The problem of chapter A3.1

[MaxforCherubim]

The trick can not work:

def demean_axis(arr, axis):

    means = arr.mean(axis)
    indexer = [slice(None)] * arr.ndim
    indexer[axis] = np.newaxis
    
    return arr - means[indexer]

Here is the way to figue out:

def demean_axis(arr, axis):

    means = arr.mean(axis)
    indexer = [slice(None)] * arr.ndim
    indexer[axis] = np.newaxis
    
    return arr - means[*indexer]