1. Introduction to GIS
PythonScript
CGIS-NURIntroduction to ArcGIS II

2. Lesson 6 overview How do I create a new script?
Introduction to GIS
Lesson 6 overview
How do I create a new script?
How do I write/change a script?
How do I run a tool from a script?
How do I set an environment setting in a script?
What syntax do I use?
What functionality is available?
How do I run a script from an ArcGIS application?
How do I fix my errors?
CGIS-NURIntroduction to ArcGIS II

3. Why write scripts? Automate workflow
Introduction to GIS
Why write scripts?
Automate workflow
Copy all incoming data into a geodatabase
Perform project, clip, buffer operations on multiple data sets
Run code at specific dates and times
Windows AT command
Windows scheduler
Easily distribute code
A script is a self-contained, single file
CGIS-NURIntroduction to ArcGIS II

4. Introduction to GIS
Points of interest
Scripting ArcObjects do not replace standard ArcObjects
Customize or interact with the interface
Developers (Desktop, Engine, Server)
Can use many scripting/programming languages
VBScript, JScript, Perl, Python, VBA, VB, C++, etc.
Anything that supports COM
Users do not have to learn a proprietary language
ESRI primarily supports Python
Installed with ArcGIS 9
Samples, documentation, help
CGIS-NURIntroduction to ArcGIS II

5. The Python scripting language
Introduction to GIS
The Python scripting language
What is Python?
An open-source, object-oriented, scripting language
Can view and modify source code
Support for large projects
Easy to use
Why use Python?
Offers IDEs with debugging tools
Modular – can be broken apart
Cross platform
Ability to compile scripts
Installed with ArcGIS 9, ESRI samples provided
PythonWin
CGIS-NURIntroduction to ArcGIS II

6. The Basics of Python Introduction to GIS
CGIS-NURIntroduction to ArcGIS II

7. Lesson overview Where to write code Commenting code
Introduction to GIS
Lesson overview
Where to write code
Commenting code
Strings, numbers, and lists
Line continuation
Functions, modules, and statements
Decision making and looping
Case sensitive rules
CGIS-NURIntroduction to ArcGIS II

8. Where to write code There are many places to write Python code
Introduction to GIS
Where to write code
There are many places to write Python code
Text editor: Notepad, Wordpad, etc.
Python command prompt
IDE: PythonWin, IDLE, and so on
IDEs allow you to perform all jobs from one location
Write, save, run, and debug code from one location
Command prompt and both IDEs installed with ArcGIS
Lectures and exercises use PythonWin
CGIS-NURIntroduction to ArcGIS II

9. PythonWin interface Menus, toolbars, and context menus Script window
Introduction to GIS
PythonWin interface
Menus, toolbars, and context menus
Script window
Write and save code
Interactive window
Test lines of code
Report messages
Benefits
Windows look and feel
All in one application
CGIS-NURIntroduction to ArcGIS II

10. Comments Comment: A non-executable line of code
Introduction to GIS
Comments
Comment: A non-executable line of code
One number sign (#) for green and italicized
Two number signs (##) for grey
Can comment and uncomment blocks of code
Highlight code and use script window's context menu
CGIS-NURIntroduction to ArcGIS II

11. Variables in Python Variables are dynamically typed
Introduction to GIS
Variables in Python
Variables are dynamically typed
No declaration keyword
No type assignment
fc = "C:/Student/PYTH/Database/rwanda.shp"
Variables are case sensitive
scale = 10000
Scale = 20000
Variables can hold different data types
Strings, numbers, lists, tuples, dictionaries, files
Two different variables!
CGIS-NURIntroduction to ArcGIS II

12. Strings Variables can hold strings
Introduction to GIS
Strings
Variables can hold strings
folder = "C:/Student"
whereClause = "[STREET_NAM] = 'CATALINA'"
Strings surrounded in double (") or single (‘) quotes
Can embed one string in another
Pathnames use two back (\\) or one forward (/) slash
Strings can be combined together
gdbPath = "C:\\malaria.mdb"
fc = “roads"
fullPath = gdbPath + "\\" + fc
Strings are indexed
fc = “roads.shp"
newFC = fc[:-4]
CGIS-NURIntroduction to ArcGIS II

13. Numbers and lists Variables can hold numbers and expressions
Introduction to GIS
Numbers and lists
Variables can hold numbers and expressions
num1 = 1.2
num2 = 3 + 5
Variables can hold lists
numList = [1, 2, 3]
fcList = ["Roads", "Streets", "Parcels", "Zipcodes"]
Lists are indexed
fc1 = fcList[1]
fc2 = fcList[0:2]
fc3 = fcList[0:-1]
fc4 = fcList[2:]
CGIS-NURIntroduction to ArcGIS II

14. Variable naming conventions
Introduction to GIS
Variable naming conventions
Uppercase versus lowercase
First word lowercase, capitalize each successive word
outputFieldName = "Rwanda"
Acronym at the beginning, use lowercase letters
gdbPath = "C:\\malaria.mdb"
fc = "roads.shp"
Acronym in the middle or at the end, use uppercase letters
inputFC = "roads.shp"
Avoid special characters (e.g. / \ & * !)
Use descriptive variable names
CGIS-NURIntroduction to ArcGIS II

15. Line continuation Line continuation characters
Introduction to GIS
Line continuation
Line continuation characters
Parentheses ( ), brackets [ ], and braces { }
Backslash \
Indentation is automatic
CGIS-NURIntroduction to ArcGIS II

16. Decision making syntax
Introduction to GIS
Decision making syntax
Testing conditions
Colons used at end of each condition
Indentation defines what executes for each condition
Python automatically indents when you press Enter
Use tabs or spaces, must be consistent
Two equal signs for conditions, one for assignment
CGIS-NURIntroduction to ArcGIS II

17. Looping syntax While loops, counted loops, and list loops
Introduction to GIS
Looping syntax
While loops, counted loops, and list loops
Colons used at end of each statement
Indentation defines what executes for the loop
CGIS-NURIntroduction to ArcGIS II

18. Demo Used Syntax Examples Adapting scripts for own use
Introduction to GIS
Demo
Used Syntax
Examples
Adapting scripts for own use
CGIS-NURIntroduction to ArcGIS II