If else if in ArcMap Field Calculator (Python)

Question

Help! I think I am missing something that must be so obvious but I cannot figure out what I am doing wrong. Here's some background:

I have one short integer field (MajAspNum) that has values 1-10. I have another text field (Direction) that needs to be filled. I am trying to use the Field Calculator to calculate it but am not succeeding in any way. I should know what I'm doing but I just can't seem to make it work.

Pre-logic Script Code:
def des(num):
if num = 1:
 return "Flat"
elif num = 2:
 return "North"
elif num = 3:
 return "Northeast"
elif num = 4:
 return "East"
elif num = 5:
 return "Southeast"
elif num = 6:
 return "South"
elif num = 7:
 return "Southwest"
elif num = 8:
 return "West"
elif num = 9:
 return "Northwest"
elif num = 10:
 return "North"
else:
 return "N/A"
Direction = 
des (!MajAspNum!)

It gives me a GeoProcessing error of invalid syntax on line 2. I have tried just selecting by attributes in the attributes table and then using field calculator more simply on just those but that gives me a very weird error that literally makes no sense. I'm hoping my error is a really obvious fix to someone out there!

• Tom: The answers are correct; however the issue for which you were getting the error message is that tests for equality require two equals signs: if num ==1:

Answer 1

def des(num):
 aList=['Flat', 'N', 'NE', 'E','SE','S','SW','W','NW','N']
 if num in range(1,11):return aList[num-1]
 return 'N/A'

Alternatively select valid records and use:

['Flat', 'N', 'NE', 'E','SE','S','SW','W','NW','N'][ !MajAspNum! -1]

Answer 2

A switch statement is ideal for what you want to do. Since Python doesn't support switch statements, you can use dictionary mapping to accomplish the same thing.

def des(num):
 the_dict = {1: 'Flat',
 2: 'North',
 3: 'Northeast',
 4: 'East',
 5: 'Southeast',
 6: 'South',
 7: 'Southwest',
 8: 'West',
 9: 'Northwest',
 10: 'North'
 }
 return the_dict.get(num, 'N/A')

• Fezter: I think this is the best solution. Switch statement (or in this case, a dictionary), is the right call.

Answer 3

here it is in vbs, i can do it in python later when i have the time.

dim result1
if [MajAspNum] = "1" then
 result1 = "flat"
Elseif [MajAspNum] = "2" then
 result1 = "north"
Elseif [MajAspNum] = "3" then
 result1 = "northeast"
...
Else result1 = "N/A"
end if

^^ codeblock

Direction = result1

I found this searching the site, Writing conditional (if/then) statements into Field Calculator of ArcGIS for Desktop using Python parser? it has the correct syntax for python.