On Fri, Sep 19, 2014 at 3:15 PM, Steven D'Aprano
<steve+comp.lang.pyt...@pearwood.info> wrote:
> However, as far as I am aware, there are no built-ins that will fail that
> test, yet. Although the iteration order of dicts and sets is arbitrary, I
> think that (at least to date) it will be the same order every time you
> iterate over the dict or set within a single run of the Python interpreter.
> (Provided the dict or set hasn't changed.)
>
> That's not a language guarantee though. It's an implementation detail. In
> principle, it could be different each time:
>
> s = set("abcd")
> list(s)
> => returns ['d', 'a', 'b', 'c']
> list(s)
> => returns ['c', 'a', 'd', 'b']Possibly for the set, but the dict is guaranteed some measure of stability: https://docs.python.org/3.4/library/stdtypes.html#dict-views """If keys, values and items views are iterated over with no intervening modifications to the dictionary, the order of items will directly correspond.""" Also, a little above: """ iter(d) Return an iterator over the keys of the dictionary. This is a shortcut for iter(d.keys()). """ So if iterating over d.keys() and then d.values() with no mutations is guaranteed to give the same order, then so is iterating over d.keys(), then d.keys(), then d.values(), and since there's no magic in iterating over d.values(), it logically follows that iterating over d.keys() twice will give the same order. But yes, it's conceivable that the set might change iteration order arbitrarily. I don't know of any good reason for it to, but it certainly isn't forbidden. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
