On Fri, Jul 17, 2009 at 10:03 AM, Darren Dale <dsdale24@gmail.com> wrote:

On Mon, Jul 13, 2009 at 7:12 PM, Darren Dale <dsdale24@gmail.com> wrote:

2009/7/13 Stéfan van der Walt <stefan@sun.ac.za>

Hi Darren

2009/7/13 Darren Dale <dsdale24@gmail.com>:

> I've put together a first cut at implementing __array_prepare__, which
> appears to work, and I would like to request feedback. Here is an overview
> of the approach:

This is pretty neat! Do you have a quick snippet at hand illustrating its use?

That would be helpful, wouldn't it? The attached script is a modified version of RealisticInfoArray from http://docs.scipy.org/doc/numpy/user/basics.subclassing.html . It should yield the following output:

starting with [0 1 2 3 4]
which is of type <class '__main__.MyArray'>
and has info attribute = "information"
subtracting 3 from [0 1 2 3 4]
subtract calling __array_prepare__ on [0 1 2 3 4] input
output array is now of type <class '__main__.MyArray'>
output array values are still uninitialized:
[139911601789568 39578752 139911614885536 39254560
48]
__array_prepare__ is updating info attribute on output
__array_prepare__ finished, subtract ufunc is taking over
subtract calling __array_wrap__ on [0 1 2 3 4] input
output array has initial value: [-3 -2 -1 0 1]
__array_wrap__ is setting output endpoints to 0
yielding [ 0 -2 -1 0 0]
which is of type <class '__main__.MyArray'>
and has info attribute = "new_information"

This is a gentle ping, hoping to get some feedback so this feature has a chance of being included in the next release.

I have a question about the C-api. If I want to make the default implementation of __array_prepare__ (or __array_wrap__, is anyone out there?) simply pass through the output array:

static PyObject *
array_preparearray(PyArrayObject *self, PyObject *args)
{
    PyObject *arr;

    if (PyTuple_Size(args) < 1) {
        PyErr_SetString(PyExc_TypeError,
                        "only accepts 1 argument");
        return NULL;
    }
    arr = PyTuple_GET_ITEM(args, 0);
    if (!PyArray_Check(arr)) {
        PyErr_SetString(PyExc_TypeError,
                        "can only be called with ndarray object");
        return NULL;
    }
    return arr;
}