Partially unpacking a sequence

[Paul McGuire]

<tkpmep at hotmail.com> wrote in message
news:1144352710.190839.165580 at z34g2000cwc.googlegroups.com...
> I have a list y
> >>>y
> ['20001201', 'ARRO', '04276410', '18.500', '19.500', '18.500',
> '19.500', '224']
>
> from which I want to extract only the 2nd and 4th item by partially
> unpacking the list. So I tried
> >>>a,b = y[2,4]
> Traceback (most recent call last):
>   File "<interactive input>", line 1, in ?
> TypeError: list indices must be integers
>
> Out of curiosity, I tried
> >>>a,b = y[2:4]
> >>>a
> '04276410'
> >>> b
> '18.500'
>
> Why does this work (to a point  - it gives me items 2 and 3, not 2 and
> 4 as I require) and not my first attempt? What is the right syntax to
> use when partially upacking a sequence?
>
> Thanks in advance
>
> Thomas Philips
>

a,b = y[2],y[4]

or

a,b = y[2:5:2]

or

a,b = ( y[i] for i in (2,4) )


-- Paul