> >>> my_string = "It might be 11:45 PM"
> >>> # ... many lines later ...
> >>> f"It is {hh}:{mm} {am_or_pm}" = my_string
>
> What are hh, mm, and am_or_pm now?  Do we raise an exception?  Do we run the line having no real idea whether they have been assigned at all? How do we even check whether an assignment took place?

You can get this with ANY unpacking form. I don't see how this is any different. In fact, this kind of usage - where the template is in the source code but the data comes from a variable - would be the normal