Hello everyone. I created an issue on the mypy GitHub here, as I didn't know about this mailing list: https://github.com/python/mypy/issues/9472 I have been a Python programmer for 12 years now, and in my day-to-day job, I use TypeScript constantly now. The type checking in TypeScript is now very mature and quite easy to use, and I find myself every day wanting more for my back end Python code of what I already have for my front end TypeScript code. I think one lesson I've learned from my 3+ years of TypeScript use is that the TypeScript utility types are very useful, in particular the `Parameters` and `ReturnType` utility types, as documented here: https://www.typescriptlang.org/docs/handbook/utility-types.html#parametersty... Shantanu on GitHub was kind enough to point out that these utility types have been brought up before in a PEP, and rejected. See here: https://www.python.org/dev/peps/pep-0612/#defining-parametersof I believe it is worth reconsidering the efficacy of these utility types. As an end-user of TypeScript and Pyright, I can say that they make a lot of sense to me, and they are easy to explain to the people I train and manage. The specifics of how they are implemented I can't comment on, as I don't understand the full complexity of the Python type systems, but I can certainly say that they are obvious to the people I work with, and very useful, as we use them often in TypeScript code. The prior art on the part of TypeScript seems to indicate the utility types are useful as a general concept. I believe that if these utility types are implemented, they will form a part of solving the problem of how to correctly specify types for function decorators. Because it will be very easy to extract the parameters and return type of a Callable, you will be able to write a new type for a function that aliases one part and changes another part, such as using the same arguments for a function F as before, with a new return type, or the same return type as before, with a ParamSpec or list of arguments, etc. What does everyone else think about this topic?