[C++-sig] Re: throw_error_already_set()

[David Abrahams]

"Niall Douglas" <s_sourceforge at nedprod.com> writes:

> Now I have my custom exception which interrogates python and builds a 
> very useful C++ exception replete with python traceback, I'd like 
> this to be generated whenever there's a python exception raised.
>
> Unfortunately, the C++ exception error_already_set appears to be 
> thrown not only for python exceptions but also for internal BPL 
> errors

Specifics, please.

I think you're misinterpreting things.  Internal errors in BPL are
always handled with assert(), and never with exceptions.

> I'd far prefer BPL to keep throwing error_already_set when it 
> can't match parameter types etc. and throw my exception when it's 
> just a plain python problem. OTOH, BPL seems to set the python error 
> state when it throws error_already_set so maybe this is okay.

OK.  Sorry, is there a problem or not?

> Is it possible to modify BPL to do this

I don't think so.  Well, OK, we could provide a hookable error
handler.  I'd worry how it'd interact with threads, though.

Why don't you just look at the python error state at the catch
point?

> or am I relegated to wrapping every BPL call with a
> try...catch(error_already_set &)? 

I think you need to re-evaluate your EH strategy.  You must be
embedding Python.  You should handle Boost.Python errors in the same
place where you handle other exceptions in your program.

> I did notice there only appears to be one place where
> error_already_set is caught within BPL - therefore couldn't I
> literally just do a find & replace (or better, a #define
> throw_error_already_set FXPython::int_throwPythonException() so I
> don't have problems with merging new releases)

No comment.  Modify your private copy of the Boost.Python sources at
your peril (or not).

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com