Python C extension: How to DECREF a C array of PyArrayObjects

Question

I am creating some C extension code for python (example below). Part of the function requires me to iterate arrays passed in as arguments, preform a calculation on each element, and return an array of the calculated values.

I am using NpyIter_MultiNew as it can iterate over multiple arrays and also create an appropriate array for the output.

NpyIter_MultiNew requires a C array of PyArrayObject * as input (here op). op is filled from the output of PyArray_FROM_OTF. These are new references and so I need to clean up at the end of the code.

The question I have is what do I need to `DECREF on? (i.e. what should go in the <>)

Option 1:

Py_XDECREF(op);

Option 2:

Py_XDECREF(op[0]);
Py_XDECREF(op[1]);
Py_XDECREF(op[2]);

Option 3:

Py_XDECREF(op[0]);
Py_XDECREF(op[1]);
Py_XDECREF(op[2]);
Py_XDECREF(op);

I think Py_XDECREF(op[0]) might also be unnecessary. I suspect that op[0] remains as NULL and is simply used as a flag to NpyIter_MultiNew to indicate the creation of a new array. The new output array is recovered from output = NpyIter_GetOperandArray(iter)[0];

Note: The references used in PyObject * args_in[2] are borrowed and so no INCREF or DECREF is required.

static PyObject *
UseArray(PyObject * args){

    PyObject * args_in[2];

    PyArrayObject * op[3] = {NULL, NULL, NULL};
    npy_uint32 op_flags[3];

    PyArrayObject * output = NULL;

    // python inputs
    if (!PyArg_ParseTuple(args, "OO", &args_in[0], &args_in[1])){
        goto fail;
    }

    // output array
    op[0] = NULL;
    op_flags[0] = NPY_ITER_WRITEONLY | NPY_ITER_ALLOCATE;

    // input array
    op[1] = (PyArrayObject *) PyArray_FROM_OTF(args_in[0], NPY_DOUBLE, NPY_ARRAY_IN_ARRAY);
    op_flags[1] = NPY_ITER_READONLY;
    if (op[1] == NULL){
        goto fail;
    }
    op[2] = (PyArrayObject *) PyArray_FROM_OTF(args_in[1], NPY_DOUBLE, NPY_ARRAY_IN_ARRAY);
    op_flags[2] = NPY_ITER_READONLY;
    if (op[2] == NULL){
        goto fail;
    }

    // iterate
    iter = NpyIter_MultiNew(3, op, NPY_ITER_EXTERNAL_LOOP, NPY_KEEPORDER, NPY_NO_CASTING, op_flags, NULL);
    <<iterator code>>

    // get output array
    output = NpyIter_GetOperandArray(iter)[0];
    Py_INCREF(output);

    if (NpyIter_Deallocate(iter) != NPY_SUCCEED){
        goto fail;
    }

    <<DECREF op>>

    return PyArray_Return(output);

    fail:
        <<DECREF op>>
        Py_XDECREF(output);
        return NULL;
}

Python C extension: How to DECREF a C array of PyArrayObjects

0 Answers0