In a counties shapefile, I have two fields named population2001 and population2010. I would like to create a third field with the difference between 2001 and 2010 using arcpy and the update cursor to better learn how to use cursors. My code:
import arcpy arcpy.env.workspace = r"C:\Users\Documents\geodatabase.gdb" ndCounties = r"C:\Users\Documents\geodatabase.gdb\Counties" #add the new field arcpy.AddField_management(ndCounties, "difference", "LONG", field_length = 10) fields = ['POP2001', 'POP2010', 'difference'] with arcpy.da.UpdateCursor(ndCounties, fields) as cursor: for row in cursor: if row == 'POP2001': row = 1 row = 2 elif row == 'POP2010': row = 2 row = 3 row = row - row cursor.updateRow(row)
When I run this code, I get this error:
TypeError: unsupported operand type(s) for -: 'float' and 'NoneType'
I'm not exactly sure if this is the right way of doing this field subtraction.