If you maintain a library, how can you innovate without breaking the projects that depend on it? Follow semantic versioning, add APIs conservatively, add parameters compatibly, use DeprecationWarnings and publish a deprecation policy, guide your users on how to upgrade, and make wise choices about when to break backwards compatibility. Slides can be found at: https://speakerdeck.com/pycon2019 and https://github.com/PyCon/2019-slides"