Using Python to combine middle parts of two fields into third field

Question

Below is how I used the Update Cursor in my final script. As you can see getValue was used a few times, perhaps there is a cleaner way to do this? But my concatenated field wouldn't populate properly otherwise.

    sourceRows = arcpy.UpdateCursor(inFeatures)
    source = sourceRows.next() 

    while source:
        fieldString1 = source.getValue(fieldName1)
        fieldString2 = source.getValue(fieldName2)
        concatString= (str(source.getValue(fieldName2))[1:7] + str(source.getValue(fieldName1))[1:7])
        source.setValue(fieldName3, concatString)
        sourceRows.updateRow(source)
        source = sourceRows.next()
    del source, sourceRows

I have a script that creates three fields in a feature class. The script adds the X and Y coordinates to the first two fields. I would like data found in the middle parts of the first two fields to populate the third field. Does anyone know how to find the middle part of a field using Python? I see where VBScript seems to have a MID function but I haven't found anything for Python yet. Below is what the third field (fieldName3) should look like.

fieldName1     fieldName2   fieldName3
12345.321       36789.321   67892345
24680.5425      98765.432   87654680

Do you see how I want data to be combined in fieldName3? Below is the script as I have it now.

import arcpy
from arcpy import env
arcpy.env.overwriteOutput = True

env.workspace = "D:/gisfiles/test.gdb/"

inFeatures = "fc"
fieldName1 = "xCoord"
fieldName2 = "yCoord"
fieldName3 = "Combined"
fieldPrecision = 18
fieldScale = 11

expression1 = "float(!SHAPE.CENTROID!.split()[0])"
expression2 = "float(!SHAPE.CENTROID!.split()[1])"

arcpy.AddField_management(inFeatures, fieldName1, "DOUBLE", fieldPrecision, fieldScale)
arcpy.AddField_management(inFeatures, fieldName2, "DOUBLE", fieldPrecision, fieldScale)
arcpy.AddField_management(inFeatures, fieldName3, "DOUBLE", fieldPrecision, fieldScale)

arcpy.CalculateField_management(inFeatures, fieldName1, expression1,
                            "PYTHON")
arcpy.CalculateField_management(inFeatures, fieldName2, expression2,
                            "PYTHON")

sourceRows = arcpy.UpdateCursor(inFeatures)
source = sourceRows.next()

while source:
        **#Instead of 12345 I need an expression to combine fieldName1 and fieldName2**
        source.setValue(fieldName3, "12345")
        sourceRows.updateRow(source)
        source = sourceRows.next()
del source, sourceRows

Answer 1

You can populate fieldName3 by using string slicing and concatenation, as Chap Cooper recommended.

Here is essentially what you want to do:

while source:
    source.setValue(fieldName3, str(fieldname2)[1:5] + str(fieldname1)[1:5])
    sourceRows.updateRow(source)
    source = sourceRows.next()
del source, sourceRows

Answer 2

If you want to round your coordinates and and have a bit more flexibility on lengths of character used for each coordinate, try this function:

def short_coord(x, y, len=4):
    div = 10**len
    return (str(int(round(x, 0) % div)).rjust(len, '0') + 
            str(int(round(y, 0) % div)).rjust(len, '0'))

You can test it out:

>>> short_coord(98765.432, 24680.5425)
'87654681'
>>> short_coord(95.432, 120.5425, len=3)
'095021'

Note: I assume the inputs are floating point numbers, and the expected output is a string. Also, in case you are wondering, % is the handy modulo operator.

Answer 3

possibly change it to:

sourceRows = arcpy.UpdateCursor(inFeatures)  
for source in sourceRows:    
    source.fieldName3 == str(fieldname2)[1:5] + str(fieldname1)[1:5])
    sourceRows.updateRow(source)     
    del source

del sourceRows 

if source.setValue doesn't work, which occassionally it doesn't, for whatever reason...