DECREFing and PyArray functions in C Extensions

[Roger Hansen]

* Travis Oliphant

[snip]
> This is still my advice, but I would reword it: 
> 
> Every PyArrayObject that you successfully receive from a
> PyArray_XXXXXX call has an increased reference count (you own a
> reference). Unless you are returning the object to the user (using
> return PyArray_Return(obj) or PyArray_BuildValue with the "N"
> construct) you must DECREF the object before leaving the subroutine
> or you will create a memory leak..

[snip]

OK! Lets say I have a Python program with a NumPy array and a loop,
and for efficiency reasons I decide to write the loop as an extension,
like this:

static PyObject * 
foo(PyObject *self, PyObject* args)
{
  PyArrayObject *array;
  double* a;            /* C ptr to the NumPy array data field */

  if (!PyArg_ParseTuple(args, "O!", &PyArray_Type, &array)) {
    return NULL;  /* Error indicator */
  }

  ...   /* Check if array has right dimension, etc. */

  n = array->dimensions[0];    /* Get the length of the array */
  a = (double*) array->data;   /* Set the pointer to the NumPy data */

  for (i=0; i<n; i++) {
    x = (double) i/(n-1);
    a[i] = f(x);
    /* more general: *(array->data+i*array->strides[0]) = f(x) */
  }

  Py_INCREF(Py_None);  return Py_None;
}   

where f is some function. I don't need to DECREF array in this
example since PyArg_ParseTuple does not increase the reference count,
right?




Suddenly-wondering-if-I've-messed-it-up'ly y'rs
Roger