def set_to_interval_set(s):
    """ Convert python set to interval set

    >>> set_to_interval_set(set())
    []
    >>> set_to_interval_set({1, 2, 5, 7, 9, 10, 11})
    [(1, 2), (5, 5), (7, 7), (9, 11)]
    """
    intervals = []
    l = list(s)
    l.sort()
    if len(l) > 0:
        i = 0
        current_interval = [l[i], l[i]]
        i += 1
        while i < len(l):
            if l[i] == current_interval[1] + 1:
                current_interval[1] = l[i]
            else:
                intervals.append(tuple(current_interval))
                current_interval = [l[i], l[i]]
            i += 1
        if current_interval not in intervals:
            intervals.append(tuple(current_interval))
    return intervals
