sorted unique elements from a list; using 2.3 features

[Skip Montanaro]

    >>> input=[5, 3, 1, 2, 5, 4, 3, 4, 1, 1, 5, 4, 5, 1, 4, 3, 2, 2, 4, 1]
    >>> output=dict( zip(input ,range(len(input)) ) ).keys()
    >>> output
    [1, 2, 3, 4, 5]

    Peter> I always got a sorted output.

You just got lucky.  Perturb your input list a tad:

    >>> input=[5, -1, 1, 2, 5, 4, 3, 4, 1, 1, 5, 4, 5, 1, 4, 3, 2, 2, 4, 1]
    >>> output=dict( zip(input ,range(len(input)) ) ).keys()
    >>> output
    [1, 2, 3, 4, 5, -1]

Skip