On Thu, Feb 11, 2010 at 4:28 PM, Burcin Erocal <[email protected]> wrote:
> Hi,
>
> I'm in Kaiserslautern, at a workshop on connecting mathematical
> software for polyhedral geometry with software packages for Gröbner
> basis (polymake, gfan, singular).
>
> I tried to code a small example demonstrating how to call Sage from
> other C programs. I have a Cython module with the following:
>
> import sage.all
> from sage.rings.arith import factor
>
> cdef public do_something_in_sage(int** res, int n):
> print "do_something_in_sage called, input:",n
> t = factor(n)
> print t
>
>
> Now I want to link/load this as a C library. It seems that initializing
> Python with
>
> Py_Initialize();
> PySys_SetArgv(1, argv);
>
> then importing the module with
>
> PyObject* sage_module = PyImport_ImportModule("sage_link");
>
> doesn't quite work. Python decides to include the directory
> $SAGE_LOCAL/lib64/python2.6/lib-dynload/ instead of
> $SAGE_LOCAL/lib/python2.6/lib-dynload/ (Note lib64 vs. lib). If I add
> the latter to sys.path manually, things work as expected.
>
> Does anyone know where this lib64/lib problem comes from?
>
> Is it possible to avoid having to import the Cython module? Or to make
> the necessary blurb to call cython functions less scary?
>
>
> You can find the latest version of my attempts here:
>
> http://sage.math.washington.edu/home/burcin/sage_link/
I never tried Sage, but I routinely use Python (numpy, scipy, ...)
from inside our C++ solvers, here is what I do in the main.cpp:
Py_Initialize();
PySys_SetArgv(argc, argv);
if (import_hermes2d___hermes2d())
throw std::runtime_error("hermes2d failed to import.");
where the import_hermes2d___hermes2d was automatically generated by
Cython from my hermes2d/_hermes2d.pyx file. Here is the whole file:
http://github.com/certik/hermes2d/blob/6def0aab2ab3da425b1dd4f500783107e80ae72b/python/hermes2d/_hermes2d.pyx
copying some relevant parts:
import sys
import traceback
global_namespace = {"verbose": False}
cdef api void cmd(char *text):
n = run_cmd(text, global_namespace)
global_namespace.update(n)
cdef api void set_verbose_cmd(int verbose):
global_namespace["verbose"] = verbose
cdef api object run_cmd(char *text, object namespace):
try:
verbose = namespace.get("verbose")
if verbose:
print "got a text:", text
if verbose:
print "evaluting in the namespace:"
print namespace
code = compile(text, "", "exec")
eval(code, {}, namespace)
if verbose:
print "new namespace:"
print namespace
return namespace
except SystemExit, e:
try:
exit_code = int(e)
except:
exit_code = -1
exit(exit_code)
except:
etype, value, tb = sys.exc_info()
s = "".join(traceback.format_exception(etype, value, tb))
s = "Exception raised in the Python code:\n" + s
throw_exception(s)
and here is how I use matplotlib to plot some finite element base
functions from within C++:
insert_object("v", array_double_c2numpy(v->val, n));
insert_object("x", array_double_c2numpy(e->x, n));
insert_object("y", array_double_c2numpy(e->y, n));
insert_object("counter", int_c2py(counter));
cmd("import util");
cmd("util.plotxy(x, y, v, counter)");
where util.py is my python script which plots it. It works like a
charm. So keep me posted how you use Sage from C/C++, I am interested
in your approach.
Ondrej
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