Introduction to Python for Computational Science and Engineering [pdf]
> As Python 2.x is still the default Python on many system and there are a fair number of research codes out there based on Python 2, we will use Python 2.x in this book.This is so unfortunate. Scientific computing is riddled with technical debt and starting with Python 2 today is fairly irresponsible. If you're already invested in Python 2 and have code/training written up, fine. But if you're learning it just now, as the book's audience obviously is, picking Python 3 should be a no brainer.