topic Re: Update Cursor not updating field with value in Python Questions

Update Cursor not updating field with value

RoyHewitt — Tue, 14 Feb 2012 15:39:49 GMT

I'm writing a script for field staff that clips all wetlands in a watershed, calculates area (hectares) and multiples by a sampling factor to see how many hectares need to be sample

Here is a sample of the update cursor part of the code:

         rows = arcpy.UpdateCursor(newWetland) row = rows.next()  while row:      if row.getValue(wetlandTypeField) == 'Estuarine and Marine Wetland':           totalHectares = row.getValue(areaField)           sampleArea = (totalHectares * .25) # Sample 25% of this type           row.setValue(sampleField, sampleArea)           rows.updateRow(row)           row = rows.next()      elif row.getValue(wetlandTypeField) == 'Freshwater Emergent Wetland':           totalHectares = row.getValue(areaField)           sampleArea = (totalHectares * .25) # Sample 25% of this type           row.setValue(sampleField, sampleArea)           rows.updateRow(row)           row = rows.next()

There are several more elif blocks for each wetland type in the dataset.

When I type in the python window:

print sampleArea

I get the correct area, however, it does not update the row. The help files indicate that the second parameter of the row.setValue() method is supposed to be an object. Could that be the problem?

Any help would be appreciated.
Roy

Re: Update Cursor not updating field with value

DanPatterson_Retired — Tue, 14 Feb 2012 15:54:31 GMT

have you tried to use the "for row in rows:" syntax as shown in the online help for updaterow?
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001q000000

Re: Update Cursor not updating field with value

RoyHewitt — Tue, 14 Feb 2012 16:23:45 GMT

I rewrote the code to use the for loop. I got the same problem at first (all null values in the attribute table), I went into field calculator and closed it without entering any code and VOILA, the correct values were in the table.

I'm not sure if they would have been had I gone into the field calculator after running the while loop or not, but success none the less.

Is there any "refresh" method that would fix this??

Thanks again!

Re: Update Cursor not updating field with value

DanPatterson_Retired — Tue, 14 Feb 2012 17:24:33 GMT

The table doesn't get refreshed. Run scripts etc, then open the table, don't expect updates unless you are using the field calculator directly.