On Tue, 29 Nov 2022 at 01:33, Steven D'Aprano <st...@pearwood.info> wrote: > > On Mon, Nov 28, 2022 at 11:13:34PM +0000, Oscar Benjamin wrote: > > On Mon, 28 Nov 2022 at 22:56, Brett Cannon <br...@python.org> wrote: > > As I understand it, we could make sets ordered, but only at the cost of > space (much more memory) or time (slower) or both. > > I am sure that Guido is correct that **if** somebody comes up with a > fast, efficient ordered set implementation that doesn't perform worse > than the current implementation, we will happily swap to giving sets a > predictable order, as we did with dicts. (Practicality beats purity -- > even if sets are *philosophically* unordered, preserving input order is > too useful to give up unless we gain something in return.)
Let's split this into two separate questions: 1. Is it *innately* good that set order is non-deterministic? 2. Are there some other reasons why it is good to choose a model that implies *non-deterministic* set order? The answer to 1. is emphatically NO. In fact the question itself is badly posed: why are we even asking about "set order" rather than the benefits of determinism in general? If I want my code to be deterministic then that's just something that I want regardless of whether sets, dicts, floats etc are involved. As for point 2. the fact that sets are currently non-deterministic is actually a relatively new thing in Python. Before hash-randomisation set and dict order *was* deterministic but with an arbitrary order. That was only changed because of a supposed security issue with hash collisions. Prior to that it was well understood that determinism was beneficial (honestly I don't understand why I have to state this point explicitly: determinism is almost always best in our context). Please everyone don't confuse arbitrary order, implementation defined order and non-deterministic order. There is no reason why sets in Python need to have a *non-deterministic* order or at least why there shouldn't be a way to control that. There is no performance penalty in making the order *deterministic*. (If you think that there might be a performance penalty then you haven't understood the suggestion!) > > It would be useful to have a straight-forward way to sort a set into a > > deterministic ordering but no such feature exists after the Py3K > > changes (sorted used to do this in Python 2.x). > > `sorted()` works fine on homogeneous sets. It is only heterogeneous sets > that are a problem, and in practice, that usually means None mixed in > with some other type. That is of course precisely the context for this thread! -- Oscar _______________________________________________ Python-Dev mailing list -- python-dev@python.org To unsubscribe send an email to python-dev-le...@python.org https://mail.python.org/mailman3/lists/python-dev.python.org/ Message archived at https://mail.python.org/archives/list/python-dev@python.org/message/YGXJBLQOQBZL5ZTEPJ2V2B3KUCXDXSK2/ Code of Conduct: http://python.org/psf/codeofconduct/
