[lxml-dev] Custom Elements question

[Alex Klizhentas]

Thanks Stefan,

All the nodes in that tree should have the same type, that's why the default
class lookup scheme for parser works fine.

BTW, I have one more question, to set the xml:id i use the following
construct:

def xml_id(v):
    # helper function to create name space attributes
    return {'{http://www.w3.org/XML/1998/namespace}id': v}

and the following construct:

N.child1("text",xml_id("some_id"))

following the examples from the site.

to get the id I use:

class NodeBase(etree.ElementBase):
    ...
    def get_node_id(self,id):
        searched = self.find(".//*[@{
http://www.w3.org/XML/1998/namespace}id='%s']"%(id,))
        if searched is None:
            raise NodeNotFoundError(id)
        return searched


I have two questions:

1. what way is faster to get the element by Id? should I use find or xpath
to achieve the better performance?
2. is there a way to set xml:id using xml - prefix?

Thanks,
Alex

2008/5/2 Stefan Behnel <stefan_ml at behnel.de>:

> Hi,
>
> another bit of reasoning here.
>
> Stefan Behnel wrote:
> > Alex Klizhentas wrote:
> >> I've extended the ElementBase object using the approach described in
> the
> >> tutorial, but SubElement does not work as desired:
> >>
> >> class NodeBase(etree.ElementBase):
> >>      def append(self,child):
> >>  print "aaa"
> >>  return etree.ElementBase.append(self,child)
> >>
> >> etree.SubElement(root,"child") #no "aaa" printed
> >
> > That's because SubElement() does not call .append().
> [...]
> > SubElement() does not call .makeelement() either. It's implemented in
> plain C.
>
> One important reason is that this allows lxml.etree to append the new
> libxml2
> node at the C level *before* the decision is taken which Python class
> should
> be used to represent it. This might have an impact on the class lookup if
> it
> considers the parental relation when taking its decision (lxml.objectify
> does
> that, for example).
>
> But that's the only difference I can see between etree.SubElement() and
> your
> Python implementation. And you could even work around it by doing
> something
> like this:
>
> def SubElement(parent, tag, attrib={}, **extra):
>     attrib = attrib.copy()
>     attrib.update(extra)
>     element = parent.makeelement(tag, attrib)
>     parent.append(element)
>     del element
>     return parent[-1]
>
> However, you might want to avoid that if you know you won't need it, e.g.
> when
> using the "namespace" or "default" lookup scheme.
>
> Stefan
>
>


-- 
Regards,
Alex
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://codespeak.net/pipermail/lxml-dev/attachments/20080502/e5f1c6a6/attachment-0001.htm