Function PyArray_GetField

numpy/core/src/multiarray/methods.c:376–442

NUMPY_API Get a subset of bytes from each element of the array steals reference to typed, must not be NULL */

  steals reference to typed, must not be NULL
*/
NPY_NO_EXPORT PyObject *
PyArray_GetField(PyArrayObject *self, PyArray_Descr *typed, int offset)
{
    PyObject *ret = NULL;
    PyObject *safe;
    static PyObject *checkfunc = NULL;
    int self_elsize, typed_elsize;

    if (self == NULL) {
        PyErr_SetString(PyExc_ValueError,
            "self is NULL in PyArray_GetField");
        return NULL;
    }

    if (typed == NULL) {
        PyErr_SetString(PyExc_ValueError,
            "typed is NULL in PyArray_GetField");
        return NULL;
    }

    /* check that we are not reinterpreting memory containing Objects. */
    if (_may_have_objects(PyArray_DESCR(self)) || _may_have_objects(typed)) {
        npy_cache_import("numpy.core._internal", "_getfield_is_safe",
                         &checkfunc);
        if (checkfunc == NULL) {
            Py_DECREF(typed);
            return NULL;
        }

        /* only returns True or raises */
        safe = PyObject_CallFunction(checkfunc, "OOi", PyArray_DESCR(self),
                                     typed, offset);
        if (safe == NULL) {
            Py_DECREF(typed);
            return NULL;
        }
        Py_DECREF(safe);
    }
    self_elsize = PyArray_ITEMSIZE(self);
    typed_elsize = typed->elsize;

    /* check that values are valid */
    if (typed_elsize > self_elsize) {
        PyErr_SetString(PyExc_ValueError, "new type is larger than original type");
        Py_DECREF(typed);
        return NULL;
    }
    if (offset < 0) {
        PyErr_SetString(PyExc_ValueError, "offset is negative");
        Py_DECREF(typed);
        return NULL;
    }
    if (offset > self_elsize - typed_elsize) {
        PyErr_SetString(PyExc_ValueError, "new type plus offset is larger than original type");
        Py_DECREF(typed);
        return NULL;
    }