[Python-Dev] PEP 431 Updates

[Steven D'Aprano]

On 28/01/13 23:52, Antoine Pitrou wrote:
> Le Mon, 28 Jan 2013 22:31:29 +1000,
> Nick Coghlan<ncoghlan at gmail.com>  a écrit :
>>
>>>> 6. Under "New collections"
>>>>
>>>> Why both lists and sets?
>>>
>>> Because pytz did it. But yes, you are right, an ordered set is a
>>> better solution. Baseing it on OrderedDict seems like a hack,
>>> though. I could implement a custom orderedset, of course.
>>
>> Sets themselves have an honourable history of just being a thin
>> wrapper around dictionaries with all the values set to None (although
>> they're not implemented that way any more). Whether you create an
>> actual OrderedSet class, or just expose the result of calling keys()
>> on an OrderedDict instance is just an implementation detail, though.
>
> Why the complication? Just expose a regular set and let users call
> sorted() if that's what they want.

An OrderedSet is not a sorted set.

An OrderedSet, like an OrderedDict, remembers *insertion order*, it does
not automatically sort the keys. So if datetime needs an ordered set, and
I have no opinion on whether or not it really does, calling sorted() on a
regular set is not the solution.


-- 
Steven