In this article by Silas Toms, the author of the book ArcPy and ArcGIS - Second Edition, we will demonstrate how to use ModelBuilder, which ArcGIS professionals are already familiar with, to model their first analysis and then export it out as a script.
With the Python environment configured to fit our needs, we can now create and execute ArcPy scripts. To ease into the creation of Python scripts, this article will use ArcGIS ModelBuilder to model a simple analysis, and export it as a Python script. ModelBuilder is very useful for creating Python scripts. It has an operational and a visual component, and all models can be outputted as Python scripts, where they can be further customized.
This article we will cover the following topics:
Modeling a simple analysis using ModelBuilder
Exporting the model out to a Python script
Window file paths versus Pythonic file paths
String formatting methods
(For more resources related to this topic, see here.)
Prerequisites
The following are the prerequisites for this article: ArcGIS 10x and Python 2.7, with arcpy available as a module.
For this article, the accompanying data and scripts should be downloaded from Packt Publishing's website. The completed scripts are available for comparison purposes, and the data will be used for this article's analysis. To run the code and test code examples, use your favorite IDE or open the IDLE (Python GUI) program from the Start Menu/ArcGIS/Python2.7 folder after installing ArcGIS for Desktop. Use the built-in "interpreter" or code entry interface, indicated by the triple chevron >>> and a blinking cursor.
ModelBuilder
ArcGIS has been in development since the 1970s. Since that time, it has included a variety of programming languages and tools to help GIS users automate analysis and map production. These include the Avenue scripting language in the ArcGIS 3x series, and the ARC Macro Language (AML) in the ARCInfo Workstation days as well as VBScript up until ArcGIS 10x, when Python was introduced. Another useful tool introduced in ArcGIS 9x was ModelBuilder, a visual programming environment used for both modeling analysis and creating tools that can be used repeatedly with different input feature classes.
A useful feature of ModelBuilder is an export function, which allows modelers to create Python scripts directly from a model. This makes it easier to compare how parameters in a ModelBuilder tool are accepted as compared to how a Python script calls the same tool and supplies its parameters, and how generated feature classes are named and placed within the file structure. ModelBuilder is a helpful tool on its own, and its Python export functionality makes it easy for a GIS analyst to generate and customize ArcPy scripts.
Creating a model and exporting to Python
This article and the associated scripts depend on the downloadable file SanFrancisco.gdb geodatabase available from Packt. SanFrancisco.gdb contains data downloaded from https://datasf.org/ and the US Census' American Factfinder website at https://factfinder.census.gov/faces/nav/jsf/pages/index.xhtml. All census and geographic data included in the geodatabase is from the 2010 census. The data is contained within a feature dataset called SanFrancisco. The data in this feature dataset is in NAD 83 California State Plane Zone 3, and the linear unit of measure is the US foot. This corresponds to SRID 2227 in the European Petroleum Survey Group (EPSG) format.
The analysis which will create with the model, and eventually export to Python for further refinement, will use bus stops along a specific line in San Francisco. These bus stops will be buffered to create a representative region around each bus stop. The buffered areas will then be intersected with census blocks to find out how many people live within each representative region around the bus stops.
Modeling the Select and Buffer tools
Using ModelBuilder, we will model the basic bus stop analysis. Once it has been modeled, it will be exported as an automatically generated Python script. Follow these steps to begin the analysis:
Open up ArcCatalog, and create a folder connection to the folder containing SanFrancisco.gdb. I have put the geodatabase in a C drive folder called "Projects" for a resulting file path of C:ProjectsSanFrancisco.gdb.
Right-click on geodatabase, and add a new toolbox called Chapter2Tools.
Right-click on geodatabase; select New, and then Feature Dataset, from the menu. A dialogue will appear that asks for a name; call it Chapter2Results, and push Next. It will ask for a spatial reference system; enter 2227 into the search bar, and push the magnifying glass icon. This will locate the correct spatial reference system: NAD 1983 StatePlane California III FIPS 0403 Feet. Don't select a vertical reference system, as we are not doing any Z value analysis. Push next, select the default tolerances, and push Finish.
Next, open ModelBuilder using the ModelBuilder icon or by right-clicking on the Toolbox, and create a new Model. Save the model in the Chapter2Tools toolbox as Chapter2Model1. Drag in the Bus_Stops feature class and the Select tool from the Analysis/Extract toolset in ArcToolbox. Open up the Select tool, and name the output feature class Inbound71. Make sure that the feature class is written to the Chapter2Results feature dataset. Open up the Expression SQL Query Builder, and create the following SQL expression : NAME = '71 IB' AND BUS_SIGNAG = 'Ferry Plaza'.
The next step is to add a Buffer Tool from the Analysis/Proximity toolset. The Buffer tool will be used to create buffers around each bus stop. The buffered bus stops allow us to intersect with census data in the form of census blocks, creating the representative regions around each bus stop.
Connect the output of the Select tool (Inbound71) to the Buffer tool. Open up the Buffer tool, add 400 to the Distance field, and change the units to Feet. Leave the rest of the options blank. Click on OK, and return to the model:
Adding in the Intersect tool
Now that we have selected the bus line of interest, and buffered the stops to create representative regions, we will need to intersect the regions with the census blocks to find the population of each representative region. This can be done as follows:
First, add the CensusBlocks2010 feature class from the SanFrancisco feature dataset to the model.
Next, add in the Intersect tool located in the Analysis/Overlay toolset in the ArcToolbox. While we could use a Spatial Join to achieve a similar result, I have used the Intersect tool to capture the area of intersect for use later in the model and script.
At this point, our model should look like this:
Tallying the analysis results
After we have created this simple analysis, the next step is to determine the results for each bus stop. Finding the number of people that live in census blocks, touched by the 400-foot buffer of each bus stop, involves examining each row of data in the final feature class, and selecting rows that correspond to the bus stop. Once these are selected, a sum of the selected rows would be calculated either using the Field Calculator or the Summarize tool. All of these methods will work, and yet none are perfect. They take too long, and worse, are not repeatable automatically if an assumption in the model is adjusted (if the buffer is adjusted from 400 feet to 500 feet, for instance).
This is where the traditional uses of ModelBuilder begin to fail analysts. It should be easy to instruct the model to select all rows associated with each bus stop, and then generate a summed population figure for each bus stop's representative region. It would be even better to have the model create a spreadsheet to contain the final results of the analysis. It's time to use Python to take this analysis to the next level.
Exporting the model and adjusting the script
While modeling analysis in ModelBuilder has its drawbacks, there is one fantastic option built into ModelBuilder: the ability to create a model, and then export the model to Python. Along with the ArcGIS Help Documentation, it is the best way to discover the correct Python syntax to use when writing ArcPy scripts.
Create a folder that can hold the exported scripts next to the SanFrancisco geodatabase (for example, C:ProjectsScripts). This will hold both the exported scripts that ArcGIS automatically generates, and the versions that we will build from those generated scripts. Now, perform the following steps:
Open up the model called Chapter2Model1.
Click on the Model menu in the upper-left side of the screen.
Select Export from the menu.
Select To Python Script.
Save the script as Chapter2Model1.py.
Note that there is also the option to export the model as a graphic. Creating a graphic of the model is a good way to share what the model is doing with other analysts without the need to share the model and the data, and can also be useful when sharing Python scripts as well.
The Automatically generated script
Open the automatically generated script in an IDE. It should look like this:
# -*- coding: utf-8 -*-
# ---------------------------------------------------------------------------
# Chapter2Model1.py
# Created on: 2017-01-26 04:26:31.00000
# (generated by ArcGIS/ModelBuilder)
# Description:
# ---------------------------------------------------------------------------
# Import arcpy module
import arcpy
# Local variables:
Bus_Stops = "C:ProjectsSanFrancisco.gdbSanFranciscoBus_Stops"
Inbound71 = "C:ProjectsSanFrancisco.gdbChapter2ResultsInbound71"
Inbound71_400ft_Buffer = "C:ProjectsSanFrancisco.gdbChapter2ResultsInbound71_400ft_Buffer"
CensusBlocks2010 = "C:ProjectsSanFrancisco.gdbSanFranciscoCensusBlocks2010"
Intersect71Census = "C:ProjectsSanFrancisco.gdbChapter2ResultsIntersect71Census"
# Process: Select
arcpy.Select_analysis(Bus_Stops, Inbound71, "NAME = '71 IB' AND BUS_SIGNAG = 'Ferry Plaza'")
# Process: Buffer
arcpy.Buffer_analysis(Inbound71, Inbound71_400ft_buffer, "400 Feet", "FULL", "ROUND", "NONE", "")
# Process: Intersect
arcpy.Intersect_analysis("C:ProjectsSanFrancisco.gdbChapter2ResultsInbound71_400ft_Buffer #;C:ProjectsSanFrancisco.gdbSanFranciscoCensusBlocks2010 #",Intersect71Census, "ALL", "", "INPUT")
Let's examine this script line by line. The first line is preceded by a pound sign ("#"), which again means that this line is a comment; however, it is not ignored by the Python interpreter when the script is executed as usual, but is used to help Python interpret the encoding of the script as described here: http://legacy.python.org/dev/peps/pep-0263.
The second commented line and the third line are included for decorative purposes. The next four lines, all commented, are used for providing readers information about the script: what it is called and when it was created along with a description, which is pulled from the model's properties. Another decorative line is included to visually separate out the informative header from the body of the script. While the commented information section is nice to include in a script for other users of the script, it is not necessary.
The body of the script, or the executable portion of the script, starts with the import arcpy line. Import statements are, by convention, included at the top of the body of the script. In this instance, the only module that is being imported is ArcPy.
ModelBuilder's export function creates not only an executable script, but also comments each section to help mark the different sections of the script. The comments let user know where the variables are located, and where the ArcToolbox tools are being executed.
After the import statements come the variables. In this case, the variables represent the file paths to the input and output feature classes. The variable names are derived from the names of the feature classes (the base names of the file paths). The file paths are assigned to the variables using the assignment operator ("="), and the parts of the file paths are separated by two backslashes.
File paths in Python
To store and retrieve data, it is important to understand how file paths are used in Python as compared to how they are represented in Windows. In Python, file paths are strings, and strings in Python have special characters used to represent tabs "t", newlines "n", or carriage returns "r", among many others. These special characters all incorporate single backslashes, making it very hard to create a file path that uses single backslashes. File paths in Windows Explorer all use single backslashes.
Windows Explorer: C:ProjectsSanFrancisco.gdbChapter2ResultsIntersect71Census
Python was developed within the Linux environment, where file paths have forward slashes. There are a number of methods used to avoid this issue. The first is using filepaths with forward slashes. The Python interpreter will understand file paths with forward slashes as seen in this code:
Python version: "C:/Projects/SanFrancisco.gdb/Chapter2Results/Intersect71Census"
Within a Python script, the Python file path with the forward slashes will definitely work, while the Windows Explorer version might cause the script to throw an exception as Python strings can have special characters like the newline character n, or tab t. that will cause the string file path to be read incorrectly by the Python interpreter.
Another method used to avoid the issue with special characters is the one employed by ModelBuilder when it automatically creates the Python scripts from a model. In this case, the backslashes are "escaped" using a second backslash. The preceding script uses this second method to produce the following results:
Python escaped version: "C:ProjectsSanFrancisco.gdbChapter2ResultsIntersect71Census"
The third method, which I use when copying file paths from ArcCatalog or Windows Explorer into scripts, is to create what is known as a "raw" string. This is the same as a regular string, but it includes an "r" before the script begins. This "r" alerts the Python interpreter that the following script does not contain any special characters or escape characters. Here is an example of how it is used:
Python raw string: r"C:ProjectsSanFrancisco.gdbSanFranciscoBus_Stops"
Using raw strings makes it easier to grab a file path from Windows Explorer, and add it to a string inside a script. It also makes it easier to avoid accidentally forgetting to include a set of double backslashes in a file path, which happens all the time and is the cause of many script bugs.
String manipulation
There are three major methods for inserting variables into strings. Each has different advantages and disadvantages of a technical nature. It's good to know about all three, as they have uses beyond our needs here, so let's review them.
String manipulation method 1: string addition
String addition seems like an odd concept at first, as it would not seem possible to "add" strings together, unlike integers or floats which are numbers. However, within Python and other programming languages, this is a normal step. Using the plus sign "+", strings are "added" together to make longer strings, or to allow variables to be added into the middle of existing strings. Here are some examples of this process:
>>> aString = "This is a string"
>>> bString = " and this is another string"
>>> cString = aString + bString
>>> cString
The output is as follows:
'This is a string and this is another string'
Two or more strings can be "added" together, and the result can be assigned to a third variable for using it later in the script. This process can be useful for data processing and formatting.
Another similar offshoot of string addition is string multiplication, where strings are multiplied by an integer to produce repeating versions of the string, like this:
>>> "string" * 3
'stringstringstring'
String manipulation method 2: string formatting #1
The second method of string manipulation, known as string formatting, involves adding placeholders into the string, which accept specific kinds of data. This means that these special strings can accept other strings as well as integers and float values. These placeholders use the modulo "%" and a key letter to indicate the type of data to expect. Strings are represented using %s, floats using %f, and integers using %d. The floats can also be adjusted to limit the digits included by adding a modifying number after the modulo. If there is more than one placeholder in a string, the values are passed to the string in a tuple.
This method has become less popular, since the third method discussed next was introduced in Python 2.6, but it is still valuable to know, as many older scripts use it. Here is an example of this method:
>>> origString = "This string has as a placeholder %s"
>>> newString = origString % "and this text was added"
>>> print newString
The output is as follows:
This string has as a placeholder and this text was added
Here is an example when using a float placeholder:
>>> floatString1 = "This string has a float here: %f"
>>> newString = floatString % 1.0
>>> newString = floatString1 % 1.0
>>> print newString
The output is as follows:
This string has a float here: 1.000000
Here is another example when using a float placeholder:
>>> floatString2 = "This string has a float here: %.1f"
>>> newString2 = floatString2 % 1.0
>>> print newString2
The output is as follows:
This string has a float here: 1.0
Here is an example using an integer placeholder:
>>> intString = "Here is an integer: %d"
>>> newString = intString % 1
>>> print newString
The output is as follows:
Here is an integer: 1
String manipulation method 3: string formatting #2
The final method is known as string formatting. It is similar to the string formatting method 1, with the added benefit of not requiring a specific data type of placeholder. The placeholders, or tokens as they are also known, are only required to be in order to be accepted. The format function is built into strings; by adding .format to the string, and passing in parameters, the string accepts the values, as seen in the following example:
>>> formatString = "This string has 3 tokens: {0}, {1}, {2}"
>>> newString = formatString.format("String", 2.5, 4)
>>> print newString
This string has 3 tokens: String, 2.5, 4
The tokens don't have to be in order within the string, and can even be repeated by adding a token wherever it is needed within the template. The order of the values applied to the template is derived from the parameters supplied to the .format function, which passes the values to the string.
The third method has become my go-to method for string manipulation because of the ability to add the values repeatedly, and because it makes it possible to avoid supplying the wrong type of data to a specific placeholder, unlike the second method.
The ArcPy tools
After the import statements and the variable definitions, the next section of the script is where the analysis is executed. The same tools that we created in the model--the Select, Buffer, and Intersect tools, are included in this section. The same parameters that we supplied in the model are also included here: the inputs and outputs, plus the SQL statement in the Select tool, and the buffer distance in the Buffer tool.
The tool parameters are supplied to the tools in the script in the same order as they appear in the tool interfaces in the model. Here is the Select tool in the script:
arcpy.Select_analysis(Bus_Stops, Inbound71, "NAME = '71 IB' AND BUS_SIGNAG = 'Ferry Plaza'")
It works like this: the arcpy module has a "method", or tool, called Select_analysis. This method, when called, requires three parameters: the input feature class (or shapefile), the output feature class, and the SQL statement. In this example, the input is represented by the variable Bus_Stops, and the output feature class is represented by the variable Inbound71, both of which are defined in the variable section. The SQL statement is included as the third parameter. Note that it could also be represented by a variable if the variable was defined preceding to this line; the SQL statement, as a string, could be assigned to a variable, and the variable could replace the SQL statement as the third parameter. Here is an example of parameter replacement using a variable:
sqlStatement = "NAME = '71 IB' AND BUS_SIGNAG = 'Ferry Plaza'"
arcpy.Select_analysis(Bus_Stops, Inbound71, sqlStatement)
While ModelBuilder is good for assigning input and output feature classes to variables, it does not assign variables to every portion of the parameters. This will be an important thing to correct when we adjust and build our own scripts.
The Buffer tool accepts a similar set of parameters as the Select tool. There is an input feature class represented by a variable, an output feature class variable, and the distance that we provided (400 feet in this case) along with a series of parameters that were supplied by default. Note that the parameters rely on keywords, and these keywords can be adjusted within the text of the script to adjust the resulting buffer output. For instance, "Feet" could be adjusted to "Meters", and the buffer would be much larger. Check the help section of the tool to understand better how the other parameters will affect the buffer, and to find the keyword arguments that are accepted by the Buffer tool in ArcPy. Also, as noted earlier, all of the parameters could be assigned to variables, which can save time if the same parameters are used repeatedly throughout a script.
Sometimes, the supplied parameter is merely an empty string, as in this case here with the last parameter:
arcpy.Buffer_analysis(Inbound71,Inbound71_400ft_buffer,
"400 Feet", "FULL", "ROUND", "NONE", "")
The empty string for the last parameter, which, in this case, signifies that there is no dissolve field for this buffer, is found quite frequently within ArcPy. It could also be represented by two single quotes, but ModelBuilder has been built to use double quotes to encase strings.
The Intersect tool
The last tool, the Intersect tool, uses a different method to represent the files that need to be intersected together when the tool is executed. Because the tool accepts multiple files in the input section (meaning, there is no limit to the number of files that can be intersected together in one operation), it stores all of the file paths within one string. This string can be manipulated using one of the string manipulation methods discussed earlier, or it can be reorganized to accept a Python list that contains the file paths, or variables representing file paths as a list, as the first parameter in any order. The Intersect tool will find the intersection of all of the strings.
Adjusting the script
Now is the time to take the automatically generated script, and adjust it to fit our needs. We want the script to both produce the output data, and to have it analyze the data and tally the results into a spreadsheet. This spreadsheet will hold an averaged population value for each bus stop. The average will be derived from each census block that the buffered representative region surrounding the stops intersected.
Save the original script as "Chapter2Model1Modified.py".
Adding the CSV module to the script
For this script, we will use the csv module, a useful module for creating Comma-Separated Value spreadsheets. Its simple syntax will make it a useful tool for creating script outputs. ArcGIS for Desktop also installs the xlrd and xlwt modules, used to read or generate Excel spreadsheets respectively, when it is installed. These modules are also great for data analysis output.
After the import arcpy line, add import csv. This will allow us to use the csv module for creating the spreadsheet.
# Import arcpy module
import arcpy
import csv
The next adjustment is made to the Intersect tool. Notice that the two paths included in the input string are also defined as variables in the variable section. Remove the file paths from the input strings, and replace them with a list containing the variable names of the input datasets, as follows:
# Process: Intersect
arcpy.Intersect_analysis([Inbound71_400ft_buffer,CensusBlocks2010],Intersect71Census, "ALL", "", "INPUT")
Accessing the data: using a cursor
Now that the script is in place to generate the raw data we need, we need a way to access the data held in the output feature class from the Intersect tool. This access will allow us to aggregate the rows of data representing each bus stop. We also need a data container to hold the aggregated data in memory before it is written to the spreadsheet.
To accomplish the second part, we will use a Python dictionary. To accomplish the first part, we will use a method built into the ArcPy module: the Data Access SearchCursor.
The Python dictionary will be added after the Intersect tool. A dictionary in Python is created using curly brackets {}. Add the following line to the script, below the analysis section:
dataDictionary = {}
This script will use the bus stop IDs as keys for the dictionary. The values will be lists, which will hold all of the population values associated with each busStopID. Add the following lines to generate a Data Cursor:
with arcpy.da.SearchCursor(Intersect71Census, ["STOPID","POP10"]) as cursor:
for row in cursor:
busStopID = row[0]
pop10 = row[1]
if busStopID not in dataDictionary.keys():
dataDictionary[busStopID] = [pop10]
else:
dataDictionary[busStopID].append(pop10)
This iteration combines a few ideas in Python and ArcPy. The with...as statement is used to create a variable (cursor), which represents the arcpy.da.SearchCursor object. It could also be written like this:
cursor = arcpy.da.SearchCursor(Intersect71Census, ["STOPID","POP10"])
The advantage of the with...as structure is that the cursor object is erased from memory when the iteration is completed, which eliminates locks on the feature classes being evaluated.
The arcpy.da.SearchCursor function requires an input feature class, and a list of fields to be returned. Optionally, an SQL statement can limit the number of rows returned. The next line, for row in cursor:, is the iteration through the data. It is not a normal Pythonic iteration, a distinction that will have ramifications in certain instances. For instance, one cannot pass index parameters to the cursor object to only evaluate specific rows within the cursor object, as one can do with a list.
When using a Search Cursor, each row of data is returned as a tuple, which cannot be modified. The data can be accessed using indexes.
The if...else condition allows the data to be sorted. As noted earlier, the bus stop ID, which is the first member of the data included in the tuple, will be used as a key. The conditional evaluates if the bus stop ID is included in the dictionary's existing keys (which are contained in a list, and accessed using the dictionary.keys() method). If it is not, it is added to the keys, and assigned a value that is a list that contains (at first) one piece of data, the population value contained in that row. If it does exist in the keys, the list is appended with the next population value associated with that bus stop ID. With this code, we have now sorted each census block population according to the bus stop with which it is associated. Next we need to add code to create the spreadsheet. This code will use the same with...as structure, and will generate an average population value by using two built-in Python functions: sum, which creates a sum from a list of numbers, and len, which will get the length of a list, tuple, or string.
with open(r'C:ProjectsAverages.csv', 'wb') as csvfile:
csvwriter = csv.writer(csvfile, delimiter=',')
for busStopID in dataDictionary.keys():
popList = dataDictionary[busStopID]
averagePop = sum(popList)/len(popList)
data = [busStopID, averagePop]
csvwriter.writerow(data)
The average population value is retrieved from the dictionary using the busStopID key, and then assigned to the variable averagePop. The two data pieces, the busStopID and the averagePop variable are then added to a list.This list is supplied to a csvwriter object, which knows how to accept the data and write it out to a file located at the file path supplied to the built-in Python function open, used to create simple files.
The script is complete, although it is nice to add one more line to the end to give us visual confirmation that the script has run.
print "Data Analysis Complete"
This last line will create an output indicating that the script has run. Once it is done, go to the location of the output CSV file and open it using Excel or Notepad, and see the results of the analysis. Our first script is complete!
Exceptions and tracebacks
During the process of writing and testing scripts, there will be errors that cause the code to break and throw exceptions. In Python, these are reported as a "traceback", which shows the last few lines of code executed before an exception occurred. To best understand the message, read them from the last line up. It will tell you the type of exception that occurred, and preceding to that will be the code that failed, with a line number, that should allow you to find and fix the code. It's not perfect, but it works.
Overwriting files
One common issue is that ArcGIS for Desktop does not allow you to overwrite files without turning on an environment variable. To avoid this issue, you can add a line after the import statements that will make overwriting files possible. Be aware that the original data will be unrecoverable once it is overwritten. It uses the env module to access the ArcGIS environment:
import arcpy
arcpy.env.overwriteOutput = True
The final script
Here is how the script should look in the end:
# Chapter2Model1Modified.py
# Import arcpy module
import arcpy
import csv
# Local variables:
Bus_Stops = r"C:ProjectsSanFrancisco.gdbSanFranciscoBus_Stops"
CensusBlocks2010 = r"C:ProjectsSanFrancisco.gdbSanFranciscoCensusBlocks2010"
Inbound71 = r"C:ProjectsSanFrancisco.gdbChapter2ResultsInbound71"
Inbound71_400ft_buffer = r"C:ProjectsSanFrancisco.gdbChapter2ResultsInbound71_400ft_buffer"
Intersect71Census = r"C:ProjectsSanFrancisco.gdbChapter2ResultsIntersect71Census"
# Process: Select
arcpy.Select_analysis(Bus_Stops,
Inbound71,
"NAME = '71 IB' AND BUS_SIGNAG = 'Ferry Plaza'")
# Process: Buffer
arcpy.Buffer_analysis(Inbound71,
Inbound71_400ft_buffer,
"400 Feet", "FULL", "ROUND", "NONE", "")
# Process: Intersect
arcpy.Intersect_analysis([Inbound71_400ft_buffe,CensusBlocks2010],
Intersect71Census, "ALL", "", "INPUT")
dataDictionary = {}
with arcpy.da.SearchCursor(Intersect71Census, ["STOPID","POP10"]) as cursor:
for row in cursor:
busStopID = row[0]
pop10 = row[1]
if busStopID not in dataDictionary.keys():
dataDictionary[busStopID] = [pop10]
else:
dataDictionary[busStopID].append(pop10)
with open(r'C:ProjectsAverages.csv', 'wb') as csvfile:
csvwriter = csv.writer(csvfile, delimiter=',')
for busStopID in dataDictionary.keys():
popList = dataDictionary[busStopID]
averagePop = sum(popList)/len(popList)
data = [busStopID, averagePop]
csvwriter.writerow(data)
print "Data Analysis Complete"
Summary
In this article, you learned how to craft a model of an analysis and export it out to a script. In particular, you learned how to use ModelBuilder to create an analysis and export it out as a script and how to adjust the script to be more "Pythonic". After explaining about the auto-generated script, we adjusted the script to include a results analysis and summation, which was outputted to a CSV file. We also briefly touched on the use of Search Cursors. Also, we saw how built-in modules such as the csv module can be used along with ArcPy to capture analysis output in formatted spreadsheets.
Resources for Article:
Further resources on this subject:
Using the ArcPy DataAccess Module withFeature Classesand Tables [article]
Measuring Geographic Distributions with ArcGIS Tool [article]
Learning to Create and Edit Data in ArcGIS [article]
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