November 2021 The strange world of Python, as used by big investment banks High finance is a foreign country; they do things differently there Today will I take you through the keyhole to look at a group of software systems not well known to the public, which I call "Bank Python". Bank Python implementations are effectively proprietary forks of the entire Python ecosystem which are in use at many (but not all) of the biggest investment banks. Bank Python differs considerably from the common, or garden-variety Python that most people know and love (or hate). Thousands of people work on - or rather, inside - these systems but there is not a lot about them on the public web. When I've tried to explain Bank Python in conversations people have often dismissed what I've said as the ravings of a swivel-eyed loon. It all just sounds too bonkers. I will discuss a fictional, amalgamated, imaginary Bank Python system called "Minerva".…