Performing row update within Select By Location based on field within selected feature class using ArcPy?

Question

I am trying to select address points from address feature class within a selected zip code from zipcode feature class and populate the address feature class field "ZipCode" with the "Zip_Code" field from the zipcode feature class that is selected. What I have so far doesn't produce an error, but continues to run and the ZipCode field is not being populated.

I am new to python.

Following is what I have so far.

#Set variables for feature classes
addresses = "Addresses"
zipcodes = "Zip_Codes"

#Perform Select by Location to create the zipcode data from ZipCodes to Addresses
#Create layer file
address_layer = "addr"
zipcode_layer = "zip"

if arcpy.Exists(zipcode_layer):
    arcpy.Delete_management(zipcode_layer)

arcpy.MakeFeatureLayer_management(zipcodes, zipcode_layer)
result = arcpy.GetCount_management(zipcode_layer)
print("There are {0} zip codes in the Zip_Codes feature class".format(result))

if arcpy.Exists(address_layer):
    arcpy.Delete_management(address_layer)

arcpy.MakeFeatureLayer_management(addresses, address_layer)

#Update zipcode field in Addresses feature class based on selectbylocation on Zip_Codes
#Initiate count to 1
count = 1
fieldListA = ["ZipCode"] #Zip code field from addresses variable
fieldListZ = ["Zip_Code"] #Zip code field from zipcodes variable
with arcpy.da.UpdateCursor(addresses, fieldListA) as upCursor:
    for row in upCursor:
        #Select all address points within the selected Zip_Code field within zipcode_layer
        arcpy.SelectLayerByLocation_management(address_layer, "WITHIN", zipcode_layer)
        result = arcpy.GetCount_management(address_layer)
        #print("There are {0} addresses".format(result))

        strZip = row[0]
        upCursor.updateRow(row)

        count = count + 1

Answer 1

From your code it looks like you want to populate a field in the adress layer with the number of selected features and not the actual zip codes from zip_code layer.

You are not assigning a value to row, so upCursor.updateRow(row) will do nothing. An assignment is for example:

row[0] = 12345

If you want to fetch the zip code from overlapping zip code polygon you can do i with a cursor inside the cursor, se code below. I dont recommend this on large data sets since it will have to go through all polygons for each Point. You should use Spatial Join tool instead.

import arcpy

address = r'C:\database.gdb\adresses'
zipcodes = r'C:\database.gdb\zipcodes'

with arcpy.da.UpdateCursor(address, ['SHAPE@','zipfield_to_update']) as ucursor:
    for update_row in ucursor:
        with arcpy.da.SearchCursor(zipcodes, ['SHAPE@', 'zipfield_to_read']) as scursor:
            for search_row in scursor:
                if update_row[0].within(search_row[0]):
                    update_row[1] = search_row[1]
                    ucursor.updateRow(update_row)

You could also do this on selections, like you try in your code and it will propably be quicker.

Answer 2

In your code snippet below you create a row object named row on the second line, and then on the last line you update the cursor row using the current value of row which you have not modified in between. You have read the first item in row when you did strZip = row[0] but you have not written anything to it.

with arcpy.da.UpdateCursor(addresses, fieldListA) as upCursor:
    for row in upCursor:
        #Select all address points within the selected Zip_Code field within zipcode_layer
        arcpy.SelectLayerByLocation_management(address_layer, "WITHIN", zipcode_layer)
        result = arcpy.GetCount_management(address_layer)
        #print("There are {0} addresses".format(result))

        strZip = row[0]
        upCursor.updateRow(row)