Function PyArray_InitializeDatetimeCasts

numpy/core/src/multiarray/datetime.c:4085–4284

* This registers the castingimpl for all datetime related casts. */

 * This registers the castingimpl for all datetime related casts.
 */
NPY_NO_EXPORT int
PyArray_InitializeDatetimeCasts()
{
    int result = -1;

    PyType_Slot slots[3];
    PyArray_DTypeMeta *dtypes[2];
    PyArrayMethod_Spec spec = {
        .name = "datetime_casts",
        .nin = 1,
        .nout = 1,
        .casting = NPY_UNSAFE_CASTING,
        .flags = NPY_METH_SUPPORTS_UNALIGNED,
        .dtypes = dtypes,
        .slots = slots,
    };
    slots[0].slot = NPY_METH_resolve_descriptors;
    slots[0].pfunc = &time_to_time_resolve_descriptors;
    slots[1].slot = _NPY_METH_get_loop;
    slots[1].pfunc = &time_to_time_get_loop;
    slots[2].slot = 0;
    slots[2].pfunc = NULL;

    PyArray_DTypeMeta *datetime = PyArray_DTypeFromTypeNum(NPY_DATETIME);
    PyArray_DTypeMeta *timedelta = PyArray_DTypeFromTypeNum(NPY_TIMEDELTA);
    PyArray_DTypeMeta *string = PyArray_DTypeFromTypeNum(NPY_STRING);
    PyArray_DTypeMeta *unicode = PyArray_DTypeFromTypeNum(NPY_UNICODE);
    PyArray_DTypeMeta *tmp = NULL;

    dtypes[0] = datetime;
    dtypes[1] = datetime;
    if (PyArray_AddCastingImplementation_FromSpec(&spec, 1) < 0) {
        goto fail;
    }
    dtypes[0] = timedelta;
    dtypes[1] = timedelta;
    if (PyArray_AddCastingImplementation_FromSpec(&spec, 1) < 0) {
        goto fail;
    }

    /*
     * Casting between timedelta and datetime uses legacy casting loops, but
     * custom dtype resolution (to handle copying of the time unit).
     */
    spec.flags = NPY_METH_REQUIRES_PYAPI;

    slots[0].slot = NPY_METH_resolve_descriptors;
    slots[0].pfunc = &datetime_to_timedelta_resolve_descriptors;
    slots[1].slot = _NPY_METH_get_loop;
    slots[1].pfunc = &legacy_cast_get_strided_loop;
    slots[2].slot = 0;
    slots[2].pfunc = NULL;

    spec.name = "timedelta_and_datetime_cast";
    dtypes[0] = timedelta;
    dtypes[1] = datetime;
    if (PyArray_AddCastingImplementation_FromSpec(&spec, 1) < 0) {
        goto fail;