I'm trying to use field calculator to assign values to a new field I created. I wan't to assign the value from the first field unless that field is empty, if it is empty use field 2, if that is empty use field 3. Here is what I have thus far. I feel it is way off but not sure where to go from here.

New_Size: My new field

wmDeviceEq: First field to check for new field name

wmDevice_4: Second ""

wmDevice_5: Third ""


  • What happens? Please, update the question with relevant information. Commented Nov 23, 2015 at 17:21
  • Nothing happens, I get an error for syntax on second line.
    – Jeff C
    Commented Nov 23, 2015 at 18:09

2 Answers 2


In the codeblock, you can only use parameters, not field names. You'll need to create parameters for each of your field names, like so:

def Reclass(f1, f2, f3):
    New_size = f1 # this doesn't actually do anything
    if f1 == '':
        return f2
    elif f2 == ''
        return f3
    else: # is this cutoff?
        return f1 # New_size maybe?

and then

Reclass(!wmDeviceEq!, !wmDevice_4!, !wmDevice_5!)

What if f3 (wmDevice_5) is empty? Not sure if your picture is showing a cuttoff else statement.

Are the values in the fields actually empty strings? Shapefiles store a single space " " and feature classes in a geodatabase typically use <Null>, which in Python would be None.

If the fields are actually empty strings and only one field will ever have data, you don't need the code-block at all.

"".join((!wmDeviceEq!, !wmDevice_4!, !wmDevice_5!))

As an aside, a nested if statement would be something like this:

if result > 10:
    print("Greater than 10")
    if result < 100:
        print("and less than 100")
        print("It's big...")
    print("Too small!")
  • "If the fields are actually empty strings and only one field will ever have data, you don't need the code-block at all. "".join((!wmDeviceEq!, !wmDevice_4!, !wmDevice_5!)) " I think what you gave me at the beggining will get me to what I was needing. but could you explane this join a little more? Also, if all three of the fields are empty then the new column(New_Size) needs to be left empty as well, or assign some kind of filler such as "none" or "unassigned" maybe.
    – Jeff C
    Commented Nov 23, 2015 at 18:04
  • @JeffC, "".join() concatenates a list of strings with the the delimiter, which in this case, is an empty string. If you wanted a comma, say, it'd be ",".join()
    – Paul
    Commented Nov 23, 2015 at 18:36


I edited the code and came up with this

def Reclass( ph1, ph2, ph3 ):
  New_Size = ph1
  if ph1 == ' ':
      return ph2
  elif ph2 == ' ':
      return ph3
  elif ph3 == ' ':
      print ("NULL")

and then

Reclass(!wmDeviceEq!, !wmDevice_4!, !wmDevice_5!)

When it runs my new field pulls values from only ph2... enter image description here Also not sure about that final elif. it's meant to fill a space that has no value to pull, with a "Null".

I tried the "".join() function but it places spaces every time it moves to the next field, like so. enter image description here

Won't work unless there is a way to remove those spaces before the values in the New_Size field.

  • This should probably be a new question or an edit to the original. You can remove extra spaces by adding .strip() so it'd be something like "".join((!wmDeviceEq!, !wmDevice_4!, !wmDevice_5!)).strip()
    – Paul
    Commented Nov 23, 2015 at 21:11
  • Will that also remove the spaces within the text in each field? I have to have the spaces that exist within "35-HR OCR".
    – Jeff C
    Commented Nov 23, 2015 at 22:26
  • the Python docs are great.
    – Paul
    Commented Nov 23, 2015 at 22:30

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