code: def get_levels(self, arcs):
          
          levels = set(map(lambda arc: arc["end"] - arc["start"], arcs))
          return sorted(list(levels))
docs: 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.