Typing is a keystone of modern Python and the foundation of many new and exciting projects in the Python ecosystem, but millions of lines of existing code do not take full advantage of typing capabilities. How can typing add value to those codebases and support the teams working on them?

This talk explores how adding type annotations to existing code - with no other changes! - can offer an entry point and a hand up, from helping engineers engage with unfamiliar applications to planning refactors. We'll explore real examples from a production code base, see how typing existing code can be implemented as a practice, and highlight the benefits adopting this mode of engagement can offer an engineering team.