I think he&#x27;s talking about PEP 0484. As I understand it they go into separate files and there is a gradual typing system. The inspiration came from mypy <a href="http:&#x2F;&#x2F;mypy-lang.org&#x2F;" rel="nofollow">http:&#x2F;&#x2F;mypy-lang.org&#x2F;</a> and the point is mainly for IDEs and convenience in development currently, though they could be used for optimizations in implementations other than the reference interpreter.