def get_levels(self, arcs):
levels = set(map(lambda arc: arc["<STR_LIT:end>"] - arc["<STR_LIT:start>"], arcs))<EOL>return sorted(list(levels))<EOL>
Calculate available arc height "levels".
        Used to calculate arrow heights dynamically and without wasting space.

        args (list): Individual arcs and their start, end, direction and label.
        RETURNS (list): Arc levels sorted from lowest to highest.