Indeed, numpy is awesome. I used to do my computational experimenting (some of them including neural networks) the plain way (using classic data structures, the languages' built-in arithmetic operators and functional facilities) in many different languages. Once I've tried Python with numpy my mind was blown, it's so much faster than anything. Now I feel like I enjoyed writing functional code more but given the performance difference I can hardly imagine coming back. So the very reason I use Python is performance.