Defined function not working but code works in an IF statement

Question

Apologies for the lack of comments and notes in the scripts, they're a copy paste from large one. The attached Scipt_working.py works fine and updates the fields as I require.

As I have several fields which require the same conversion and there's many more values to convert I thought I'd create a function with a couple of variables for the fields. However, I can't get the function to work. The attached script Scipt_function_not_working.py doesn't work and I'm not sure why.

Any ideas where I've gone wrong?

Thanks in advance.

Script_working.py.zip

Script_function_not_working.py.zip

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NiklasNorrthon · Answer

Just a couple general code review comments:

Your renamefld function is a perfect candidate for a dictionary lookup, and errors should be handled as errors.
field_map = { 
    71 : "Natural Forest",
    72 : "Planted Forest - Pre-1990",
    73 : "Post 1989 Forest",
    # et cetera
    }

class SubtypeConversionError(Exception):
    pass

def renamefld(a):
    try:
        return field_map
    except KeyError:
        raise SubtypeConversionError("Error with converting subtype %d to text" % a)

Anonymous User · Answer

Original User: mpc

Hi Duncan,

Thanks for your input on this, you were spot on. With a couple of changes I managed to get the result I needed. The code for Arc10 is slightly different so I've copied it below. The "global" variable option I used is very useful! Unfortunately I couldn't get row.x to work and had to hard code the fields.

Markdef renamefld(a):
    try:        
        if a == 71:
            return "Natural Forest"
        elif a == 72:                
            return"Planted Forest - Pre-1990"
        elif a == 73:
            return "Post 1989 Forest"
        elif a == 74:
            return "Grassland - With woody biomass"
        elif a == 75:
            return "Grassland - High producing"
        elif a == 76:
            return "Grassland - Low producing"
        elif a == 77:
            return "Cropland - Perennial"
        elif a == 78:
            return "Cropland - Annual"
        elif a == 79:
            return "Wetland - Open water"
        elif a == 80:
            return "Wetland - Vegetated non forest"
        elif a == 81:
            return "Settlements"
        elif a == 82:            
            return "Other"
        else:
            print "Error with converting subtype to text"
            return "!"
    except:
        print arcpy.GetMessages()

def region(a):
    try:        
        if a == 1:
            return "Northland"
        elif a == 2:
            return "Auckland"
        elif a == 3:            
            return "Waikato"
        elif a == 4:            
            return "Bay of Plenty"
        elif a == 5:            
            return "Gisborne"
        elif a == 6:            
            return "Hawkes Bay"
        elif a == 7:            
            return "Taranaki"
        elif a == 8:            
            return "Manawatu-Wanganui"
        elif a == 9:            
            return "Wellington"
        elif a == 12:            
            return "West Coast"
        elif a == 13:
            return "Canterbury"           
        elif a == 14:            
            return "Otago"
        elif a == 15:            
            return "Southland"
        elif a == 16:            
            return "Tasman"
        elif a == 17:            
            return "Nelson"            
        elif a == 18:            
            return "Marlborough"
        else:
            print "Error with converting region to text"
            return "!"
    except:
        print arcpy.GetMessages()

global row, cur

cur = arcpy.UpdateCursor(inMemFc)

for row in cur:

LUM_Region = row.LUM_REG_ID    
    regvalue = region(LUM_Region)

if regvalue != "!":
        row.LUM_REGION = regvalue
        cur.updateRow(row)
        
    LUC_ID = row.LUC_ID

fldvalue = renamefld(LUC_ID)

if fldvalue != "!":
        row.LUC_NAME = fldvalue
        cur.updateRow(row)

PREV_LUC_ID = row.PREV_LUC_ID

fldvalue = renamefld(PREV_LUC_ID)

if fldvalue != "!":
        row.PREV_LUC_N = fldvalue
        cur.updateRow(row)

IMPR_LUC_I = row.IMPR_LUC_I

fldvalue = renamefld(IMPR_LUC_I)

if fldvalue != "!":
        row.IMPR_LUC_N = fldvalue
        cur.updateRow(row)

Hornbydd · Answer

Mark,

I don't have ArcGIS 10 so I've had to do this in 9.3 python, so the code is a little different. My knowledge of Python ain't great but I realised you are not actually returning a value and what was getting passed to the function was is a string and you were not writing the new string back to the row. So below is some code that worked on a table I knocked up, hope you understand it?

Duncan
import arcgisscripting
gp =arcgisscripting.create(9.3)
gp.workspace= r"C:	emp"

def renamefld(a):
    
    if a == 1:
        return "Natural Forest"
    elif a == 2:                
        return "Planted Forest - Pre-1990"
    else:
        # Return an ! so we know not to attempt to update row       
        print "Error with converting subtype to text"
        return "!"

# Create update cursor
rows = gp.UpdateCursor("test.dbf")
row = rows.Next()

while row:
    # Get row information
    id = row.id
    type = row.type

# Call function to change type 
    type = renamefld (id)
    
    # update row object    
    if type != "!":
        row.type = type
        rows.updateRow(row)
    
    row = rows.Next()

# release cursor
del row
del rows