"Paul Rubin" <http://[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > "Steve R. Hastings" <[EMAIL PROTECTED]> writes: > > In the all() example, if there *are* no values in S, then none of the > > values can be != 0, and IMHO all() should return False. > > That goes against the usual meaning of "all" in, say, mathematical logic. > > Usually, "for all X in S, PRED(x) is true" means: > there does not exist X in S so that PRED(x) is false. > How do you get this "usually" stuff? I would agree that this is usually implemented as a short-circuited loop through the list, that breaks out at the first False value. But I would not be quick to equate "commonality of implementation" with "meaning".
> So, all(empty sequence) should be true. "should be"? Or "usually turns out to be"? To my mind, the *meaning* of all() is that every element in the list asserts True. But this is with an initial assumption that all() is False, unless I test every value and find them to be True. Since I assume False to begin with, I get no values in the list to contradict the assumption, and so all([]) returns False. It would seem that the resolution rests on which initial condition we choose, False or True. Perhaps we should consult a more formal mathematical resource for this. -- Paul "If it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic." -- http://mail.python.org/mailman/listinfo/python-list
