/objectify/pytype"
...       xmlns:other="otherURI"
...       xmlns="myURI"
...       version="v2.0">
...   <a attr1="foo" attr2="bar">1</a>
...   <a py:pytype="float">1.2</a>
...   <a py:pytype="str">1.2</a>
...   <b py:pytype="int">1</b>
...   <b xsi:type="integer">2</b>
...   <b xsi:type="string">2</b>
...   <c>what</c>
...   <c>is</c>
...   <c>this</c>
...   <c>good</c>
...   <c>for?</c>
...   <d/>
...   <e>2006/08/09 13:19:01.000000+02:00</e>
...   <other:e>from another namespace</other:e>
...   <sub1>
...     <sub2>
...        <sub3>
...          <other:x>387.38</other:x>
...        </sub3>
...     </sub2>
...   </sub1>
...   <sub1>
...     <sub2>
...        <sub3>
...          <other:x>387.38</other:x>
...        </sub3>
...     </sub2>
...   </sub1>
...   <sub1>
...     <sub2>
...        <sub3>
...          <other:x>387.38</other:x>
...        </sub3>
...     </sub2>
...   </sub1>
... </root>
... """)
prefixDict = dict(root.nsmap)
del prefixDict[None]
prefixDict[''] = root.nsmap[None]
print etree.XPath('//other:x', prefixDict)(root)
[Decimal("387.38"), Decimal("387.38"), Decimal("387.38")]
What's not so nice is that nsmap uses None for the empty prefix whereas XPath seems to expect an empty string in the prefix-URI-dict.
Plus I'm not sure if you can simply use the root element nsmap, as I did
here.

Holger
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Re: [lxml-dev] Bug in XPath evaluation - not a bug :)

jholg＠gmx.de