I'm pretty new to Python and this is my first post on this forum so I could use some help. I am currently attempting to run some code in the Field Calculator in a model in order to replace string characters (hyphen, period, space) with an underscore ('_'). Here's what I have now.

def customReplace(Layer):
repList = ['-', ' ', '.'];
rep = '_'
for repList in Layer:
    return Layer.replace(repList, rep)
    return Layer

Im getting a syntax error: ERROR 000539: SyntaxError: unexpected EOF while parsing (, line 1) Failed to execute (Calculate Field (2)).

Anybody out there give me a hand?

By the way, I defined the above function in the pre-logic script code area and I'm calling it via

customReplace( !Layer! )

4 Answers 4


I am not completely sure to understand the aim of your script, but here are some comments

def customReplace(fieldV): # you must indent after your def
    repList = ['-', ' ', '.'] #remove the ;
    rep = '_'
    for old in repList: #I guess you want to replace the values in replist
        b = b.replace(old, rep) #here you need return, not print
    return b #no need to use else, but you must unindent

note that you need to put the function in a code block and call it with the name of the field


  • SO I thought your help worked because it ran without error, however I checked the field values after running and got some strange results. I really just need to run the replace() function but I need mutliple "old values" (hyphen, period, and space) and only one new value to replace with (an underscore). Maybe I need to rethink and not use lists....?
    – user37090
    Commented Sep 24, 2014 at 20:27
  • the for loop is supposed to replace each value of your list with "_", it is done one by one as you cannot use the list n one go. Can you tell more precisely what's wrong ?
    – radouxju
    Commented Sep 24, 2014 at 21:19

I am assuming you mean field value that needs changed and not your layer name since you mentioned Field Calculator

Same logic could be applied in a script for actual layer names too though

Ok.. I understand you and have it down.

(1) Make sure your parser is marked for python.

(2) In the Pre-Logic Script Code:

def customReplace(fieldValue):
  repList = ["DRG", "2014"] #my examples, change to yours
  repValue = "_"
  for item in repList:
    if item in fieldValue:
      fieldValue = fieldValue.replace(item, repValue)
  return fieldValue

(3) In the 2nd box, make sure you call this function and pass in the field you're editing.

See my photo for more info.Screenshot

  • Fantastic. That worked very well. I was hung up on how to access the values in repList where you used for item... if item in fieldValue:....etc. Very helpful. Thanks.
    – user37090
    Commented Sep 24, 2014 at 20:37

I'm not sure what you're trying to do exactly. Is Layer supposed to be a feature class or shapefile, or a field?

One, all the lines in the function should be indented. Two, you can't have a semicolon end a line. Three, Layer is probably a reserved word, don't use it. Four, repList isn't in Layer; that loop will either error out or give you unexpected results. Five, while not exactly an error, is there a point in returning Layer in the else clause?

I don't think what you want is that hard, but what exactly are you trying to do?

  • Layer is the name of the field I am calculating with the python expression. Not sure if there is a need to return Layer if there is no replacement strings to be made?
    – user37090
    Commented Sep 24, 2014 at 20:10
  • I'm creating a model that imports all geometries of a cad drawing (point, polyline, annotation, multipatch, polygon) and then creating featureclasses from a common field value in each cad geometry, the field being 'Layer'. But first I have to get the field values without spaces, hyphens, or periods in the names. Does that make any sense?
    – user37090
    Commented Sep 24, 2014 at 20:14

I wanted to provide another alternative to my previous answer

I am more of a fan of using the python interactive window and an UpdateCursor for most of my attribute table changes. When I wrote my above answer, I wrote it in the interactive window and translated it to the field calculator. My interactive code was:

replaceList = ["DRG", "2014"]
replaceValue = "_"

rows = arcpy.UpdateCursor(#LAYERNAME)
for row in rows:
  currentValue = row.getValue("UniqueID") #your field name as a parameter
  for item in replaceList:
    if item in currentValue:
      currentValue = currentValue.replace(item, replaceValue)
    row.setValue("UniqueID", currentValue)

Notes... Typically I am more of a fan of using syntax like currentValue = row.FIELDNAME instead of getValue, and the same goes with setting it like row.FIELDNAME = currentValue. Using setValue and getValue are good for understanding the process, but I prefer the shorter syntax.

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