On Fri, Jul 10, 2020 at 1:28 PM Ronald Oussoren <ronaldousso...@mac.com> wrote:
> > > On 10 Jul 2020, at 14:08, Stestagg <stest...@gmail.com> wrote: > > >> Adding indexing to views adds another requirement to the dict >> implementation: >> > > Yes, that's the proposed change > > >> indexing for sequences at least suggests that access is O(1). >> > That makes it impossible to use, as an example, a linked list to preserve >> insertion order. >> > > The docs for the Sequence abc explicitly talk about situations where > index is not O(1), and say that while not ideal, this is valid (mentioning > linked-lists by name). > > > Its a quality of implementation issue. A sequence where item access is > not O(1) is not invalid, but surprising and likely to cause performance > problems because users tend to expect that item access is O(1). > Yes, as the docs say. But this has been raised a few times in the thread, and it orthogonal to the 'we may want to make arbitrary changes to how dicts work in the future' debate. > > > The current existing `dict` implementation does not support O(1) index > lookup from a view, (as discussed previously), so a change to linked-lists > would not change this runtime O characteristic. > > > The current views don’t support indexing at all, that’s the whole point of > this thread. > The intent of my statement was: The current implementation of dict does not allow any reasonable implementation of dict_keys/dict_values/dict_items with O(1) index behaviour. I.e. the performance scalability of any future changes to the dict_* types that add direct indexing is *not* likely to be adversely affected by changes to the implementation of dict(), unless somehow iteration in O(n) time becomes impossible.
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