topic Re: Update Cursor to Calculate Field in Python Questions

Update Cursor to Calculate Field

KevinWilliams — Sat, 07 Dec 2013 16:09:03 GMT

I'm trying to use an update cursor to calculate a field. Basically, I'm trying to avoid division by 0 by looking in row[0] and see if it's 0. My code thus far is:

import arcpy
fc="C:/Temp/crimeGrid.shp"
fields="'MEAN_GRIDC', 'SUM_Join_C', 'crimeRate')
with arcpy.da.UpdateCursor(fc,fields) as cursor:
    for row in cursor:
        if (row[0] > 0):
            row[2] = row[1]/row[0]
        else:
            row[2] = 0
        cursor.updateRow(row)

Any ideas or help on what I'm missing? I presume that it's the calculation aspect of my code.

Re: Update Cursor to Calculate Field

Anonymous User — Sat, 11 Dec 2021 17:56:59 GMT

You need to pass the fields variable in as a python list type (using [ ] ). See more about python types [url=http://docs.python.org/2/tutorial/datastructures.html]here[/url].

import arcpy
fc = "C:/Temp/crimeGrid.shp"
fields = ['MEAN_GRIDC', 'SUM_Join_C', 'crimeRate']
with arcpy.da.UpdateCursor(fc,fields) as cursor:
    for row in cursor:
        if row[0] > 0:
            row[2] = row[1]/row[0]
        else:
            row[2] = 0
        cursor.updateRow(row)

This should do the trick.

Re: Update Cursor to Calculate Field

KevinWilliams — Sat, 07 Dec 2013 22:58:17 GMT

I tried your suggestion, but still no luck. However, looking at the ArcGIS 10.1 resource documentation, it should be as shown. I can't help but think it has something to do with the division of the rows... row[2] = row[1]/row[0].

Re: Update Cursor to Calculate Field

KevinWilliams — Sat, 07 Dec 2013 23:07:41 GMT

Sorry for the ridiculous question. I continually thought it was in the division of rows, so I looked into my fields a little closer. Turns out, Row[0] and Row[1] were Double and Row[2] was Long. Fixed that aspect and the code works as is.