Either puzzle 4 has a bug in it or I'm losing my mind. (Possible answer to solution below, so don't read if you want to go in fresh)

    # FILL ME IN (roughly 2 lines)
    if local_i < size and local_j < size:
        out[local_i][local_j] = a[local_i][local_j] + 10

Results in a failed assertion:

     AssertionError: Wrong number of indices

But the test cell beneath it will still pass?