[Python-Dev] Proposal: add odict to collections (original) (raw)

Cesare Di Mauro cesare at pronto.it
Sun Jun 15 08:20:22 CEST 2008

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.

Cesare

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