[Python-Dev] Subtle difference between f-strings and str.format()

[Chris Angelico]

On Thu, Mar 29, 2018 at 11:28 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> On Wed, Mar 28, 2018 at 06:27:19PM +0300, Serhiy Storchaka wrote:
>
>> The optimizer already changes
>> semantic. Non-optimized "if a and True:" would call bool(a) twice, but
>> optimized code calls it only once.
>
> I don't understand this. Why would bool(a) be called twice, and when did
> this change? Surely calling it twice would be a bug.
>
> I just tried the oldest Python 3 I have on this computer, 3.2, and bool
> is only called once.

Technically not bool() itself, but the equivalent. Here's some similar code: