Retrieve Unique Values from gisdata

import arcpy
from arcpy import env

env.workspace = "c:/data"

patch_shp = "test.shp"

field = "GRIDCODE"

valueList = []

rows = arcpy.SearchCursor(patch_shp)
for row in rows:
    valueList.append(row.getValue(field))

uniqueSet = set(valueList)
uniqueList = list(uniqueSet)
uniqueList.sort()

del rows
del row

print uniqueList