Parse multiple field in field calculator using python

Question

I'm trying to fill a blank field depending on the contents of three other fields using python in the field calculator.

Sample code is something like:

def getClass(Text1,Text2,Text3):
 if Text1 is None:
 return Text2
 elif Text2 is None:
 return Text3 
 else:
 return Text1

I can retrieve the value of the first field but never the 2nd two. I know this isn't the right way but I can't figure out the nesting levels... Any ideas?

UPDATE: Fixed by stripping out the white space. Credit to this post Using Calculate Field tool to calculate on null fields?

def getClass(Text1,Text2,Text3):
 if Text1.strip():
 x = Text1
 elif Text2.strip():
 x = Text2 
 elif Text3.strip():
 x = Text3
 else:
 x = "NA";
 return x

• recurvata: Are the Text fields actually Null, or just empty, i.e. '' ?
• Josh J: Text fields are empty ''

Answer 1

Use the "not equal" operator for the field calculator.

def getClass(Text1,Text2,Text3):
 if Text1 != None:
 return Text1
 elif Text2 != None:
 return Text2 
 elif Text3 != None:
 return Text3
 else:
 return None;

You may also want to account for the possibility that none of the input fields have a value, as seen in the code snippet I posted.

Also, checkout this post about the difference between using the "is" operator versus "==":

https://stackoverflow.com/questions/132988/is-there-a-difference-between-and-is-in-python

• GeoJohn: @recurvata brings up a good point in the comment above. If you need to account for empty strings in place of <Null>, you could modify the boolean expressions like so ---> if Text1 != None and Text1 != "":
• Paul: A simpler way would just be if Text1: -- Both None and empty strings '' are false-y values in Python.
• Josh J: I've tried all of the options mentioned and they return Text1 but not Text2 or Text3. This is the same whether I use None or '' and != or if Text1:. Is this a job that field calculator can't handle and should I switch to arcpy instead?
• recurvata: Can't tell if you mean '' above or ' ' (an empty space) in your comment above. Empty space is likely incorrect. If no values are Null, testing for None won't help. '' or ' ' will always return Text1 in your code above, since '' and ' ' both != None; that is, your first test is always True, thereby returning Text1. Same with if Text1:
• Josh J: Fixed. Using this post gis.stackexchange.com/questions/81143/…

Answer 2

You need to make sure you're passing the other fields in the function call at the bottom. getClass(!Field1!, !Field2, !Field3!)