I have browsed answers to similar questions but I still can't figure it out. I have created a new field called "namemonyr" in all of 646 shapefiles. I now want to populate that field using (preferably part of) the input file name. My files are currently named e.g. "cl_Arthur_Apr_12.shp". I want the namemonyr field to be filled in with the string "Arthur_Apr_12". The name, month and year elements are different in every shapefile name. I need to know when I output the tables as CSV files which subject the data came from and for what period - I need this info in the table, not just in the file name. I have the iterator working fine.

I have tried using the field calculator in model building using the expression

!%Name%[3:]! to remove the cl_ element of the file name.

The error message reads:

ERROR 000539: Invalid field
failed to execute (Calculate Field)

I have tried using the Parse Path tool to get the file name as the Value that then goes into the Expression part of the field calculator. But I don't really understand this tool.

I have tried variations on these. Nothing is working!

I am very new to ArcGIS and Python and have never used Python coding.

1 Answer 1


I'm not sure where %Name% is coming from, so I may not be able to answer your question entirely, but wrapping something in exclamation points is how you get a value out a field in a python code block. %Name% is a model builder variable, not a field name. So remove the the exclamation points and just use %Name%[3:] and see if that works.

  • Hi there, I tried that but it got a slightly different error message which now says NameError: name 'cl_Aurthur_Apr_12' is not defined. Name is the name of the files in the iterator. My understanding is that %Name% iterates through each shapefile in the folder you are working in.
    – Aoibh
    Nov 13, 2014 at 17:14
  • 1
    oh, then you probably need to wrap it in quotes so python treats it as a string, instead of a variable name. "%Name%"[3:]
    – MWrenn
    Nov 13, 2014 at 18:35
  • That worked @MWrenn! Is it in appropriate to say I love you?! thanks so much!
    – Aoibh
    Nov 14, 2014 at 10:04

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