When convert two sets with the same elements to lists, are the lists always going to be the same?

[Peng Yu]

On Fri, May 4, 2012 at 12:43 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> On 5/4/2012 8:00 AM, Peng Yu wrote:
>>
>> On Fri, May 4, 2012 at 6:21 AM, Chris Angelico<rosuav at gmail.com>  wrote:
>>>
>>> On Fri, May 4, 2012 at 8:14 PM, Peng Yu<pengyu.ut at gmail.com>  wrote:
>>>>
>>>> Thanks. This is what I'm looking for. I think that this should be
>>>> added to the python document as a manifestation (but nonnormalized) of
>>>> what "A set object is an unordered collection of distinct hashable
>>>> objects" means.
>>>
>>>
>>> There are other things that can prove it to be unordered, too; the
>>> exact pattern and order of additions and deletions can affect the
>>> iteration order. The only thing you can be sure of is that you can't
>>> be sure of it.
>>
>>
>> I agree. My point was just to suggest adding more explanations on the
>> details in the manual.
>
>
> I am not sure how much clearer we can be in the language manual. The word
> 'unordered' means just that. If one imposes an arbitrary linear order on an
> unordered collection, it is arbitrary. It is frustrating that people do not
> want to believe that, and even write tests depending on today's arbitrary
> serialization order being deterministic indefinitely. There is a section
> about this in the doctest doc, but people do it anyway. I will think about a
> sentence to add.

You can just add the example that you posted to demonstrate what the
unordered means. A curious user might want to know under what
condition the "unorderness" can affect the results, because for
trivial examples (like the following), it does seem that there is some
orderness in a set.

set(['a', 'b', 'c'])
set(['c', 'b', 'a'])

-- 
Regards,
Peng