Uisng Python Parser of Field Calculator with ArcPy?

Question

I have a point shapefile with two columns i want to process. The first column is aspect and the second is aspect_m60, there is only one row with the aspect of my point. I have tried to write a script in Python for ArcGIS 10.2.2 because i want to put it in my code but with no success. The code is this:

# Calculate Field
import arcpy
# Set environment settings
arcpy.env.workspace = "c:/W/Sik"
# Set local variables
inTable = "Point"
fieldName = "aspect_m60"
expression = "getCalc(!aspect!, !aspect_m60!)"
codeblock = """def getCalc(aspect, aspect_m60):
   if (aspect < 60):
      aspect_m60 = (aspect - 60) + 360
   if (aspect = 60):
      aspect_m60 = aspect - 60
   else:
      aspect_m60 = aspect - 60"""

Answer 1

It is much more intuitive, in my opinion, to work with Cursors (rather than trying to emulate the field calculator in a script) for this type of problem. This is how you would port the problem over to an Update Cursor:

import arcpy

# The input FC
fc = "C:/W/Sik.gdb/yourFC"

with arcpy.da.UpdateCursor(fc, ["aspect", "aspect_m60"]) as cursor:
    for row in cursor:
        # row[0] = "aspect"
        # row[1] = "aspect_m60"
        if row[0] < 60:
            row[1] = (row[0] - 60) + 360
        elif row[0] == 60:
            row[1] = row[0] - 60
        else:
            row[1] = row[0] - 60

        cursor.updateRow(row)

Answer 2

You are trying to set the field within the code block, when actually you need the code block to return the value you're looking for. If you just just add return aspect_m60 after the else block, it should work fine.

Think of the code block as a place to write functions whose results can be used in your field calculator expression.

Answer 3

Your function is not returning anything. I've modified your code to return the value of aspect_m60.

# Calculate Field
import arcpy
# Set environment settings
arcpy.env.workspace = "c:/W/Sik"
# Set local variables
inTable = "Point"
fieldName = "aspect_m60"
expression = "getCalc(!aspect!)"
codeblock = """def getCalc(aspect):
   if (aspect < 60):
      aspect_m60 = (aspect - 60) + 360
   if (aspect = 60):
      aspect_m60 = aspect - 60
   else:
      aspect_m60 = aspect - 60
   return aspect_m60"""

Answer 4

As a couple others have pointed out, you're missing a return value. You're also confusing the assignment operator = for an equality operator == (in the 2nd if). The if structure is also incorrect (if/if/else), and will calculate the wrong value for anything less than 60 (should be if/elif/else).

If you still want to use CalculateField (the other answer with UpdateCursor is perfectly valid), the code block below would be what you intended.

codeblock = """def getCalc(aspect, aspect_m60):
    if aspect < 60:
        aspect_m60 = (aspect - 60) + 360
    elif aspect == 60:
        aspect_m60 = aspect - 60
    else:
       aspect_m60 = aspect - 60
    return aspect_m60
"""