[lxml-dev] lxml namespaces

[Stefan Behnel]

> On 2007-01-07 16:24:15 +0100, "Maxim Sloyko" <m.sloyko at gmail.com> said:
>> I have a little problem with XML namespaces.
>> In my application I have two XML processors, that process the same
>> document, one after the other.  The first one looks for nodes in 'ns1'
>> namespace, and substitutes them, according to some algorithm. After
>> this processor is finished, it is guaranteed that there are no more
>> 'ns1' nodes left in the tree.

Sounds a bit like a case for XSLT to me.


>> 'ns1' namespace dclaration is still
>> there, in the root node (well, I put it there manually). Now, when
>> this namespace is no longer needed, I want to get rid of it, because
>> it confuses some other processors (namely, my browser)
>>
>> So, the question is, how do I do that?
>> del tree.getroot().nsmap['ns1']
>> does not seem to do the trick :(

Hmmm, I think the easiest way to remove unused namespaces from a document is:

    new_nsmap = dict(p,n for p,n in root.nsmap.items() if n != NS_TO_REMOVE)
    new_root = etree.Element(root.tag, root.attrib, new_nsmap)
    new_root.text = root.text
    new_root.tail = root.tail
    new_root[:] = root[:]
    root = new_root

That's somewhat costly, but it's a rare usecase anyway... or use XSLT.

Honestly, assuring tree correctness if ".nsmap" was writable is not at all
trivial. You'd have to

- check which namespaces are being added and which are removed (incl.
parental inheritance, prefix override issues, ...)
- verify that removed namespaces are no longer used anywhere in the subtree
- replace the namespace declarations on the node, keeping pointers to the
old ones
- fix all namespace references in the subtree
- free the now-unused namespace declarations

The "fix all namespaces" bit is easy (should just work with the usual
moveNodeToDocument() dance), but I'm not feeling like implementing the
first steps right now...

Stefan