[Python-ideas] Unpacking a dict

Ethan Furman ethan at stoneleaf.us
Wed May 25 14:21:00 EDT 2016

On 05/25/2016 11:12 AM, Paul Moore wrote:
> On 25 May 2016 at 17:08, Ethan Furman wrote:

>> Here's a real-world use-case:  The main software app I support passes a
>> `values` dict around like the plague.  When doing interesting stuff I often
>> unpack some of the values into local variables as that reads better, types
>> better, and makes it easier to reason about the code (it's on 2.7 so for
>> that I'll have to use Random's  example).
>> So for me, unpacking a dict with friendly syntax would be useful, and
>> unpacking four or five keys from a 20-element dict will be far more useful
>> than having to unpack them all.
> Thanks. That's the sort of use case I thought might exist - and it
> sounds to me as if you'd get much more benefit from a syntax that
> allowed "partial" unpacking:
> {"a": x, "b": y} = dict(a=1, b=2, c=3)
> gives x=1, y=2 with no error.
> I can't think of a good example where Michael's original proposal that
> this would give a ValueError would be a better approach.

Agreed.  The ValueError approach would make this useless for me.


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