... lyr = arcpy.mapping.ListLayers(mxd, 'layer_name_in_mxd)[0] if lyr.supports('SYMBOLOGY'): lyr.symbology.valueField = field_name lyr.symbology.classBreakValues = [0, 0.01, 0.05, 0.5, 0.75, 1] lyr.symbology.classBreakLabels = ['<1%', '1-5%', '5-50%', '50-75%', '>75%'] ... arcpy.RefreshActiveView()
... with arcpy.da.SearchCursor(lyr, (field_name)) as cur: max_v = max([v[0] for v in cur]) ... if lyr.supports('SYMBOLOGY'): lyr.symbology.valueField = field_name lyr.symbology.classBreakValues = [0, 0.01 * max_v, 0.05 * max_v, 0.5 * max_v, 0.75 *max_v, max_v] ... arcpy.RefreshActiveView()