topic Re: Test for Null values Field Calculator in Python Questions

Test for Null values Field Calculator

AdamCox1 — Thu, 07 Feb 2013 20:29:39 GMT

Ok, I just finished reading a bunch of threads on this, but need to double check this issue. I want to put something like this

def i(x):
  if x is None:
    return "Used to be Null"
  else:
    return x

into the code-block, but I've tried all sorts of variations that have been suggested, x == None, x == "", if not x, but nothing has produced any change in the values.

Am I missing something, or is this just not going to work and I'll have to use update cursors to perform operations like this?

I'm using 10.0 SP5.

Thank you!

Re: Test for Null values Field Calculator

MathewCoyle — Sat, 11 Dec 2021 16:43:03 GMT

May be a bug, there were a lot of issues with null values in 10.0 I believe.

NIM079575 - Field Calculator does not recognize <Null>

NIM059424 - Null values in the feature class do not get replaced when using Python in the Field Calculator.

NIM086737 - The Select by Attributes tool using "IS NULL" on a joined field does not return selections in ArcGIS 10 SP5.

NIM063379 - A Field Calculator error dialog opens in PythonWin for an assignment of a null value to a text field in a shapefile.

I believe this was the work around.

def i(x):
    var = x
    if var:
        return "Used to be Null"
    else:
        return var

Re: Test for Null values Field Calculator

AdamCox1 — Sat, 11 Dec 2021 16:43:06 GMT

Hello and thanks for the reply,

Unfortunately, that work around still produces nothing. I happened to be working with a joined table, but after removing the join, still no luck. It doesn't even work to flip it around and say

def i(x):
  var = x
  if var:
    return var
  else:
    return "not null anymore"

Because I'm starting with all Null values, I think my first step will just be to write "NULL" to the entire field, which works, and then query against the string "NULL". Any other ideas would be welcome, too, of course.

Thanks!

Re: Test for Null values Field Calculator

MathewCoyle — Sat, 11 Dec 2021 16:43:07 GMT

That is odd, it works for me.

Edit: Sorry no, I was using a cursor.

rows = arcpy.UpdateCursor(layer)
for row in rows:
    var = row.AREAESTIMATED
    if var:
        row.TAG = 1
    else:
        row.TAG = 0
    rows.updateRow(row)

Re: Test for Null values Field Calculator

forestknutsen1 — Sat, 11 Dec 2021 16:43:10 GMT

I also have had this problem, ultimately I gave up on the field calculator and made a stand alone python program to to the job.

import arcpy, os

arcpy.env.workspace = "Z:\myTest.gdb" #path to your geodatabase

rows = arcpy.UpdateCursor("test") #test is the name of the feature class you wish to work with 


for row in rows:
    if row.test1 == None: #test1 would be the name of the field in the feature calss 
        row.test1 = "Used to be Null"

    rows.updateRow(row)

del row
del rows