Question

In Python 2.2 (don’t ask), what’s the neatest way to sort a list and remove duplicates?

I can obviously write a function that would sort() then iterate, but am wondering if there’s an idiomatic one-liner.

edit: The list is short, so efficiency is not a concern. Also, the elements are immutable.

Answer 1

For old python versions, and since you’re using strings, there’s no one-liner I can think of, but a pattern would probably be this, using dictionaries:

def sorted_uniq(your_list):
    table = {}
    for s in your_list:
        table[s] = None
    k = table.keys()
    k.sort()
    return k

Adapted from an ancient ActiveState code snippet thread that Alex Martelli himself wrote several comments on: http://code.activestate.com/recipes/52560/

A shorter way with list comprehensions:

def sort_uniq(alist):
   d = {}
   mod_list = [d.setdefault(i,i) for i in alist if i not in d]
   mod_list.sort()
   return mod_list

---

Aside from Steven’s neat (yet slightly unattractive) one liner, I think this heads toward the fewest lines and most idiomatic way of doing it with Python 2.2:

Thanks to Steven Rumbalski in the comments, the 2nd version can be condensed further with python’s zip function:

def sort_uniq(alist):
   mod_list = dict(zip(alist,alist)).keys()
   mod_list.sort()
   return mod_list

If list.sort() didn’t operate by side effect, we’d have a one liner. 😉