Function prepare_index

numpy/core/src/multiarray/mapping.c:277–738

* Prepare an npy_index_object from the python slicing object. * * This function handles all index preparations with the exception * of field access. It fills the array of index_info structs correctly. * It already handles the boolean array special case for fancy indexing, * i.e. if the index type is boolean, it is exactly one matching boolean * array. If the index type is fancy, the boolean

 * @returns the index_type or -1 on failure and fills the number of indices.
 */
NPY_NO_EXPORT int
prepare_index(PyArrayObject *self, PyObject *index,
              npy_index_info *indices,
              int *num, int *ndim, int *out_fancy_ndim, int allow_boolean)
{
    int new_ndim, fancy_ndim, used_ndim, index_ndim;
    int curr_idx, get_idx;

    int i;
    npy_intp n;

    PyObject *obj = NULL;
    PyArrayObject *arr;

    int index_type = 0;
    int ellipsis_pos = -1;

    /*
     * The choice of only unpacking `2*NPY_MAXDIMS` items is historic.
     * The longest "reasonable" index that produces a result of <= 32 dimensions
     * is `(0,)*np.MAXDIMS + (None,)*np.MAXDIMS`. Longer indices can exist, but
     * are uncommon.
     */
    PyObject *raw_indices[NPY_MAXDIMS*2];

    index_ndim = unpack_indices(index, raw_indices, NPY_MAXDIMS*2);
    if (index_ndim == -1) {
        return -1;
    }

    /*
     * Parse all indices into the `indices` array of index_info structs
     */
    used_ndim = 0;
    new_ndim = 0;
    fancy_ndim = 0;
    get_idx = 0;
    curr_idx = 0;

    while (get_idx < index_ndim) {
        if (curr_idx > NPY_MAXDIMS * 2) {
            PyErr_SetString(PyExc_IndexError,
                            "too many indices for array");
            goto failed_building_indices;
        }

        obj = raw_indices[get_idx++];

        /**** Try the cascade of possible indices ****/

        /* Index is an ellipsis (`...`) */
        if (obj == Py_Ellipsis) {
            /* At most one ellipsis in an index */
            if (index_type & HAS_ELLIPSIS) {
                PyErr_Format(PyExc_IndexError,
                    "an index can only have a single ellipsis ('...')");
                goto failed_building_indices;
            }