topic Re: Arcmap Python Label Expression Function "Null" in Python Questions

Arcmap Python Label Expression Function "Null"

DevinUnderwood2 — Sun, 12 Dec 2021 03:43:49 GMT

I am having difficulty with python parser label function to replace null values with "Unknown Plan" and leave everything else as is. The Unknown Plan is not displaying in the map label.

I have the following:

def FindLabel ( [PLAN] ):
    if  ([PLAN]) is  None:
         return "Unknown Plan"
    else:
        return [PLAN]‍‍‍‍‍

Any idea it is not working ?

Re: Arcmap Python Label Expression Function "Null"

DanPatterson_Retired — Wed, 02 Nov 2016 22:47:12 GMT

line 2 the ( ) brackets aren't needed

line 3 is indented improperly

Re: Arcmap Python Label Expression Function "Null"

JoshuaBixby — Wed, 02 Nov 2016 22:49:23 GMT

Not to ask the obvious, but is the [PLAN] field an empty string instead of NULL?

Re: Arcmap Python Label Expression Function "Null"

DevinUnderwood2 — Wed, 02 Nov 2016 22:52:52 GMT

I made Dan's suggested changes and still no luck.

I should of elaborated what string PLAN field is. The blank fields are Null.

Re: Arcmap Python Label Expression Function "Null"

JoshuaBixby — Wed, 02 Nov 2016 23:09:15 GMT

Nulls show up as <Null>, I think you have empty strings.

Re: Arcmap Python Label Expression Function "Null"

DevinUnderwood2 — Wed, 02 Nov 2016 23:13:00 GMT

Good point, I have empty strings, how would I represent empty strings, not Null ?

Re: Arcmap Python Label Expression Function "Null"

JoshuaBixby — Sun, 12 Dec 2021 03:43:51 GMT

This will treat NULL and empty strings the same way:

def FindLabel ( [PLAN] ):
    if  [PLAN] in  (None, ""):
        return "Unknown Plan"
    else:
        return [PLAN]‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Arcmap Python Label Expression Function "Null"

DanPatterson_Retired — Wed, 02 Nov 2016 23:46:37 GMT

Joshua... fix line 3... it bugs me

Re: Arcmap Python Label Expression Function "Null"

DevinUnderwood2 — Sun, 12 Dec 2021 03:43:54 GMT

def FindLabel ( [PLAN] ):
    if  [PLAN] in  (None, " "):
        return "Unknown Plan"
    else:
        return [PLAN]‍‍‍‍‍

This work perfect, thank you. Good to know that an empty string treated the same for label expressions and the field calculator. Null is not though, having to use None to represent Null in label expressions.

Re: Arcmap Python Label Expression Function "Null"

TedKowal — Thu, 03 Nov 2016 15:10:44 GMT

What happens when there are multiple spaces......

Would not [PLAN].strip() in (None, "") work better and a little more bullet proof?

------ I still say Python has issues with nulls, empty, NA and spaces ....

Re: Arcmap Python Label Expression Function "Null"

DevinUnderwood2 — Thu, 03 Nov 2016 15:16:18 GMT

I agree that in general, nulls, empty, NA and spaces always present issues which I don't remember how to address right away.

Technically, my empty fields do not have spaces since I never typed anything in, I would assume?

So, you bring up a good point, what exactly are the empty fields represented by ?

Re: Arcmap Python Label Expression Function "Null"

JoshuaBixby — Thu, 03 Nov 2016 15:41:37 GMT

Too bad it isn't SE, you could just fix it for me.

Re: Arcmap Python Label Expression Function "Null"

TedKowal — Thu, 03 Nov 2016 17:18:12 GMT

For me the empty cells would be null, lot's depends on how the database/tables have been defined...

Using the old VBA scripting language this was never an issue...but with python (I have to check for everything!) Not to mention unprintable control characters.... but this is off subject...... I am a very reluctant python users.... vb rest in peace!

Re: Arcmap Python Label Expression Function "Null"

DanPatterson_Retired — Sun, 12 Dec 2021 03:43:57 GMT

As you said ... 'old vba scripting' ....

In python there is only one None, everything is an empty version of a type...

a refresher... /blogs/dan_patterson/2016/11/03/before-i-forget-18-those-pesky-null-things

and a clear statement

>>> type("")
<class 'str'>
>>> type(None)
<class 'NoneType'>‍‍‍‍‍‍‍‍

Re: Arcmap Python Label Expression Function "Null"

TedKowal — Thu, 03 Nov 2016 19:09:36 GMT

But in practice it does not seems to work out that way! I have a multi page function that I am building that test all sorts of nasties.... that should have been picked up by "None". -- lots of your refresher stuff found its way in my function! (I mean def)

Miss my onesize fits all code from vb ... if trim([myfield]) & "" = "" then ... Never really had to test for blank or null stuff.....ahhh but life moves on!

Re: Arcmap Python Label Expression Function "Null"

curtvprice — Fri, 04 Nov 2016 15:20:22 GMT

See a freewheeling discussion of these issues -- Much Ado About Nothing‌

Re: Arcmap Python Label Expression Function "Null"

DanPatterson_Retired — Fri, 04 Nov 2016 15:25:55 GMT

Ahhh yes... brings back fond memories when we had Nothing better to do than philosophize

Re: Arcmap Python Label Expression Function "Null"

curtvprice — Fri, 04 Nov 2016 15:30:02 GMT

GeoNet at its best - I learned a lot from that thread.

Re: Arcmap Python Label Expression Function "Null"

DevinUnderwood2 — Sun, 12 Dec 2021 03:43:59 GMT

Great feedback, thanks.

With your help I was able to use the following python label expression in my mapbook.

For any water pipeline attributed with, "abandon", do not label. Also, if any pipeline is null then label as seen below.

def FindLabel ([PLAN], [AGENCY]):
    if [AGENCY] == "ABANDON":
        return None
    elif [PLAN] in  (None, " "):
        return "Plan ?"
    else:
        return [PLAN]‍‍‍‍‍‍‍‍‍‍‍‍‍‍

I need to also only show pipeline labels for pipe greater than 50 feet. I tested out the following and it doesn't work. I would then need to add it to my current expression.

Any ideas what is wrong with my expression.

Thanks

def FindLabel ( [SHAPE.LEN], [PLAN]  ):
    if [SHAPE.LEN]  > 50:
        return [PLAN]
    else:
        return [PLAN] ‍‍‍‍‍‍‍‍‍‍

Re: Arcmap Python Label Expression Function "Null"

TedKowal — Sun, 12 Dec 2021 03:44:02 GMT

You cannot simply pass the geometry into a label string (At least I have never figured out how) so you would have to do something like this:

import arcpy
lyrName = "AADT_2015"
shapeDict = {}
with arcpy.da.SearchCursor(lyrName, ("OID@","SHAPE@LENGTH")) as cursor:
   for row in cursor:
      shapeDict[row[0]] = row[1]

def FindLabel([OBJECTID]):
   oid = int([OBJECTID])
   if shapeDict[oid] > 50:
      return "BIG"
   else:
      return "Small"‍‍‍‍‍‍‍‍‍‍‍‍‍

Personally I feel that is over kill..... If I were doing it I would create a new field say myLength as a double... use the field calculator to calculate the segment length (!shape.length! I believe )...then pass [myLength] to your label function as you wrote it above using [myLength] instead of [SHAPE.LEN]