request for comments/advices about mapping PetscCookie -> Python Type

Lisandro Dalcin dalcinl at
Fri Oct 10 13:31:19 CDT 2008

In petsc4py, I've just implemented support for compose()/query() in my
base Object class. However, I wanted to implement query() in such a
way that 'dynamic_cast' (in the C++ sense, i.e, downcast) the composed
PETSc object and return to Python code an instance of the appropriate
Python type. Then, if you compose() a Mat, then query() will return a

I manages all this inside a private python dictionary mapping
PetscCookie -> Python type. Of course, this required to make sure that
ALL PetscXXXInitializePackage() have been called before adding stuff
to my dict. All is working fine; moreover, this machinery is also
being used in slepc4py and tao4py (yes, I have those...), then after
importing slepc4py or tao4py, the dictionary is populated as

Then, the question are: Do this approach sound good enough? Is it too
much hackery? Can I relly in the long future that this approach will
always work?

BTW, now I have a clear use case for initalizing all the XXX_COOKIE's
to 0 in core PETSc. This will really help me to spot package
initialization problems. In fact, I had to manage some of those
problems in petsc-2.3.2, petsc-2.3.3 and tao-1.9 .

PS: The renaming DA_COOKIE -> DM_COOKIE does not play well with all
this, but I do not care about it right now.

Lisandro Dalcín
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594

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