IF/ELIF statement returning NULL for values that are not calculated with field calculator in Python

Question

I am using field calculator to change several values of field. I am receiving NULL values for those which are not in my function. What is the cause of this and a workaround?

In the code below; I would like to change only the values in my function. If a value is not in the function; the code automatically sets the new value as NULL.

import arcpy
codeblock = """def replacestring(DAMAGING_PARTY):
 output = None
 if DAMAGING_PARTY == "Arizona Pipeline contact is Chad":
 output = "Arizona Pipeline Company"
 elif DAMAGING_PARTY == "James A Shirley Construction":
 output = "James A. Shirley Construction, Inc."
 elif DAMAGING_PARTY == "NPL Construction (Kevin Sena)":
 output = "NPL Construction"
 elif DAMAGING_PARTY == "NPL Construction DENNIS PARKHOUSE":
 output = "NPL Construction"
 elif DAMAGING_PARTY == "Rami / Benito Sustaita":
 output = "Rami Alabassi"
 elif DAMAGING_PARTY == "Shea Homes (Contractor Working for)":
 output = "Shea Homes"
 elif DAMAGING_PARTY == "Shea Homes/Rudy Andrade":
 output = "Shea Homes"
 elif DAMAGING_PARTY == "W A RASIC CONSTRUCTION/CODY ROLLER":
 output = "W A RASIC CONSTRUCTION"
 elif DAMAGING_PARTY == "WARASICK CONSTR COMPANY/GIANCARLO PAMDOSI":
 output = "W A RASIC CONSTRUCTION"
 elif DAMAGING_PARTY == "Young Construction; contact Rick Musmecci":
 output = "Young Construction"
 return output"""
ShortCodeExpression = "replacestring(!DAMAGING_PARTY!)"
table = r'table'
arcpy.CalculateField_management(table, "DAMAGING_PARTY", ShortCodeExpression, "PYTHON_9.3", codeblock)

• jbchurchill: You might try an "else:" at the end with DAMAGING_PARTY == DAMAGING PARTY ? I wouldn't expect that to work though. If not, you are going to have to either loop through with a cursor, or do a selection on each of the possible values (I've done the latter).

Answer 1

You are setting output = None at the beginning of your script, so anything that doesn't specifically set output is returned as a NULL at the end when you return the value. Instead of setting output at the start, just return each value in your if/elif chain, and then an else to return the current value.

codeblock = """def replacestring(DAMAGING_PARTY):
 if DAMAGING_PARTY == "Arizona Pipeline contact is Chad":
 return "Arizona Pipeline Company"
 elif DAMAGING_PARTY == "James A Shirley Construction":
 return "James A. Shirley Construction, Inc."
 elif DAMAGING_PARTY == "NPL Construction (Kevin Sena)":
 return "NPL Construction"
 elif DAMAGING_PARTY == "NPL Construction DENNIS PARKHOUSE":
 return "NPL Construction"
 elif DAMAGING_PARTY == "Rami / Benito Sustaita":
 return "Rami Alabassi"
 elif DAMAGING_PARTY == "Shea Homes (Contractor Working for)":
 return "Shea Homes"
 elif DAMAGING_PARTY == "Shea Homes/Rudy Andrade":
 return "Shea Homes"
 elif DAMAGING_PARTY == "W A RASIC CONSTRUCTION/CODY ROLLER":
 return "W A RASIC CONSTRUCTION"
 elif DAMAGING_PARTY == "WARASICK CONSTR COMPANY/GIANCARLO PAMDOSI":
 return "W A RASIC CONSTRUCTION"
 elif DAMAGING_PARTY == "Young Construction; contact Rick Musmecci":
 return "Young Construction"
 else:
 return DAMAGING_PARTY 
 """

Answer 2

You start by setting output = None inside of your function. You then change the value of output to some other value based on your if/else statements. For every case that is not specifically called out in your function you are still left with output = None.

So, when it comes time to return output you end up returning and writing NULL.

• Geoffrey West: Are you suggesting that I remove output = None and return output?
• Radar: @Midavalo already has a solid answer with updated code, but I just wanted to mention that you always need to return something, even if that something is 'NULL'. In this case you just want to return the value that already exists in the field.