[Cython] Higher fidelity translations from C++ exception to Python exception?

[Dag Sverre Seljebotn]

Barry Warsaw <barry at python.org> wrote:

>So if you have code like the following:
>
>cdef class Database:
>    cdef open(self, path) except +raise_py_error:
>        something_that_can_throw_a_cpp_exception(path)
>
>you can write
>
>cdef int raise_py_error():
>    raise Something
>
>to kind of turn a C++ exception into a Python exception.  The problem
>appears
>to be that you cannot include in the Python exception any information
>contained in the C++ exception, because there's no access to the C++
>exception
>that was thrown.
>
>The generated code does a `catch(...)` so you lose that useful
>information.
>AFAICT, there's no way to find out within the catch clause (or anything
>called
>by that clause) what C++ exception occurred.
>
>It would sure be useful if raise_py_error() was passed the exception
>instance
>that was caught.  Then at least our handler could extract some useful
>information to relay to the Python level.  E.g. in the case above, it
>might
>tell us that the `path` is nonexistent.

But that requires something more than a catch(...), right? There must be more syntax introduced in the Cython language to map C++ exceptions to constructor functions (taking exceptions of different types). Do you have a concrete proposal for how that could look like?

Dag 

>
>Cheers,
>-Barry
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