can somebody tell me how can i count character in a field either using field calculator or cursor.

i tried the below code :

import arcpy

inputFeatureClass = arcpy.GetParameterAsText(0)
InputField = arcpy.GetParameterAsText(1)
expression = "len(!" + InputField + "!)"


but result is null.

i tried cursor :

import arcpy

#taking input from user

    inputFeatureClass = arcpy.GetParameterAsText(0)
    InputField = arcpy.GetParameterAsText(1)

    cursor = arcpy.da.UpdateCursor (inputFeatureClass, [InputField, "CountChr"])
    for row in cursor:
        row[1] = len(row[0])
    del cursor

but result is again null

can somebody tell me why this is happening ?

  • Is your input field a text field and your count field a numeric field? Commented Sep 25, 2015 at 20:04
  • Yes InputField is a text field, and i am adding a a new field name "Countchr" and counting characters in it from InputField(see code) Commented Sep 25, 2015 at 20:23
  • What's the field type for the field "Countchr"? Commented Sep 25, 2015 at 20:24
  • Wrong spatial extent could be a reason for weird fc behavior
    – FelixIP
    Commented Sep 25, 2015 at 21:09
  • 1
    perhaps wrongly, but i often start throwing in print() statements to debug - what do you get if you print row[0] to the screen (or write to a file if there are too many rows to print to screen)? Commented Sep 26, 2015 at 12:15

2 Answers 2


If you have some values that are null, that may be causing the issue. Try using the following codeblock in the field calculator:

def length(field):
    return len(field) if field else 0


CountChr = length(!yourFieldName!)

You need to pass the field name behind the input field parameter before converting the expression variable to a string. Otherwise the field name passed to calculate field will simply be "len (!InputField!) instead of the actual field name for that parameter. Try changing

expression = "len(!" + InputField + "!)"


expression = "len(!{0}!)".format(InputField)

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