Those aren't the only two options. Like GP I don't like f-strings, but there was something introduced before that: the format function.

  "The thing is {foo}, and also {foo} again".format(foo=x+y)

It also supports positional with empty {}. And like f-strings, you can put formatting information after a colon.

%-based printf-style did also have named variables like this but it seemed less known.