Summing all record in field and putting value in new field

Question

I try to sum all record in "AREA" field and put a value in "SUM" field for calculate a "Ratio" field by using Python.

But I struck in a sum part.

Here is my code :

arcpy.AddField_management(outclip, "AREA", "DOUBLE", 2, "", "", "", "", "")
arcpy.AddField_management(outclip, "SUM", "DOUBLE", 2, "", "", "", "", "")
arcpy.AddField_management(outclip, "Ratio", "DOUBLE", 2, "", "", "", "", "")

arcpy.CalculateField_management(outclip ,'AREA','!shape.area@SQUAREKILOMETERS!','PYTHON')
#arcpy.CalculateField_management(outclip ,'SUM', ['AREA', 'SUM'])','PYTHON')

Answer 1

You can use cursors like this:

import arcpy

fc = r'C:\folder\data.gdb\featureclass' #Change to your data source
fields = ['AREA','SUM','Ratio']

totsum = sum([row[0] for row in arcpy.da.SearchCursor(fc, fields[0])]) #List all values in area field and sum them

#Update/calculate sum and ratio fields
with arcpy.da.UpdateCursor(fc, fields) as cursor:
    for row in cursor:
        row[1] = totsum #[1] is index of SUM field in fields list
        row[2] = row[0]/totsum #[0] is AREA, [2] RATIO
        cursor.updateRow(row)

(You dont need the SUM field)