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

[Tim Peters]

[Serhiy Storchaka <storchaka at gmail.com>]
> ...
> This is not new. The optimizer already changes semantic.
> Non-optimized "if a and True:" would call bool(a) twice, but optimized code
> calls it only once.

I have a hard time imaging how that could have come to be, but if it's
true I'd say the unoptimized code was plain wrong.  The dumbest
possible way to implement `f() and g()` is also the correct ;-) way:

result = f()
if not bool(result):
    result = g()

For the thing you really care about here, the language guarantees `a`
will be evaluated before `b` in:

    '{}{}'.format(a, b)

but I'm not sure it says anything about how the format operations are
interleaved.  So your proposed transformation is fine by me (your #3:
still evaluate `a` before `b` but ignore that the format operations
may occur in a different order with respect to those).