Dear pythoneers,
In Chapter 12 ("Writing a C extension") in the Numerical Python manual, in the
first example PyArray_ContiguousFromObject is used together with PyDECREF, while
in the last example PyArray_ContiguousFromObject is used but the arrays are not
PyDECREF'ed before the function returns. From Chapter 13 ("C API Reference") it
seems that a PyDECREF is needed in both cases. Or am I missing something here?
Is PyDECREF not needed for some reason in the last example?
Thanks in advance,
Michiel de Hoon
U Tokyo
First example:
==============
static PyObject *
trace(PyObject *self, PyObject *args)
{
PyObject *input;
PyArrayObject *array;
double sum;
int i, n;
if (!PyArg_ParseTuple(args, "O", &input))
return NULL;
array = (PyArrayObject *)
PyArray_ContiguousFromObject(input, PyArray_DOUBLE, 2, 2);
if (array == NULL)
return NULL;
n = array->dimensions[0];
if (n > array->dimensions[1])
n = array->dimensions[1];
sum = 0.;
for (i = 0; i < n; i++)
sum += *(double *)(array->data + i*array->strides[0] + i*array->strides[1]);
Py_DECREF(array);
return PyFloat_FromDouble(sum);
}
Last example:
=============
static PyObject *
matrix_vector(PyObject *self, PyObject *args)
{
PyObject *input1, *input2;
PyArrayObject *matrix, *vector, *result;
int dimensions[1];
double factor[1];
double real_zero[1] = {0.};
long int_one[1] = {1};
long dim0[1], dim1[1];
extern dgemv_(char *trans, long *m, long *n,
double *alpha, double *a, long *lda,
double *x, long *incx,
double *beta, double *Y, long *incy);
if (!PyArg_ParseTuple(args, "dOO", factor, &input1, &input2))
return NULL;
matrix = (PyArrayObject *)
PyArray_ContiguousFromObject(input1, PyArray_DOUBLE, 2, 2);
if (matrix == NULL)
return NULL;
vector = (PyArrayObject *)
PyArray_ContiguousFromObject(input2, PyArray_DOUBLE, 1, 1);
if (vector == NULL)
return NULL;
if (matrix->dimensions[1] != vector->dimensions[0]) {
PyErr_SetString(PyExc_ValueError,
"array dimensions are not compatible");
return NULL;
}
dimensions[0] = matrix->dimensions[0];
result = (PyArrayObject *)PyArray_FromDims(1, dimensions, PyArray_DOUBLE);
if (result == NULL)
return NULL;
dim0[0] = (long)matrix->dimensions[0];
dim1[0] = (long)matrix->dimensions[1];
dgemv_("T", dim1, dim0, factor, (double *)matrix->data, dim1,
(double *)vector->data, int_one,
real_zero, (double *)result->data, int_one);
return PyArray_Return(result);
}
--
Michiel de Hoon, Assistant Professor
University of Tokyo, Institute of Medical Science
Human Genome Center
4-6-1 Shirokane-dai, Minato-ku
Tokyo 108-8639
Japan
http://bonsai.ims.u-tokyo.ac.jp/~mdehoon
Hello, is there any place I can download a Windows installer for numarray
0.8.1? I upgraded to 0.8.2 a while back, but it does not work with
McMillan's Installer. 0.8.1 worked fine, but I neglected to keep a copy of it.
As for why it doesn't work with Installer, I'm not sure. At least part of
the problem is that it is hardcoded to load LICENSE.TXT in __init__.py in a
way that is incompatible with Installer.
I tried removing the loading of LICENSE.TXT (which I realize is a
questionable thing to do; I was just trying to get it working), but it
doesn't work after that either.
In python, if na is a numarray:
>>> na
array([[0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
[1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1]])
I can type
>>> nb = na[:,:4]
>>> nb
array([[0, 1, 0, 1],
[1, 0, 1, 0]])
>>> nb[0][0]=17
>>> na
array([[17, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0],
[ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1]])
nb and na share data.
How do you write nb = na[:,:4] in a C extension module?
Thanks,
Daniel Holth
JDH,
sf.net seems to be ignoring my messages, so would you relay this
question:
how do you write nb = na[:,:4], creating a slice of na that references
nb, in an extension?
thanks,
Daniel Holth
--=-=-=--
Hi,
I need a little help here. I need to write some Numeric arrays (coming
from some simulations) to ASCII files. I'm sure it's a well known topic
and I'd be happy not to have to reinvent the wheel. I've both 1-dim and
2-dim arrays and I'd like to get something like this:
- 1-dim array ASCII file:
0.1 0.2 0.3 etc...
- 2-dim array ASCII file:
0.1 0.2 0.3
0.4 0.5 0.6
etc....
How can I get them?
Thanks in advance,
Andrea.
---
Andrea Riciputi
"Science is like sex: sometimes something useful comes out,
but that is not the reason we are doing it" -- (Richard Feynman)
