example.pyx

import numpy as np
import scipy.linalg.blas

cdef extern from "f2pyptr.h":
    void *f2py_pointer(object) except NULL

ctypedef int dgemm_t(
	char *transa, char *transb,
	int *m, int *n, int *k,
	double *alpha,
	double *a, int *lda,
	double *b, int *ldb,
	double *beta,
	double *c, int *ldc)

# Since Scipy >= 0.12.0
cdef dgemm_t *dgemm = <dgemm_t*>f2py_pointer(scipy.linalg.blas.dgemm._cpointer)

def myfunc():
    cdef double[::1,:] a, b, c
    cdef int m, n, k, lda, ldb, ldc
    cdef double alpha, beta

    a = np.array([[1, 2], [3, 4]], float, order="F")
    b = np.array([[5, 6], [7, 8]], float, order="F")
    c = np.empty((2, 2), float, order="F")

    alpha = 1.0
    beta = 0.0
    lda = 2
    ldb = 2
    ldc = 2
    m = 2
    n = 2
    k = 2
    dgemm("N", "N", &m, &n, &k, &alpha, &a[0,0], &lda, &b[0,0], &ldb, &beta, &c[0,0], &ldc)
    print(np.asarray(c))
    print(np.dot(a, b))

f2pyptr.h

#ifndef F2PYPTR_H_
#define F2PYPTR_H_

#include <Python.h>

void *f2py_pointer(PyObject *obj) 
{
#if PY_VERSION_HEX < 0x03000000
    if (PyCObject_Check(obj)) {
        return PyCObject_AsVoidPtr(obj);
    }
#endif
#if PY_VERSION_HEX >= 0x02070000
    if (PyCapsule_CheckExact(obj)) {
        return PyCapsule_GetPointer(obj, NULL);
    }
#endif
    PyErr_SetString(PyExc_ValueError, "Not an object containing a void ptr");
    return NULL;
}

#endif