On 29 March 2018 at 08:09, Tim Delaney <timothy.c.delaney@gmail.com> wrote:
On 29 March 2018 at 07:39, Eric V. Smith <eric@trueblade.com> wrote:
I’d vote #3 as well.

> On Mar 28, 2018, at 11:27 AM, Serhiy Storchaka <storchaka@gmail.com> wrote:
> There is a subtle semantic difference between str.format() and "equivalent" f-string.
>    '{}{}'.format(a, b)
>    f'{a}{b}'
> In most cases this doesn't matter, but when implement the optimization that transforms the former expression to the the latter one ([1], [2]) we have to make a decision what to do with this difference. 

Sorry about that - finger slipped and I sent an incomplete email ...
If I'm not mistaken, #3 would result in the optimiser changing str.format() into an f-string in-place. Is this correct? We're not talking here about people manually changing the code from str.format() to f-strings, right?

I would argue that any optimisation needs to have the same semantics as the original code - in this case, that all arguments are evaluated before the string is formatted.

I also assumed (not having actually used an f-string) that all its formatting arguments were evaluated before formatting.

So my preference would be (if my understanding in the first line is correct):

1: +0
2a: +0.5
2b: +1
3: -1

Tim Delaney