[Python-3000] dict view operations

["Martin v. Löwis"]

>>> What use case are you thinking of that this would address?
>> It would allow to treat the items view as a proper set (which
>> it still is).
> 
> Can you give some examples?

You mean, actual applications where people would want to perform
set operations on .items()? No - I was just trying to give a
solution to the theoretical problem that Georg brought up.

> I can too easily think of examples that
> fail with this approach:
> 
> d = {1: 1, 2: 2}
> iv = set(d.items())
> (1, 1) in iv
> 
> The latter expression would be False, (while it currently is True),
> since (1,1) has a different hash value than Association((1, 1)).

Right. Since the elements in the view/set would not be plain
two-tuples, this would have to be spelled as

Association((1,1)) in iv

Of course, it violates the principle that things that compare equal
should also hash equal; to restore that principle, one would have
to make associations not compare equal to two-tuples (and then
not make them a subtype anymore, either).

Regards,
Martin