ws scripting startslides

Getting Started with Scripting in ArcGIS 9 Transcript

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Copyright © 2005 ESRI. All rights reserved. 1

Presenter: Krista Page ESRI Redlands, California

Getting Started with Scripting in ArcGIS 9

Welcome to the Getting Started with Scripting in ArcGIS 9 Live Training Seminar. My name is

Krista Page and I will be your presenter for this seminar. With me today is Jeremiah Lindemann

who will be helping to answer your questions.


Copyright © 2004 ESRI. All rights reserved.

Seminar overviewTopics

Introduction to scriptingWhat Python offersWhat ArcGIS offers

FormatTopics two and three are followed by a software demonstration, review, and Q & A session

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In this seminar, we will cover three topics. Topic number one is a quick introduction to scripting.

In topic two, we will discuss what scripting functionality Python offers. And in topic number

three, we will discuss what scripting functionality ArcGIS offers.

Topics two and three are followed by a software demonstration, a review, and a Q & A session.

During the presentation, you can send Jeremiah and me questions. During the Q & A session, we

will do our best to answer as many questions as possible.



Introduction to scripting

So, let's get started with topic number one: Introduction to scripting.



Why write scripts?Automate work flow

Project and clip all feature classes in a geodatabaseUpdate a feature class with daily GPS readings

Run code at specific dates and timesEasily distribute code

Scripts are self-contained filesEasy to write

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There are many reasons why people write scripts. But the number one reason that most people

write scripts is to automate a workflow. For example, maybe you have to project and clip a series

of feature classes in a geodatabase. Instead of projecting and clipping each feature class on a task

by task basis, you can throw the whole process into a script, and have the script do the tedious

work for you.

Another example might be that you have to update a feature class with daily GPS readings. Every

day you receive new GPS readings and every day you have to take those readings and manually

add them to an existing feature class. Instead of repeating this task every day, you can write a

script that will automatically update the feature class for you. With scripts, you can even set them

to run at a specific date and time.

Being able to run a script at a specific date and time is another reason that people write scripts.

Having the flexibility to run that script in the middle of the night when there is not much demand

on the server might be a huge benefit to some people.

A third reason that people write scripts is because they are very easy to distribute. Scripts are

stored in a single, self-contained file. There are no extra files to worry about.


The final reason that people write scripts is because they tend to be easy and quick to write. If you

compare a scripting language to a programming language (like Visual Basic), you will find that

scripting languages generally require fewer lines of code and have much simpler syntax.



Scripting languages ArcGIS 9 provides a scripting environmentMany languages are supported

Perl, VBScript, JScript, Python, and many moreESRI primarily supports Python

Installed with ArcGIS 9Samples and help documentation

3 of 21

Many legacy ESRI products offer a scripting environment. For example, ArcInfo Workstation has

AML. ArcView 3.x has Avenue. And now ArcGIS 9 provides a scripting environment as well.

Unlike previous versions of the software, ArcGIS 9 allows the user to pick from numerous

scripting languages, none of which are owned or managed by ESRI.

Some of these scripting languages include: Perl, VBScript, JScript, and Python.

Now since there are so many languages, ESRI had to choose one to primarily support. And we

chose Python. Python is installed with ArcGIS 9 and most samples and help documentation are

presented with Python code. All the code in this seminar will also use Python.



Scripting functionality

What Python offers What ArcGIS offers

Location to write and execute code

4 of 21

Now for anyone out there that currently uses AML, Avenue, or Visual Basic, you might be

wondering "What exactly can be done with ArcGIS 9 scripting"? And for those of you who have

never done any scripting, I am sure you are wondering the same thing. Well for the next 55

minutes we are going to focus on that question: "What can be done with ArcGIS 9 scripting?"

"What functionality is available?"

Well there is really two parts to the answer of this question. The underlying scripting language

itself offers some functionality, and this functionality will vary from language to language. And

then ArcGIS offers some functionality that is language independent. The following two topics in

this seminar are divided up based on these two parts. First we will look at what the scripting

language offers (in our case Python), and then we will look at what ArcGIS offers. So let's go

through a quick list of the functionality that we are going to cover…

The first thing that Python offers is a location to write and execute code.






Data types

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The second thing that Python offers is a series of data types, including: strings, numbers, lists,

files, etc.






Data types

Modules and functions

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The third thing that Python offers is a wealth of functionality tied up in modules and functions.






Data types


Statements

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And the fourth thing that Python offers is a series of statements. All four of these things—

location to write and execute code, data types, modules and functions, and statements—are

specific to Python. Other scripting languages, such as VBScript or JScript, do offer similar

functionality, but in a different flavor.






Data types


Statements

Tools and environment settings

4 of 21

Now the first thing that ArcGIS offers is a set of geoprocessing tools and environment settings

that can be run, or set, from any supported scripting language.






Data types


Statements


Data descriptions

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The second thing that ArcGIS offers is the ability to create data descriptions.






Data types


Statements


Data descriptions

Data lists

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The third thing that ArcGIS offers is the ability to create lists of data.






Data types


Statements


Data descriptions

Data lists

Row manipulation

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ArcGIS also offers the ability to manipulate rows in a table or feature class.






Data types


Statements


Data descriptions

Data lists

Row manipulation

Geometries

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The fifth thing that ArcGIS offers is the ability to work with geometries, for example, create new

point or line features.






Data types


Statements


Data descriptions

Data lists

Row manipulation

Geometries

Location to execute code

4 of 21

And the final thing that ArcGIS offers is an execution environment; an interface to run your script

from. Now all of this functionality—tools and environment settings, data descriptions, data lists,

row manipulation, geometries, and location to execute code—is available for any supported

scripting language. It is not just specific to Python.






Data types


Statements


Data descriptions

Data lists

Row manipulation

Geometries


4 of 21

Well let's take a look at what Python can do. The next four slides correspond to these four boxes



What Python offers

What Python offers.



Location to write and execute codeThe PythonWin application

PythonWin installed with ArcGIS 9Write, test, debug, save, run code from one location

5 of 21

The first thing that Python offers is an environment where you can write and execute your code.

The application is called PythonWin, and it is installed with ArcGIS 9. In the scripting world,

PythonWin is kind of the equivalent to one stop shopping. From PythonWin, you can write, test,

debug, save, and run your code all from one location.





Write

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You will write most of you code in what's called a script window.





Test

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You can test individual lines of code in the Interactive Window.





Debug

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PythonWin offers a set of debugging tools built right into the application. These tools will help

find your errors.





Save

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You can save any of the code that you write using the Save button on the Standard toolbar.





Run

5 of 21

And you can run your code by clicking the running man icon on the Standard toolbar.



Data typesNumbers

num = 1.2exp = 3 + 5

Stringsfolder = "C:/Student"whereClause = "[STREET_NAM] = 'CATALINA'"

ListsfcList = ["Roads", "Streets", "Parcels"]fcList[1] ---> "Streets"

Filescoord = open("C:\\XY.txt", "r").read()

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The second thing that Python offers is data type support. Python can store and work with many

types of data. The four most common types of built-in data types that Python supports are:

numbers, strings, lists, and files. Tuples and dictionaries are also common built-in types, but we

don't have enough time to discuss them all.

Numbers are simply numeric values. They can store integers, floating-point values, complex

numbers, and the result of an expression.

Strings are an ordered collection of characters used to store and represent text-based information.

Strings can store something as simple as a path name, or something a little more complex, like a

where clause.

Lists are a collection of ordered values that are indexed – meaning you can pull individual values

out of the list. The indexing starts at zero.

Files store the contents of a file. In Python, you can open, read, and write to files.



Modules and functionsModule: A file that contains functionsFunction: A task that returns a value

7 of 21

The third thing that Python offers is modules and functions. A module is simply a file that

contains functions. And a function is simply a task that returns a value. Most of Python's

functionality is locked up in dozens and dozens of modules.



Modules and functionsModule: A file that contains functionsFunction: A task that returns a value

The math moduleimport mathmath.sqrt(64)math.pi

The string moduleimport stringstring.split("-155.3 -43.5")string.upper("c:\\student")

The os.path moduleimport os.pathos.path.basename("C:\\Student\\Streets.shp")os.path.dirname("C:\\Student\\Streets.shp")

7 of 21

To access the functions in a module, you need to import the module. In the example on the slide,

three modules are being imported: the math module, the string module, and the os.path module.

Once the module is imported, you can access the functions in a module by prefixing the name of

the module to the name of the function. For example, to access the square root function in the

math module, type math.sqrt. This function returns a value of eight.

Some modules contain dozens of functions, and other modules contain just a few. In total there

are hundreds of functions available to any Python programmer.



StatementsPerform a task, but do not return a value

8 of 21

The fourth thing that Python offers (and the last thing that we will look at for Python

functionality) is statements. Statements are very similar to functions, in that they perform some

task, but they differ from a function because statements do not return a value to the user.



StatementsPerform a task, but do not return a value

Import a moduleimport mathimport string

Report output to the Interactive Windowprint "Hello"

Conditional statements if…elif…else

Loopswhilefor…in

Error handlingtry…except

8 of 21

Here are some examples of very common statements that you will use over and over again in

your geoprocessing scripts.

The first one is the “import” statement that we just looked at on the last slide. The import

statement imports a module.

The second one is the “print” statement. This statement is generally used to send output from a

script window to the Interactive Window (the window that we use for testing).

The third set of statements are conditional statements. Every programming or scripting language

has the ability to make decisions. Python uses the “if – elif – else” statements for decision

making.

Python also supports looping and uses the while and for statements to manage loops.

To handle and trap errors, use the “try” and “except” statements. If you throw all of your code

into a try statement, and there is an error with that code, Python will automatically skip to the

except statement. In the except statement, you, as the programmer, gets to decide how to handle

the error.






Data types


Statements


Data descriptions

Data lists

Row manipulation

Geometries


9 of 21

Well we just looked at the four main things that Python has to offer: a location to write and

execute code, the support for many data types, dozens of modules and hundreds of functions, and

many built-in statements.

Python also offers a lot of additional functionality (like the ability to make your own classes), but

we obviously don’t have time to cover everything. What we are looking at is the basics.



Software Demonstration

At this point let's do a software demonstration to hammer home some of these concepts.

I’d like to move over to Python Win, which is the application that allows us to write our code,

debug our code, test our code, save our code—everything can be done from this particular

application, and this application is installed with ArcGIS 9. Down at the bottom, we see the

Interactive window. This is the location where you can test your code. We can open a brand new

Script window by going to File>New.

In the Script window is generally where you write your code, so let’s save the Script window.

Once you write some code in your Script window, you can run it by clicking this running-man

icon. If your script happens to produce an error, you can debug the script using the debugging

tools up here on the Debugger toolbar.

So, let’s write some code. The first thing I want to take a look at are those modules and functions.

And remember, to import a module, we use the “import” statement. So, let’s import the Math

module. The Math module is one of the modules we looked at back in the presentation. Now,

from the Math module, we can grab the Square-Root function. We can grab the square root of 64,

which would return a value of 8. To test this, to see the output from this, we might throw the


“print” statement in front of the math.sqrt function. The print statement will send output down to

this Interactive window. So, let’s click our Run icon, and notice, down in the Interactive window,

a value of 8 is returned.

Now, math is just one of the dozens and dozens of modules that are available for you to work

with. If we take a look in Python’s Help, there’s a Global Module Index that will take you in and

show you all of the different modules that you can work with in Python. And, there are lots of

these different modules. Math is a module that we just took a look at. If you click on the Math

module link, it will take you into that module. You can actually scroll through and see all of the

different functions that are available for that particular module. If we scroll down far enough, we

will find that Square-Root function that we just worked with.

A couple other modules that we took a look at in the presentation were the String module and the

os.path module. Those have links as well. You can just click on the String link or the os.path link,

and that will take you into their modules and show you the functions that are available for those

modules.

Okay. Well, let’s leave functions and modules for a minute and take a look at some of Python’s

functionalities—some of its other functionality. Now, let’s take a look at its Conditional

statements. So, I’m going to use the “if-elif-else” statement. I’m just going to type a little bit of

code, let’s say “X = 6”, then I’m going to say, “If X = 5, then I want to print down to the

interactive window, the value of ‘5’.” Then I’m going to say, “Else If X = 2, then what I want to

print down to the interactive window is a value of ‘2’.” “Else, If X is not equal to (==) 5, or not

equal to (==) 2, let’s print down to the Interactive window, ‘not 5 or 2’.”

So this is just some very simple code, showing you how to use Python’s Conditional statements.

In this particular example, we assign X a value of ‘6’, and then we start testing the value of X. If

X=5, we jump in and do this statement, and then the Conditional statement is over. But, if it’s not

equal to 5, we test to see if it’s equal to 2. If it is 2, then this statement is executed. If it’s not 5 or

2, then this final statement is executed. So, hopefully, if you’re following the logic, you’ll realize

that, if we run this script, that “not 5 or 2” should be printed down to the Interactive window. So,

let’s run the script, and down in the Interactive window that’s exactly what we see: “not 5 or2.”

So, again, a very simple syntax, here, or a very simple example, here, but I want to point out the

syntax. Notice at the end of each condition we use a colon. That is something that you have to do


in Python, at the end of each Condition, use that colon. And the colon is what causes the

indentation when you press Enter. Also notice that, for the Conditional statement, there’s no “End

If” statement. There’s no way to tell Python that this Conditional statement is over, and that’s

because Python uses indentation. As soon as you un-indent your code, Python knows that that

particular condition is over. Okay, so, for those of you who have worked with programming or

scripting languages before, that might be something new for you to get used to.

Well, I want to continue on, looking at Python’s looping ability, so, what I want to do is I want to

comment out all of this code—I’m just selecting it all—so that it doesn’t run again. I then right-

click, click Source Code, and click Comment Out Region. Okay, now that code will not execute.

So, let’s take a look at Python’s While loop. I’m going to assign X another value of 10, and I’m

going to say, “While X is less than 20:—notice when I press Enter, it automatically indents for

me—I’m going to print the value of X to the interactive window. I press Enter again—it’s still

indented—and then I’m going to increment the value of X by one, press Enter again. To un-

indent, I can just press Enter a second time. So, this is Python’s While loop. Again, very simple

example. We assign X a value of 10, and then we go into the While Loop. While X is less than

20, as long as X is less than 20, go into this loop and perform these actions. At this point, X is

less than 20, it’s equal to 10, so we go into the loop, print the value of X to the Interactive

window, and then increment X by one, so that it’s now equal to 11. So, when we run this loop, we

just see the value starting at ten, print it to the Interactive window, all the way up to 19. Once it

hits the value of twenty, it no longer goes into the loop. So let’s run this code.

If we come down to our interactive window, and we scroll down—we see the value of 10, all the

way down to the value of 19, and it stops at 19. Again, a very simple example, but showing you

how Python’s looping works. Again, you have to use that colon and notice there’s no End While

or End Loop statement. As soon as you un-indent, Python knows that that loop is over. Okay,

well let’s Comment Out this code—again we’ll just select it, we’ll right-click, go to Source Code

and click Comment Out Region.

The final thing I want to take a look at, here, is Python’s data types. So, we just looked at

Python’s modules and functions, and we looked at Python’s Conditional statements and loops.

Now I want to look at those data types a little bit. I mentioned there’s a number of different types


of data types—numeric would be one of them, and we see that X can store a value of 10, that is a

numeric value—but a couple other ones that I want to look at are the List and the String.

So let’s make a variable that holds a list—we’ll call it fcList, and we’ll set it equal to a series of

feature class names. So let’s say Roads, Streams, and we’ll go with Landuse. And notice that lists

are surrounded in brackets. Okay, that’s what defines a list in Python. Now lists are indexed and

they start the indexing at zero. So, for example, if I said pull value zero to the list, I’d get Roads.

If I said pull value one out, I’d get Streams, and pull value two out, I would get Land-Use. With

lists you can also grab a range. So, for example, I’m going to grab, from my list, values 0 to 2,

and I want to print that result down to the Interactive window, so I use that “print” statement.

Now, the funny thing about Python’s lists is it will start at this position—the start position—and

grab Roads, and it goes to position number 2, but it never grabs that last position. So, in this case,

we’ll get 0 to 1—it should return Roads and Streams. So let’s run this code, and that’s exactly

what we see down in the Interactive window, the values of Roads and Streams.

Now, the last data type I want to take a look at is Strings. So in a variable called FC, I’m going to

store a string called Railroads.shp, so this would represent a particular name of a shapefile. Now,

strings are also indexed, and I can pull out a series of values, and what I’d like to pull out, here, is

value 0—everything from the beginning—but I want to cut off the last four values. I actually

want to cut off the dot, the ‘s’, the ‘h’, and the ‘p’. So, now, if I run this, what I should see down

in the Interactive window is Railroads, without the .shp extension. So, I’m going to run this code,

we’ll scroll down to the bottom of our Interactive Window, and that’s exactly what we see: the

last output was Railroads.

Now, this might be useful to you, for example, if you want to convert a series of feature classes

or, sorry, a series of shapefiles into feature classes in the geodatabase, but you want to drop the

.shp extension, this might be a very easy way for you to do that. Just grab everything from the

beginning and drop the last four characters.

Okay, well that’s all I’m going to show you in the Python Win application. Now, just as a review

here, or just as a sum: Python has full support for data types, loops, conditional statements, and it

gives you access to hundreds of functions, which are stored in modules. So, let’s return to our

presentation, and let’s do a review of the topics we have covered so far.



Review and Q & AReasons to write scripts

Automate work flowRun code at specific dates and timesEasy to write and distribute

ArcGIS 9 scripting environmentWhat Python offers

Location to write and execute codeData typesModules and functionsStatements

10 of 21

There are four main reasons why people write scripts: to automate a workflow, to have the

flexibility of running a program at a specific date and time, to have an easy way to distribute

functionality to a user, and because they are very easy and quick to write. ArcGIS 9 provides a

scripting environment where users can choose to code in one of many different languages. ESRI

has chosen to primarily support Python. Python offers a lot of functionality, including, but not

limited to, a location to write and execute code, the support for many data types, dozens of

modules and hundreds of functions, and many built-in statements. At this point we are going to

take a few minutes to answer some of your questions. I will now turn it over to you, Jeremiah.

Okay. Thanks, Krista.

Question From Peter in Anglewood: Where can I download Python Win from?

Answer So, first, to reiterate what Krista mentioned, is that when we install ArcGIS, Python and

Python Win is included, so you don’t need to worry about going out and installing anything. You

automatically get this scripting environment to use when you install ArcGIS Desktop. Now, if

you have the case where you don’t have ArcGIS Desktop yet, and you want to start looking at

Python, and you know you’re going to be working with it in ArcGIS in the future, you can

download Python for free. So, that’s one of the advantages of using Python, is that it’s free. If you


want to download Python, there are actually two parts that you would need to have to use Python

Win. You first need Python, which gives you access to the scripting language itself, which you

can download from www.python.org. That’s a free download, and that just gives you access to

Python itself. And then you also need a separate download for Python Win, which was the

application Krista was using to write the scripts. There are also links on python.org to download

Python Win, as well.

Question From multiple users: How do you start Python Win?

Answer Well, once you have Python Win installed, it just is easy from going to the Start menu,

going to Programs, and you should see an option for Python Win.

Question From Jim in Rochester: Does Python have a debugger?

Answer Yes. One of the advantages of using the Python Win application Krista was using is that

it does have a debugger. It has its own debugging toolbar. This means that we can set up break

points, to see where our code might be having problems—step through our code, line-by-line, to

examine it more closely, see where we may have made syntax errors or how we are interacting

with our data.

Question From Cindy in Oakland: Can I run a script at any time? And, how can I do this?

Answer Well, you can do this with the Windows “at” command or using the Windows

Scheduler. This is by going into the Control Panel. And then, what you’ll do is you’ll just point to

that Python file, the py file, and you’ll tell it what time you want to run it.

Question From Cindy in Oakland: If I want to run a geoprocessing script outside of ArcMap, can

I do that as well?”

Answer Yes. We don’t even need to have ArcMap or ArcCatalog open. As a matter of fact, what

Krista’s been showing is just what we can do with Python itself. We haven’t even gotten into

ArcObjects yet—is what she’ll be getting into next—and you can run these scripts without having

ArcMap or ArcCatalog open.

Okay. I’ll turn it over to Krista now.

Okay. We’ll take two more questions, here.


http://www.python.org/

Question From Robert in Austin: Is Python 2.3 okay? Or should I uninstall it and revert to

Python 2.2?

Answer Well, Robert, when you install ArcGIS 9, what gets installed by default is Python 2.1,

and that’s fine, but you can also overwrite that and install Python 2.3 on your own. Now, there

will be a few minor differences between something like Python 2.1 and 2.3. For example, in

Python 2.3, Boolean values are returned as true (t-r-u-e) and false (f-a-l-s-e), whereas, in 2.1,

they’re returned as a zero and a one. So, there are a few minor differences like that, but nothing

that should prevent you from using any of the valid versions of Python.

I’ll take one more question here.

Question From Mel, from Alabama asks, What are the most common modules to import for

GIS?

Answer There are probably four different modules that I use a lot: the os.path module is very

useful—it allows you to grab the base names and the directory names for different paths; the

String module, if you want to do any sort of string manipulation, which is very common, and

we’ll actually take a quick look at the String module in some code that’s coming up—that’s a

very useful one; the Math module, if you want to do any sort of mathematical calculations, maybe

do some mathematical calculations to add new values into a new field—that might be a useful

module for you; and the final module that we use a lot is the XYX, or the Sys module, and in that

module there are a number of things that you would work with. For example, there’s a function in

there called Exit, which is very useful. It allows you to prematurely exit a script. And the other

one that you will use a lot in there is the ARGV function, which allows you to accept dynamic

input from the user.



Review questionLocate the Review question link in the upper-left corner of your browser window. Click this link now.

11 of 21

And now I am going to ask you a question… Before I do, locate the review question link in the

upper-left corner of your browser window.



Review questionWhich of the following performs a task but does not return a value?A) A functionB) A statementC) A moduleD) A script

To submit your answer, click A, B, C, or D then click the Send button.

12 of 21

Here is the question: Which of the following "performs a task, but does not return a value"? Is it

A, a function; B, a statement; C, a module; or D, a script. To submit your answer, click A, B, C,

or D then click the Send button. We will answer this question towards the end of the seminar.



What ArcGIS offers

Our third and final topic focuses on what ArcGIS has to offer.






Data types


Statements


Data descriptions

Data lists

Row manipulation

Geometries


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The ArcGIS functionality is available regardless of the underlying scripting language that you

decide to use. ArcGIS offers: tools and environment settings, data descriptions, data lists, row

manipulation, geometries, and a location to execute your code. The next six slides correspond to

these six boxes.



Tools and environment settingsTools: up to 455

Union, Buffer, Project, Import from CAD, Delete, Geocode Addresses, Hillshade, Create TIN, Feature Outline Masks, Create Routes, Mean Center, Build, and much more…

Environment settings: 22Workspace, Cell Size, Output Coordinate System, Compression, Tile Size, Output Extent, and much more…

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The first thing that ArcGIS offers is a set of geoprocessing tools and environment settings that

you can run or set from any geoprocessing script.

A tool is simply a geoprocessing operation (like a buffer, clip, projection, or data conversion).

And an environment setting is simply a common setting that is applied to all tools. For example,

maybe you want all of the outputs from your buffer and clip operations to go to one folder. If this

is the case, you can assign that folder to the workspace environment setting. All geoprocessing

tools will then honor that setting.






import win32com.clientgp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")

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The first thing you do when you start to write a script is type in these two lines of code. The first

line imports a module. This module allows you to work with ArcGIS's geoprocessing

functionality. The second line of code gives you access to the geoprocessing functionality. You

usually store that functionality in a variable called gp. From gp you can access all your tools and

environment settings.






import win32com.clientgp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")gp.Workspace = "C:\\Data\\Canada.mdb"gp.Buffer("Streams", "NoBuildZone", 100)gp.Erase("LandUse", "NoBuildZone", "BuildZone")

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After you have created the gp variable, just prefix it to any tool or environment setting. In the last

three lines of code, we are setting a workspace, buffering a feature class, and erasing features

from a feature class. The third line of code uses the workspace environment setting, and the last

two lines of code use the buffer and the erase tools. Any environment settings or tools can be

called in this fashion.



Data descriptionsFeature classes, geodatabases, feature datasets, coverages, folders, rasters, tables

dscFC = gp.Describe("C:\\SanDiego.mdb\\Zipcodes")if dscFC.ShapeType == "Polygon":## Calculate the area

15 of 21

The second thing that ArcGIS offers is the ability to create data descriptions. You can describe

feature classes, geodatabases, feature datasets, coverages, and many other types of data. Once you

have described a data set, you can use that description in your code.

In the example on the slide, we are describing the Zipcodes feature class and storing the

descriptive information in a variable called d-s-c-F-C. One of the descriptive pieces of

information that you can get for a feature class is its shape type. Using Python's if statement, test

to see if the Zipcodes feature class is a polygon feature class. If so, we will do some area

calculations.

Now maybe you are wondering what other descriptive pieces of information you can get for a

feature class…




dscFC = gp.Describe("C:\\SanDiego.mdb\\Zipcodes")if dscFC.ShapeType == "Polygon":## Calculate the area

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Well here is a list of the available properties. You can get the feature type, whether the feature

class has M or Z values, a list of fields, the extent, and many more. Each type of data you

describe will have a different set of properties. Let's look at one more example…




dscRD = gp.Describe("C:\\Tahoe\\erelev")gp.Clip("arhill", dscRD.Extent, "erhill")

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In this example, we are describing the e-r-e-l-e-v raster dataset. The raster dataset is represented

by the blue outline. The descriptive information is stored in the d-s-c-R-D variable. One of the

descriptive pieces of information that you can get for a raster dataset is the extent. We use that

information as input into the clip tool. We clip the green dataset (a-r-hill) to the extent of the blue

dataset (e-r-e-l-e-v) and call the output e-r-hill.

If you are wondering what other descriptive pieces of information you can get for a raster dataset,

let's have a look…




dscRD = gp.Describe("C:\\Tahoe\\erelev")gp.Clip("arhill", dscRD.Extent, "erhill")

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You can get the band count, the compression type, the mean cell height, the pixel type, and many

more.



Data listsFields, indexes, rasters, tables, workspaces, datasets, feature classes

gp.Workspace = "C:\\Tahoe"rdList = gp.ListRasters("h*")rd = rdList.Next()while rd:

gp.BuildPyramids(rd)rd = rdList.Next()

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The third thing that ArcGIS offers is the ability to create lists of data. You can get a list of all the

fields in a table or feature class, all the rasters in a folder, all the feature classes in a folder, and

many other lists are available as well. Once you get a list of data, you can use Python's while

statement to loop through each value in the list.

In the example on the slide, we are listing all of the raster datasets in the Tahoe folder that begin

with the letter H. We then loop through the entire list, building pyramids for each raster dataset.

BuildPyramids is a geoprocessing tool.



Row manipulation (cursors)Read, edit, assign attribute valuesAdd and delete rows

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The fourth thing that ArcGIS offers is row manipulation. You can read, edit, and assign attribute

values to rows. You can also add and delete rows. This functionality is referred to as cursors.

In the example on the slide, we want to replace all the occurrences of the word INTERSTATE

with INT. We want the table on the left to look like the table on the right.



Row manipulation (cursors)Read, edit, assign attribute valuesAdd and delete rows

gp.Workspace = "C:\\SanDiego.mdb"cur = gp.UpdateCursor("Freeways","[Fwy_Name] LIKE 'INT*'")row = cur.Next()while row:

row.Fwy_Name = string.replace(row.Fwy_Name,"INTERSTATE","INT")

cur.UpdateRow(row)row = cur.Next()

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Here is the code to do this. Notice that we use a cursor to access the rows in the Freeways feature

class that have the letters INT. We then use Python's “while” statement to loop through each

individual row. For each row we use Python's replace function (available from the string module)

to replace all the occurrences of INTERSTATE with INT.



GeometriesRead, create, and edit geometries

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The fifth thing that ArcGIS offers is the ability to read, create, and edit geometries (or, x/y

coordinates). In the example on the slide, we want to add one new feature to this coffee shops

feature class. We need to create an x/y point for the coffee shop location.



GeometriesRead, create, and edit geometriesgp.Workspace = "C:\\Redlands.mdb"cur = gp.InsertCursor("CoffeeShops")row = cur.NewRow()row.Name = "Starbucks"pnt = gp.CreateObject("Point")pnt.X = 481423pnt.Y = 3767370row.Shape = pntcur.InsertRow(row)del cur

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Here is the code to do that. We use a cursor to create a new row. We then create a new point that

stores the x and y coordinates. Finally, we assign this point to the row's shape field.




Dialog

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The sixth thing that ArcGIS offers (and the last thing that we will look at for ArcGIS

functionality) is a location to execute your code.

You can tie your script into a tool in ArcToolbox and run that script as a dialog from ArcMap or

ArcCatalog.




Dialog

Command line

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You can also run a script from the Command Line environment, just like any other tool.




Dialog

ModelCommand line

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And finally, you can add your script to a model and run the script from there. You can take the

output from your script tool and make it input into another tool.

So that was the last thing that we are going to look at for ArcGIS functionality.



Review question resultsTo view the results, click the Review question link in the upper-left corner of your browser window.

Which of the following performs a task but does not return a value?

A) A functionB) A statementC) A moduleD) A script

20 of 21

Before we do the software demonstration, let's see how many of you got the correct answer to the

review question. For "which of the following performs a task but does not return a value", the

correct answer is…



Review question resultsTo view the results, click the Review question link in the upper-left corner of your browser window.

Which of the following performs a task but does not return a value?

A) A functionB) A statementC) A moduleD) A script

20 of 21

B) A statement.



Software Demonstration

At this point, let’s do a software demonstration that will focus on different scripts that can be

created using the ArcGIS scripting functionality. So, at this point I’d like to move over to

ArcMap.

In this ArcMap session, I have a map document open called sandiego.mxd. Within this map

document I have three different feature classes open: the Oceans feature class, the Zipcodes

feature class, and the Hotels feature class. Also notice that I have a toolbox called Custom

Tools—a toolbox that I created—that stores five different scripts. The ‘S’ symbol represents a

script symbol. Behind each one of these tools is a Python script, and we’ve taken that Python

script and we’ve attached it to a tool in ArcToolbox. As soon as you do that, it becomes part of

what’s called the geoprocessing framework, and you can now run this script from many different

locations. For example, I can double-click on a script and it opens up a dialog and I can run this

script from this location. It puts a nice front-end user interface on this particular script.

Something else that I can actually do is I can open what’s called the Command Line window, and

in the Command Line window I can type in the name of that script. Notice when I type in

Convert, that particular script pops up. So, again, as soon as you add it to a tool in ArcToolbox, it


behaves like any other tool and I can run it from this particular environment. Also, notice that the

usage pops up as well, telling me exactly what I need to input.

The other place that you can run this script is from a model. So, if I add a new model, or an empty

model, to my Custom Tools toolbox, I can take any one of these scripts and drag them into the

model and run them from a model. I could take the output from this convert XY to point script,

and I could attach this output to maybe another geoprocessing tool and run these tools in

succession.

So, what I’d like to do at this point is go through these different scripts and show you how some

of the functionality was created, or how some of the scripts were written. The first script I want to

look at is this Delete Files script. If I double-click on this script, there’s a description over here

that tells me that this script deletes a set of files from a folder. Okay, notice I have a default folder

in here called D:\DemoData\JunkFolder. Also notice there’s a drop-down list where you can

choose which kind of files you want to delete. Notice that mxd is one of those types.

So, let’s go over to ArcCatalog and see what we have in that JunkFolder. Okay, so in JunkFolder

I have a series of map documents, and I want to delete those map documents, but I don’t want to

have to open ArcCatalog to do that. I just want to be able to run this script from ArcMap and

clean up data when necessary. So, let’s go back over to that Delete Files script, double-click it,

specify that we want to delete mxd files, and click Okay. When the script has finished running, hit

Close on the progress dialog, go back over to ArcCatalog, right-click on JunkFolder and do a

Refresh, and notice that all those map documents are gone. Pretty simple script, but it performs

some very useful functionality.

Now let’s right-click this script tool—you can right-click any script tool, and you can click Edit—

and what it actually does, is it pops up that script tool inside of Python Win, and you can see

everything behind that tool was just some Python code. Now, the majority of this is just

comments, and if we look at the actual code that performed that—here it is, right here—not a lot

of code, maybe six or seven lines of code to perform something fairly useful. Notice, in here,

we’re not really using any ArcGIS functionality, we’re using straight Python functionality. So, we

import two different modules, SYS and OS. We use the SYS to grab dynamic input from the user,

using that ARGV function. Also notice, from the OS module, that we’re using some of its


functions: we’re listing the directories in a particular folder, and then we’re also removing them,

or deleting them.

Well, let’s take a look at our next script, called Shapefile Information. Now, what this script does

is it reports the name, shape type, and number of fields for each shapefile in a folder. Okay, so a

fairly simple script. It’s just going to report some shapefile information right to a progress dialog.

So, I’m going to click Okay. I’ve got a folder selected. Notice I can put default values in here. I

can also browse to my own location. But, I’m going to click Okay, and in this progress dialog, it’s

going to go through and it’s going to list the information for all the shapefiles that it found in that

folder. Notice that it found a shapefile called Cities—it’s reporting that it’s a point shapefile and

that it has eight fields. Okay, then it reports the next shapefile, and so on and so forth, until it’s

reported every shapefile in that folder. Okay, and again, this is just being sent to the progress

dialog, but we could also send this to a text file, or some other location.

Well, let’s take a quick look at that script. Again, if we right-click and we go to Edit, this script

opens in Python Win. You can just see that there is some Python code in here. And what the

Shapefile information script makes use of is those data descriptions that we talked about in the

presentation. Notice that we call a Describe on a particular shapefile, and then we can get some

fields information, we can describe the fields. Somewhere we must also be describing the shape

type, because we get that back, as well; the point, line, or polygon. And, again, just making use of

those describe objects.

Okay, well the next script that I want to take a look at is called Report Geodatabase Contents.

Now, what this script does is it reports the names of all the feature datasets, feature classes,

tables, and rasters in a geodatabase to a text file. Okay, so that might be kind of handy—it’s

something that’s been handy for me—is I pick a particular geodatabase and I report the contents

of it to a text file. So, let’s run this script. And it’ll take a second to run. When it’s finished

executing, I can click the Close button, and we can go into ArcCatalog and take a look at that text

file. Now I’ll just refresh my JunkFolder, and notice a new file called GDBReport has been

added, and it gives us some information on what’s stored inside that geodatabase. There’s one

feature dataset called Census; within there, there’s a series of feature classes. Notice there are also

some stand-alone feature classes, and there’s a table, as well. Okay. So a fairly handy tool if

you’re looking for a quick report on what’s in your geodatabase.


Let’s go back to ArcMap and we’ll right-click on that tool, and we’ll click Edit, and take a quick

look at it in Python Win. Now, what this makes use of—what this particular script makes use

of—is those data lists. Remember, we can list a lot of different types of data. The first thing we

list is the feature datasets, and then, within each feature dataset, we make a list of the feature

classes. We then scroll down and we make a list of stand-alone feature classes. We make a list of

tables and a list of rasters. Okay, and all of this is being written—every single time—out to a

particular text file. So, again, we’re making use of those data lists.

Okay. Well, let’s look at our next script: Point Count. Now, what this particular script does is it

calculates the number of points in a polygon and stores a count in a field in the polygon feature

class. This tool assumes the field already exists. Now, let me explain to you what this does. Here

we have a polygon feature class called ZIPcodes, and we also have a point feature class called

Hotels. So, we want to figure out how many hotels are within each ZIP Code and store that in a

field in the ZIPcodes feature class. If I open the ZIPcodes feature class, this tool does assume that

there’s already a field that we can use to store this information. We currently have a field called

Hotel Count that we can use. If you didn’t have a field, you could just add it, and there’s also a

geoprocessing tool called Add Field that would allow you to do this right inside of the script. But

let’s go ahead and run that particular script tool. The polygon feature class is ZIP Codes, the point

feature class is Hotels, and the field that stores the count is called Hotel Count. Okay. Notice how

these are all available directly from drop-down lists. Click OK. It’s going to run through and

count each of those hotels in each ZIP Code and store that information in the field. If we open the

ZIPcodes feature class, we scroll over to the end, here, and let’s do a sort descending—we’ll see

that ZIP Code number 92101 has the largest number of hotels: 18, and that makes sense. If

you’ve ever been to the city of San Diego, which is in Southern California, you’ll know that this

is the downtown core area of San Diego.

If we right-click that script tool and go to Edit—open that in Python. What this script makes use

of is row manipulation. Using those particular cursors, we go through and we add the new value

to each one of those rows in that field. The last script that I want to look at is called Convert XY

to Point. Now, what this script does is it converts a text file with x and y coordinates to a point

feature class. So, maybe you have some text files storing some GPS readings and you want to

convert those to a feature class, and you want this to be automated. This particular tool can do

that. So, we’re going to send, or we’re going to use the Attractions text file—it has some GPS


readings in there—and we’re going to convert it to a feature class called Attractions in the San

Diego geodatabase. So let’s run this tool.

Now we can add that Attractions feature class—here it is, right here, just created for us—and

we’ll give it a little bit of symbolization so you guys can see it. And now all of these new point

features have been added to the attractions feature class, based on GPS readings in a text file.

These include things like, maybe museums and parks in the city of San Diego.

Well, let’s take a quick look at the code behind this script. Now, what this script is kind of

showing off is the ability to work with geometry. If we scroll down through the script, you’ll see

that we have to make a new point feature. And then, in that point feature, we assign different X

and Y values, creating brand new points to store in that Attractions feature class.

Now, the last thing that I want to mention is maybe you’re wondering how can I look at some

existing scripts, and a great way to do that is to look at some of the scripts that are actually

shipped with the software. So, for example, in the Conversion Tools toolbox, there’s a number of

tools that are actually built on scripts—any of these ones with the little ‘S’ icon. So, you can

right-click any of these and click Edit, and that code will actually open in Python Win and you

can view it, and see how ESRI creates their scripts, and maybe borrow some of that code to write

one of your own scripts, etc. There are a number of different tools that come with the software

that are actually stored as Python scripts.



Review and Q & AWhat ArcGIS offers

Tools and environment settingsData descriptionsData listsRow manipulationGeometriesLocation to execute code

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Let's do a review of the last topic that we just covered. ArcGIS offers a lot of scripting

functionality: tools and environment settings, data descriptions, data lists, row manipulation,

geometries, and a location to execute your code. ArcGIS also offers a lot of additional

functionality (for example, error checking, error handling, and messaging). We just don't have

time to cover it all.

At this point we are going to take a few minutes to answer some of your questions. Back to you,

Jeremiah.

Thanks Krista.

Question From multiple users: Does the number of ArcGIS functionalities available to me

depend on whether I have ArcView, ArcEditor or ArcInfo?

Answer Yes, it does depend on which license level you have. The second part of this lecture,

Krista’s largely talked about what we can do from ArcGIS within Python. One of the major

things that we’re going to be doing is running geoprocessing tools, or tools that are inside

ArcToolbox. Now, those tools that you get inside ArcToolbox differ, depending on whether you


have ArcView, ArcEditor, or ArcInfo. If you have the full ArcInfo seat and all extensions, you

get nearly five hundred tools. But, you get quite a few tools, even with the ArcView seat. You get

about a hundred tools. So, it just depends on which seat you have and you need to be aware of

which tools you have available to you, whether or not you can use them within a Python script.

Question From Elizabeth in Milton: Is it possible to first create a model, then export it to a

script?

Answer Yes, you can do that. So, if you’re familiar with using the geoprocessing framework, we

can also create models and chain together tools—execute one tool after another. We take our

models and then we can export them to either a Python J Script or VB Script. So, this is a great

way to establish a workflow—a general workflow: which tools you want to execute—and then

we can put in our logic into our script, set up the branching or the looping after we have the

general flow in place.

Question From Michael in Salem: What is the best way to get help and find parameters for the

geoprocessing tools?

Answer Well, probably the best way to find out what parameters and what syntax you need for a

specific tool—for instance, if I want to run the clip tool in Python—would be to go into

ArcToolbox, right-click the tool, and choose Help. You’re going to get a lot of information about

how to use a tool, what the tool’s intended purpose was, and at the very bottom of the page, each

tool within ArcToolbox will have a script example. All these examples are within Python. So, that

will tell you what parameters are needed, and you can still see the general syntax for how to get

that tool to be used within Python.

In just a moment, Krista’s going to get back to a little bit more about other resources where we

can find out more information—more help for running our geoprocessing scripts.

Question From Oliver in Cambridge: Can I describe shapefiles?

Answer Yes, we can. Krista had a couple slides in there where she was describing raster datasets

and, in the demo, she ran a method that was called List Feature Classes. Now, a shapefile is just

another type of feature class, so you can also describe shapefiles and get information about them:

what is the type? Is it a point, line, or polygon? What are its extents? If you want more

information about which type of objects you can describe, again, go into the ArcGIS Desktop

Help. It gives you information on geoprocessing and what you can do. And there’s also a PDF

called The Geoprocessor.pdf. This will give you information on everything that you can do within


scripting. It has it all nicely diagramed-out, so you can see the workflow—what one object will

lead to another.

Question From multiple users: Does Python supply auto-completion? So, when I type in a

variable and hit a doc, can I see what methods or what tools I can use?

Answer Now Python Win does not support a true auto-completion when using the geoprocessing

tools. The reason is because the geoprocessing environment is dynamic. Meaning that, if you’re

going to be using the geoprocessor to run tools, you can have a wide variety of tools inside of

ArcToolbox depending on which license you have, and you might also put custom tools inside

ArcToolbox. For instance, you can run a model from a script. So, right up front, Python doesn’t

know which tools you have inside ArcToolbox, so it’s not aware of which tools it should be able

to run. However, you will see some completion, for instance, if I run the Add Field tool within

Python, and then I want to use it again later on, it will recognize I use it within the script, so then

I will see some auto-completion.

Question From multiple users: Why would you use Python versus using ArcObjects and VBA?

Answer Well, you can stick with ArcObjects and VBA—it can be used to do just about anything

that you want within ArcMap and ArcCatalog. Python offers a much simpler environment. You

don’t have to get into ArcObjects as much; you don’t have to write as much code. So, in general,

you can write less code to accomplish some general workflows. Now, using geoprocessing

functionality within Python, you can think of it as basically doing everything that you can do

within ArcToolbox. So, if you have general workflows you want to establish with tools from

ArcToolbox, you can use Python to quickly put together a script that will accomplish those

workflows. Now, within ArcObjects and VBA that’s where you get a little bit more robust

environment. You want to create a tool where you can interact with the display and select things

and interactively work with the ArcMap environment, then you’d probably still want to work

with VBA and ArcObjects, but Python offers you a much more flexible environment to quickly

get a script up and running.

Okay. I’ll turn it back over to Krista.

Okay. We have time for maybe just a couple more, here.


Question From someone in Lancaster: If you want to share scripts with other users, do you

distribute the entire mxd, mxt, or just the scripts?

Answer Well, this is how it works. You can just send the script to someone, you can send them

the py file, and they can open that in Python Win and run it directly from Python Win. Or, the

other option you can do is, you probably noticed in my demonstration, I had a series of those

scripts attached to tools inside of a toolbox. So, what you could actually do is distribute the

toolbox, which is a tbx file. In that case, those scripts are already attached to the toolbox. Now, if

you do that, you have to send the py files, as well.

Question From Terrell in Lawrence: We converted some models to Python scripts. They ran

successfully one time then, on repeated trials, we had errors. What might be missing?

Answer Well, a lot of people who start off with Python, they’ll run a script the first time, and it

works great. And then they go to run it a second time, and it gives them errors. And I guarantee

that the problem is probably that you ran it the first time and the output data already exists, and

now you’re trying to run it the second time, and Python gives you an error because the data was

created in the first run of the script. So, what you can actually do—there’s a property called

Overwrite Output—and you can say GP.overwriteoutput is equal to one, you can throw that at the

top of your script, and that should solve your problem.

Okay. Well, I think we’re out of time, so let’s just finish off, here.



For more informationInstructor – led training

Introduction to Geoprocessing Scripts using Python

Virtual Campus training Geoprocessing with ArcGIS 9

DocumentationWriting Geoprocessing Scripts.pdf

ESRI Support Center(http://support.esri.com/geoprocessing) Python home page (www.python.org)

Hopefully after this session you have a better understanding of what can be done with scripting at

ArcGIS 9. To learn more about how to script, you can take the two-day, instructor-led class called

Introduction to Geoprocessing Scripts Using Python. To learn more about geoprocessing in

general, you can take the Virtual Campus course, Geoprocessing with ArcGIS 9. There’s also a

lot of documentation to help you get started with ArcGIS 9 scripting; see the Writing

Geoprocessing Scripts PDF in the ESRI Library folder; visit ESRI support page; or visit Python’s

Web page. From Python’s Web page you can download the software, enter discussion forums,

and go through some tutorials.


Thanks for participating

On behalf of myself, Jeremiah, and the Virtual campus team, we would like to thank you for

participating in this seminar.


ws scripting startslides

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