Using nested If statement in Python parser of ArcGIS Field Calculator?

Question

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 ""

Field_Calculator_Image

• John Powell: What happens? Please, update the question with relevant information.
• Jeff C: Nothing happens, I get an error for syntax on second line.

Answer 1

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")
 else:
 print("It's big...")
else:
 print("Too small!")

• Jeff C: "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.
• Paul: @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()

Answer 2

@Paul

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.

• Paul: 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()
• Jeff C: Will that also remove the spaces within the text in each field? I have to have the spaces that exist within "35-HR OCR".
• Paul: the Python docs are great.