Using ArcPy to multiply fields in attribute table?

Question

I am trying to identify a method to multiply 2 fields in the same attribute table and write the product of the calculation into an added field. The code creates the empty fields, now I just want to understand how to use arcpy to run a field calculation.

This is what I have so far:

# Set the local parameters
inFeatures = "ESR_States"
joinField = "STID"
joinTable = "ESR_Weather"
# Join two feature classes by the STID field 
arcpy.JoinField_management (inFeatures, joinField, joinTable, joinField)
# Add fields to ESR_States
fieldName1 = "POT_PROD"
fieldName2 = "POT_CONSU"
fieldName3 = "SELF_SUS"
fieldName4 = "FUTURE_POP"
arcpy.AddField_management(inFeatures, fieldName1, "LONG")
arcpy.AddField_management(inFeatures, fieldName2, "LONG")
arcpy.AddField_management(inFeatures, fieldName3, "LONG")
arcpy.AddField_management(inFeatures, fieldName4, "LONG")
arcpy.CalculateField_management()

Community · Accepted Answer · 2017-04-13 12:33:56Z

3

I think the easiest way to learn "how to use ArcPy to run a field calculation" is to:

Go to the Search window and find the Calculate Field tool
Open its tool dialog
Configure a test calculation and run the tool
Open the Geoprocessing | Results window
Right-click on the Calculate Field run that you see there
Choose Copy As Python Snippet
Paste the code snippet into your script
Modify the code thus pasted, if necessary

If you need more help with using the Field Calculator from ArcPy than this then I recommend reviewing our self-assembling FAQ on ArcPy and the Field Calculator.

edited Apr 13, 2017 at 12:33

CommunityBot

1

answered Sep 17, 2016 at 23:00

PolyGeo♦

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Add a comment |

Midavalo · Accepted Answer · 2016-09-18 01:37:57Z

I rarely use the Calculate Field tool to alter attributes in Python, but rather an Update Cursor as I find the syntax easier and the Python cleaner. Note that a cursor operates on a row by row basis. Here is an example of how you would multiply two fields and write the product to a third field. This script assumes you have already created the fields "field1", "field2" and "field3".

import arcpy

fc = r'C:\path\to\your.gdb\featureclass'

with arcpy.da.UpdateCursor(fc, ["field1", "field2", "field3"]) as cursor:
    for row in cursor:
        row[2] = row[0] * row[1] # This means field3 = field1 * field2
        cursor.updateRow(row)

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