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PYTHON: AN INTRODUCTION

PYTHON: AN INTRODUCTION. David Wynne, Clinton Dow. Agenda. What is Python?.

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PYTHON: AN INTRODUCTION

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  1. PYTHON: AN INTRODUCTION David Wynne, Clinton Dow

  2. Agenda

  3. 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 ArcGIS • Free, cross-platform, easy to learn, widelyuseful, great community

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

  5. ArcGIS Pro and Python http://esriurl.com/PythonProMigration • Python continues to be an important language • Migration from 10.x • Most geoprocessing tools • Mapping changes: arcpy.mappingvs.arcpy.mp • Pro uses Python 3, 10.x uses Python 2 • Analyze Tools For Pro • Future note: ArcGIS Pro 1.3 uses a conda distribution

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

  7. Python 101 - Comments

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

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

  10. Python 101 - iteration • Python has for and whilestatements for looping • Colon at end of statement • Indentation determines what is executed

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

  12. Python basics Demo

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

  14. 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)

  15. ArcPy • Access point to ArcGIS functionality through Python • Desktop, Server, Engine, and Pro • Geoprocessing tools • Functions like ListFeatureClasses, Describe • Classes like Polygon, SpatialReference, FieldMap • Modules • Mapping: arcpy.mapping / arcpy.mp • Data access: arcpy.da • Map algebra: arcpy.sa • Network Analyst: arcpy.na

  16. Run geoprocessing tools • import arcpy • Follow tool syntax • arcpy.toolname_toolboxalias(arguments)orarcpy.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)

  17. Geoprocessing and Python Demo

  18. 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)

  19. 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

  20. Geoprocessing tool messages • Three types of messages • Informative, warning, error • Displayed in ArcMap / Pro • Results • Messages window • Python window • To access messages in Python • arcpy.GetMessages()

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

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

  23. 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

  24. Batch processing (ListFeatureClasses)

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

  26. Writing a Python script Demo

  27. 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

  28. Please take our Survey Your feedback allows us to help maintain high standards and to help presenters Find your event in the Esri Events App Find the session you want to review Scroll down to the bottom of the session Answer survey questions and submit

  29. Python at User Conference http://esriurl.com/PythonUC16

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