[C++-sig] Python converters for raw pointers: request for help

[Michele De Stefano]

Ok. Let me clarify (I looked at the link you suggested, but I've not
found the answers I was looking for).

There exist a "petsc4py" package, which can be extended using its C
API. This package, already exposes PETSc types (and also the Mat
type). petsc4py is not programmed using Boost Python.

Now, assume I already have a C++ function that takes a Mat parameter;
to make it simple, let's take

void print_Mat(Mat m) {
   ... // The implementation is not interesting
};

I'd like to expose this function to Python, with a seamless
integration mechanism, using Boost Python.

Unfortunately, if I use the petsc4py API, I have to expose a wrapper
for "print_Mat", in this way:

void print_Mat_Wrap(const object& mat_obj) {
    Mat m( PyPetscMat_Get(mat_obj.ptr()) );
    ... // The rest is not important
}

I don't know anything of the petsc4py implementation, but I know that
it already exposes PETSc Mat to Python. I know also that, using the
petsc4py C API, the only way to retrieve a Mat from a
PyObject* is through the PyPetscMat_Get function, whose signature is this one:

Mat (*PyPetscMat_Get)(PyObject *);

I know for sure that Mat objects are not allocated with the C++ new
operator (I don't know if this is a useful information for you).

What I'd really like to do, would be to write a from-Python-converter
from a PyObject* (containing a petsc4py exposed Mat) into a Mat, in
order to be able to directly expose my "void print_Mat(Mat m)" without
writing any wrapper ... but I didn't manage to properly make it ...

Is this possible ?


2009/10/26 Randolph Fritz <rfritz333 at gmail.com>:
> Additional thought.  Take a look at:
>  <http://wiki.python.org/moin/boost.python/PointersAndSmartPointers#OSGexample>
> & see if it helps clarify some of the problems.
>
> --
> Randolph Fritz
>  design machine group, architecture department, university of washington
> rfritz at u.washington.edu -or- rfritz333 at gmail.com
>
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-- 
Michele De Stefano
http://www.linkedin.com/in/micdestefano
http://xoomer.virgilio.it/michele_de_stefano