XPath to find nearest ancestor element that contains an element that has an attribute with a certain value

Question

ancestor::foo[bar[@attr=\"val\"]]

I thought this would work, but it\'s not. I need to find the nearest foo element going up in the tree tha

Answer 1

If you have a file like this:

and you want the foo nodes with the ids 2 and 3, i.e. the closest foos to their bar descendants having attr=val, the following works:

//foo[descendant::bar[@attr="val"] and not(descendant::foo)]

If you omit and not(descendant::foo) you get additionally the foo with the id 0.

The other answers didn't work for me on the general case of my example.

You can test it in Python with:

from lxml import etree
tree = etree.parse('example.xml')
foos = tree.xpath('//foo[descendant::bar[@attr="val"] and not(descendant::foo)]')
for foo in foos:
    print(foo.attrib)

which prints:

{'id': '2'}
{'id': '3'}

Notice that the xpath used is not efficient. I would love to learn a more efficient one.