Re: [xml] using "raise" in Python error handler callbacks

[Andrew McDermott <andymcd mac com>]

On 31 Mar 2005, at 22:43, Daniel Veillard wrote:

> On Thu, Mar 31, 2005 at 10:25:41PM +0100, Andrew McDermott wrote:
> > Whilst experimenting with the Python bindings I noticed that 
> > exceptions
> > are not propagated when using registerErrorHandler().  If I run the
> > following I get the error message:
> >
> >         /etc/passwd : failed to parse.
> >
> > However, there is no Traceback for the "raise".  Is this correct?
> >
> > import libxml2
> > import sys
>
>   You have
>     Python calling C calling Python.
> the internal exception in the callback does not cross the C boundary
> I don't see how this could work without disastrous side effects like
> memory leaks or general instability in the program.

I was reading a section from the link below which gave me the 
impression this was possible.

http://www.cs.bham.ac.uk/resources/ums/PythonDoc/ext/callingPython.html

The return value of PyEval_CallObject() is ``new'': either it is a 
brand new object, or it is an existing    object whose reference count 
has been incremented. So, unless you want to save it in a global 
variable, you should somehow Py_DECREF() the result, even (especially!) 
if you are not interested in its value.

Before you do this, however, it is important to check that the return 
value isn't NULL. If it is, the Python function terminated by raising 
an exception. If the C code that called PyEval_CallObject() is called 
from Python, it should now return an error indication to its Python 
caller, so the interpreter can print a stack trace, or the calling 
Python code can handle the exception. If this is not possible or 
desirable, the exception should be cleared by calling PyErr_Clear(). 
For example:

Isn't it the case that the calling sequence starts within Python so it 
should be possible to return an error indication?

> Daniel
>
> --
> Daniel Veillard      | Red Hat Desktop team http://redhat.com/
> veillard redhat com  | libxml GNOME XML XSLT toolkit  
> http://xmlsoft.org/
> http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/