Ten Million Users and Ten Years Later: Python Tutor's Design Guidelines for Building Scalable and Sustainable Research Software in Academia

Research software is often built as prototypes that never get widespread usage and are left unmaintained after a few papers get published. To counteract this trend, we propose a method for building research software with scale and sustainability in mind so that it can organically grow a large userbase and enable longer-term research. To illustrate this method, we present the design and implementation of Python Tutor (pythontutor.com), a code visualization tool that is, to our knowledge, one of the most widely-used pieces of research software developed within a university lab. Over the past decade, it has been used by over ten million people in over 180 countries. It has also contributed to 55 publications from 35 research groups in 13 countries. We distilled lessons from working on Python Tutor into three sets of design guidelines: 1) user experience design for scale and sustainability, 2) software architecture design for long-term sustainability, and 3) designing a sustainable software development workflow within academia. These guidelines can enable a student to create long-lasting software that reaches many users and facilitates research from many independent groups.