[Python-ideas] Fwd: Why do equality tests between OrderedDict keys/values views behave not as expected?

[Franklin? Lee]

So the issues are:

1. OrderedDict().values() does not implement __eq__. It uses object
equality, which means identity.
1a. dict().values() does not implement __eq__.

2. OrderedDict().keys().__eq__ does not respect order.

I'd argue that keys() should be ordered comparisons, and values()
could be. As a plus, this could be more efficient than unordered
comparisons, since it's just
    return all(x == y for x, y in zip(self.keys(), other.keys()))
instead of packing each into a set and comparing the sets. But what
would be the point of comparing values views?

On the other hand, I guess dict().values().__eq__ should stay
unimplemented. What would it mean? MultiSet comparison? Values in
general aren't even hashable, so they can't be stuck into a hash-based
set structure. Maybe explicitly make it NotImplemented.


On Thu, Dec 17, 2015 at 4:40 AM, Alexandre Figura
<ipipomme+python at gmail.com> wrote:
>
> Hi,
>
> I recently compared OrderedDict instances while writing unit tests, and
> discovered an interesting behavior. If I create two ordered dictionaries
> with the same keys/values in the same order, I observe that their values are
> not equal when I compare them.
>
> I recently asked a question about this on Stackoverflow:
> http://stackoverflow.com/questions/34312674/why-values-of-an-ordereddict-are-not-equal
>
> Moreover, another user observed that keys of ordered dictionaries are
> compared in an order insensitive way:
> http://stackoverflow.com/questions/34320600/why-does-the-ordereddict-keys-view-compare-order-insensitive
>
> Are there any reasons for such implementation choices? As it appears
> disturbing for many people, would it be possible to update these behaviors?
>
> Best Regards,
> Alexandre.
>
>
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