On Mon, Jun 29, 2020 at 11:57 AM Stestagg <stest...@gmail.com> wrote:
> 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,
>
My first thought was no -- even though dicts are ordered, they really
aren't a Sequence in the same way.
But making the various dict sequences does add some convenience, and I
can't see how it would cause any problems.
As it happens, I have run into the use cases @Stestagg presents.
But I'm curious -- what do people see as the downsides? I'm not coming up
with any.
Note: there may be implementation issues -- you couldn't really do it
efficiently without poking in to the inner workings of the dict object, but
I imagine that's surmountable.
> 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.
the other solution to that is to call iter() and next():
In [2]: a_dict
Out[2]: {0: 5, 1: 6, 2: 7, 3: 8, 4: 9}
In [3]: next(iter(a_dict.items()))
Out[3]: (0, 5)
But yeah, that's pretty klunky -- and gets quite inefficient if you want
something other than the first one.
-CHB
> 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 <h...@matfyz.cz> 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 <h...@matfyz.cz> 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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--
Christopher Barker, PhD
Python Language Consulting
- Teaching
- Scientific Software Development
- Desktop GUI and Web Development
- wxPython, numpy, scipy, Cython
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