I have a piece of code where the goal is to search through the field names within a feature, select any field based on a specific character (in this case "z") and then use that selected field within a Field Calculator Expression. My experience with python is limited, see the code below;

for var in List_Input:

filename = os.path.splitext(os.path.basename(str(var)))[0]
arcpy.Select_analysis(var, env+"\\"+filename, "")
var_sel = env+"\\"+filename
VRField = arcpy.ListFields(var_sel,)

VRField_Calc = ""
for field in VRField:
    if "z" in field.name:
        VRField_Calc = field.name
        arcpy.CalculateField_management(var_sel,"VR_Rate", [VRField_Calc+" + 2"])

The bottom half of the code is where the issues arise. How to pass the "VRField_Calc" (field name) into the Calculate Field Expression?

  • You need to tell it which field. "VR_Rate" should be the VRField_Calc variable.
    – Barbarossa
    Commented Jul 16, 2015 at 13:19
  • the function works as follows; CalculateField_management (in_table, field, expression, {expression_type}, {code_block}) within my equation var_sel = input table, "VR_Rate" = field. I just need to know how to pass the VRField_Calc (variable containing the found field) into the Expression. I am intentionally calculating the "VR_Rate" field. I wish for it to contain VRField_Calc +2 (in this example).
    – user52640
    Commented Jul 16, 2015 at 13:25
  • Fantastic, thank you for you help. This works great!
    – user52640
    Commented Jul 16, 2015 at 13:38

1 Answer 1


Try this:

arcpy.CalculateField_management(var_sel, "VR_Rate", '!' + VRField_Calc + '! + 2', "PYTHON_9.3")

To search for a specific field before calculating:

findField = 'some_field_name'

for field in VRField:
if field.name == findField:
    arcpy.CalculateField_management(var_sel, "VR_Rate", '!' + field.name + '! + 2', "PYTHON_9.3")
  • What about searching for a specific field name before calculating?
    – artwork21
    Commented Jul 16, 2015 at 13:52
  • @artwork21 See edits.
    – Barbarossa
    Commented Jul 16, 2015 at 14:07

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