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
