[Python-talk] Help with custom sort

[Kent Johnson]

Cole Tuininga wrote:
> Hey folks - I'm still a bit rusty here and could use some help.
> 
> I have a list of dictionaries that I want to sort based off of a key
> which I'll hypothetically call 'key'.  I figured that I'd just write a
> small little comparison function to hand to sort.

A better way to do this is with the key= parameter to sort(). The 
argument is a function that returns the proper key.

operator.itemgetter() is a factory that produces a function that will 
fetch an indexed item from its argument. So if I understand your problem 
you can do
   from operator import itemgetter
   dict_list.sort(key=itemgetter('key'))

More here:
http://personalpages.tds.net/~kent37/kk/00007.html

Kent

>  Something along the
> lines of:
> 
> dict_list = [<my list of dictionaries>]
> 
> def sort_func(x, y):
> 	<magic here>
> 
> dict_list.sort(sort_func)
> 
> The thing is, I'd like to just compare the two strings in sort_func and
> I can't remember the syntax.  In perl, I'd just do something like:
> 
> sub sort_func {
> 	return $a{'key'} cmp $b{'key'};
> }
> 
> The "cmp" function will take care of doing the string comparison and
> return the correct value of (-1, 0, 1).  Is there a similar thing in
> Python that I'm just forgetting?  Or am I stuck doing separate tests for
>> , =, and < ?
> 
> Thanks in forgetfulness....
>