Mailman 3 January 2004 - NumPy-Discussion

PyArray_ContiguousFromObject & PyDECREF
by Michiel Jan Laurens de Hoon May 16, 2011

May 16, 2011

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

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numarray-0.8.1
by Austin Luminais Feb. 2, 2004

Feb. 2, 2004

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.

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array resizing?
by Daniel Holth Jan. 30, 2004

Jan. 30, 2004

Is it possible for a C function to take an array from Python and resize it for returned results?

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[Daniel Holth <dholth@fastmail.fm>] numarray question
by John Hunter Jan. 30, 2004

Jan. 30, 2004

Daniel asked me to forward this, as apparently he has had trouble getting mail through.

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shape, size
by Daniel Holth Jan. 30, 2004

Jan. 30, 2004

apoligies if this is a duplicate... How do you write nb = na[:,:4] in a C extension module? Thanks, Daniel Holth

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shape, size
by Daniel Holth Jan. 30, 2004

Jan. 30, 2004

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

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Protect Yourself now
by Chuck Meadows Jan. 30, 2004

Jan. 30, 2004

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numarray question
by Daniel Holth Jan. 29, 2004

Jan. 29, 2004

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 --=-=-=--

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Writing arrays to files.
by Andrea Riciputi Jan. 29, 2004

Jan. 29, 2004

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)

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None
by numpy-discussion＠lists.sourceforge.net Jan. 28, 2004

Jan. 28, 2004

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