Function array_descr_set

numpy/core/src/multiarray/getset.c:450–595

* If the type is changed. * Also needing change: strides, itemsize * * Either itemsize is exactly the same or the array is single-segment * (contiguous or fortran) with compatible dimensions The shape and strides * will be adjusted in that case as well. */

 * will be adjusted in that case as well.
 */
static int
array_descr_set(PyArrayObject *self, PyObject *arg, void *NPY_UNUSED(ignored))
{
    PyArray_Descr *newtype = NULL;

    if (arg == NULL) {
        PyErr_SetString(PyExc_AttributeError,
                "Cannot delete array dtype");
        return -1;
    }

    if (!(PyArray_DescrConverter(arg, &newtype)) ||
        newtype == NULL) {
        PyErr_SetString(PyExc_TypeError,
                "invalid data-type for array");
        return -1;
    }

    /* check that we are not reinterpreting memory containing Objects. */
    if (_may_have_objects(PyArray_DESCR(self)) || _may_have_objects(newtype)) {
        static PyObject *checkfunc = NULL;
        PyObject *safe;

        npy_cache_import("numpy.core._internal", "_view_is_safe", &checkfunc);
        if (checkfunc == NULL) {
            goto fail;
        }

        safe = PyObject_CallFunction(checkfunc, "OO",
                                     PyArray_DESCR(self), newtype);
        if (safe == NULL) {
            goto fail;
        }
        Py_DECREF(safe);
    }

    /*
     * Viewing as an unsized void implies a void dtype matching the size of the
     * current dtype.
     */
    if (newtype->type_num == NPY_VOID &&
            PyDataType_ISUNSIZED(newtype) &&
            newtype->elsize != PyArray_DESCR(self)->elsize) {
        PyArray_DESCR_REPLACE(newtype);
        if (newtype == NULL) {
            return -1;
        }
        newtype->elsize = PyArray_DESCR(self)->elsize;
    }

    /* Changing the size of the dtype results in a shape change */
    if (newtype->elsize != PyArray_DESCR(self)->elsize) {
        /* forbidden cases */
        if (PyArray_NDIM(self) == 0) {
            PyErr_SetString(PyExc_ValueError,
                    "Changing the dtype of a 0d array is only supported "
                    "if the itemsize is unchanged");
            goto fail;