[Python-Dev] Re: syntactic shortcut - unpack to variably sized list

[Nick Coghlan]

Terry Reedy wrote:
> "Carlos Ribeiro" <carribeiro at gmail.com> wrote in message 
> news:864d37090411190724440dfe38 at mail.gmail.com...
> 
>>For more than a few arguments, it seems to be silly to require the
>>user to write it as:
>>a,b,c,d,e = t[0],t[1],t[2],t[3],t[4:]
> 
> 
> and also impossible.
> 
>>>>t=range(10)
>>>>a,b,c,d=t[:4]; e=t[4:]
>>>>a,b,c,d,e
> 
> (0, 1, 2, 3, [4, 5, 6, 7, 8, 9])

Hmm. . .

_>>>t = range(10)
_>>>a, b, c, d, e = t[:4] + [t[4:]]
_>>>a, b, c, d, e
_(0, 1, 2, 3, [4, 5, 6, 7, 8, 9])

So this actually can scale (sort of) to longer tuples.

Anyway, I don't have any real objection to iunpack. If it was designed to work 
on any iterator (return the first few elements, then return the partially 
consumed iterator), I'd be +1 (since, as Carlos pointed out, slicing doesn't 
work for arbitrary iterators).

Something like:

_>>>def iunpack(itr, numitems, defaultitem=None):
_...    for i in range(numitems):
_...        try:
_...            yield itr.next()
_...        except StopIteration:
_...            yield defaultitem
_...    yield itr

_>>> g = (x for x in range(10))
_>>> a, b, c, d, e = iunpack(g, 4)
_>>> a, b, c, d, e
_(0, 1, 2, 3, <generator object at 0xa0cd02c>)

_>>> a, b, c, d, e = iunpack(g, 4)
_>>> a, b, c, d, e
_(4, 5, 6, 7, <generator object at 0xa0cd02c>)

_>>> a, b, c, d, e = iunpack(g, 4)
_>>> a, b, c, d, e
_(8, 9, None, None, <generator object at 0xa0cd02c>)

Cheers,
Nick.
I think we're now to the stage of violently agreeing with each other. . .

-- 
Nick Coghlan               |     Brisbane, Australia
Email: ncoghlan at email.com  | Mobile: +61 409 573 268