Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am only in the beginning stages of learning Python.

I have a column, 'QUANTITY_SOLID', that I want to take the sum of all of its rows. I understand I can do this with 'SUMMARY_STATISTICS', but i'm not trying to create another entire table nor do anything other than simply SUM up that column. Once I have it summed up, I want to insert the sum into a new NULL field that I have created - I am attempting to do this via the 'CALCULATE_FIELD' tool.




Any helpful suggestions on where to go from here would be greatly appreciated, thank you!

share|improve this question
Are you looking for a Python scripting solution or do you need to do this entirely in the field calculator? – Aaron Aug 7 '14 at 21:21
@ Aaron, Honestly either would be fine. I'm trying to learn as much Python as I can but learning how to do it either way would be great. – JumpInTheFire Aug 7 '14 at 21:32
I think JumpinInTheFire is appropriate! You need to use a cursor, in this case an arcpy.da.searchcursor and arcpy.da.updatecursor. Google that and if you have difficulty understanding them I'll provide some code. – Michael Miles-Stimson Aug 7 '14 at 21:34
up vote 7 down vote accepted

Cursors are the way to go for this type of problem.

First, create a list of values using a Search Cursor and a generator expression:

b = sum(row[0] for row in arcpy.da.SearchCursor(fc, 'QUANTITY_SOLID'))

Then run an Update Cursor to populate the QUANTITY_SOLID_SUM field:

with arcpy.da.UpdateCursor(fc, ['QUANTITY_SOLID_SUM']) as cursor:
    for row in cursor:

Finally, update the rows with the value from the generator

    row[0] = b

import arcpy

# Define the feature class
fc = r'C:\path\to\your\fc'

# Use a generator expression to populate a list from the 'QUANTITY_SOLID' field
b = sum(row[0] for row in arcpy.da.SearchCursor(fc, 'QUANTITY_SOLID'))

with arcpy.da.UpdateCursor(fc, ['QUANTITY_SOLID_SUM']) as cursor:
    for row in cursor:
        row[0] = b
share|improve this answer
I like that Aaron for the simplicity! Please note JumpinInTheFire that that is not a field calculator expression. – Michael Miles-Stimson Aug 7 '14 at 21:41
Awesome, thank you both for the help, I greatly appreciate it. I didn't intend for you to write the code (just to push me in the right direction), but either way thanks! – JumpInTheFire Aug 7 '14 at 21:51
There's no need to sum up the values each iteration; remove it from the for loop. For that matter, you can pass a generator expression directly into sum, a la summed = sum(row[0] for row in arcpy.da.SearchCursor(fc, 'QUANTITY_SOLID')) – Paul Aug 7 '14 at 22:14
Good call @Paul. Post updated to address comments. – Aaron Aug 7 '14 at 22:23

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.