Issue seems to be silent incorrect behavior, what happens if you attempt to run python code containing f-strings using an older python version. Does it raise an exception? That's good! What happens now if you write code for 3.7 which takes advantage of the new ordering and someone grabs it from your repo and runs it using 3.2, it would happily give incorrect results and noone is the wiser.

If you expect this situation you can assert the language version.

But the whole point is that some developer won’t expect that someone would run their code on an older Python, isn’t it?