how can I sort a bunch of lists over multiple fields?

[Steven Bethard]

James Stroud wrote:
> Oops, last one had a typo:
> 
> 
> a = ['bob', 'greg', 'cindy', 'alice']
> b = ['fred','barney','betty','wilma','pebbles','bambam']
> c = ['jed', 'granny', 'jethro', 'ellie-mae']
> d = ['bob','carol','ted','alice']
> 
> e = [a,b,c,d]
> 
> for ary in e:
>   print ary
> 
> e.sort(lambda x,y:cmp(x[1],y[1]))
> 
> for ary in e:
>   print ary
> 
> e.sort(lambda x,y:cmp(x[0],y[0]))
> 
> for ary in e:
>   print ary

I would probably use the key= argument instead of the cmp= argument. 
Not only is it easier, but it'll probably be faster too:

py> lst = [['bob', 'greg', 'cindy', 'alice'],
...        ['fred', 'barney', 'betty', 'wilma', 'pebbles', 'bambam'],
...        ['jed', 'granny', 'jethro', 'ellie-mae'],
...        ['bob', 'carol', 'ted', 'alice']]
py> import operator
py> lst.sort(key=operator.itemgetter(3))
py> lst
[['bob', 'greg', 'cindy', 'alice'], ['bob', 'carol', 'ted', 'alice'], 
['jed', 'granny', 'jethro', 'ellie-mae'], ['fred', 'barney', 'betty', 
'wilma', 'pebbles', 'bambam']]
py> lst.sort(key=operator.itemgetter(0))
py> lst
[['bob', 'greg', 'cindy', 'alice'], ['bob', 'carol', 'ted', 'alice'], 
['fred', 'barney', 'betty', 'wilma', 'pebbles', 'bambam'], ['jed', 
'granny', 'jethro', 'ellie-mae']]
py> lst.sort(key=operator.itemgetter(slice(2)))
py> lst
[['bob', 'carol', 'ted', 'alice'], ['bob', 'greg', 'cindy', 'alice'], 
['fred', 'barney', 'betty', 'wilma', 'pebbles', 'bambam'], ['jed', 
'granny', 'jethro', 'ellie-mae']]

Note that you can pass slice objects to operator.itemgetter, so the last 
example is like "key=lambda x: x[:2]".

STeVe