1 Getting Started With Python

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Getting Started With Python In ArcGIS

David Wynne


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8:308:30 9:30: Python 101 and9:30: Python 101 and ArcPyArcPy 101101

Essentials of the languageEssentials of the language

UsinUsin ArcPArcP to execute eo rocessin toolsto execute eo rocessin tools

Python windowPython window

9:309:30 10:00: Script and Script tool basics10:00: Script and Script tool basics

Creating a standalone scriptCreating a standalone script Creating a script toolCreating a script tool

10:0010:00 10:15: Ma automation10:15: Ma automation

10:1510:15 10:45: Break10:45: Break

10:4510:45 11:00: Raster analysis and Map Algebra11:00: Raster analysis and Map Algebra

11:0011:00 11:45: Tool Design and Validation11:45: Tool Design and Validation


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Python 101Python 101


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ESRI has embraced Python forESRI has embraced Python for ArcGISArcGIS 1010

Python is the language that fulfil ls the needs of our userPython is the language that fulfil ls the needs of our user

communitcommunit

Easy to learnEasy to learn

Excellent for beginners and expertsExcellent for beginners and experts

u a e or arge pro ec s or sma scr p su a e or arge pro ec s or sma scr p s CrossCross--platformplatform


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Clear, easy to read syntaxClear, easy to read syntax

Easy to use, makes it simple to get startedEasy to use, makes it simple to get started

Including lists and dictionariesIncluding lists and dictionaries

Comes with a large standard libraryComes with a large standard library

Supports raising and catching exceptionsSupports raising and catching exceptionsCode can be grouped into modules and packagesCode can be grouped into modules and packages

uppor s o ecuppor s o ec --or en e programm ngor en e programm ng

http://www.python.org/about/


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..

ESRI has ful ly embraced Python as its language forESRI has ful ly embraced Python as its language for

automationautomation

1.1. ArcPyArcPy sitesite--packagepackage

Includes mapping and Map Algebra supportIncludes mapping and Map Algebra support

Successor to theSuccessor to the arcgisscriptingarcgisscripting modulemodule2.2. Python windowPython window

3.3. Python script tool frameworkPython script tool framework


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dispatchbased Geoprocessor

.

arcgisscripting module

Cross- latform

Python 2.4

arcgisscripting module, 9.3 version

Pythonic

Python 2.5

ArcP site- acka e

Mapping & Map Algebra support

Python window

.


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ArcPyArcPy 101101


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A cornerstone for automation inA cornerstone for automation in ArcGISArcGIS

data analysisdata analysis

data conversiondata conversion

data managementdata management

map automationmap automation

ArcPyArcPy is a native Python siteis a native Python site--packagepackage

Access to 800+Access to 800+ eo rocessineo rocessin toolstools

Provides embedded reference documentation for eachProvides embedded reference documentation for each

function, class and modulefunction, class and module

Python editorPython editor

Familiar toFamiliar to arcgisscriptingarcgisscripting usersusers


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Improved coding experience, such as:Improved coding experience, such as:

CursorsCursors

ClassesClasses

MultiMulti--value parameters can be expressed as Python listsvalue parameters can be expressed as Python lists

Ability to convertAbility to convert rastersrasters to and fromto and from NumPyNumPy arraysarrays

ArcPyArcPy is supported by modules, including:is supported by modules, including:

A ma in moduleA ma in module arc .ma inarc .ma in

A Spatial Analyst module (arcpy.sa) to support map algebraA Spatial Analyst module (arcpy.sa) to support map algebra

AA GeostatisticalGeostatistical Analyst module (arcpy.ga)Analyst module (arcpy.ga)


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An embedded Interactive Python window withinAn embedded Interactive Python window within ArcGISArcGIS

Can accessCan access ArcPyArcPy, including tools and environments, including tools and environments

Can access an other P thon functionalitCan access an other P thon functionalit

Better code completion and intelligenceBetter code completion and intelligence

The P thon window is for:The P thon window is for:

Testing ideasTesting ideas

Experimenting with and learning PythonExperimenting with and learning Python

Building quick and easy workflows in PythonBuilding quick and easy workflows in Python


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Demo:Demo:

A tour ofA tour of ArcPyArcPyandand


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Desktop helpDesktop help

Resource CenterResource Center http://resourcesbeta.esri.com/http://resourcesbeta.esri.com/


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Tools are accessed as functions onTools are accessed as functions on arcpyarcpy

Environments as properties from arcpy.env classEnvironments as properties from arcpy.env class

# ~~~ PYTHON CODE ~~~

import arcpy

# Set the workspacearcpy.env.workspace = "c:/st_Johns/GISData.gdb"

# Execute Geoprocessing tool

arcpy.Intersect_analysis(["roads","urban_area","urban_roads",

5 " oin"


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Script writers set the environment and tools use itScript writers set the environment and tools use it

General settingsGeneral settings

Current Workspace, Output Spatial Reference, ExtentCurrent Workspace, Output Spatial Reference, Extent

Raster analysis settingsRaster analysis settings

Cell Size, MaskCell Size, Mask

arcpy.env.workspacearcpy.env.workspace

arcpy.env.outputCoordinateSystemarcpy.env.outputCoordinateSystem

arcpy.env.extentarcpy.env.extentarc .env.cellSizearc .env.cellSize

arcpy.env.maskarcpy.env.mask


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xecu ng a oo w pro uce ypes o messages.xecu ng a oo w pro uce ypes o messages.

Informative messages (severity = 0)Informative messages (severity = 0)

Warning messages (severity = 1)Warning messages (severity = 1) Error messages (severity = 2)Error messages (severity = 2)

# start try block

try:

arcpy.Buffer("c:/ws/roads.shp", "c:/outws/roads10.shp", 10)

,

# print the tool messages

except arcpy.ExecuteError:print arcpy.GetMessages(2)

# Any other error

except Exception as e:

.


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Functions perform useful scripting tasksFunctions perform useful scripting tasks

AccessAccess geoprocessinggeoprocessing tool messages (tool messages (GetMessagesGetMessages))

List data to for batch rocessinList data to for batch rocessin ListFeatureClassesListFeatureClasses ListFieldsListFields, nine other List functions), nine other List functions)

Retrieve a datasets properties (Retrieve a datasets properties (DescribeDescribe))

import arcpy

# Set the workspace for ListFeatureClasses function

" ". .

# For each fc, create a scratch name and clipfor fc in arcpy.ListFeatureClasses():

outName = arcpy.CreateScratchName("clipped_" + fc,

"", "featureclass",

arcpy.env.workspace)

" ". _ , ,


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Returns an object with dynamic propertiesReturns an object with dynamic properties

Allows script to determine properties of dataAllows script to determine properties of data

, , ,, , ,

Shape type (point, polygon, line, etc)Shape type (point, polygon, line, etc)

Spatial referenceSpatial reference

Extent of featuresExtent of features List of f ieldsList of f ields

Lo ic can be added to a scri t to branch if statementLo ic can be added to a scri t to branch if statement

based data propertiesbased data properties


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# Describe a feature class

d = arcpy.Describe("c:/base.gdb/rivers")

# Branch based on the

# in uts Sha eT e ro ert

if d.shapeType == "Polygon":

arcpy.FeatureToLine_management(inFC, outFC)

e se:

arcpy.CopyFeatures_management(inFC, outFC)


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Most tool parameters can be easily definedMost tool parameters can be easily defined

Such as a path or buffer distanceSuch as a path or buffer distance

Such as a spatial reference or field mappingSuch as a spatial reference or field mapping

Classes can be used to define parametersClasses can be used to define parameters

prjFile = "c:/North America Equidistant Conic.prj"

Create a s atial reference usin a ro ection file

spatialRef = arcpy.SpatialReference(prjFile)

# Run CreateFeatureclass using the spatial referencearc .CreateFeatureclass mana ement in utWorks ace_

outputName, "POLYLINE", "", "", "", spatialRef)


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Cursors allowsCursors allows

Iteration over the set of rows in a tableIteration over the set of rows in a table

Abilit to insert new rows into a tableAbilit to insert new rows into a table

Geometry accessGeometry access

Cursors have three formsCursors have three forms

Search, Insert and UpdateSearch, Insert and Updateimport arcpy

# Print road name and road type

for row in arcpy.SearchCursor("D:/data.gdb/roads"):

print Road name: row.roadname

pr n oa ype: row.ge a ue roa ype

del row


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Demo:Demo:

Converting GPS in XMLConverting GPS in XMLto useable Geographic datato useable Geographic data


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ArcPyArcPy cursors support iterationcursors support iteration

At 9.3rows = gp.SearchCursor(myTable)

row = rows.next()

while row:

print row.GetValue(Rank)

row = rows.next()

At 10

for row in arcpy.SearchCursor(myTable)print row.GetValue(Rank)


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Cursors support creation of new geometriesCursors support creation of new geometries

# Open an insert cursor for the feature class

cur = arcpy.InsertCursor(fc)

# Create array and point objectsptList = [arcpy.Point(358331, 5273193),

arcpy.Point(358337, 5272830)]lineArray = arcpy.Array(ptList)

# Create a new row for the feature classfeat = cur.newRow()

# Set the geometry of the new feature to the

# array of pointsfeat.Shape = lineArray

# Insert the featurecur.insertRow(feat)

# Delete objectsdel cur, feat


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Creating Python script toolsCreating Python script tools


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Map automation toolsMap automation tools


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BREAK!BREAK!


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Raster analysis and Map AlgebraRaster analysis and Map Algebra


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Returned output from Spatial Analyst toolsReturned output from Spatial Analyst tools

Used to represent a raster dataset on diskUsed to represent a raster dataset on disk

Can be used as in uts to tools and S atial Anal st MaCan be used as in uts to tools and S atial Anal st MaAlgebra expressionsAlgebra expressions

Supports operators (or arithmetic operations in MapSupports operators (or arithmetic operations in Map

Has properties and methods for analysisHas properties and methods for analysis

raster.minraster.min

raster.maxraster.max

raster.saveraster.save()()


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Spatial Analyst module that integrates Map Algebra intoSpatial Analyst module that integrates Map Algebra into

PythonPython

Includes all S atial Anal st toolsIncludes all S atial Anal st tools Supports operators in Map Algebra expressionsSupports operators in Map Algebra expressions

Helper classes that can be used to support complex parameterHelper classes that can be used to support complex parameter

--

from arcpy.sa import *

demm = Raster("DEM") / 3.28

slpdeg = Slope(demm, "DEGREE")

= " " " ", , ,


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NumPyNumPy is a 3is a 3rr party Python library for scientif ic computingparty Python library for scientif ic computing

A powerful array objectA powerful array object

So histicated anal sis ca abilitiesSo histicated anal sis ca abilities

ArcPyArcPy Raster objects can be converted toRaster objects can be converted to NumPyNumPy arraysarrays

for analysisfor analysis

as er o um y rrayas er o um y rray ,, um y rray o as er um y rray o as er

inras = "ras100"

conver ras er o umnpy array.

rasArray = arcpy.RasterToNumPyArray(inras)

# ARRAY SLICING: et the total sum of ever third value

# from every third row of the raster

sampArray = rasArray[::3,::3]

sum = NUM.sum(sampArray)

pr n sum


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Demo:Demo:

Working with Map AlgebraWorking with Map Algebraandand NumPyNumPy


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Tool Design and ValidationTool Design and Validation


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