PYTHON AN INTRODUCTION David Wynne Clinton Dow What

PYTHON: AN INTRODUCTION David Wynne, Clinton Dow

• What is Python? • Python 101 • Trouble-shooting Arc. GIS Python Agenda • Arc. Py • Geoprocessing tools in Python • Batch processing • Python and Arc. GIS Pro

What is Python? • “Python is an easy to learn, powerful language… (with) high-level data structures and a simple but effective approach to object-oriented programming. Python’s elegant syntax and dynamic typing…make it an ideal language for scripting…in many areas and on most platforms. ” – python. org • Scripting language of Arc. GIS • Free, cross-platform, easy to learn, widely useful, great community

Why use Python and Arc. GIS? • Automate repetitive tasks • Make your own geoprocessing tools • Add geoprocessing to web applications • Customize Desktop apps • Extend the capabilities of Arc. GIS

Arc. GIS Pro and Python • Python continues to be an important language • Migration from 10. x • - Most geoprocessing tools - Mapping changes: arcpy. mapping vs. arcpy. mp - Pro uses Python 3, 10. x uses Python 2 - Analyze Tools For Pro Future note: Arc. GIS Pro 1. 3 uses a conda distribution http: //esriurl. com/Python. Pro. Migration

Python 101 - IDEs • Python code is written in. py files - • Where do I write Python code? - • Or an interactive Python prompt (Python command line, Python window in Arc. GIS) IDEs such as Wing IDE, Py. Charm, Spyder, Py. Scripter, Python IDLE, … How do I run? - Double-click. py, from command line, IDEs, Arc. GIS

Python 101 - Comments

Python 101 - Strings and string manipulation • Combining strings • Pathname manipulations

Python 101 - Conditional logic • Python has logic for testing conditions - if, else statements - Colon at end of each condition - Indentation determines what is executed - == tests equality; other operators like >, <, !=

Python 101 - iteration • Python has for and while statements for looping - Colon at end of statement - Indentation determines what is executed

Python 101 - libraries and import • Python is “batteries included” • Python has a broad collection of 3 rd party libraries • Can organize your own functionality and import it - • Organize and re-use Additional libraries are loaded using import

Python basics Demo

Arc. GIS Python window • Both Desktop and Pro have an embedded, interactive Python command line • Access to Python and modules within Arc. GIS applications • Experiment with Python code interactively

Python building blocks • Module: a Python file where functions live; import • Package: a collection of related modules • Function: a defined piece of functionality that performs a specific task; requires arguments • Class: a blueprint to create an object • math. sqrt(100)

Arc. Py • Access point to Arc. GIS functionality through Python - Desktop, Server, Engine, and Pro 1. Geoprocessing tools 2. Functions like List. Feature. Classes, Describe 3. Classes like Polygon, Spatial. Reference, Field. Map 4. Modules 1. Mapping: arcpy. mapping / arcpy. mp 2. Data access: arcpy. da 3. Map algebra: arcpy. sa 4. Network Analyst: arcpy. na

Run geoprocessing tools • import arcpy • Follow tool syntax • - arcpy. toolname_toolboxalias(arguments) or arcpy. toolboxalias. toolname(arguments) - Include input and output parameters How do I use a specific tool? - Tool help page - Copy as Python Snippet - help(arcpy. Buffer_analysis)

Geoprocessing and Python Demo

Geoprocessing environment settings • Control the processing environment of the tools you run - See tool help for honored environments • Productivity and code cleanup • Environments are properties on arcpy. env (over 50)

Troubleshooting • Why do errors occur? - • Incorrect tool use, typos, syntax, logic errors My script doesn’t work? - Examine the messages - Use Python exception handling - Debug the script in an IDE

Geoprocessing tool messages • Three types of messages - • • Informative, warning, error Displayed in Arc. Map / Pro - Results - Messages window - Python window To access messages in Python - arcpy. Get. Messages()

Python exception handling • try / except statements - Try to do something, and if an exception occurs, do something else • Many different exception types • An arcpy. Execute. Error exception occurs when a geoprocessing tool fails

Arc. Py functions • An Arc. Py function for many jobs • Support geoprocessing workflows • Enable automation of manual tasks

Batch processing • • Automating a process to run multiple times - Clip every feature class in a geodatabase to a common boundary - Calculate statistics for every raster in a folder List functions used in Python to perform batch processing - Also arcpy. da. Walk

Batch processing (List. Feature. Classes)

Getting data properties • Describe functions reads data properties • Returns an object with properties like: - Data type - Shape type - Spatial reference

Writing a Python script Demo

Conda is part of Pro at 1. 3 • “Conda is an open source package management system and environment management system for installing multiple versions of software packages and their dependencies and switching easily between them. ” -- http: //conda. pydata. org/docs/ • Conda solves limitations in core Python infrastructure - Handling dependencies - Locating, compiling Python libraries - Managing multiple Python versions

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Python at User Conference http: //esriurl. com/Python. UC 16 Tues Wed Python: An Introduction 8: 30 Python: Beyond the Basics 10: 15 Python: Building Geoprocessing tools 1: 30 Thurs Python: Raster Analysis 8: 30 1: 30 Python: Arc. Py Tips and Tricks 1: 30 Harnessing the Power of Python in Arc. GIS using the Conda Distribution 3: 30 Python Map Automation: Introduction to arcpy. mapping / arcpy. mp 1: 30 Advanced Map Automation with Python in Arc. GIS for Desktop 3: 15