06.11.17 05:01, INADA Naoki пише:
FYI, Raymond's original compact dict (moving last item to slot used
for deleted item) will break OrderedDict. So it's not easy to implement
than it looks.
OrderedDict uses linked list to keep which slot is used for the key.
Moving last item will break it.
It means odict.__delitem__ can't use PyDict_DelItem anymore and
OrderedDict should touch internal structure of dict.
All this is implementation details. We did have little time for
coordinated changing dict and OrderedDict implementations before
releasing 3.6, and left existing coupling. This also prevents from
in-place compactization of dict items.
We could add a private flag to dict that denotes whether this dict is
ordered or no. The ordinal dict could be more compact, while OrderedDict
left ordered. And I like your issue31265.
The current dict implementation still is young. It takes several
optimizations in 3.7 (thank to you Inada) and AFAIK there are still not
merged patches. I would wait until it become more stable before making
change in language specification.
I think current OrderedDict implementation is fragile loose coupling.
While two object has different file (dictobject.c and odictobject.c),
OrderedDict depends on dict's internal behavior heavily.
It prevents optimizing dict. See comment here.
https://github.com/python/cpython/blob/a5293b4ff2c1b5446947b4986f98ecf5d52432d4/Objects/dictobject.c#L1082
I don't have strong opinion about what should we do about dict and OrderedDict.
But I feel PyPy's approach (using same implementation and just override
__eq__ and add move_to_end() method) is most simple.
I think that the coupling with dict and OrderedDict should be more
robust, but left private. Dict implementation should be aware of
OrderedDict and provide some private methods for using in OrderedDict,
but not restrict the optimization of unordered dicts.
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