[PyQt] sip: extend exception support

[Phil Thompson]

On Wed, 15 Aug 2012 15:54:11 +0200, Mathias.Born at gmx.de wrote:
> Phil,
> 
> sip can already propagate C++ exceptions into Python in cases
> where Python calls a C++ function which throws an exception.
> 
> However, if I extend a C++ class in Python and call a corresponding
> (Python-)method in C++ via the wrapper, the sip generated
> wrapper code checks for a Python exception, but doesn't throw an
> excpetion itself.
> For example:
> 
> ========= <code generated by sip> =======================
> boost::optional<int> sipVH_ltse_app_0(sip_gilstate_t
sipGILState,PyObject
> *sipMethod,const std::string& a0)
> {
>     boost::optional<int> sipRes;
>     PyObject *resObj = sipCallMethod(0,sipMethod,"N",new
>     std::string(a0),sipType_std_string,NULL);
> 
>     if (!resObj ||
>    
sipParseResult(0,sipMethod,resObj,"H5",sipType_boost_optional_1800,&sipRes)
>     < 0)
>         PyErr_Print();
> 
>     Py_XDECREF(resObj);
>     Py_DECREF(sipMethod);
> 
>     SIP_RELEASE_GIL(sipGILState)
> 
>     return sipRes;
> }
> =========================================================
> 
> Here, "PyErr_Print" is called if the Python implementation of
> the method raises an exception. This is fine for Qt which
> cannot deal with exceptions, but in general I would find it
> much more helpful if the wrapper code generated by sip
> threw a C++ exception itself to signal the problem to the
> caller.
> 
> Just define a class, e.g. "SIPPyException" (derived from
> std::exception), which becomes part of the API and is always used
> in such cases.
> In order not to break existing code, it would only be used in
> classes or methods which are annotated appropriately.
> (So an additional annotation is necessary to activate this behavior.)
> 
> I believe an extension like this would make sip a lot more useful
> for embedding Python into a C++ program.
> 
> Best Regards,
> Mathias Born

Try current hg or tonight's snapshot. See the all_throw_cpp_exception
%Module argument and the /ThrowsCppException/ and /NoThrowsCppException/
function annotations.

Not heavily tested.

Phil