[XML-SIG] finding the NS URI for a prefix in a DOM

[Rich Salz]

Fred L. Drake, Jr. wrote:
> I don't think we have a good way to do that now, but it could be done
> in a DOM-independent way by walking up the tree looking at namespace
> declarations.

That's what I do in ZSI.  Here's the code, which might be of use ...

_attrs = lambda E: (E.attributes and E.attributes.values()) or []

def GetElementNSdict(self, elt):
     '''Get a dictionary of all the namespace attributes for an
     element.  The dictionaries are cached, and we recurse up the tree
     as necessary.
     '''
     d = self.ns_cache.get(id(elt))
     if not d:
         if elt != self.dom: d = self.GetElementNSdict(elt.parentNode)
         for a in _attrs(elt):
             if a.namespaceURI == XMLNS.BASE:
                 if a.localName == "xmlns":
                     d[''] = a.nodeValue
                 else:
                     d[a.localName] = a.nodeValue
         self.ns_cache[id(elt)] = d
     return d.copy()