[Python-ideas] Enhancing dict.values

[Guido van Rossum]

On Thursday, May 26, 2016, Steven D'Aprano <steve at pearwood.info> wrote:

> I think this is important enough to get a change in subject line, lest
> it be lost in the dict unpacking thread.
>
>
> On Thu, May 26, 2016 at 11:28:25PM +0100, Nathan Schneider wrote:
>
> > Instead of special syntax, what if dict.values() returned a tuple when
> > given keys as arguments:
> >
> >    partner_id, product_id, ship_to, product_ids = my_dict.values(
> >            'partner_id', 'product_id', 'ship_to', 'product_ids')
> >
> > That avoids repeating the dict variable, at least. And as there is
> > dict.update(), I don't see the need for a new syntax for assigning to
> > multiple keys.
>
> I like this idea. I think it beats the status quo:
>
> partner_id = my_dict['partner_id']
> product_id = my_dict['product_id']
> # etc.
>
> and the various "dict unpacking" syntax suggested, e.g.:
>
> {'partner_id': partner_id, 'product_id': product_id, **catch_all} = my_dict
>
>
> and it's less magical than variants that extract the names from the left
> hand side:
>
> partner_id, product_id, ship_to, product_ids = **my_dict
>
> It naturally and trivially supports the case where assignment targets
> aren't names, and where keys are not identifiers:
>
> obj.partner_id, products[the_id] = my_dict.values('partner id', 'is')
>
> It's still a bit repetitive in the simple case where the keys are the
> same as the variable names, but without compiler magic, what else are
> you going to do?
>
> +1
>

Interesting. It should probably have a different name. What type should it
return? Iterator? Sequence? It can't really be a ValuesView because that
class is just a view on the hash table. Even though you technically *could*
combine this functionality into values(), I don't think it would be helpful
to do so -- if only because of the surprising edge case where if you were
to pass it a list of keys to extract using **args, if the list is empty,
values() would default to its original behavior or returning all keys, in
hash table order.

--Guido
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