I mostly like Martin's suggested wording, but would also note that I filed issue 17960 to tighten up the requirements for when we expect assigning to locals() to work.

To save folks reading the whole referenced email, I think it would be worth defining that modifying the namespace returned by locals() will affect the runtime namespace at module and class scope and when using exec, but will have no effect at function scope (as locals() returns a copy of the namespace in that case).