It's a regression as far as code readability goes for fairly straightforward reasons: almost everything in Matlab is a matrix. Matrices are not first class citizens in Python, and it matters. I use Python a hell of a lot more than Matlab, but for examining how an algorithm works (say, for implementing in another language or modifying it to do tricks), Matlab wins. Go look at these PRML collections in Python and Matlab and see if you disagree: