def set_difference(in_this_set1, but_not_in_this_set2):
    """**set_difference(in_this_set, but_not_in_this_set)** -> Returns the elements that are in the set1 but not on the set2

<code>
    Example:

        set_difference(set([1, 2, 3, 4]), set([2, 3]))

    Returns:

        set([1, 4])

</code>

    """
    s1 = set(in_this_set1)
    s2 = set(but_not_in_this_set2)
    return s1.difference(s2)