def Sum(a, axis, keep_dims):
    """
    Sum reduction op.
    """
    return np.sum(a, axis=axis if not isinstance(axis, np.ndarray) else tuple(axis),
                  keepdims=keep_dims),
def Sum ( a , axis , keep_dims ) : return np . sum ( a , axis = axis if not isinstance ( axis , np . ndarray ) else tuple ( axis ) , keepdims = keep_dims ) ,
Sum reduction op.