Function PyArray_FromIter

numpy/core/src/multiarray/ctors.c:3800–3949

NUMPY_API * * steals a reference to dtype (which cannot be NULL) */

 * steals a reference to dtype (which cannot be NULL)
 */
NPY_NO_EXPORT PyObject *
PyArray_FromIter(PyObject *obj, PyArray_Descr *dtype, npy_intp count)
{
    PyObject *iter = NULL;
    PyArrayObject *ret = NULL;
    npy_intp i, elsize, elcount;

    if (dtype == NULL) {
        return NULL;
    }

    iter = PyObject_GetIter(obj);
    if (iter == NULL) {
        goto done;
    }

    if (PyDataType_ISUNSIZED(dtype)) {
        /* If this error is removed, the `ret` allocation may need fixing */
        PyErr_SetString(PyExc_ValueError,
                "Must specify length when using variable-size data-type.");
        goto done;
    }
    if (count < 0) {
        elcount = PyObject_LengthHint(obj, 0);
        if (elcount < 0) {
            goto done;
        }
    }
    else {
        elcount = count;
    }

    elsize = dtype->elsize;

    /*
     * Note that PyArray_DESCR(ret) may not match dtype.  There are exactly
     * two cases where this can happen: empty strings/bytes/void (rejected
     * above) and subarray dtypes (supported by sticking with `dtype`).
     */
    Py_INCREF(dtype);
    ret = (PyArrayObject *)PyArray_NewFromDescr(&PyArray_Type, dtype, 1,
                                                &elcount, NULL,NULL, 0, NULL);
    if (ret == NULL) {
        goto done;
    }

    char *item = PyArray_BYTES(ret);
    for (i = 0; i < count || count == -1; i++, item += elsize) {
        PyObject *value = PyIter_Next(iter);
        if (value == NULL) {
            if (PyErr_Occurred()) {
                /* Fetching next item failed perhaps due to exhausting iterator */
                goto done;
            }
            break;
        }

        if (NPY_UNLIKELY(i >= elcount) && elsize != 0) {