From the looks of your code I believe you are trying to select all cities within a county, sum the population of the cities and update a field in the counties feature class with this value. You can easily do this by creating a spatial join. You can right-click on the counties feature class in ArcMap's table of contents > Joins and Relates > Joins. Specify to join attributes spatially and choose to sum the fields.This will produce a new output feature class with the summed population (and summed outputs of all other numeric fields) of all cities within each county. If you do not want a new feature class, and the other summed numeric fields, you can use python. Here is the code that I was able to get to work:import arcpy
from arcpy import env
env.workspace = r"C:\temp\python\test.gdb"
env.overwriteOutput = True
cities = "Cities"
counties = "Counties"
arcpy.MakeFeatureLayer_management(cities, "cities_feat")
list = []
# Get max OBJECTID for loop
rows = arcpy.SearchCursor(counties)
for row in rows:
OID = row.getValue("OBJECTID")
list.append(OID)
maxOID = list[-1]
del row, rows
x = 1
while x <= maxOID:
list2 = []
arcpy.MakeFeatureLayer_management(counties, "counties_feat", "OBJECTID = " + str(x))
arcpy.SelectLayerByLocation_management("cities_feat", "WITHIN", "counties_feat")
rows = arcpy.SearchCursor("cities_feat")
for row in rows:
pop = row.getValue("POPULATION")
list2.append(pop)
sumlist = sum(list2)
rows2 = arcpy.UpdateCursor("counties_feat")
for row2 in rows2:
row2.URBPOP = sumlist
rows2.updateRow(row2)
x += 1
del row, rows, row2, rows2
