Python – Getting Started · oriented programming. ... Debug the script in an IDE Python - Getting Started. Esri UC2013 . ... Getting Started resources.ArcGIS.com Analysis,

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Technical Workshop

2013 Esri International User ConferenceJuly 8–12, 2013 | San Diego, California

Python – Getting StartedDrew Flater, Ghislain Prince

Esri UC2013 . Technical Workshop .

Does this describe you?

New to Python scripting

Comfortable using ArcGIS but want to become more efficient

Moving to Python from other scripting language like VB, AML

Python - Getting Started


Agenda

What is Python and why use it?Python 101What is ArcPy?Scripting geoprocessing toolsTroubleshootingArcPy functionsBatch processing



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, widely useful, great community



Why use Python and ArcGIS?

Automate repetitive tasksDevelop custom toolsAdd geoprocessing to web applicationsCustomize Desktop apps Extend the capabilities of ArcGIS



Python 101

Where do I write Python code?Python file is text with .py extensionIDE like PyScripter, Wing IDE ($), PythonWinPython window in ArcGIS

How do I run? …Double-click, IDE, ArcGISWhat are variables?

A name that stores a value; assigned using =

input = "C:/Data/Roads.shp"distance = 50both = [input, distance]

# Variables act as substitutes for raw valuesarcpy.Buffer_analysis(input, "Roads_buffer.shp", distance)



Python 101

Python has logic for testing conditionsif, else statementColon at end of each conditionIndentation determines what is executed== tests equality; other operators like >, <, !=

var = "a"if var == "a":

# Execute indented linesprint("variable is a")

else:print("variable is not a")



Python 101

Techniques for iterating or loopingWhile loops, for loopsColon at end of statementIndentation determines what is executed

x = 1while x < 5:

print(x)x = x + 1

x = [1, 2, 3, 4]for num in x:

print(num)



Python building blocks

Function: a defined piece of functionality that performs a specific task; requires arguments Module: a Python file where functions live; import

Package: a collection of related modules

math.sqrt(100) … 10

Python Standard Library / Built-insos, sys, math, datetime, urllib2



ArcPy

Site package that adds ArcGIS functionality to PythonAccess to 800+ geoprocessing toolsFunctions, classes and modules

Helper functions like ListFeatureClasses, DescribeClasses that can be used to create complex objects like SpatialReference, FieldMapModules that provide specialized functionality like Mapping, SpatialAnalyst, NetworkAnalyst, DataAccess

Enhancement of arcgisscripting module (pre-10.0)Your old scripts

gs will work



ArcGIS Python window

Embedded, interactive Python window Access to Python and modules within ArcGIS applicationsGreat for experimenting with Python code and learning tool syntax


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Run Geoprocessing tools

Demo


Run geoprocessing tools

import arcpy

Follow tool syntaxarcpy.toolname_toolboxalias()

Enter input and output parameters

How do I use a specific tool?Tool help pageCopy as Python Snippethelp(arcpy.Buffer_analysis)



Geoprocessing environment settings

Use geoprocessing environments as global parameters

See tool help for honored environmentsProductivity and code cleanuparcpy.env

arcpy.env.workspace = "C:/Data"

arcpy.env.extent = "0 0 100 100"

arcpy.env.outputCoordinateSystem = 4326 #WKID


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Troubleshooting

Why do errors occur?Incorrect tool use, typos, syntax, ...or bugs

My script doesn't work!? Help!View geoprocessing messagesUse Python error handlingDebug the script in an IDE



Geoprocessing messages

Three types of messagesInfo, warning, error

Displayed in the Python window

Errors displayed in IDE

To see other messagesarcpy.GetMessages



Python error handling

Try…Except…Try to do something, and if an error occurs, do something else

# Start Try blocktry:

arcpy.Buffer_analysis("Roads.shp", … )# If an error occursexcept:

# Print that Buffer failed and why

print("Buffer failed")print(arcpy.GetMessages())



Use try except logic and debug a script

Troubleshooting

Demo


ArcPy Functions


ArcPy functions

Perform useful tasksList data: ListFeatureClassesGet data properties: Describe

Enables automationof manual tasks



Batch processing

Automating a geoprocessing operation to run multiple times

Clip every feature class in a geodatabase to a boundaryCalculate statistics for every raster in a folder

List functions used in Python to perform batch processing



arcpy.ListFeatureClasses

# Set the workspacearcpy.env.workspace = "C:/Data/FileGDB.gdb/FDs"

# Get a list of all feature classesfcList = arcpy.ListFeatureClasses()

# Print the names of the feature classesfor fc in fcList:print(fc)



Getting data properties

Describe function reads data propertiesReturns an object with properties

Data type Shape typeSpatial referenceFields

# Describe a feature classdesc = arcpy.Describe("C:/Data/Roads.shp")

print(desc.shapeType)>>> "Polyline"



Batch processing

Demo


Resources


resources.ArcGIS.comAnalysis, Python

arcpy.wordpress.comGIS Stack Exchange, Stack Overflow

Python ReferencesPython Scripting for ArcGISby Esri PressLearning Python by LutzThe Python Standard Library by Example by Hellmannpython.org

training.esri.comesriurl.com/uc13python

More Python sessions

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Python – Getting Started · oriented programming. ... Debug the script in an IDE Python - Getting Started. Esri UC2013 . ... Getting Started resources.ArcGIS.com Analysis,