1. Using Python in the Field Calculator
ArcGIS Desktop

2. Seminar Overview Python overview Python string functions
Python numeric functions

3. Python Overview

4. Python What is Python? Programming language Object-oriented
Started in early 1990s by Guido van Rossum
Named after Monty Python’s Flying Circus
Why Do We Love It?
Free
Quick to learn
Easy to code
Easy to read
Many users (lots of help)

5. Python and ArcGIS Desktop
Label Expression
Field Calculator
Python Window

6. Python Overview Python Syntax Basics: Python is case sensitive!
In python, surround column(field) names with !!

7. Simple python expressions may contain:
Column(field) names
!Street_Name!
Literal text
“meters” or ‘meters’
Mathematical and string operators
+ - / *
Functions
.upper()

8. Working with Strings (alpha numeric values)

9. Python Syntax: Strings
Strings are Surrounded by quotes
Double “”
Single ‘’
Backslash (\) is a special character
\n = new line
\t = tab
Strings can be defined with either double quotes or single quotes. Can mix and match double and single quotes in a script, however, a string that is started with a double quote must end with a double quote, and a string that is started with a single quote must end with a single quote.

10. String Operators String Concatenation +
Python checks the field type. If you are using a + with numbers, Python does math. If you are using a + with strings, the strings get concatenated.
!STATUS! + “AS OF 2016”
!STATUS! + \t + “2016”
!VALUE! + 100
Cannot add strings to numbers, or vice versa.

11. Working with Functions
Lots of functions for manipulating data.
column_name>.<function>(function_parameters)
Some functions don’t have parameters
!street_name!.upper()

12. String Functions Built-in Functions .upper() .lower() .title()
.capitalize
.replace(<findstr>, <replacestr>)
Many others…
!Company!.upper()

13. String Functions !Field1!.replace(<old>,<new>)
“COUNTY_NAME” = REPLACE(“COUNTY_NAME”,’County’,’’)
Replaces a portion of a string
strings are case sensitive in expressions

14. Python Slicing Used to extract a portion of a text string
!Field1![start:num_characters]
Zero-based
“COMPANY_ABREVIATION” = !COMPANY_CODE![0:2]
“UNIQUE_ID’ = !PARCEL_NUM![-5:]
strings are case sensitive in expressions

15. Working with Numeric Values

16. Number Operators/Functions
Mathematic
*, /, +, -
Round
round(x [,n])
x rounded to n decimal places
Truncate
math.trunc(x)
Truncates number x to an integer
For round, Python rounds away from zero. round(0.5) is 1.0 and round(-0.5) is -1.0.

17. Number Tricks EXPRESSION RESULT !Elevation_ft! * 0.3048 Feet  Meters
!Elevation_m! *
Meters  Feet
!Area_km2! *
km2  Acres
!Area_acres! *
Acres  km2
round(!PROD! * !Royalty!, 2)
$ format
!Part1! / !Total!
% percentage

18. Getting Help Help buttons on tools Arc GIS Desktop help:
“SQL (Structured Query Language), reference” in Index
“Fundamentals of Field Calculations”

19. Thanks for attending!