topic Re: How to slice a word in the label expression in Python Questions

How to slice a word in the label expression

PeterVersteeg — Wed, 07 Dec 2016 20:23:02 GMT

Hallo,

I have a field with city names and I want to slice the name in the label expression to only the 1st character.

I want to do this in python. looking at the internet i have this but it is not working:

def Label ( [CityName] 😞

s = [CityName]

s1 = s[1:]

return s1

i am working with arcgis for desktop 10.3.1

greetings Peter

Re: How to slice a word in the label expression

JoeBorgione — Wed, 07 Dec 2016 20:53:58 GMT

I got this to work:

def wtf (instring):
s= instring[:1] ####### Notice the position of the colon(:)
return s

Above is in the feild calculator, in a label expression be sure to choose python as the parser and check Advanced:

Re: How to slice a word in the label expression

PeterVersteeg — Thu, 08 Dec 2016 06:37:41 GMT

i stil got a string error

Re: How to slice a word in the label expression

FC_Basson — Sat, 11 Dec 2021 22:43:11 GMT

You could simplify the definition function even further:

def FindLabel ( [CITY_CODE] ):
   return [CITY_CODE][:1]‍‍

Re: How to slice a word in the label expression

FC_Basson — Sat, 11 Dec 2021 22:43:13 GMT

It's probably due to an empty/Null attribute value, which could be returned as None. Try this definition expression:

def FindLabel ( [CITY_CODE] ):
 try:
   return [CITY_CODE][:1]
 except AttributeError:
   pass‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How to slice a word in the label expression

PeterVersteeg — Thu, 08 Dec 2016 07:54:53 GMT

Your right there a NULL values and that was causing the error. My code works if I remove the NULL values but I need same on NULL.

your code is giving me the same error.

Greetings Peter

Re: How to slice a word in the label expression

FC_Basson — Sat, 11 Dec 2021 22:43:16 GMT

That's weird, because I tested the expression on a layer with Null values in the attribute filed and it worked. How about adding a None type check in there?

def FindLabel ( [CityName] ):
  try:
    if [CityName] is not None:
      return [CityName][:1]
  except AttributeError:
    pass‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: How to slice a word in the label expression

PeterVersteeg — Thu, 08 Dec 2016 08:13:11 GMT

That is weird. i now got a other error

this is my field properstie

Re: How to slice a word in the label expression

FC_Basson — Thu, 08 Dec 2016 08:16:16 GMT

You have a left bracket in front of the CityName field in the if statement - I see I made the same error in my previous reply

Re: How to slice a word in the label expression

PeterVersteeg — Sat, 11 Dec 2021 22:43:19 GMT

I think it was my mistake I got a extra ( in the code.

your code is working correctly. It is a more difficult code then I would think for such a simple task but I am really glad it works.

Thank you

def FindLabel ( [CityName] ):
  try:
    if [CityName] is not None:
      return [CityName][:1]
  except AttributeError:
    pass

Re: How to slice a word in the label expression

JoeBorgione — Thu, 08 Dec 2016 12:38:48 GMT

Error trapping is as much an art as it is a science .