I am trying to use an UpdateCursor fill in a field but I keep getting an error, can anyone tell me what I am doing wrong? My code is below:

import arcpy

fc= "C:\Users\Keri\Desktop\GEP_690\Project Data\FINAL_PROJECT.gdb\NYC_Demographics_2010"
with arcpy.da.UpdateCursor(fc, ["Total1","White","Pct_White"]) as cursor:
    for field in cursor:
        if field[0]==0:
            field[2] = field[1] / field[0]
print "Complete."

del row

del cursor

This is the error I keep getting:

Traceback (most recent call last):
  File "C:\Python27\ArcGIS10.2\Lib\site-packages\pythonwin\pywin\framework\scriptutils.py", line 326, in RunScript
    exec codeObject in __main__.__dict__
  File "C:\GEP_662\Lab9.py", line 15, in <module>
TypeError: sequence size must match size of the row
  • As a side note, del row and del cursor are not needed when using a cursor in a with statement.
    – Aaron
    Apr 17, 2015 at 13:24
  • Thank you for your insight, I did not know that, just learning python
    – Keri
    Apr 17, 2015 at 21:08

1 Answer 1


Use the cursor.updateRow(field) instead of cursor.updateRow([field]). You should supply an object, not the list.

  • 2
    This will solve the problem, but to be a little more specific, field already is a list (an update cursor returns a set of lists, one per row). When you write [field] you are actually passing a list with one a single entry, and that entry is a list, e.g. [['field1','field2']].
    – mr.adam
    Apr 17, 2015 at 13:42
  • Thank you Mr.adamn, Now I see why I was getting that error message. You were so helpful!!!!!
    – Keri
    Apr 17, 2015 at 21:12

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