Message 250541 - Python tracker

I'll probably ensure that all of the parsing errors contain "format string" or "f-string" or similar. That way the regex check is easier, and the user can search for it more easily.

It remains to be seen how these are referenced in the documentation. "f-string" seems much easier to say and search for, but seems too slangy for the docs. But "format string" seems ambiguous and hard to search for. I guess time will tell.