Python script for filling <Null> values with previous value in one field

Question

I have a table (inside a File Geodatabase) that looks like this:

I need the values of Owner attribute to be automatically filled with the previous non-Null value. As Such:

Is there a Python script, usable in Field Calculator, that can achieve this?

Answer 1

You can do this directly within the CalculateField tool; use the following code block:

prevval = None

def calcowner(ownerval):
    global prevval
    val = prevval if ownerval is None else ownerval
    prevval = val
    return val

And the expression:

calcowner(!Owner!)

Note that this probably won't work in ArcGIS 10.0 due to a bug that was fixed in 10.1, but 10.1+ should be good:

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

Answer 2

This can be done with a custom python parser function like:

Here we evaluate if value is NULL or not, if not write value to text file, if NULL pull value from text file:

def update(val):
  if val:
    f = open('C:/Temp/temp.txt','w')
    f.write(val)
    f.close()
    return val
  else:
     f = open('C:/Temp/temp.txt','r')
     for v in f:
         return v
     f.close()

And add the function call in the text box below the pre logic one:

update(!theFieldName!)