Python for Arc Gis

8/6/2019 Python for Arc Gis

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Python Programming forArcGIS

David Quinn Daniel Sheehan

[email protected] [email protected]

9.00 - 12.00January 27, 2011
http://[email protected]/http://[email protected]/http://[email protected]/http://[email protected]/


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Outline

1 Introduction to Python and ArcGIS

2 Programming Principles and Modules

3 ModelBuilder

4 Reading and Writing Data

All slides, code and data available here:

http://tinyurl.ie/iap
http://tinyurl.ie/iaphttp://tinyurl.ie/iap


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Python

Python is a programming language that lets you work more

quickly and integrate your systems more effectively 1

1http://www.python.org/


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Python + ArcGIS

Python can interact with ArcGIS and be used to repeat many

types of analyses.

Why Python?

It is now an integral part of ArcGIS

Easy to read syntax

Large user community

Useful for scripts to control other programs


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How does Python work with ArcGIS?

With ArcGIS 9.3:

Python has some limitations (some commands are not yet

compatible)

Many functions in ArcGIS require strings to be passed

back and forth

With ArcGIS 10:

Much better integration (if you can, upgrade)


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Logistics

We will be using the IDLE programming environment

Windows: START Programs Python2.X IDLE

MAC: Applications Python2.X IDLE2

The class will assume people are using both ArcGIS 9.3 and

ArcGIS 10

2

Until we start using ArcGIS (Section ??), you can use Python onWindows/Linux/Mac for the following exercises.


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Programming Concepts

Three Concepts

1 Variables

2 Control Structures ( If statements and For Loops )

3 Functions

Python is case sensitive and reads whitespace (use space-bar,

not tab key)


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The Print function and Strings

# th is is a commentprint "hello world"

"" " AlternativeCommentingStyle """


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The Print function and Strings

# th is is a commentprint "hello world"

# this is a variable that contains a str ingname = "will iam"# Print out the variable that contains the stringprint name


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Integers and Floats

# declare variablesint_sample = 10float_sample = 10.0

# printing variables# cast nonstr ing variable as a str ing using str ()print "The value of this integer is : " + s t r ( int_sample )print "The value o f t h i s f l o a t i s : " + s t r ( float_sample )


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ifstatement

x = 2

# Condition checks i f statement is truei f x == 1:

print ' x i s 1! '


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if / elif / elsestatement

x = 2

# Condition checks i f statement is true

i f x == 1:print ' x i s 1! '

e l i f x ==2:print ' x i s 2! '

else :print 'x is not known. : ( '


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for loop

for i in range( 3 ) :

# convention is to use 4 spaces to indent# python reads whitespace at the begining of a li neprint i


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while loop

# define jj = 1

# ' while ' less than some conditionwhile j < 3:

print j#increment jj += 1


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Three ways to access a folder

# Accessing a folder

path = "C: \ \ folderName \ \ "

path = "C: / folderName/ "

path = r "C:\folderName\"


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Importing Modules

Use the importcommand:

# Count number of fi l e s in a directory

import osf i l e s = os . l i s t d i r ( path )len ( f i l e s )

A module is a list of python programs that can be accessed.Commonly used modules are: os, sys, glob


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glob

Here the glob module is being imported:

import glob # use the glob module

path = " /Users/ djq /Documents/ personal / " # set the folder path

for i in glob . glob ( path + ' * ' ) : # loop through al l f i lesprint i

Try replacing * with *.txt


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Importing the ArcGIS module

ArcGIS 9.3:import arcgisscripting

ArcGIS 10:import arcpy


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Exercise 1: Reading folder contents

1 Download zip file from course site: http://tinyurl.ie/iap

2 Using the glob module print out:

a list of all the files

a list of shapefiles
http://tinyurl.ie/iaphttp://tinyurl.ie/iap


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Model Builder

ModelBuilder3

3

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_ModelBuilder
http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_ModelBuilderhttp://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_ModelBuilderhttp://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_ModelBuilderhttp://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_ModelBuilder


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Exercise 2: ModelBuilder

Using ModelBuilder:

1 Buffer center.shp 1km

2 Clip road_network.shp file to buffer

3 Export model as Python

Exercise 3: Convert ModelBuilder


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Exercise 3: Convert ModelBuilder

Code into a loop

Using the code from ModelBuilder

1 Identify relative filepaths and restructure code

2 Iterate through this loop 5 times, buffering 1km each time

3 Clip road_network.shp to buffer and make 5 new

shapefiles

W iti t T t Fil


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Writing to a Text File

# Create a f i l e ( 'a ' means append)f = open( "C: \example. t xt " , 'a ' )# I f f i l e does not e xi st i t w i l l be created

# W r i t e r e s u l t s t o a f i l ef. write ( " I am the content of your f i l e \n" )

# Use these commands when finishedf. flush ( )f. close ( )

Try reading the contents of your file using f.read()

E i 4 Fil M i l ti


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Exercise 4: File Manipulation

Create a folder called tmp-folder:

Make 20 text files called File1.txt, File2.txt .... File20.txt

Write a text string into each file

T


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Tomorrow

Functions

Attribute tables - Reading/Writing

Packaging scripts into toolboxes

Q ti | ? | C t


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Questions | ? | Comments

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