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PYTHON: BUILDING GEOPROCESSING TOOLS. David Wynne, Geri Miller. Why we build geoprocessing tools. Your work becomes part of the geoprocessing framework Easy to access and run from within ArcGIS Familiar look and feel Make a mistake? Re-run from the previous result
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PYTHON: BUILDING GEOPROCESSING TOOLS David Wynne, Geri Miller
Why we build geoprocessing tools • Your work becomes part of the geoprocessing framework • Easy to access and run from within ArcGIS • Familiar look and feel • Make a mistake? Re-run from the previous result • Run from Python, ModelBuilder, as a service • Add to a tool bar • No UI programming
Geoprocessing Tool Commandments Thou shall … … have unique parameter names within the tool … keep the cost of validation to a minimum … always have an output, even if it must be derived … populate all output data elements within validation … not test the validity of any derived value within validation … have a coded value domain for every Boolean … test the function from a script, a model, a dialog, and the command line
Deconstructing a geoprocessing tool • A geoprocessing tool does three things • Defines parameters • Validates parameters • Executes source code
Script tools vs Python toolboxes • Using Python, we can build tools in two ways: • Which do I use? • “A tool is a tool”
Parameters • Parameters are how you interact with a tool • Simple rules to guide behaviors • Does an input exist? • What are valid fields for this data? • Is this value an expected keyword?
Key parameter properties • Data type • Feature layers, raster layers, table views, … • String, Boolean, long, double, … • Direction • Input, output • Parameter type • Required, optional, derived
Parameter Dependencies (‘obtained from’) • Some data types are dependent on other parameters • Field, SQL Expression, Field Info provide little value on their own • Set a dependency to a different data type
Parameters - Symbology • Control the appearance of output by setting symbology • Set using a layer file either as : • Parameter property • Or in your source code • Important if you want to vary the symbology based on logical criteria
Filters • Filters are used to limit choices to acceptable values • For example: • A number between 1 and 10 • A string parameter with keywords • A file parameter that will only accept files with a .txt extension
Parameters - Defaults • Set a parameter default by value or by environment • Some data types match closely with geoprocessing environments • Can configure a parameter to use an environment by default
Parameters – Validation • As parameters are entered and modified, validation responds and interacts • Tools validate parameters in two ways • Basic (‘free’) validation, such as: • Does the input (or output) exist? • Is it the right data type? • Does this value match its filter? • Have all required parameters been supplied? • Additional rules and behavior you add
Validation • Provides more control • Parameter interaction • Calculate defaults • Enable or disable parameters • Setting parameter errors and messages • Defining output characteristics • Chain tools in ModelBuilder
Validation • Responding to: • value (or valueAsText) • altered • hasBeenValidated
Validation: ModelBuilder • Describe outputs for chaining in ModelBuilder • Data variables in ModelBuilder includedescriptions of data • By updating the schema, subsequent tools can see pending changes prior to execution
Validation: Messages • Control over parameter messages • Evaluate system messages, and relax or change • Add more stringent errors based on your own criteria
Validation – Feature Layers • The type of a layer parameter changes depending if the input is a layer or feature class
Working with validation:Script tools and Python toolboxes Demo
Making your Python code work as a tool • Receiving parameters • Script tool – arcpy.GetParameter / GetParameterAsText • Python toolbox – parameter.value / parameter.valueAsText • Internal • Messages – arcpy.AddMessage / AddWarning / AddError … • Progressor (step or ‘cylon eye’) • Control actions (or not) after a cancellation • Derived values, if any, are pushed back to the tool
Cancelling toolsAdded at 10.4, Pro 1.1 • When a tool is cancelled… • ... by default, code will be cancelled after the current line • Using new environments, can respond to the cancellation • arcpy.env.autoCancelling • arcpy.env.isCancelled
Distributing your toolshttp://esriurl.com/extendingGP • Can ‘share’ a toolbox • Simply share the files or package a result • However, to have your tools blend seamlessly, distribute as a Python package • Are easily distributable • Toolboxes appear as System Toolboxes • Toolboxes become available through arcpy • Supports dialog side-panel help and localized messages • Requires specific structure
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