On Tue, Feb 23, 2016 at 11:08 AM, Jon Ribbens <jon+use...@unequivocal.co.uk> wrote: > On 2016-02-22, Steven D'Aprano <st...@pearwood.info> wrote: >> On Tue, 23 Feb 2016 05:48 am, Marko Rauhamaa wrote: >>> Jon Ribbens <jon+use...@unequivocal.co.uk>: >>>> I was under the impression that the point of UUIDs is that you can be >>>> *so* confident that there won't be a collision that for all practical >>>> purposes it's indistinguishable from being certain. >>> >>> Yes, if you generate a random 128-bit number, it will be unique -- >> >> If you generate a second random 128 bit number, you have a chance of 1 in >> 2**128 of a collision. All you can say is that it will be *very probably* >> unique. (I might even allow "almost certainly" unique.) > > If you are not prepared to say that something with a > 340282366920938463463374607431768211455 / > 340282366920938463463374607431768211456 chance of being true > is not "certainly true" then I'm not sure how you would not > be too scared to ever leave the house. Or not leave the house. > I mean, you're probably going to be hit by 10^25 meteorites, > which sounds painful. > >> If you generate 2**128 + 1 such numbers, you are *guaranteed* to > > ... have expired due to the heat death of the universe.
Maybe... but by the time you get to 2**64 of them, you have a 50% chance of a collision. (That's either utterly intuitive or completely counter-intuitive, depending on who you are.) ChrisA -- https://mail.python.org/mailman/listinfo/python-list
