How to get an xpathContext from an xmlNode in python.

Question

Hi, big fan of xpath on .net, and sax in python, but first time using xpath in python.

I have a small script, that uses xpath to select some nodes from a doc, iterates through them, and then ideally uses xpath again to get the relevant data from them. However I can't get that last bit, once I have the xmlNode I cannot get a context from it.

import libxml2
import urllib

doc = libxml2.parseDoc(
        urllib.urlopen('http://somemagicwebservice.com/').read())
ctxt = doc.xpathNewContext()
listitems = ctxt.xpathEval('//List/ListItem')
for item in listitems:
    itemctxt = item.xpathNewContext()
    title = itemctxt.xpathEval('//ItemAttributes/Title')
    asin = itemctxt.xpathEval('//Item/ASIN')
    itemctxc.xpathFreeContext()
ctxt.xpathFreeContext()
doc.freeDoc()

However the itemctxt = item.xpathNewContext() bit fails with

itemctxt = item.xpathNewContext()
AttributeError: xmlNode instance has no attribute 'xpathNewContext'

Any ideas how to use xpath on a xmlNode? I can't find any good online info. Thanks

Answer 1

I don't think an XPathContext makes sense on an element? Try creating a new XPathContext, and setting it's node to the current element.

That said, I haven't used libxml2 directly, so it's a bit of a wild guess. I typically uses lxml, that exposes an ElementTree API around libxml2 and libxslt. It's much easier to use, and does indeed allow xpath() on elements. Of course, if you already have a lot of code using libxml2 you probably don't want to switch, but in that case you might want to take a look at lxmls source to see how it does it.

http://codespeak.net/svn/lxml/trunk/src/lxml/xpath.pxi

http://codespeak.net/svn/lxml/trunk/src/lxml/_elementpath.py

Seems good starting places.