[Tutor] I can't work out how to sort lists of lists

[Corran Webster]

At 9:23 AM +1200 20/3/01, Phil Bertram wrote:
>Hi all,
>
>I have a list thus,
>
>a=[  (8,9,10), (1,2,3), (5,6,7)  ] 
>
>I wish to sort the list by the second element of each tuple.
>
>I can not seem to work out how to get the sort method's compare 
>function to work.
>
>Any ideas ?

Perhaps the simplest way is to define your own comparison function:

def cmpsecond(x, y):
   return cmp(x[1], y[1])

a.sort(cmpsecond)

should do the trick.  You can write it more concisely with a lambda as:

a.sort(lambda x, y: cmp(x[1], y[1]))

For more info on tricks you can use with custom comparison functions, 
see the Sorting Mini-HOWTO.

http://py-howto.sourceforge.net/sorting/sorting.html

Regards,
Corran