[Python-Dev] Proposal: add odict to collections

[Cesare Di Mauro]

In data 15 giugno 2008 alle ore 07:43:32, Raymond Hettinger <python at rcn.com> ha scritto:

> For an insertion order dictionary, there was also a question about
> how to handle duplicate keys.
>
> Given odict([(k1,v1), (k2,v2), (k1,v3)]), what should the odict.items() return?
>
>    [(k1,v3), (k2,v2)]
>    [(k2,v2), (k1,v3)]
>
> The first maintains the original sort order and is consistent with the usual
> idea that d[k]=v simply replaces the value but does not alter the hash table.
> It is a bit weird though because v3 appears earlier than v2 which was
> inserted earlier.  It's especially weird for keys that are equal but not
> identical: d[0]=v1  d[0.0]=v3.  Do you want 0.0 to remain associated
> with v3 or should the items list contain a pair that was not in the original
> insertion list, (0, v3)?
>
> The second one is a bit weird because a key "loses its place" whenever
> the value is updated.
>
> IIRC, previous discussions showed an interest in odicts but that
> there were a lot of questions of the specific semantics of the API.
> This would no doubt be compounded by attempts to emulate
> dict views. Regardless, there should probably be a PEP and
> alternate pure python versions should be posted on ASPN so people
> can try them out.
> post
>
>
> Raymond

The same problem happens with dictionary updates:

d = {}
d[k1] = v1
d[k2] = v2
d[k1] = v3

The last instruction just replaces the existing entry, so I'm +0 for the first result.

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