On Wed, 1 Jul 2020 at 05:36, Christopher Barker <python...@gmail.com> wrote:
>
> On Tue, Jun 30, 2020 at 11:55 AM Rhodri James <rho...@kynesim.co.uk> wrote:
>>
>> Don't get me wrong, if it's not going to cause performance issues I
>> think being able to index views would be great, but I don't think this
>> is the right way to justify it.
>
> I wasn't justifying it -- I was simply saying that no one ever specifically
> decided that we DIDN'T want to be able to index dict views -- when they were
> created, it simply wasn't an option. Now it is, so we need to rethink it.
>
> > if it's not going to cause performance issues
>
> I can't see how it could possibly *cause* performance issues. It isn't as
> great performance as we would like, but I think it's still as good, and
> probably much better, than any other way to accomplish the same thing.
If indexing is O(N) then repeated indexing can be a lot less efficient
e.g. if order is the same size as d then this is O(N):
items = list(d.items())
for n in order:
do_stuff(items[n])
If the items view itself is indexable with O(N) cost then you can
avoid constructing the list but the result is quadratic:
for n in order:
do_stuff(items[n])
Standard containers right now are all O(1) for indexing so I think it
would be surprising that quadratic behaviour could result from
indexing an object rather than making a copy of it.
--
Oscar
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