Field Calculator Python Expression Issues

Question

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)
else:
    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! )

Answer 1

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 = '_'
    b=fieldV
    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

customReplace(!Layer!)

Answer 2

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.

Answer 3

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?

Answer 4

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)
  rows.updateRow(row)

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.