Replacing the values of an “L” shape section of a Python 2D numpy array

Question

Say I have the following 2d array:

[[a, a, a, a],
 [a, a, b, a],
 [a, a, b, a],
 [a, c, c, a],
 [a, a, a, a]]

And I want to transform it into the following:

[[a, a, a, a],
 [a, a, d, a],
 [a, a, d, a],
 [a, d, d, a],
 [a, a, a, a]]

I am currently doing it in 2 steps: like arr[1:4,2]=d and arr[3, 1:3]=d

Is there a way to do it in only one step, which would also not impact the performance?

Answer 1

Probably it is not possible, you can't get L shape in just on slicing, need at least 2 slicings to form an L.