Where typing is really useful, in my experience, is in an external API. Most heavily used libraries in most dynamic languages, not only Python, ought to have a

Where typing is really useful, in my experience, is in an external API. Most heavily used libraries in most dynamic languages, not only Python, ought to have assertions with type checks for parameters. In the external API calls to the lib. Inside of a lib you should have tests anyway, so type declarations shouldn't be important.