def _prod(sizes):
    """
    Product of tiny list of sizes. It is faster than numpy.prod and torch.prod.
        
        Parameter
        ---------
            sizes : list or tuple
                Size of inputs, output, or weights, usually 2/3/4 dimensions.

        Performance
        -----------
            profile : 20 it/s
            torch.prod : 500 it/s
            numpy.prod : 700 it/s
            _prod : 1500 it/s
    """
    ans = 1
    for s in sizes:
        ans *= s
    return ans