[Python-ideas] Indicate if an iterable is ordered or not

[Guido van Rossum]

What do you want to do with this knowledge?

On Tue, Sep 24, 2013 at 9:15 AM, Eric Snow <ericsnowcurrently at gmail.com> wrote:
> Iterables are not necessarily ordered (e.g. dict vs. OrderedDict).
> Sequences are but Sets aren't.  I'm not aware of any good way
> currently to know if an arbitrary iterable is ordered.  Without an
> explicit indicator of ordered-ness, you must know in advance for each
> specific type.
>
> One possible solution is an __isordered__ attribute (on the class),
> set to a boolean.  The absence of the attribute would imply False.
>
> Such an attribute would be added to existing types:
>
> * collections.abc.Iterable (default: False)
> * list (True)
> * tuple (True)
> * set (False)
> * dict (False)
> * collections.OrderedDict (True)
> * ...
>
> Thoughts?
>
> -eric
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-- 
--Guido van Rossum (python.org/~guido)