[Python-ideas] Unpacking a dict

[Paul Moore]

On 25 May 2016 at 14:11, Michael Selik <michael.selik at gmail.com> wrote:
> Clojure also supports mapping destructuring. Let's add that to Python!
>
>     py> mapping = {"a": 1, "b": 2, "c": 3}
>     py> {"a": x, "b": y, "c": z} = mapping
>     py> x, y, z
>     (1, 2, 3)
>     py> {"a": x, "b": y} = mapping
>     Traceback:
>     ValueError: too many keys to unpack
>
>
> This will be approximately as helpful as iterable unpacking was before PEP
> 3132 (https://www.python.org/dev/peps/pep-3132/).

Neither this, nor the **rest extension you proposed, does what I think
would be the most common requirement - get a set of elements and
*ignore* the rest:

>>> mapping = {"a": 1, "b": 2, "c": 3}
>>> {"a": x, "b": y} = mapping
>>> # Note no error!
>>> x, y, z
(1, 2)

I'd still like to see some real-world use cases though - there are
lots of options as the above example demonstrates, and nothing to
guide us in deciding which would be the most useful one to choose.

Paul