[Tutor] help with slice

[Alan Gauld]

"washakie" <washakie at gmail.com> wrote

> Could someone please explain 'slices' also for dictionaries?

So far as I know slices don;t work for dictionaries directly - 
dictionaries
don't have the concept of order. However you could get a list of
keys and apply a slice to that, although I'm not sure how it
would ever be useful.

> basically, I'd like to know how you would call every 3rd element in 
> a list
> of lists...
>
> My logic says: ThirdElems=List[:][2]
> Which to me reads, for every item in List (which are lists), return 
> the
> third item.but this doesn't work.

This actually says take a copy of the list and give me
the 3rd element of that copy.

You need to use a list comprehension:

thirds = [sublist[2] for sublist in myList]

HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
Temorarily at:
http://uk.geocities.com/alan.gauld@btinternet.com/
Normally:
http://www.freenetpages.co.uk/hp/alan.gauld