Tool definitions in a Python toolbox

Tools are added to a .pyt file as classes. Each tool class must include, at a minimum, an __init__ and execute method. Optionally, you can use getParameterInfo, isLicensed, updateParameters, and updateMessages methods to add control to the behavior of the tool.

Methods used to define a working tool class

Tool method	Required or optional	Description
__init__	Required	Initializes the tool class.
getParameterInfo	Optional	Defines the tool's parameters.
isLicensed	Optional	Returns whether the tool is licensed to execute.
updateParameters	Optional	Called each time the user changes a parameter on the tool dialog box. After returning from updateParameters, geoprocessing calls its internal validation routine.
updateMessages	Optional	Called after returning from the internal validation routine. You can examine the messages created from internal validation and change them if desired.
execute	Required	The tool's source code.
postExecute	Optional	Called after the execute method completes and outputs are processed and added to the display.

Setting a tool class __init__ method

The __init__ method in a tool class is a standard Python class initialization method. For a tool in a Python toolbox, the __init__ method is used to set properties of the tool, including the tool's label and description properties. The tool's name is established by the name of the class itself (in the example below, the tool name is CalculateSinuosity).

The __init__ method establishes tool properties such as the label and description. Below, a tool named CalculateSinuosity is created.

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."

Note:

Python syntax rules enforce most geoprocessing conventions when naming a Python toolbox tool class. However, avoid underscores in a tool class name, as they cause errors when running tools from ArcGIS Server.

The following properties can be set in a tool's __init__ method.

Property	Description
category	The name of the toolset in which the tool is located. A toolset is a way to organize tools in a toolbox.
description	The description for the tool.
label	The label is the display name for the tool as shown in the Geoprocessing pane.