Add and Calculate Field in Table with ArcPy?

Question

I have written the following script to iterate it as a tool for all my tables with ModelBuilder, but i have a problem wth my codeblock. I want to add a field FID to all my tables and to add the values 0,1,2,3,4... for all rows of table. Each table has different number of rows. I am using ArcGIS 10.2.2 for Desktop.

The code i have written is this.

# Import system modules
import arcpy
import os
from arcpy import env
arcpy.overwriteoutput = True

# Set environment settings
inWorkspace = arcpy.GetParameterAsText(0)
inTable = arcpy.GetParameterAsText(1)
outTable = arcpy.GetParameterAsText(2)
data_type = ""


# Set local variables
# fieldName1 
# fieldName2 
fieldName1 = "FID_1"
fieldName2 = "Same"

arcpy.AddField_management(inTable, fieldName1, "DOUBLE", "", "", "", "", "NON_NULLABLE")
arcpy.AddField_management(inTable, fieldName2, "DOUBLE", "", "", "", "", "NON_NULLABLE")

arcpy.Copy_management(inTable, outTable, data_type)

# Calculate Field FID_1
fieldname = fieldName1
expression = "getCalc(!FID_1!)"
codeblock = """def getCalc(FID_1):
    FID_1 = 1
    for row in FID_1:
       FID_1 = FID_1 + 1
       return FID_1"""
# Execute CalculateField 
arcpy.CalculateField_management(inTable, fieldname, expression, "PYTHON_9.3", codeblock)

I am newbie in Python.

DWynne · Accepted Answer · 2015-05-20 21:23:01Z

3

You're in need of a global variable where you can increment your new fid_1 field as CalculateField moves from record to record. Substitute this in for your last few lines of code:

(Your first record will have a value of 0, the second will be 1, the third will be 2,...)

codeblock = """id = -1
def getCalc():
    global id
    id += 1
    return id
"""
expression = 'getCalc()'
# Execute CalculateField 
arcpy.CalculateField_management(inTable, fieldname, expression, "PYTHON_9.3", codeblock)

answered May 20, 2015 at 21:23

DWynne

2,40412 silver badges22 bronze badges

@SWynne excellent that wa the answer. And the arcpy.Copy_management(inTable, outTable, data_type) after that, but why do i need this global variable?

Konstantin
– Konstantin

2015-05-20 23:06:46 +00:00
Commented May 20, 2015 at 23:06
A code block function will get called once for each record in the table. Without global, id will be -1 every time getCalc is called. global adds the variable to the outer scope, ensuring the value persists between calls to the function.

DWynne
– DWynne

2015-05-20 23:14:32 +00:00
Commented May 20, 2015 at 23:14

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