Steven D'Aprano <steve+pyt...@pearwood.info> added the comment:
> My confusion stems from the fact that I expected the unpacking of a
> set to return the same output as that obtained from the unpacking of a
> list.
Why did you expect that?
Sets aren't lists. Lists are ordered, so they hold their items in a
specific order. Sets are unordered, so there is no guarantee what order
you will see when you unpack them.
If you create the list [foo, bar, baz] then the output will always be
[foo, bar, baz] on every platform. That's a guarantee.
Sets are unordered, as documented, so there are no guarantee about what
order you will see: it might be {foo, baz, bar} or {bar, baz, foo} or
{foo, bar, baz} or {baz, foo, bar}, any permutation is equally valid,
regardless of what order you created the set.
> 1. repr is apparently platform-dependent
Quite likely. Since there's no guarantee what order you will see,
there's no guarantee that the order won't change from platform to
platform, or version to version.
> 2. Testing reviewer's assertion: "The specific order you see will
> depend on the specific values in the set, as well as the order that
> they were inserted, deleted, and/or re-inserted in some arbitrary
> way."
> This counter example, where element 0 is moved to the second position,
> shows that there is not such order dependence:
Your example shows that the output order changes when you change the
input order, in an unpredicatable, arbitrary way, just like I said.
That's not a counter-example.
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue38853>
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