[Python-ideas] Generator unpacking

[Jared Grubb]

> On Feb 14, 2016, at 10:57, Georg Brandl <g.brandl at gmx.net> wrote:
> 
> On 02/14/2016 08:43 AM, Nick Coghlan wrote:
>> On 14 February 2016 at 07:40, Greg Ewing
>> <greg.ewing at canterbury.ac.nz
>> <mailto:greg.ewing at canterbury.ac.nz>> wrote:
>> 
>> 
>>    Another possibility is
>> 
>>       a, b, ... = value
>> 
>> 
>> Now, *that* spelling to turn off the "implicit peek" behaviour in iterable
>> unpacking I quite like.
>> 
>>    arg_iter = iter(args)
>>    command, ... = arg_iter
>>    run_command(command, arg_iter)
>> 
> 
> Assigning to Ellipsis?  Interesting idea, but I'd probably go a bit further
> in the similarity to star-assignment:
> 
>    a, b, *... = value
> 
> Ellipsis could then be a general "throw-away" lvalue.  This would make it
> possible to say
> 
>    a, ..., b, ... = some_function()
> 
> i.e. skip exactly one item in unpacking.

That looks harder to read than what you can currently do:

    a, _, b, _ = some_function()

But I do like the asterisk+ellipsis.

>> Although again, the main downside would be that "..." here means something
>> rather different from what it means as a subscript element.
> 
> Keep in mind that Ellipsis is also a legal rvalue anywhere else.  I.e.
> this would be legal (and a no-op):
> 
>    ... = ...
> 
> But thinking about it, this is also legal at the moment:
> 
>    [] = []
> 
> Interestingly, this raises:
> 
>    () = ()
> 
> cheers,
> Georg
> 
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