+1. People are still on Python 2.x. If you want safety, add a nice upgrade path so people can actually start using it easily on their existing codebases. Tag

+1. People are still on Python 2.x. If you want safety, add a nice upgrade path so people can actually start using it easily on their existing codebases. Tag the old API as potentially dangerous/unsafe/deprecated/ugly and warn (or error out if you can opt into a strict mode per-file) so people can upgrade incrementally without waiting for all their dependencies to first (who won't because they have no upgraded users), and without breaking all their tests in one mega-commit.