Using Python for Field calculator?

Question

I have problem with Field Calculator, using ArcGIS 10.2. I tried to write a statement but I don't know what is wrong.

I have two columns:

The first contains a number code. Every code represents some text data. For example: "1" means "trees,etc."

The second column (string) is empty and should contain text data. Could you help me with Python ?

Answer 1

Your code is not correctly formatted Python code:

1. Indentation is important in Python, as it defines where functions and conditions start and end.
2. You need a : after the function definition
3. The correct operator for equality-comparison is the == and not simply = which assigns a value to a variable.

Also, with respect to the field calculator in ArcGIS, if you use a function to calculate your value, you also will need to check the "Show Codeblock" check box.

In your case, you have two possibilities:

1. Your if/else-statement is very simple, so you could rewrite in a single Python line, and there is no need for a codeblock:

   "SampleText" if !Coded! == 1 else "SampleText_2"
   

2. Using a code block, with the code block checkbox activated, the code block should be:

   def Text_d(Coded):
       if Coded == 1:
           return "SampleText"
       else:
           return "SampleText_2"
   

   and then in the "Coded=" box below you would need to write:

   Text_d(!Coded!)
   

   This second method gives you the possibility to use many Python functionalities such as nested conditions:

   def Text_d(Coded):
       if Coded == 1:
           return "SampleText"
       elif Coded == 2:
           return "SampleText_2"
       else:
           return "SampleText_3"