code: def get_zoom_levels(process_zoom_levels=None, init_zoom_levels=None):
      
      process_zoom_levels = _validate_zooms(process_zoom_levels)
      if init_zoom_levels is None:
          return process_zoom_levels
      else:
          init_zoom_levels = _validate_zooms(init_zoom_levels)
          if not set(init_zoom_levels).issubset(set(process_zoom_levels)):
              raise MapcheteConfigError(
                  "init zooms must be a subset of process zoom")
          return init_zoom_levels
docs: Validate and return zoom levels.