unary star

[VanL]

I like this idea -- I frequently find myself in situations where I want 
to take only the first item from a list.  (I usually reverse the list, 
and then pop() it.)

I would vastly prefer a

first, *rest = some_list

type syntax.

> At first blush, I like the idea of unary * being more widely
> applicable.
> 
> I see one difficulty: what if you want to expand a sequence of
> sequences?  That is, what if you have
>     S = ((c, d), (e, f))
> and want to produce
>     (a, b, c, d, e, f)
> ?  If unary * worked, this would (I presume) be
>     (a, b, **S)
> which looks misleadingly like the **kwargs syntax.  A reader might
> expect that S is a dict.  Moreover, you couldn't use this in a
> function call; you'd have to add whitespace: * *S.  Ick.
> 

Here is the way out of that difficulty: make the unary ** only 
applicable to dicts.  Expanding a nested list would require a paren.

Examples:

mylist = [1,2,3]
mytuple = (1,2,3)
mydict = {'1': 1, '2': 2, '3':3}
mynestedlist = [[1,2], [3,4]]

first, *rest = mylist
print first, rest, mylist
1 [2,3] [2,3]

first, *rest = mytuple
print first, rest, mytuple
1 (2,3) (1,2,3)

first, *rest = mydict
SyntaxError: Unary * not supported for dict

enumerated = **mydict
print enumerated
[('1', 1), ('2', 2), ('3', 3)]

**mynestedlist
SyntaxError: Unary ** not supported for list

*mynestedlist
[1,2] [3,4]

*(*mynestedlist)
[1,2,3,4]


Just some ideas.  I think that this might even be worthy of a PEP?

VanL