with this code:

f"{b'def'}"

I get this from mypy:

On Python 3 '{}'.format(b'abc') produces "b'abc'", not 'abc'; use '{!r}'.format(b'abc') if this is desired behavior [str-bytes-safe]

That message doesn't make it clear whether there's any issue with my code, because it's about a different string formatting.
And if it is an issue, it doesn't tell me what formatted string literal to use if this is desired behavior.