def unique(s):
    """returns the unique values of a list.

    Example Usage:
    
    >>> x=[1,1,2,3,4,4,5]
    >>> unique(x)
    [1, 2, 3, 4, 5]
    """
    n = len(s)
    if n == 0:
        return []

    u = {}
    for x in s:
        u[x] = 1

    return u.keys()