ndarray, select rows and columns

In [1]: import numpy as np

In [4]: arr = np.array( range(12)).reshape( 3, 4)

In [5]: arr
Out[5]: 
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])

In [6]: arr[0,:]
Out[6]: array([0, 1, 2, 3])

In [7]: arr[:,0]
Out[7]: array([0, 4, 8])