6

This should be simple but I've spent days trying everything to get it to work. I need to update a field in a layer based on two other fields. I can't even get it to update based on one field. Could someone please tell me whats wrong. So in this script I want to be classifying the outfield as "poor" if the infield is "Sandy". I will also have another field of numbers (and infield2 = "10").

rows = arcpy.UpdateCursor(infc) #this is my feature layer
for row in rows:
    if row.getValue(Infield1) == "Sandy":
        row.setValue(Outfield, "poor")
    else:
        row.setValue(Outfield, "none")
    rows.updateRow(row)
del rows

Thanks for all the answers. The script only works if written like this: I did not want to name the field names though, but at least it works.

The only way I could do a range 5 - 10 was to put > 5 and <10 (see line 23)

for row in rows:
    if row.getValue("Texture") == "Sandy" and row.getValue("Humus") < 10:
        row.setValue("Richness", "poor")
    elif row.getValue("Texture") == "Sandy" and row.getValue("Humus") > 10:
        row.setValue("Richness", "medium")
    elif row.getValue("Texture") == "Sandy-Clay" and row.getValue("Humus") < 5:
        row.setValue("Richness", "poor")
    elif row.getValue("Texture") == "Sandy-Clay" and row.getValue("Humus")  >= 5 and row.getValue("Humus")  <= 10:
        row.setValue("Richness", "medium")
    elif row.getValue("Texture") == "Sandy-Clay" and row.getValue("Humus") > 10:
        row.setValue("Richness", "rich")
    elif row.getValue("Texture") == "Clay" and row.getValue("Humus") < 5:
        row.setValue("Richness", "poor")
    elif row.getValue("Texture") == "Clay" and row.getValue("Humus") > 5:
        row.setValue("Richness", "rich")
    else:
        row.setValue("Richness", "unclassified")
    rows.updateRow(row)
del rows, row
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0

4 Answers 4

Reset to default
5 
    cur = arcpy.UpdateCursor(infc, "Where Infield1 = 'Sandy'") #this is my feature layer
    for row in cur:
        row.Outfield = "poor"
        cur.updateRow(row)
        del row
    del cur

    cur = arcpy.UpdateCursor(infc, "Where Infield1 <> 'poor'") #this is my feature layer
    for row in cur:
        row.Outfield = "none"
        cur.updateRow(row)
        del row
    del cur

or

cur = arcpy.UpdateCursor(infc) 
for row in cur:
    if row.Infield1 == "Sandy":         
        row.Outfield = "poor"    
    else:         
        row.Outfield = "none"    
    cur.updateRow(row) 
    del row
del cur

Is how I would do this. Too many times I have had issues trying to retrieve values with getValue(fieldname) so I reference the columns themselves as row.columnName and it works fine

Hope this helps.

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4
  • thanks. It seems my script doesn't work with Infield1 etc instead of the actual name of the field.
    – Nevu
    Sep 27, 2011 at 14:57
  • 1
    I believe that in the first instance which uses a "where" statement to return specific rows, you need to have quotations marks "" around the field name in the case of shapefiles and brackets [] for geodatabase feature classes.
    – Jason Bellino
    Sep 27, 2011 at 15:05
  • ahh! I had it working after removing the brackets and changing the field names to the actual field name. But now it doesn't seem to work. I also tried it with the cur method and nothing happens even though it says completed what have I done wrong..I tried with [] instead as well rows = arcpy.UpdateCursor(infc) for row in rows: if row.getValue("Texture") == "Sandy": row.setValue("Richness", "poor") else: row.setValue("Richness", "none") rows.updateRow(row) del rows
    – Nevu
    Sep 27, 2011 at 16:01
  • Could you edit your original question with the new pieces of code you've been trying and having trouble with? It's difficult to piece together what you've done and where things might be going wrong.
    – Jason Bellino
    Sep 27, 2011 at 17:21
3

Try removing the parentheses from your "if" statements so that you have:

if row.getValue("Infield1") == "Sandy":
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1
  • Glad I could help out! @Hairy posted some good alternatives using the "row.fieldname" method instead of the "row.getValue()" and "row.setValue()" which I find a little more straightforward when working with fixed field names. PS - don't forget to upvote us and accept an answer! :)
    – Jason Bellino
    Sep 27, 2011 at 14:58
1

Change

del rows

to

del rows, row
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1
  • 1
    thanks, but it works with either del rows, row or del rows
    – Nevu
    Sep 27, 2011 at 14:45
1

You can always use "with" that allows objects like files/cursores to be used in a way that ensures they are always cleaned up promptly and correctly. But it needs the table/fc field names to be passed as arguments as well.

fields = ('InField1', 'Outfield')
    try:
        with arcpy.da.UpdateCursor(infc,fields) as cursor:
           for row in cursor:
               if row[0]== "Sandy":         
                   row[1] = "poor"    
               else:         
                   row[1] = "none"    
               cursor.updateRow(row)
    except Exception, e:
        # If an error occurred, print line number and error message
        tb = sys.exc_info()[2]
        print "Line %i" % tb.tb_lineno
        print e.message
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4
  • You're mixing and matching search with update cursors. You're also mixing and matching the data access module with the normal cursor. You need to pass field names differently.
    – Paul
    Aug 13, 2013 at 23:53
  • @Paul, thank you for poiting it out! i've edited the code to use normal module instead of the da module, like he used to. I forgot da module requires fields as argument as well!
    – neverMind
    Aug 14, 2013 at 4:28
  • Not to nitpick, but normal cursors (as far as I know) do not support with statements. At least in 10.1 SP1 I have never been able to get them to work.
    – Paul
    Aug 14, 2013 at 4:31
  • Ok, I thought i've used it before, but I obviously confused.
    – neverMind
    Aug 14, 2013 at 4:36

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