python. how to get attribute value with libxml2

Question

I was using MINIDOM but it does not provide xpath methods.

I am now trying to use libxml2 but I am having trouble retrieving attribute values.

An extract of my xml looks as follow:

<Class name="myclass1" version="0">
    <Owner user-login="smagnoni"/>
</Class>

and I wrote the following code:

import libxml2
doc = libxml2.parseFile(file)
ris = doc.xpathEval('*/Class[@name="'+className+'" and @version="'+classVersion+'"]/Owner')
print str(ris[0])

which returns:

<Owner user-login="smagnoni"/>

How do I get just "smagnoni"? Parsing the string by hand feels overworked. but I did not find a method comparable to .getAttribute("attribute-name") in minidom.

Can anyone suggest the proper method or direct me to documentation?

I can't find this in their (seemingly lacking) documentation either. It might possibly have a .get method. You could also consider using the 'industry standard' lxml library. — supakeen
– supakeen, Commented Jul 22, 2011 at 14:39
lxml uses libxml2 and provides a nicer interface (the ElementTree api). — lambacck
– lambacck, Commented Jul 22, 2011 at 14:45
ikanobori is right, don't use the default libxml2 python bindings, use lxml, which is a much better interface to the same library. — agf
– agf, Commented Jul 22, 2011 at 14:47

unutbu · Accepted Answer · 2011-07-22 14:44:39Z

5

.prop('user-login') should work:

import libxml2
import io
content='''\
<Class name="myclass1" version="0">
    <Owner user-login="smagnoni"/>
</Class>
'''
doc = libxml2.parseMemory(content,len(content))
className='myclass1'
classVersion='0'
ris = doc.xpathEval('//Class[@name="'+className+'" and @version="'+classVersion+'"]/Owner')

elt=ris[0]
print(elt.prop('user-login'))

yields

smagnoni

edited Jul 22, 2011 at 14:44

answered Jul 22, 2011 at 14:39

unutbu

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2 Comments

Stefano Over a year ago

by the way... do you have any link for a reference documentation?? i am really trying to guess how to use this library. I found information for c implementation but for python not so much. Even if it claims to be a stable and really good library i think it lacks in documentation. Cheers, ste

unutbu Over a year ago

@stefano: I don't know of any particularly good documentation -- I mainly use lxml. I was able to guess my way to an answer here by fiddling around with code in IPython -- Typing ris.<TAB> shows you all the attributes of ris. Poking around like this led me to elt.prop.

agf · Accepted Answer · 2011-07-22 15:08:46Z

4

for owner in ris:
    for property in owner.properties:
        if property.type == 'attribute':
            print property.name
            print property.content

edited Jul 22, 2011 at 15:08

answered Jul 22, 2011 at 14:41

agf

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2 Comments

Stefano Over a year ago

good... in this case it was easyer to use the .prop() but since in other case i may have multiple results your foor loop may help. Tnx for the help

Stefano Over a year ago

ouch... i get an error doing so: "for property in ris.properties: AttributeError: 'list' object has no attribute 'properties'" :(

lambacck · Accepted Answer · 2011-07-22 15:01:46Z

lxml uses libxml2 and provides a nicer interface (the ElementTree api) so you get most of the benefit of libxml2's speed and all of the benefit of it's xpath evaluation.

import lxml.etree as ET

doc = ET.parse(file)
owner = doc.find('/*/Class[@name="'+className+'" and @version="'+classVersion+'"]/Owner')
if owner:
    print owner.get('user-login')

The added bonus is that the Element Tree api is available by default in python2.5 (though the version in 1.5 does not include the [@name='value'] xpath syntax, that was added in python 2.7, but you can get the 1.3 api as a separate package in older 2.x versions of python).

You can import any compatible version of the ElementTree api using:

try:
  from lxml import etree
  print("running with lxml.etree")
except ImportError:
  try:
    # Python 2.5
    import xml.etree.cElementTree as etree
    print("running with cElementTree on Python 2.5+")
  except ImportError:
    try:
      # Python 2.5
      import xml.etree.ElementTree as etree
      print("running with ElementTree on Python 2.5+")
    except ImportError:
      try:
        # normal cElementTree install
        import cElementTree as etree
        print("running with cElementTree")
      except ImportError:
        try:
          # normal ElementTree install
          import elementtree.ElementTree as etree
          print("running with ElementTree")
        except ImportError:
          print("Failed to import ElementTree from any known place")

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