Python Scripting for ArcGIS

360 Pages·2014·11.13 MB·English

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PY THON
®
Scripting for ArcGIS
®
Paul A. Zandbergen
Esri Press, 380 New York Street, Redlands, California 92373-8100
Copyright © 2013 Esri
All rights reserved. First edition
Printed in the United States of America
17 16 15 14 13 1 2 3 4 5 6 7 8 9 10
Library of Congress has cataloged the print edition as follows:
Zandbergen, Paul A., 1968-
Python scripting for ArcGIS / Paul A. Zandbergen. — First edition.
pages cm
Includes index.
ISBN 978-1-58948-371-2 (pbk.)
eISBN 978-1-58948-362-0 (electronic)
1. ArcGIS. 2. Geographic information systems. 3. Graphical user interfaces (Computer systems) 4. Python (Computer program language) I. Title.
G70.212.Z36 2013
910.285’5133--dc23 2012020676
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Contents
Preface ________________________________________________xi
Acknowledgments ______________________________________xiv
Part 1: Learning the fundamentals of Python and geoprocessing __1
Chapter 1: Introducing Python ___________________________________ 3
1.1 Introduction ___________________________________________3
1.2 Exploring the features of Python _________________________3
1.3 Comparing scripting vs. programming ____________________4
1.4 Using scripting in ArcGIS _______________________________5
1.5 Python history and versions _____________________________5
1.6 About this book _______________________________________6
1.7 Exploring how Python is used ___________________________8
1.8 Choosing a Python script editor ________________________13
Points to remember ___________________________________19
Chapter 2: Geoprocessing in ArcGIS _____________________________ 21
2.1 Introduction __________________________________________21
2.2 What is geoprocessing? ________________________________21
2.3 A note on ArcObjects__________________________________23
2.4 Using toolboxes and tools ______________________________24
2.5 Learning types and categories of tools ___________________25
2.6 Running tools using tool dialog boxes ___________________26
2.7 Specifying environment settings ________________________30
2.8 Using batch processing ________________________________32
2.9 Using models and ModelBuilder ________________________34
2.10 Using scripting _______________________________________38
2.11 Running scripts as tools _______________________________41
2.12 Converting a model to a script __________________________44
2.13 Scheduling a Python script to run at prescribed times _____45
Points to remember ___________________________________47
vi Contents
Chapter 3: Using the Python window_____________________________49
3.1 Introduction __________________________________________49
3.2 Opening the Python window ___________________________49
3.3 Writing and running code ______________________________50
3.4 Getting assistance _____________________________________52
3.5 Exploring Python window options ______________________54
3.6 Saving your work _____________________________________55
3.7 Loading code into the Python window __________________56
Points to remember ___________________________________57
Chapter 4: Learning Python language fundamentals _______________59
4.1 Introduction __________________________________________59
4.2 Locating Python documentation and resources ___________59
4.3 Working with data types and structures _________________60
4.4 Working with numbers ________________________________60
4.5 Working with variables and naming _____________________62
4.6 Writing statements and expressions _____________________63
4.7 Using strings _________________________________________64
4.8 Using lists____________________________________________66
4.9 Working with Python objects ___________________________66
4.10 Using functions _______________________________________68
4.11 Using methods _______________________________________69
4.12 Working with strings __________________________________70
4.13 Working with lists ____________________________________74
4.14 Working with paths ___________________________________78
4.15 Working with modules ________________________________79
4.16 Controlling workflow using conditional statements _______81
4.17 Controlling workflow using loop structures ______________83
4.18 Getting user input ____________________________________85
4.19 Commenting scripts ___________________________________86
4.20 Working with code in the PythonWin editor _____________88
4.21 Following coding guidelines ____________________________89
Points to remember ___________________________________90
Contents vii
Part 2: Writing scripts ___________________________________________93
Chapter 5: Geoprocessing using Python _________________________95
5.1 Introduction __________________________________________95
5.2 Using the ArcPy site package ___________________________95
5.3 Importing ArcPy ______________________________________96
5.4 Working with earlier versions of ArcGIS _________________97
5.5 Using tools ___________________________________________98
5.6 Working with toolboxes _______________________________104
5.7 Using functions ______________________________________106
5.8 Using classes ________________________________________107
5.9 Using environment settings ___________________________110
5.10 Working with tool messages ___________________________112
5.11 Working with licenses ________________________________115
5.12 Accessing ArcGIS Desktop Help _______________________119
Points to remember __________________________________122
Chapter 6: Exploring spatial data _______________________________123
6.1 Introduction _________________________________________123
6.2 Checking for the existence of data _____________________123
6.3 Describing data ______________________________________125
6.4 Listing data _________________________________________127
6.5 Using lists in loops _______________________________131
for
6.6 Working with lists ___________________________________132
6.7 Working with tuples__________________________________133
6.8 Working with dictionaries ____________________________134
Points to remember __________________________________137
Chapter 7: Manipulating spatial data ____________________________139
7.1 Introduction _________________________________________139
7.2 Using cursors to access data ___________________________139
7.3 Using SQL in Python _________________________________144
7.4 Working with table and field names ____________________146
7.5 Parsing table and field names __________________________148
7.6 Working with text files _______________________________149
Points to remember __________________________________158
Chapter 8: Working with geometries ____________________________159
8.1 Introduction _________________________________________159
8.2 Working with geometry objects ________________________159
8.3 Reading geometries __________________________________160
8.4 Working with multipart features _______________________164
8.5 Working with polygons with holes _____________________167
8.6 Writing geometries ___________________________________169
8.7 Using cursors to set the spatial reference _______________172
8.8 Using geometry objects to work with geoprocessing tools__174
Points to remember __________________________________175
viii Contents
Chapter 9: Working with rasters ________________________________177
9.1 Introduction _________________________________________177
9.2 Listing rasters _______________________________________177
9.3 Describing raster properties ___________________________178
9.4 Working with raster objects ___________________________182
9.5 Working with the ArcPy Spatial Analyst module _________183
9.6 Using map algebra operators __________________________184
9.7 Using the function _______________187
ApplyEnvironment
9.8 Using classes of the module _________________188
arcpy.sa
9.9 Using raster functions to work with NumPy arrays ______192
Points to remember __________________________________193
Part 3: Carrying out specialized tasks __________________________ 195
Chapter 10: Map scripting _____________________________________197
10.1 Introduction _________________________________________197
10.2 Working with the ArcPy mapping module ______________197
10.3 Opening map documents _____________________________198
10.4 Accessing map document properties and methods _______200
10.5 Working with data frames ____________________________201
10.6 Working with layers __________________________________203
10.7 Fixing broken data sources ____________________________208
10.8 Working with page layout elements ____________________213
10.9 Exporting maps ______________________________________216
10.10 Printing maps _______________________________________218
10.11 Working with PDFs __________________________________219
10.12 Creating map books __________________________________220
10.13 Using sample mapping scripts _________________________222
Points to remember __________________________________225
Chapter 11: Debugging and error handling ______________________227
11.1 Introduction _________________________________________227
11.2 Recognizing syntax errors _____________________________227
11.3 Recognizing exceptions _______________________________230
11.4 Using debugging _____________________________________230
11.5 Using debugging tips and tricks _______________________237
11.6 Error handling for exceptions _________________________238
11.7 Raising exceptions ___________________________________239
11.8 Handling exceptions __________________________________241
11.9 Handling geoprocessing exceptions ____________________244
11.10 Using other error-handling methods ___________________247
11.11 Watching for common errors __________________________247
Points to remember __________________________________249
Contents ix
Chapter 12: Creating Python functions and classes ______________ 251
12.1 Introduction _________________________________________251
12.2 Creating functions ___________________________________251
12.3 Calling functions from other scripts ____________________255
12.4 Organizing code into modules _________________________258
12.5 Using classes ________________________________________260
12.6 Working with packages _______________________________264
Points to remember __________________________________267
Part 4: Creating and using script tools _________________________ 269
Chapter 13: Creating custom tools ______________________________ 271
13.1 Introduction _________________________________________271
13.2 Why create your own tools? ___________________________271
13.3 Steps to creating a tool _______________________________273
13.4 Editing tool code _____________________________________279
13.5 Exploring tool parameters _____________________________280
13.6 Setting tool parameters _______________________________285
13.7 Examining an example script tool ______________________290
13.8 Customizing tool behavior ____________________________293
13.9 Working with messages _______________________________294
13.10 Handling messages for stand-alone scripts and tools _____297
13.11 Customizing tool progress information _________________297
13.12 Running a script in process ___________________________301
Points to remember __________________________________302
Chapter 14: Sharing tools ______________________________________303
14.1 Introduction _________________________________________303
14.2 Choosing a method for distributing tools _______________303
14.3 Handling licensing issues _____________________________304
14.4 Using a standard folder structure for sharing tools _______305
14.5 Working with paths __________________________________306
14.6 Finding data and workspaces __________________________308
14.7 Creating a geoprocessing package ______________________310
14.8 Embedding scripts and password-protecting tools ________311
14.9 Documenting tools ___________________________________312
14.10 Example tool: Market analysis _________________________315
Points to remember __________________________________321

Appendix A Data source credits _________________________323
Index _______________________________________________327