Defining a tool in a Python toolbox

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

Methods used to define a working tool class

Tool method	Required/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.

Setting a tool class' __init__

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. 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."

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

Property	Description
canRunInBackground	If canRunInBackground is unset or set to True, the tool will respect the current Background Processing setting in the Geoprocessing Options dialog. If set to False, the tool will always run in the foreground, overriding the Background Processing setting in the Geoprocessing Options dialog. Learn more about running custom tools in the background.
category	The name of the toolset in which the tool is located. A toolset is a way to organize tools within a toolbox.
description	The description for the tool.
label	The label is the display name for the tool as shown in the Catalog window.
stylesheet	To change the default stylesheet used for the tool. If unset, the default stylesheet is used.

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