SWIG and Numpy
Please note that with current versions of NumPy (SVN), the directory contains a complete working example with simple SWIG typemaps, including also a proper file so you can install it with the standard Python mechanisms. This should help you get up and running quickly.
To get the feel how to write a truly minimalist interface, below is a relevant part of the simple SWIG interface file umfpack.i (this is for SWIG < version 1.3.29) used to wrap the UMFPACK sparse linear solver libraries. The full interface can be found in the directory in the SciPy SVN repository. If you’re using SWIG > version 1.3.29, refer to the file in SciPy SVN repository, which is slightly different.
/*!
Gets PyArrayObject from a PyObject.
*/
PyArrayObject *helper_getCArrayObject( PyObject *input, int type,
int minDim, int maxDim ) {
PyArrayObject *obj;
if (PyArray_Check( input )) {
obj = (PyArrayObject *) input;
if (!PyArray_ISCARRAY( obj )) {
PyErr_SetString( PyExc_TypeError, "not a C array" );
return NULL;
}
obj = (PyArrayObject *)
PyArray_ContiguousFromAny( input, type, minDim, maxDim );
if (!obj) return NULL;
} else {
PyErr_SetString( PyExc_TypeError, "not an array" );
return NULL;
}
return obj;
}
%}
/*!
Use for arrays as input arguments. Could be also used for changing an array
in place.
@a rtype ... return this C data type
@a ctype ... C data type of the C function
@a atype ... PyArray_* suffix
*/
#define ARRAY_IN( rtype, ctype, atype ) \
%typemap( python, in ) (ctype *array) { \
PyArrayObject *obj; \
obj = helper_getCArrayObject( $input, PyArray_##atype, 1, 1 ); \
if (!obj) return NULL; \
$1 = (rtype *) obj->data; \
Py_DECREF( obj ); \
};
ARRAY_IN( int, const int, INT )
%apply const int *array {
const int Ap [ ],
const int Ai [ ]
};
ARRAY_IN( long, const long, LONG )
%apply const long *array {
const long Ap [ ],
const long Ai [ ]
};
ARRAY_IN( double, const double, DOUBLE )
%apply const double *array {
const double Ax [ ],
const double Az [ ],
const double B [ ]
};
ARRAY_IN( double, double, DOUBLE )
%apply double *array {
double X [ ]
};
The function being wrapped then could be like:
int umfpack_di_solve( int sys, const int Ap [ ], const int Ai [ ],
const double Ax [ ], double X [ ], const double B [ ],
... );