Slicing a NumPy matrix in Python

Question

import numpy as np
A = np.array([[1, 4, 5, 12, 14],
[-5, 8, 9, 0, 17],
[-6, 7, 11, 19, 21]])
print(A[1,])
print(A[,1])

OUTPUT:
[-5 8 9 0 17]
error

Why the second statement is wrong ?

Answer 1

Because there is a comma after nothing thus program assumes it is safest to raise an error.
You can fix it by replacing the "nothing" with ":":
print(A[:, 1])

Anyways that was not slicing.