[Serhiy Storchaka <storchaka@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).