How to calculate Field using part of filename in ModelBuilder?

Question

I am new to ModelBuilder and have not been able to figure how to use part of the FC name: For example the first FC in my GDB containing around 100 files is "A1005_GPS_Residence", and I need to calculate the new field SID = "A1005".

I have seen some posts with python and manually using the Field Calculator.

I tried using one expression, shown in the screenshot, but I am not sure if I can combine field calculations with inline substitution or the like !%Name%![1:4].

Screenshot of MB

• blah238: Just a suggestion but unless you know the desired substring is ALWAYS going to be the first 5 characters it might be better to use split or a regex to get at it.
• PolyGeo: The link in your question is broken. Can you refresh or remove it, please?

Answer 1

I have attached a python script that should steer you in the right direction. You will find that custom naming in loops is much easier in python than model builder.

EDIT: Added additional code to address new information

# Import standard library modules
import arcpy, os, sys
from arcpy import env
# Allow for file overwrite
arcpy.env.overwriteOutput = True
# Set the workspace directory 
env.workspace = r"C:\temp.gdb" 
# Get the list of the featureclasses to process
fc_tables = arcpy.ListFeatureClasses()
# Loop through each file and perform the processing
for fc in fc_tables:
 print str("processing " + fc)
 # Define field name and expression
 field = "SID"
 expression = str(fc[:5]) #subsets first 5 characters of fc name
 # Create a new field with a new name
 arcpy.AddField_management(fc,field,"TEXT")
 # Calculate field here
 arcpy.CalculateField_management(fc, field, "expression", "PYTHON") 

enter image description here

• user9914: Thanks so much for all the help and for the script. It saved me hours of trying to piece bits of python code together, and a nice way to start looking into arcpy.