find xml element based on its attribute and change its value

Question

I am using python xmlElementTree and want to assign or modify a xml element value based on its attribute. Can somebody give me an idea how to do this?

For example: Here

Answer 1

larsks explains how to use XPath to find what you are after very well. You also wanted to change an attribute. The best way is probably to add a new attribute and remove the original. Once you get the nodes result, it is a list with a single entry (number).

# This returns sys/phoneNumber/1
nodes[0].get("topic")
# To change the value, use set 
nodes[0].set("topic", "new/value/of/phone/number")

Hope this helps.

Also, your ending root tag doesn't close properly.

Answer 2

For me this Elementtree snipped of code worked to find element by attribute:

import xml.etree.ElementTree as ET
tree = ET.parse('file.xml')
root = tree.getroot()


topic=root.find(".//*[@topic='sys/phoneNumber/1']").text

Answer 3

I'm not familiar with xmlElementTree, but if you're using something capable of xpath expressions you can locate a node by attribute value using an expression like this:

//number[@topic="sys/phoneNumber/1"]

So, using the etree module:

>>> import lxml.etree as etree
>>> doc = etree.parse('foo.xml')
>>> nodes = doc.xpath('//number[@topic="sys/phoneNumber/1"]')
>>> nodes
[<Element number at 0x10348ed70>]
>>> etree.tostring(nodes[0])
'<number topic="sys/phoneNumber/1" update="none"/>\n    '

Answer 4

You can access the attribute value as this:

from elementtree.ElementTree import XML, SubElement, Element, tostring

text = """
<root>
    <phoneNumbers>
        <number topic="sys/phoneNumber/1" update="none" />
        <number topic="sys/phoneNumber/2" update="none" />
        <number topic="sys/phoneNumber/3" update="none" />
    </phoneNumbers>

    <gfenSMSnumbers>
        <number topic="sys2/SMSnumber/1" update="none" />
        <number topic="sys2/SMSnumber/2" update="none" />
    </gfenSMSnumbers>
</root>
"""

elem = XML(text)
for node in elem.find('phoneNumbers'):
    print node.attrib['topic']
    # Create sub elements
    if node.attrib['topic']=="sys/phoneNumber/1":
        tag = SubElement(node,'TagName')
        tag.attrib['attr'] = 'AttribValue'

print tostring(elem)

forget to say, if your ElementTree version is greater than 1.3, you can use XPath:

elem.find('.//number[@topic="sys/phoneNumber/1"]')

http://effbot.org/zone/element-xpath.htm

or you can use this simple one:

for node in elem.findall('.//number'):
    if node.attrib['topic']=="sys/phoneNumber/1":
        tag = SubElement(node,'TagName')
        tag.attrib['attr'] = 'AttribValue'