how to get subarray of matrix in python

say I have the following array j:

[[1, 2, 3, 4, 5], 
 [7, 7, 7, 6, 4], 
 [1, 1, 2, 0, 0]]

how can I get the subarray of 2×2 so the subarray would be:

[[1, 2], 
 [7, 7],]

intuitively I assumed j[0:2][0:2] would do the trick but I get:

[[1, 2, 3, 4, 5], [7, 7, 7, 6, 4]]

>Solution :

You need to explicitly say what you want from each row:

[r[0:2] for r in j[0:2]]