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What is a Python toolbox?

Python toolboxes are geoprocessing toolboxes that are created entirely in Python. A Python toolbox and the tools contained within look, act, and work just like toolboxes and tools created in any other way. A Python toolbox (.pyt) is an ASCII-based file that defines a toolbox and one or more tools.

Once created, tools in a Python toolbox provide many advantages:

  • A script tool that you create is an integral part of geoprocessing, just like a system tool—you can open it from the Catalog pane, use it in ModelBuilder and the Python window, and call it from another script.
  • You can write messages to the Geoprocessing history window and tool dialog box.
  • Using built-in documentation tools, you can provide documentation.
  • When the script is run as a script tool, arcpy is fully aware of the application it was called from. Settings made in the application, such as arcpy.env.overwriteOutput and arcpy.env.scratchWorkspace, are available from ArcPy in your script tool.

Creating a Python toolbox

A Python toolbox can be created by right-clicking the folder in which you want to create the new toolbox and clicking New > Python Toolbox.

Initially, the Python toolbox will include a Python class named Toolbox that defines characteristics of the toolbox and a second Python class named Tool that provides a stubbed-out geoprocessing tool.

Get started

A Python toolbox example

Below is a working example of a Python toolbox containing a single tool. The tool, named CalculateSinuosity, adds a field and calculates the sinuosity of the feature—the sinuosity being a measure of how a line bends.

Note:

To use this tool, copy and paste the sample code into any Python integrated development environment (IDE), or even Notepad, and save the file with a .pyt extension.

import arcpy

class Toolbox(object):
    def __init__(self):
        self.label =  "Sinuosity toolbox"
        self.alias  = "sinuosity"

        # List of tool classes associated with this toolbox
        self.tools = [CalculateSinuosity] 

class CalculateSinuosity(object):
    def __init__(self):
        self.label       = "Calculate Sinuosity"
        self.description = "Sinuosity measures the amount that a river " + \
                           "meanders within its valley, calculated by " + \
                           "dividing total stream length by valley length."

    def getParameterInfo(self):
        #Define parameter definitions

        # Input Features parameter
        in_features = arcpy.Parameter(
            displayName="Input Features",
            name="in_features",
            datatype="GPFeatureLayer",
            parameterType="Required",
            direction="Input")
        
        in_features.filter.list = ["Polyline"]

        # Sinuosity Field parameter
        sinuosity_field = arcpy.Parameter(
            displayName="Sinuosity Field",
            name="sinuosity_field",
            datatype="Field",
            parameterType="Optional",
            direction="Input")
        
        sinuosity_field.value = "sinuosity"
        
        # Derived Output Features parameter
        out_features = arcpy.Parameter(
            displayName="Output Features",
            name="out_features",
            datatype="GPFeatureLayer",
            parameterType="Derived",
            direction="Output")
        
        out_features.parameterDependencies = [in_features.name]
        out_features.schema.clone = True

        parameters = [in_features, sinuosity_field, out_features]
        
        return parameters

    def isLicensed(self): #optional
        return True

    def updateParameters(self, parameters): #optional
        if parameters[0].altered:
            parameters[1].value = arcpy.ValidateFieldName(parameters[1].value,
                                                          parameters[0].value)
        return

    def updateMessages(self, parameters): #optional
        return

    def execute(self, parameters, messages):
        inFeatures  = parameters[0].valueAsText
        fieldName   = parameters[1].valueAsText
        
        if fieldName in ["#", "", None]:
            fieldName = "sinuosity"

        arcpy.AddField_management(inFeatures, fieldName, 'DOUBLE')

        expression = '''
import math
def getSinuosity(shape):
    length = shape.length
    d = math.sqrt((shape.firstPoint.X - shape.lastPoint.X) ** 2 +
                  (shape.firstPoint.Y - shape.lastPoint.Y) ** 2)
    return d/length
'''

        arcpy.CalculateField_management(inFeatures,
                                        fieldName,
                                        'getSinuosity(!shape!)',
                                        'PYTHON_9.3',
                                        expression)

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