Using Function in Field Calculator gives error 000539?

Question

I'm trying to populate a field using a function. When I run this in Pyscripter, it works fine:

d = {}

# Function #
def find_dups(val):
    d[val] = d.setdefault(val, -1) + 1
    return d[val]
#

expression = "find_dups(!LINK_ID!)"
arcpy.CalculateField_management(streets, "dups", expression, "PYTHON_9.3", "#")

However, when running it from arc toolbox I get this...

ExecuteError: ERROR 000539: Error running expression: find_dups(!LINK_ID!)

NameError: name 'find_dups' is not defined

Failed to execute (CalculateField).*

So it looks like it can't find the function. I tried using the field calculator in arc to get a python snippet and it gave me this...

arcpy.CalculateField_management(streets,"dups","find_duplicates(!LINK_ID!)","PYTHON_9.3","d = {}/n/ndef find_duplicates(val):/n d[val] = d.setdefault(val, -1) + 1/n    return d[val]/n")

When I tried to put this into my script, however, it didn't work??

ExecuteError: Failed to execute. Parameters are not valid.

ERROR 000989: Python syntax error: Parsing error

SyntaxError: invalid syntax (line 1)

Answer 1

Whenever you are copying a code block to a Python snippet, the new line character \n is written instead as /n which is where you are getting your syntax error. It does the same thing on my machine, running 10.1 SP1.

If you change all the forward slashes to backslashes, it should work. Another option would be to write the expression like so, as it's easier to debug and read.

exp = """d = {}
def find_dups(val):
  d[val] = d.setdefault(val,-1)+1
  return d[val]"""

arcpy.CalculateField_management(streets,"dups","find_dups(!LINK_ID!)","PYTHON_9.3",exp)