Update Cursor for Rasters?

Question

Hi,
I'm trying to use python to add a field and add some text for an attribute class. Funny thing is (actually not so funny) update cursor returns an error and destroys my raster!import arcpy
#import os
from arcpy.sa import *
from arcpy import env
arcpy.CheckOutExtension("Spatial")
arcpy.env.overwriteOutput = True

WScom4_rc = "X:\DATA\watershed_100mbuf_lc_8class.img"

arcpy.AddField_management(WScom4_rc, "Class_Name", "TEXT")
rows = arcpy.UpdateCursor(WScom4_rc)
for row in rows:
    if row.Value == 1:
        row.Class_Name = "Forest"
        rows.updateRow(row)
    if row.Value == 2:
        row.Class_Name = "Developed"    
        rows.updateRow(row)
    if row.Value == 3:
        row.Class_Name = "Fields/Pastures"
        rows.updateRow(row)
    if row.Value == 4:
        row.Class_Name = "Wetlands"    
        rows.updateRow(row)
    if row.Value == 5:
        row.Class_Name = "Water"
        rows.updateRow(row)
    if row.Value == 6:
        row.Class_Name = "Barren/Soil"    
        rows.updateRow(row)
    if row.Value == 7:
        row.Class_Name = "Open Space"
        rows.updateRow(row)
    if row.Value == 8:
        row.Class_Name = "Deforested"    
        rows.updateRow(row)
    if row.Value == 9:
        row.Class_Name = "Ice/Snow/Shadow (unclassified)"    
        rows.updateRow(row)

Here is the error code: 
Traceback (most recent call last):
  File "X:\DATA\FloodRisk2_Canada\02_Source_Data\2_Working_Source_Data\Goulds_working\FloodVul_process_script1_goulds.py", line 74, in <module>
    row.Class_Name = "Forest"
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\arcobjects\_base.py", line 35, in __setattr__
    return setattr(self._arc_object, attr, ao)
RuntimeError: ERROR 999999: Error executing function.

The input raster has a normal raster attribute table: Rowid, value, count.
The output is an empty raster where the attribute table contains Rowid, value, count, and Class, but no rows (no data).

Can update cursor be used for editing raster attributes? If so, How?

Thanks!

Rich

jskinner · Answer

Hi Rich,

I ran the same code that you posted.  The only difference that I can see is that my raster is on my local disk.  Try copying the IMG to your local C:\ drive and see if you can reproduce the same issue.

RichardThurau · Answer

Thanks Curtis and Jake for your input. 
First of all, it is very important for this work to remain in raster format: raster processing is a lot faster, and raster is required for further analysis steps.

Second, IMG is over geodatabase grid because it is interchangeable between ESRI and Erdas.

Having said that: 
Jake, I ran my script on the img you sent, and it did the same thing: erased the data, spit out an empty attribute table. Did you run the same code I posted?

Can you post your code? It would be awesome to get this working for IMGs. 
I am also running 10, sp3. It's on a 64-bit win7 machine but that shouldn't matter.

I ran the code on a geodatabase grid, and it worked the way it's supposed to. I don't like being tied to the geodatabase but for now I think it will do.

Thanks again for your input.

Rich

jskinner · Answer

This could be something specific with the raster you are using.  I tested with a .IMG using ArcGIS 10 SP3 and everything worked as it should.  I've attached the .IMG file.  See if you are able to reproduce the same issue with the attached IMG.