numpy element sum privous

1>>> a
2array([[1, 2, 3],
3       [4, 5, 6]])
4       
5>>> np.cumsum(a,axis=0)      # sum over rows for each of the 3 columns
6array([[1, 2, 3],
7       [5, 7, 9]])
8>>> np.cumsum(a,axis=1)      # sum over columns for each of the 2 rows
9array([[ 1,  3,  6],
10       [ 4,  9, 15]])
11