topic Re: Empty String on Field Calculator in Python Questions

Empty String on Field Calculator

ionarawilson1 — Thu, 25 Oct 2012 12:21:08 GMT

I am taking a web course called "Use Python in ArcGIS Desktop 10" and one of the exercises is to write a python script on the field calcualtor to change the types of schools:

def label(name, type):
if type == "HIGH":
return name + " HS"
if type == "MIDDLE":
return name + " MS"
elif type == "ELEMENTARY":
return name + " ELEM"

But the type column has one record with an empty string and I get an error because of that. I know I could use an "else" statement to take care of that but I have had this issue before and would like to know how I can include that in the python script. I tried:

if type == " ":
return name + " "

I also tried

if type is None:
return name + " "

I also tried
if len(type) == 0:
return name + " "

And a couple more statements, but nothing works. Do you guys know what I can use to account for the empty string? Thanks!!!

Re: Empty String on Field Calculator

DanPatterson_Retired — Thu, 25 Oct 2012 12:44:16 GMT

the way you have written it is " " which is a space not an empty string ie.
>>> a = ""
>>> print len(a)
0
>>> b = " "
>>> print len(b)
1
>>>

Re: Empty String on Field Calculator

ionarawilson1 — Thu, 25 Oct 2012 20:52:39 GMT

Hi Dan,

I also tried the way you mentioned but it does not work:

def label(name, type):
if type == "" :
        return name + " "
if type == "HIGH":
        return name + " HS"
if type == "MIDDLE":
      return name + " MS"
elif type == "ELEMENTARY":
     return name + " ELEM"

By the way, the return statement is indented, although it is not showing like it is here. Thanks

Re: Empty String on Field Calculator

MarcinGasior — Fri, 26 Oct 2012 08:13:20 GMT

I'm using version 10.0 sp4 and the base code provided in exercise works. It just gives <Null> in MAP_LABEL field when TYPE field is empty.

To return only school name this code works for me (there's a space character in TYPE field which look like empty):

def label(name, type):   if type == "HIGH":     return name + " HS"   elif type == "MIDDLE":     return name + " MS"   elif type == "ELEMENTARY":     return name + " ELEM"   elif type == " ":     return name

This works too:

def label(name, type):   if type == "HIGH":     return name + " HS"   elif type == "MIDDLE":     return name + " MS"   elif type == "ELEMENTARY":     return name + " ELEM"   else:     return name

Re: Empty String on Field Calculator

ionarawilson1 — Fri, 26 Oct 2012 12:45:27 GMT

Thank you m.gasior,

After applying the SP 4.0 the error went away!!! Thanks again!