topic Re: Stacked Label Expression in Python in Python Questions

Stacked Label Expression in Python

BrynDunbar — Sat, 17 Jan 2015 01:43:14 GMT

I have successfully rendered a stacked label in ArcMap using a java script labeling expression, but I cannot figure out how to do the same thing with Python in the Label Expression box.

This is what I used for java script:

function FindLabel ( [LOT], [SUBDIVISION] )

{

return [LOT] + "\r" + [SUBDIVISION];

}

How do I do this same thing by using python?

I just want to stack the my Lot label on top of my Subdivision label, but using python.

Thank you in advance for any thoughts or suggestions.

Re: Stacked Label Expression in Python

XanderBakker — Sat, 11 Dec 2021 15:50:52 GMT

It is very similar:

def FindLabel ( [LOT] , [SUBDIVISION]  ):
  return [LOT] +  "\n"  +  [SUBDIVISION]

Re: Stacked Label Expression in Python

BrynDunbar — Tue, 20 Jan 2015 21:14:18 GMT

Thank you for the reply.

I typed this into the Expression box with Python selected as the Parser and Advanced checked.

def FindLabel ( [LOT] , [SUBDIVISION] 😞

return "Name: " + [LOT] + '\n' + [SUBDIVISION]

I got an error,

Error 0 on line 0.

Error running expression:

FindLabel(ESRIExpressionArg0,ESRIExpressionArg1)

Tracedback (most recent call last):

File"<expression>", line 1, in <module>

File"<string>", line 2, in FindLabel

TypeError: cannot concatenate 'str' and 'NoneType' objects.

Does this error have to do with 'null' values? Or do I need to cast the variable or do a type conversion?

Re: Stacked Label Expression in Python

ChristianHinderman — Tue, 20 Jan 2015 21:33:14 GMT

I had a similar problem recently. I think one of the label fields must have a null value. If you only have to worry about null values in subdivision (and both fields are strings) this should work:

def FindLabel ( [LOT], [SUBDIVISION] 😞

if [SUBDIVISION]:

label = "Name: " + [LOT] + "\n" + [SUBDIVISION]

else:

label = "Name: " + [LOT]

return label

Re: Stacked Label Expression in Python

deleted-user-rmQdIupSdOqe — Tue, 20 Jan 2015 23:21:21 GMT

It is the NULL values in the fields that make these python expressions error out. The answer above solves that problem.

I have one that looks like this, where sometimes [ContractName] and [ContractYear] are null, so I nest in the if statements.

def FindLabel ([ContractName], [ContractYear]):

if [ContractName]:

if [ContractYear]:

label = [ContractName] + '\n' + [ContractYear]

else:

label = "No" + '\n' + "Contract"

return label

Re: Stacked Label Expression in Python

deleted-user-rmQdIupSdOqe — Tue, 20 Jan 2015 23:28:49 GMT

The other option is to use the labeling method "Define classes of features and label each class differently" option, setting up a SQL expression first, to filter out data that has NULL values.

Then your python label expression for that label class (my label class is Default) is:

Re: Stacked Label Expression in Python

XanderBakker — Sat, 11 Dec 2021 15:50:55 GMT

You could change the expression to:

def FindLabel([LOT] ,[SUBDIVISION]):
  return "{0}\n{1}".format([LOT], [SUBDIVISION])

It suppresses the error. However, this will return None if there is no data:

The nice part of using the python expression is that you can enhance the result, replacing the None for a different text

def FindLabel([LOT] , [SUBDIVISION]):
  return "{0}\n{1}".format([LOT] if [LOT] != None else "No LOT",  [SUBDIVISION] if [SUBDIVISION] != None else "No SUBDIVISION")

... will result in:

... or adding some formatting to the text:

def FindLabel([LOT] , [SUBDIVISION]):
  return "{0}\n{1}".format([LOT] if [LOT] != None else "<CLR red='255'>No LOT</CLR>",  [SUBDIVISION] if [SUBDIVISION] != None else "<CLR red='255'>No SUBDIVISION</CLR>")

will give:

Re: Stacked Label Expression in Python

XanderBakker — Wed, 21 Jan 2015 02:08:42 GMT

I wouldn't go for label classes in this case, since in the example above, with a simple line I am tackling 4 classes,,,

Re: Stacked Label Expression in Python

BrynDunbar — Fri, 23 Jan 2015 22:33:24 GMT

Thank you very much! This is the first time that i have used GeoNet and I am very pleased with the responses that I have received; what a great resource it is; and the sense of community that it provides for GIS users.

I used your example and put this in the Label Expression box:

def FindLabel ([LOT], [SUBDIVISION]):

if [LOT]:

if [SUBDIVISION]:

label = [LOT] + '\n' + [SUBDIVISION]

else:

label = " "

return label

It shows what I want it to show and I understand the code. This nesting idea was what I needed. Thanks again!

Re: Stacked Label Expression in Python

BrynDunbar — Fri, 23 Jan 2015 22:37:07 GMT

Thank you so much for taking the time to respond with such great ideas and examples. I will definitely spend more time with label expressions, using these examples to help me construct more complex labels. I am still quite new to coding, but it is quite satisfying when I can understand some code and when I can write code that produces something, especially with no errors.

Re: Stacked Label Expression in Python

BrynDunbar — Fri, 23 Jan 2015 22:47:05 GMT

Thanks Christian! Your response and this thread definitely helped me find the solution that I was looking for. This is what I have so far.

def FindLabel ([LOT], [SUBDIVISION]):

if [LOT]:

if [SUBDIVISION]:

label = [LOT] + '\n' + [SUBDIVISION]

else:

label = " "

return label

It labels Lots and Subdivisions, but when they are Null, you can't see the label because I made it " " say nothing but a space. I am sure there are better ways to write the code, but this seems to be doing what I want for now.

Thank you again.

Re: Stacked Label Expression in Python

DarrenWiens2 — Sat, 11 Dec 2021 15:50:58 GMT

Although it sounds like you've already found an answer to the problem, but you could take advantage of try/except to label, or skip, null values:

def FindLabel ( [LOT], [SUBDIVISION] ):
  try:
    return [LOT] +  "\r"  +  [SUBDIVISION]
  except:
    return 'this had a null value'

Another succinct way to write this is:

def FindLabel ( [LOT], [SUBDIVISION] ):
  if [LOT] and [SUBDIVISION]:
      return [LOT] + '\r' + [SUBDIVISION]