Question

So I have a working sorting algorithm in Python. (Its exact contents are irrelevant to this question.) It uses a list called ‘people’ containing class instances, and the function is hard-coded to sort that list by a specific attribute, ‘wealth’.

def my_sort(seq):
    # sorts by seq[n].wealth
    ...
my_sort(people)

Now, I’d like to generalize the function so I could sort by any attribute.

def my_sort2(seq, key):
    # sorts by seq[n].key
    ...
my_sort2(people, wealth)

But this, of course, throws an error, because it doesn’t know to consider ‘wealth’ as a class attribute. So, how is this possible to do?

Answer 1

You could pass the name of the attribute:

def my_sort2(seq, keyname):
    sort by getattr(seq[n], keyname)

my_sort2(people, 'wealth')

or a getter functor:

def my_sort2(seq, keyfunc):
    sort by keyfunc(seq[n])

my_sort2(people, operator.attrgetter('wealth'))

I prefer the latter approach as it is more generic. For example, it easily allows for computed keys.