Why aren't OrderedDicts comparable with < etc?

[Mark]

On 16 July, 10:21, Piet van Oostrum <p... at cs.uu.nl> wrote:
> >>>>> Mark <l... at qtrac.plus.com> (M) wrote:
> >M> You are right that it doesn't make sense to compare two dicts.
> >M> But OrderedDicts can be viewed logically as lists of (key,value)
> >M> tuples so they are much more like lists or tuples when it comes to
> >M> comparisons.
> >M> For example:
> >>>>> l = [("a", 1), ("z", 2), ("k", 3)]
> >>>>> l1 = l[:]
> >>>>> l1[1] = ("z", 5)
> >>>>> l < l1
> >M> True
> >M> But if you do:
> >>>>> d = collections.OrderedDict(l)
> >>>>> d1 = collections.OrderedDict(l1)
> >M> You can't use <, <=, =>, or >, even though ordered dictionaries
> >M> preserve the order and their items are just as comparable as those in
> >M> a list or tuple of tuples.
>
> But why should the order be as if the OrderedDict was a list of tuples.
> A dict can be considered as a mapping and then you might want to treat
> either the key or the value as contravariant (the key I guess). So there
> is ambiguity. Why would the view as a list of tuples for the ordering be
> the `natural' view?
>
> Maybe you may expect some kind of monotonicity such that d1<d2 implies
> d1[x]<d2[x], but that doesn't work for d1 = {1:10, 2:20} and d2 = {1:15,
> 2:5}. So maybe there is only a partial ordering?

OK, that seems to me to be a convincing argument against supporting
ordering.