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Using Python in the Field Calculator in ArcGIS Desktop

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Using Python in the Field Calculator in ArcGIS Desktop. Seminar Overview. Python overview Python string functions Python numeric functions. Python Overview. Python. What is Python?. Programming language Object-oriented Started in early 1990s by Guido van Rossum

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Using Python in the Field Calculator in ArcGIS Desktop

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  1. Using Python in the Field Calculator in 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 • Free • Quick to learn • Easy to code • Easy to read • Many users (lots of help) Why Do We Love It?

  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

  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

  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

  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:]

  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

  17. Number Tricks

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

  19. Thanks for attending!

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