Start emacs with `emacs -Q`, press C-x C-f and type in a filename that
ends in .py like "foo.py". Then type in:
x = 3
rf"hello {x} world"
The whole string will be colored as a string literal. r means "raw" which means no escape sequences and f means this is a format string where we can interpolate variables like x. Delete the leading 'r' and the highlighting will change so that {x} is not highlighted, since it's code. However, raw and format strings are not mutually exclusive and it should be considered code in both cases. If you run the snippet above in the interpreter you will get "hello 3 world".
In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.16.0, Xaw3d scroll bars)
of 2021-05-14 built on eruv
Repository revision: efc24f1e0bb127481bcc9c3054c57c4cd3c99aa9
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.6 LTS