I'm quite supportive (+1) of the proposal to add numeric indexing to the
'dict_*' views.
Given that dictionaries are now ordered, it seems reasonable to look-up,
for example, keys by index,
One simple example of where this is surprising is in the following:
>>> random.choice({'a': 1,}.keys())
TypeError: 'dict_keys' object is not subscriptable
This could be 'fixed' with a simple hack in the `random.choice` code, bit
equally, implementing __getitem__ on `dict_*` types would enrich the
interface.
Several times now, I've had the need to 'just get any key/value' from a
large dictionary. I usually try first to run `var.keys()[0]` only to be
told that I'm not allowed to do this, and instead have to ask python to
make a copy of this datastructure with a different type, just so I can
perform the index operation. This is possible, but seems redundant, and
reinforces bad practices around creating copies of potentially large
structures.
Another use-cases is doing variations of reduce() over dictionaries, where
getting an initial value from the dict, and then performing operations over
the remaining items is much simpler to do with indexing on the views.
Steve
On Mon, Jun 29, 2020 at 1:27 PM Hans Ginzel <[email protected]> wrote:
> Thank you.
>
> On Fri, Jun 26, 2020 at 02:50:22PM -0300, Joao S. O. Bueno wrote:
> >On Fri, 26 Jun 2020 at 14:30, Hans Ginzel <[email protected]> wrote:
> >> thank you for making dict ordered.
> >> Is it planned to access key,value pair(s) by index? See
> >> https://stackoverflow.com/a/44687752/2556118 for example. Both for
> >> reading and (re)writing?
> >> Is it planned to insert pair(s) on exact index? Or generally to slice?
> See
> >> splice() in Perl, https://perldoc.perl.org/functions/splice.html.
> >> …
> >>
> >These are odd requirements.
> >
> >No - Python dictionaries are ordered, by order of insertion only, but one
> >can't generally do any manipulation by the numeric index of
> >a dictionary entry - and it will stay that way.
>
> That is fully corret to respect the _insertion_ order.
>
> >If you need such an hybrid data structure, you could just have
> >a list of tuples as data structure, and use collections.abc.MutableMapping
> >to provide a dict-like interface to it (an index for better than linear
> search).
> >
> >I could create such a data structure if you want,
>
> Thank you, I will write it myself.
> H.
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