This function can be used to remove duplicates from an ordered list.

>>> def remove_dupes(l):
...     return sorted(set(l))
...
>>> remove_dupes([1,1,2,3,4,4,4,5,7,8,8,9])
[1, 2, 3, 4, 5, 7, 8, 9]

Note that although sets don't have an order, they are iterable and can be passed to the sorted builtin method (which returns a list.)