If `x` is of a signed integer type, then the output type
    is the default platform integer:

    >>> x = np.array([1, 2, 3], dtype=np.int8)
    >>> np.prod(x).dtype == int
    True

    You can also start the product with a value other than one:

    >>> np.prod([1, 2], initial=5)
    10
    r&