Repeat last column in numpy array

One possible solution:

a = np.hstack((arr, np.tile(arr[:, [-1]], 2)))
print (a)
[[1 2 3 3 3]
 [0 0 0 0 0]
 [0 2 1 1 1]]

Broadcasting is often efficient.

import numpy as np

A = np.random.randint(0, 100, (1000, 1000))

np.hstack((A, np.broadcast_to(A[:, -1][:, None], (A.shape[1], n))))

Some benchmarking if performance is an issue:

n = 1000
%timeit np.hstack((A, np.broadcast_to(A[:, -1][:, None], (A.shape[1], n))))  # 3.06 ms
%timeit np.hstack((A, np.tile(A[:, [-1]], n)))                               # 9.33 ms
%timeit np.repeat(A, [1]*(A.shape[1]-1) +[n], axis=1)                        # 12.9 ms