Re: [xml] handling xpath error - libxml

[Stefan Behnel <stefan_ml behnel de>]

Hi,

Senthil Nathan wrote:
> On 1/28/08, Stefan Behnel <stefan_ml behnel de> wrote:
> > Hi,
> >
> > Senthil Nathan wrote:
> > > I would like to how to handle the xpath error gracefully when I use the
> > > libxml api,
> > > xmlXPathEvalExpression(path, xpathCtx).
> > >
> > > If I pass a invalid path string to evaluate on the "xpathCtx", it throws
> > the
> > > error as below and stops there.
> > > But I would like to handle that error gracefully and log it accordingly
> > and
> > > proceed with my application.
> > What is the reason why you cannot just continue after this error? Just
> > call
> > xmlXPathEvalExpression() again (with a working expression) and everything
> > should be fine.
>
> In my application, when an invalid xpath string is given, during the
> xmlXPathEvalExpression( ),
> it fails with the error and just stops there. it's not continuing further
> and just hangs or stops there.
> So, I only need to break the application. Is there a better way to handle,
> in case of these xpath errors.

Ah, so it hangs *in* the eval call and does not return? I've never seen that
before. And it definitely works for me in lxml (libxml2 2.6.31):

  >>> import lxml.etree as et
  >>> root = et.XML("<root/>")
  >>> root.xpath("/roottag///*[ check='1']")
  Traceback (most recent call last):
  [...]
  lxml.etree.XPathEvalError: Invalid expression
  >>>

That's basically using this code:

  xpathCtxt.node = some_node;
  xpathObj = xmlXPathEvalExpression(c_path, xpathCtxt);


Could you supply the libxml2 version you are using and some example code that
shows the problem? Does your machine show high CPU load while it hangs? (i.e.
does it do something?)

Stefan