topic Re: Python Expression to Change Field Labels in Python Questions

Python Expression to Change Field Labels

ShawnGazzano — Wed, 13 Aug 2014 17:59:58 GMT

How is the Python expression written (i.e. what is the syntax?) to change a field's labels from its unique values to custom labels?

The field I'm working with is DISTRICT. Its unique values are 1, 2, 3, 4, and 5.

On my map, I want the districts to be labeled with their supervisors' names, instead of with their numbers.

Re: Python Expression to Change Field Labels

IanMurray — Wed, 13 Aug 2014 18:07:54 GMT

It is pretty simple.

def FindLabel ( [DISTRICT] ):
  if DISTRICT == 1:
    return "Bob Hope" #Input your supervisor name there
  elif DISTRICT == 2:
    return "Bob Costas" #Input your Supervisor name there
  elif DISTRICT == 3:
    return "Bob Marley" #Input your Supervisor name there
  elif DISTRICT == 4:
    return "Bobby Bowden" #Input your Supervisor name there
  elif DISTRICT == 5:
    return "Bob the Clown" #Input your Supervisor name there

Similar to that, just use if/elif statements to evaluate the value of District and return the name you want.

Use Python for parser and advanced expression checked.

Re: Python Expression to Change Field Labels

ShawnGazzano — Wed, 13 Aug 2014 18:22:11 GMT

I entered

def FindLabel ( [District] 😞

if District == 1:

return "Bob Hope"

but the response to clicking the Verify button was "Carriage returns are not allowed in simple expressions."

I took out the extra "=" in front of "1", but the Verify response was the same.

Re: Python Expression to Change Field Labels

IanMurray — Wed, 13 Aug 2014 18:25:39 GMT

Like I said, make sure the advanced box is checked.

It doesn't allow multiple lines of code for simple expressions, so the advanced box needs to be clicked

Re: Python Expression to Change Field Labels

ShawnGazzano — Wed, 13 Aug 2014 18:49:12 GMT

Ok, I've got Advanced checked and Python for parser. That validates the expression.

But in the Expression Verification window, the Sample Text String and Sample Label are blank.

When I press OK to get out of Expression Verification / Label Expression / Layer Properties windows, my map updates, but without labels; they are all blank.

The expression I have entered is:

def FindLabel ( [DISTRICT] 😞

if [DISTRICT] == 1:

return "Bob Hope"

Re: Python Expression to Change Field Labels

IanMurray — Wed, 13 Aug 2014 19:02:08 GMT

can you check to see if DISTRICT is a text field(string type) or a numeric type?

If text, make it if int([DISTRICT) == 1:

Re: Python Expression to Change Field Labels

XanderBakker — Wed, 13 Aug 2014 19:21:48 GMT

That's nice, I was't aware of this possibility.

If the list get a little longer, you may want to consider using a dictionary, like this:

def FindLabel([YourFieldName]):
    dct = {1: "Bob Hope", 2: "Bob Costas", 3: "Bob Marley",
          4: "Bobby Bowden", 5:"Bob the Clown"}
    district = int([YourFieldName])
    if district in dct:
        return dct[district]
    else:
        return "<ITA>Unknow supervisor</ITA>"

I used this on the feature ID (FID) field of a shapefile with values ranging from 0 to 7 and got this:

Re: Python Expression to Change Field Labels

ShawnGazzano — Wed, 13 Aug 2014 19:38:51 GMT

It's a text field.

def FindLabel ( [DISTRICT] 😞

if int( [DISTRICT] ) == 1:

return "Bob Hope"

still returns blank labels.

Re: Python Expression to Change Field Labels

IanMurray — Wed, 13 Aug 2014 19:48:50 GMT

Hmm, mine works just fine on a sample dataset. Did you make sure that you turned labels on for that layer? Also, python is case sensitive, so make sure that your field is syntactically correct(proper upper/lower case, spaces,etc. included.

Re: Python Expression to Change Field Labels

ShawnGazzano — Wed, 13 Aug 2014 20:15:41 GMT

Yes, the layer's labels are turned on, and the expression appears to be syntactically correct.

I also tried Xander's suggestion:

def FindLabel([DISTRICT]):

dct = {1: "Bob Hope", 2: "Bob Costas", 3: "Bob Marley", 4: "Bobby Bowden", 5:"Bob the Clown"}

district = int([DISTRICT])

but same result: expression is validated, but with blank labels. I'll continue to test....